Power Measurement 3720 ACM User manual

Installation
& Operation
Manual
3720 ACM
CONTENTS
Advanced Digital Power
Instrumentation Package
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Power Measurement 3720 ACM Installation and Operation Manual
Danger
During normal operation of this device, hazardous voltages are present which
can cause severe injury or death. These voltages are present on the terminal
strips of the device and throughout the connected potential transformer (PT),
current transformer (CT), status input, relay, and control power circuits. Installa-
tion and servicing should be performed only by qualified, properly trained
personnel. See Chapter 2: Installation for additional warnings.
Warning
This equipment generates, uses, and can radiate radio frequency energy and if
not installed and used in accordance with the instructions manual, may cause
interference to radio communications. It has been tested and found to comply
with the limits for a Class A computing device pursuant to Part 15 of FCC Rules,
which are designed to provide reasonable protection against such interference
when operated in a commercial environment. Operation of this equipment in a
residential area may cause interference in which case the operator will be
required to take whatever measures may be required to correct the interference.
Limitation of Liability
Power Measurement Limited reserves the right to make changes in the devices
or the device specifications identified in this Installation and Operation Manual
without notice. Power Measurement Limited advises customers to obtain the
latest version of device specifications before placing orders to verify that the
information being relied upon by the customer is current.
In the absence of written agreement to the contrary Power Measurement
Limited assumes no liability for Power Measurement Limited applications
assistance, customer’s system design, or infringement of patents or copyrights of
third parties by or arising from the use of devices described herein. Nor does
Power Measurement Limited warrant or represent that any license, either
expressed or implied, is granted under any patent right, copyright, or other
intellectual property right of Power Measurement Limited covering or relating
to any combination, machine, or process in which such device might be used.
EXCEPT TO THE EXTENT PROHIBITED BY APPLICABLE LAW, UNDER NO
CIRCUMSTANCESSHALLPOWERMEASUREMENTLIMITEDBELIABLEFOR
CONSEQUENTIALDAMAGESSUSTAINEDINCONNECTIONWITH SAID
PRODUCTANDPOWERMEASUREMENTLIMITEDNEITHERASSUMESNOR
AUTHORIZES ANY REPRESENTATIVE OR OTHER PERSON TO ASSUME FOR
IT ANY OBLIGATION OR LIABILITY OTHER THAN SUCH AS IS EXPRESSLY
SET FORTH HEREIN.
3720 ACM is a trade mark of Power Measurement Limited. Other brands and
their products are trade marks of their respective holders and should be noted as
such.
© 1999 Power Measurement Ltd.
The information contained in this document is believed to be
accurate at the time of publication, however, Power Measurement
Ltd. assumes no responsibility for any errors which may appear
here and reserves the right to make changes without notice.
TollFree
1-877-METER-IT
(1-877-638-3748)
World-Wide Web www.pml.com
WorldwideHeadquarters
POWER MEASUREMENT LTD.
2195 Keating Cross Road,
Saanichton, BC,
Canada V8M 2A5
Tel:[phone]
Fax:[phone]
Europe & Middle East
POWER MEASUREMENT EUROPE
Zaventem Business Park, Ikaroslaan 5,
B-1930 Zaventem
(Brussels), Belgium
Tel:[phone]
Fax:[phone]
Asia & Pacific
POWER MEASUREMENT
AUSTRALIA
7/16 Ledgar Road,
Balcatta, Perth
Western Australia 6021
Tel:[phone]
Fax:[phone]
Revision Date: March 24, 1999
© 1999 Power Measurement Ltd.
All rights reserved
Printed in Canada
70000-0004
For further information or technical assistance, please
contact your local Power Measurement representative,
or Customer Service at one of the following locations:
ISO 9002-94
Registration
Cert # 002188
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Power Measurement 3720 ACM Installation and Operation Manual
Throughout this operation manual, the following methods are used to highlight important
information:
NOTE
Describes important considerations related to a device setup, feature or application.
CAUTION
Alerts you to a condition which could potentially cause damage to the device or other external
equipment.
WARNING or DANGER
Warns you to avoid conditions that could potentially cause serious personal injury and/or
equipment damage.
Wiring diagrams and labels use symbols to denote the following objects:
Fuse
Potential Transformer (PT)
Current Transformer (CT)
Switchgear chassis (Earth) ground
Alternating current
Direct current
3
Three-phase alternating current
Protective conductor termainal
This device has a display timeout feature which automatically turns off the front panel display
after a programmable timeout period. When the device is shipped, this timeout period is preset
to 180 minutes (3 hours). Following a display timeout, you can turn the display back on by
pressing any button on the front panel.
CONVENTIONS
DISPLAY TIMEOUT
SYMBOLS
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Power Measurement 3720 ACM Installation and Operation Manual
Table of Contents
1 INTRODUCTION
2 INSTALLATION
2.1 Location&Mounting................................................................................................2-1
2.2 GeneralWiringConsiderations ................................................................................2-2
2.3 PowerSupplyConnections......................................................................................2-2
2.4 ChassisGroundConnection .................................................................................... 2-2
2.5 PhaseVoltageandPhaseCurrentInput Connections .............................................2-3
2.5.1 PhaseVoltage Inputs ..............................................................................2-3
2.5.2 PhaseCurrentInputs...............................................................................2-3
2.5.3 PT & CT Connection ...............................................................................2-4
2.5.4 VoltageReferenceConnection ................................................................ 2-4
2.5.5 WaveformCaptureConnections ..............................................................2-5
2.5.6 I4 CurrentInputConnections...................................................................2-5
2.5.7 Connection for Three Phase WYE(Star) Systems ...................................2-6
2.5.8 Connection for Three Phase Delta Systems ...........................................2-9
2.5.9 Connection for Single Phase Systems .................................................. 2-11
2.6 CommunicationsConnections ............................................................................... 2-12
2.6.1 Introduction ........................................................................................... 2-12
2.6.2 ISOCOM2CommunicationsCard.......................................................... 2-12
2.6.3.a MultiportCommunicationsCard(MPCC) ............................................... 2-14
2.6.3.b MultiportCommunicationsCardwithEthernet(MPE)............................ 2-15
2.6.4 RS-232Connections.............................................................................. 2-17
2.6.5 RS-485Connections.............................................................................. 2-19
2.6.6 MultiportConnections............................................................................2-23
2.7 ControlRelayConnections .................................................................................... 2-24
2.7.1 RelayApplicationPrecautions...............................................................2-25
2.7.2 Form-CRelays ...................................................................................... 2-25
2.7.3 Solid State Relays................................................................................. 2-26
2.8 StatusInputConnections ......................................................................................2-27
2.9 AuxiliaryVoltageInputConnections ...................................................................... 2-28
2.10 AuxiliaryCurrentOutputConnections.....................................................................2-29
2.11 Maintenance.......................................................................................................... 2-29
2.11.1 BatteryReplacement ............................................................................. 2-29
2.11.2 DisplayRestore ..................................................................................... 2-29
2.12 FieldServiceConsiderations .................................................................................2-30
3 GENERALOPERATION
3.1 Introduction .............................................................................................................3-1
3.2 PowerUp.................................................................................................................3-1
3.3 DisplayMode ..........................................................................................................3-1
3.3.1 FrontPanel Display .................................................................................3-1
3.3.2 FrontPanelButtons ................................................................................3-3
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Power Measurement 3720 ACM Installation and Operation Manual
Table of Contents
3.4 FieldProgramming ..................................................................................................3-6
3.4.1 Introduction .............................................................................................3-6
3.4.2 EnteringProgrammingMode ...................................................................3-6
3.4.3 ProgrammingButtonFunctions ...............................................................3-6
3.4.4 EnteringandChangingthePassword ......................................................3-6
3.4.5 AccessingandModifying Parameters .....................................................3-6
3.4.6 OperatingParameterDescriptions...........................................................3-7
3.5 Setting the Volts Scale, Amps Scale, I4 Scale, Volts Mode, and Standard Freq..3-20
3.6 DisplayFormat ...................................................................................................... 3-21
3.7 ControlRelayOperation......................................................................................... 3-21
3.8 StatusInputOperation ..........................................................................................3-22
3.9 AuxiliaryVoltageInputOperation ..........................................................................3-23
3.10 AuxiliaryCurrentOutputOperation ........................................................................3-24
3.11 Daylight Savings Time .......................................................................................... 3-24
4 MEASUREDPARAMETERSANDSTATUSINFORMATION
4.1 Introduction .............................................................................................................4-1
4.2 High-SpeedMeasurements......................................................................................4-2
4.3 Real-TimeMeasurements........................................................................................4-2
4.3.1 BaseMeasurements ...............................................................................4-2
4.3.2 MeasurementModes...............................................................................4-4
4.4 Energy .....................................................................................................................4-7
4.4.1 BaseMeasurements ...............................................................................4-7
4.4.2 MeasurementModes...............................................................................4-7
4.4.3 ResettingtheEnergyCounters................................................................4-7
4.5 PowerReadingPolarities.........................................................................................4-8
4.6 StatusInformation ...................................................................................................4-9
4.6.1 Relays, Status Inputs & Setpoints ..........................................................4-9
4.6.2 DiagnosticsParameters ..........................................................................4-9
5 TIME-OF-USESYSTEM
5.1 Introduction .............................................................................................................5-1
5.2 Programming ...........................................................................................................5-1
5.2.1 WinTOUSetup ........................................................................................ 5-1
5.2.2 Calendar ..................................................................................................5-1
5.2.3 Profiles ....................................................................................................5-1
5.2.4 Tariffs......................................................................................................5-1
5.2.5 EnergyRegisters.....................................................................................5-1
5.2.6 DemandRegisters...................................................................................5-2
5.2.7 StatusParameters ..................................................................................5-2
5.3 Access to TOU Data ...............................................................................................5-2
5.3.1 ReadingTOUData ..................................................................................5-2
5.3.2 UsingTOUDataasTriggerParameters ..................................................5-2
5.3.3 ResettingtheTOURegisters...................................................................5-2
5.4 Calculation of Energy Costs ....................................................................................5-2
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Power Measurement 3720 ACM Installation and Operation Manual
Table of Contents
6 SETPOINT SYSTEM
6.1 Introduction .............................................................................................................6-1
6.2 Setpoint Types ........................................................................................................6-3
6.2.1 Introduction .............................................................................................6-3
6.2.2 SetpointResponseTimes .......................................................................6-3
6.2.3 High-SpeedSetpoints..............................................................................6-3
6.2.4 StandardSetpoints..................................................................................6-3
6.3 TriggerParameters ..................................................................................................6-3
6.3.1 Introduction .............................................................................................6-3
6.3.2 Over & Under Setpoints with Time Delays ..............................................6-5
6.3.3 On/Off & Counter Setpoints ....................................................................6-7
6.3.4 Time-OvercurrentCurve ..........................................................................6-7
6.4 Setpoint Actions...................................................................................................... 6-8
6.4.1 Introduction .............................................................................................6-8
6.4.2 RelayControl...........................................................................................6-9
6.4.3 WaveformCaptureTriggering .................................................................. 6-9
6.4.4 WaveformRecorderTriggering .............................................................. 6-10
6.4.5 SnapshotLogTriggering........................................................................ 6-10
6.4.6 ClearingFunctions................................................................................. 6-10
6.5 ProgrammingSetpoints ......................................................................................... 6-11
6.6 PowerOutages......................................................................................................6-12
7 WAVEFORMCAPTURE&RECORDING
7.1 Introduction .............................................................................................................7-1
7.2 WaveformCapture...................................................................................................7-1
7.2.1 TheImportance of PowerQualityMonitoring...........................................7-1
7.2.2 UsingCapturedData ...............................................................................7-1
7.2.3 TriggeringfromaSetpoint .......................................................................7-1
7.2.4 TriggeringManuallyviaCommunications ................................................7-2
7.3 WaveformRecording ...............................................................................................7-3
7.3.1 UsingRecordedData...............................................................................7-3
7.3.2 ConfiguringtheRecorder .........................................................................7-3
7.3.3 TriggeringfromaSetpoint .......................................................................7-4
7.3.4 Adjusting the Trigger Point ...................................................................... 7-4
7.3.5 TriggeringManuallyviaCommunications ................................................7-6
8 ON-BOARDDATALOGGING
8.1 Introduction .............................................................................................................8-1
8.2 Event Log................................................................................................................8-1
8.3 Minimum / Maximum Logs ......................................................................................8-3
8.3.1 Preset Min/Max Log ................................................................................ 8-3
8.3.2 ProgrammableMin/MaxLogs..................................................................8-4
8.3.3 Resetting the Min/Max Logs....................................................................8-4
8.4 ProgrammableSnapshotLogs ................................................................................8-5
8.4.1 Introduction .............................................................................................8-5
8.4.2 MemoryAllocation...................................................................................8-5
8.4.3 StandardSnapshotLogs .........................................................................8-6
8.4.4 High-SpeedSnapshotLog .......................................................................8-8
8.5 Access to Logged Data .........................................................................................8-10
8.6 Time Stamp Accuracy...........................................................................................8-10
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Power Measurement 3720 ACM Installation and Operation Manual
Table of Contents
9 COMMUNICATIONS
9.1 General ....................................................................................................................9-1
9.2 RS-232CCommunication ........................................................................................9-1
9.3 RS-485Communication ...........................................................................................9-2
9.4 Setting the Unit ID & Baud Rate..............................................................................9-2
9.5 3720ACMTRANModelOperation ..........................................................................9-3
9.6 PowerMeasurement'sSCADASystem...................................................................9-3
9.7 Third-PartySystem Compatibility ............................................................................9-3
9.8 ModbusProtocol .....................................................................................................9-4
9.8.1 HardwareRequirementsandWiring.........................................................9-4
9.8.2 SettingCommunicationsParameters ......................................................9-4
9.8.3 CommunicationsProtocol........................................................................9-4
9.9 Allen-BradleyDF-1Protocol ....................................................................................9-6
9.9.1 HardwareRequirementsandWiring.........................................................9-6
9.9.2 CommunicationsProtocol........................................................................9-6
9.10 AlarmDialerProtocol...............................................................................................9-8
9.10.1 HardwareRequirementsandWiring.........................................................9-8
9.10.2 Configuration ...........................................................................................9-8
Appendices
A MECHANICAL& MOUNTINGDIMENSIONS
Basic Model ........................................................................................................... A-1
TRANModel........................................................................................................... A-2
TerminalBlock Dimensions.................................................................................... A-3
B SETPOINTPARAMETERFORM
C FIRMWAREVERSIONS
D TECHNICALSPECIFICATIONS
E MODEL/ORDERINGINFORMATION
F WARRANTYANDREGISTRATION
Warranty ................................................................................................................F-1
ProductReturnProcedure .......................................................................................F-1
Registration .............................................................................................................F-1
G TROUBLESHOOTING
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Power Measurement 3720 ACM Installation and Operation Manual
List of Figures
1. Introduction
1.1.1 3710ACMvs.3720ACMFeatureComparison.............................................................. 1-2
2. Installation
2.1.1 EnvironmentalGuidelinesforInstallation ....................................................................... 2-1
2.5.7a 4 Wire Wye: 3 Element Direct Connection (for 120/208 to 357/600 Volt Systems) ........ 2-5
2.5.7b 4 Wire Wye: 3 Element Connection Using 3 PTs ........................................................... 2-6
2.5.7c 4 Wire Wye: 2½ Element Connection Using 2 PTs........................................................ 2-7
2.5.7d 3 WireGroundedWye:3ElementDirect Connection(120/208-357/600 VoltSystems) . 2-8
2.5.8a 3 Wire Delta System: 2½ Element Connection Using 2 PTs and 3 CTs ........................ 2-9
2.5.8b 3 Wire Delta: 2 Element Connection Using 2 PTs and 2 CTs .......................................2-10
2.5.9 3 Wire Single Phase: 2 Element Direct Connection ......................................................2-11
2.6.2a CommunicationCardJumperConfiguration(ISOCOM2Type) ......................................2-12
2.6.2b ISOCOM2CardTerminalBlock ....................................................................................2-13
2.6.3a 3720MPCCConnectorConfiguration............................................................................2-14
2.6.3b 3720MPEConnectorConfiguration ..............................................................................2.15
2.6.4a RS-232CCommunicationsConnections........................................................................2-17
2.6.4b RS-232CCommunicationCableWiring .........................................................................2-18
2.6.5a RS-485IntermediateTerminalBlockConnections ........................................................2-19
2.6.5b RS-485Straight-LineandLoopTopologies ...................................................................2-20
2.6.5c RS-485Topologiesto Avoid .........................................................................................2-22
2.6.6 MPCCSampleApplication ............................................................................................2-23
2.7.2 FormCControlRelayConnections ...............................................................................2-25
2.7.3 Solid State ControlRelay Option Connections ..............................................................2-26
2.8.1 Status Input Connections for Dry Contact Sensing .......................................................2-27
2.9.1 AuxiliaryVoltageInputConnections .............................................................................2-28
2.10.1 AuxiliaryCurrentOutputConnections ...........................................................................2-28
3. GeneralOperation
3.3.1 Front Panel Display Examples....................................................................................... 3-2
3.3.2 FrontPanelFeatures ..................................................................................................... 3-3
3.4.5 FieldProgrammingExample .......................................................................................... 3-7
3.4.6a ProgrammableOperatingParameters I: Front Panel Access......................................... 3-8
3.4.6b ProgrammableOperatingParameters I: Front Panel Access (cont.).............................. 3-9
3.4.6c ProgrammableOperatingParameters I: Front Panel Access (cont.).............................3-10
3.4.6d ProgrammableOperatingParameters I: Front Panel Access (cont.).............................3-11
3.4.6e ProgrammableOperatingParametersII: CommunicationsAccessOnly ......................3-12
3.4.6f ProgrammableOperatingParametersII:CommunicationsAccessOnly(cont.) ...........3-13
3.4.6g ProgrammableOperatingParametersII:CommunicationsAccessOnly(cont.) ...........3-14
3.4.6h ProgrammableOperatingParametersII:CommunicationsAccessOnly(cont.) ...........3-15
3.4.6i ProgrammableOperatingParametersII:CommunicationsAccessOnly(cont.) ...........3-16
3.4.6j ProgrammableOperatingParametersII:CommunicationsAccessOnly(cont.) ...........3-17
3.4.6k ProgrammableOperatingParametersII:CommunicationsAccessOnly(cont.) ...........3-18
3.4.6l ProgrammableOperatingParametersII:CommunicationsAccessOnly(cont.) ...........3-19
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Power Measurement 3720 ACM Installation and Operation Manual
List of Figures
4. MeasuredParameters&StatusInformation
4.3.1 List of Real-Time Base Measurements & Display Labels............................................... 4-3
4.3.2a Listof MeasurementModesfor Real-TimeParameters ................................................. 4-4
4.3.2b ThermalDemandCalculation ......................................................................................... 4-5
4.4.2 List of Measurement Modes for Energy Parameters ...................................................... 4-7
4.5.1 PowerReadingPolarities ............................................................................................... 4-8
4.6.1 List of Relay, Status Input & Setpoint Display Labels.................................................... 4-9
4.6.2 ExtendedDiagnosticParameters..................................................................................4-10
5. Time-Of-UseSystem
5.2.2 WinTOUSetup:Calendar&ProfileSetupExample ....................................................... 5-1
5.2.4 WinTOU Setup: Register Setup & Real-Time Display Example ..................................... 5-2
6. SetpointSystem
6.1.1 SetpointCapabilities ...................................................................................................... 6-2
6.3.1 SetpointTriggerParameters .......................................................................................... 6-4
6.3.2a OverSetpointOperation................................................................................................. 6-5
6.3.2b UnderSetpointOperation ............................................................................................... 6-6
6.3.4 Time-OvercurrentCurve ................................................................................................. 6-7
6.6.1 SetpointParameterFormExample ...............................................................................6-11
7. WaveformCapture&Recording
7.2.2a M-SCADACapturedWaveformScreen .......................................................................... 7-2
7.2.2b M-SCADAHarmonicSpectrumScreen .......................................................................... 7-2
7.2.2c M-SCADAHarmonicsTableScreen .............................................................................. 7-2
7.3.1 M-SCADAWaveformRecorderScreen .......................................................................... 7-3
7.3.4 WaveformRecorderHigh-SpeedTriggerPointAdjustment ............................................ 7-5
8. On-BoardDataLogging
8.2.1 M-SCADAEventLogScreen ......................................................................................... 8-2
8.3.1 M-SCADA Preset Min/Max Log Screen ......................................................................... 8-3
8.3.2 M-SCADAProgrammableMin/MaxLogScreen ............................................................. 8-4
8.4.1 M-SCADAStandardSnapshotLogScreen .................................................................... 8-5
8.4.2 SnapshotLog Capacity Examples ................................................................................. 8-6
8.4.3a M-SCADAHistoricalTrendingScreen............................................................................ 8-7
8.4.3b One-Shotvs. GatedSnapshot Logging .......................................................................... 8-7
8.4.4 SnapshotLogging:ModesofOperation ......................................................................... 8-9
9. Communications
9.2.1 RemoteCommunicationMethods .................................................................................. 9-2
9.8.1 ModbusSingleandMulti-DropConnections................................................................... 9-5
9.9.1 AllenBradleySingleandMulti-DropConnections .......................................................... 9-7
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Power Measurement 3720 ACM Installation and Operation Manual
Introduction 1-1
1 INTRODUCTION
High Performance Power Instrumentation
The 3720 ACM is a microprocessor-based, digital 3-phase
“Smart Power Monitor/Meter” designed for use in
industrial, commercial, and utility power distribution
switchboards and substations. The 3720 ACM answers the
ever-increasing concern for ‘clean’, reliable power by
integrating the many critical aspects of power monitoring,
analysis, and control into one simple and economical
instrument. It is a state of the art alternative to traditional
analog electromechanical metering devices, replacing
numerous individual transducers and meters, and offering
many features previously unavailable in power instru-
mentation.
The 3720 ACM offers the high accuracy, reliability, and
ruggedness of its companion product, the successful
3710 ACM, while adding many new measurements and
advanced features (see Figure 1.1.1). The 3720 ACM also
matches the 3710 ACM in its mounting dimensions,
installation requirements, and in its straightforward and
flexible user interface.
The unit is based around a 13.5 MHz, 16 bit
microcontroller chip. This provides very high computa-
tional throughput, allowing the unit’s sophisticated
software to process information in real time. The unit is
self-contained and its readings and set up parameters are
maintained in nonvolatile memory. An internal 16-bit
CPU gives the 3720 ACM the processing capability to be
used as a stand-alone power monitoring and control
station or as a smart RTU in a large energy monitoring
network.
Easy Installation and Exceptional Ruggedness
The 3720 ACM is panel-mountable and provides rear-
mounted, utility approved terminal strips rated at 600V.
The 3720 ACM is exceptionally rugged, with a high
tolerance to electrical disturbances and temperature
extremes. Many special design features guarantee perfor-
mance in electrically harsh environments. The voltage,
current, status (digital), relay, supply power, and commu-
nications inputs are designed to withstand hipot, C37.90A
SWC, and fast transient tests. The 3720 ACM transformer-
coupled current inputs are fully isolated with respect to
the chassis of the unit, and provide 300 Amp surge
protection.
Inputs and Outputs
The 3720 ACM supports a variety of power distribution
configurations, including 4-wire Wye, 3-wire Delta, and
Single Phase systems. 3 phase voltage and 3 phase current
inputs are provided, as well as an additional current
input. In installations with non-linear loads, where odd
harmonics can fail to cancel, significant currents in the
neutral conductor can be produced. The 3720 ACM fourth
current input can be used optionally for monitoring
current in the neutral conductor, or for ground current
monitoring. Used in conjunction with its high-speed
setpoint system, the 3720 ACM can provide reliable
ground fault protection.
No intermediate transducers are required on phase
voltage and current inputs. When equipped with the
appropriate voltage input option, no PTs are required for
Wye systems up to 347 VAC line-to-neutral / 600 VAC
line-to-line. For higher voltage Wye systems, and all Delta
systems, PTs can be used. The transformer-coupled
current inputs accept CTs with 5 Amp full scale outputs.
A 1 Amp input version is also available. Overrange
measurement options include 125% to 1000%.
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Power Measurement 3720 ACM Installation and Operation Manual
1-2 Introduction
An auxiliary voltage input can be used to measure an external
variable such as transformer temperature or battery voltage.
Input range is 0 to 1 VAC. An auxiliary analog current
output can provide 0-20 or 4-20 mA proportional to any
measured parameter.
Four digital inputs can be used to monitor breaker status,
ground fault relay status, or any other external dry contact.
These can also be used as pulse counters to measure device
cycles, running hours, etc. An internal 30 VDC supply
provides self-excitation for ‘‘volts free’’ contact sensing.
Figure 1.1.1 3710 ACM vs. 3720 ACM Feature Comparison
Outputs include three on-board relays that can be automati-
cally controlled by an extensive user-programmable setpoint
system, or manually operated by commands made via the
communications port. Relays can perform operations ranging
from simple alarm activations to fully automated demand,
power factor, or load control. Relays can operate in a latched or
pulse mode, and can also be programmed to provide kWh
(import/export), kVARh (import/export), or kVAh output
pulsing. The basic 3720 ACM provides 10 Amp, Form C
electromechanical relays. The SSR option provides 1 Amp,
SPST solid state relays which offer longer lifetimes in continu-
ous pulsing applications.
MEASURED PARAMETERS
INPUTS & OUTPUTS
WAVEFORM CAPTURE
WAVEFORM RECORDING
SNAPSHOT (TREND) LOGS
EVENT LOG
MINIMUM / MAXIMUM
LOGS
SETPOINTS
Over 70, including sliding window demand
on 2 values, and min/max on all values.
3 phase voltage inputs, 3 phase current inputs,
neutral/ground current input, 3 relay outputs,
4 digital inputs with pulse counter on 1 input
(maximum pulse count frequency: 0.3 Hz), 1
analog voltage input, 1 analog current output.
Yes. Triggers: comm. port.
No.
Basic Model: 1 preset log with 12 parameters.
Triggered by programmable time interval.
1200 data item capacity allows up to 25
hours of recording at 15 min. intervals.
EMEM Option: Up to 12 definable param-
eters. 11,520 data item capacity allows 3
parameters to be recorded for 40 days at 15
min. intervals.
Basic Model: 50 records. Resolution: 1 sec.
EMEM Option: 100 records.
1 preset log records min/max for all
parameters.
17 standard speed. Trigger source and relay
status stored in event log. Can be used to
trigger relay control.
3 phase voltage inputs, 3 phase current inputs,
neutral/ground current input, 3 relay outputs, 4
digital inputs with scalable pulse counters on all 4
inputs (maximum pulse count frequency: 10 Hz), 1
analog voltage input, 1 analog current output.
Over 700, including harmonic distortion, K-Factor,
and time-of-use. Min/max on all values. Thermal,
sliding window and predicted demand on all values.
Yes. Triggers: comm. port or setpoint.
Yes. Triggers: comm. port or setpoint.
Basic Model: 8 programmable logs. Up to 12
definable parameters each. Triggered by program-
mable time interval or setpoint. 11,520 data item
capacity. Memory allocation for each log is user-
definable.
1 log is definable as high-speed. Can record at 2
cycle intervals, with definable stop conditions.
Basic Model: 100 records. Resolution: 1 msec.
1 preset log, plus 16 programmable logs each with
1 trigger parameter and 15 coincident parameters.
17 total: 11 standard speed, 6 high speed. Trigger
source and subsequent action(s) stored in event log.
Trigger relay control, snapshot log, waveform
capture, and/or waveform recorder.
3710ACM 3720ACM
COMMUNICATIONS Selectable RS-232 / RS-485. Selectable RS-232 / RS-485.
Optional multiport comm card supports one RS-232
and two RS-485 ports (MPCC), or one RS-232, one
RS-485 and one Ethernet port (MPE).
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Power Measurement 3720 ACM Installation and Operation Manual
Introduction 1-3
Displays and Measurements
The 3720 ACM offers hundreds of high accuracy real-time,
3-phase measured parameters and status parameters. All
parameters are quickly accessible via the front panel
display or through the meter’s communications port.
Real-time measurements include: Volts, Amps, Neutral/
Ground Current, kW, kVA, kVAR, Power Factor, and
Frequency. On-board power quality analysis capability
offers total harmonic distortion, individual harmonics
levels, and K-Factor for all eight voltage and current
inputs (to the 15th harmonic).
Thermal, sliding window and predicted sliding demand
are provided on all measurements. Minima/maxima
values are also provided on all measurements.
Energy values include kWh, kVAh, and kVARh. All
energy readings provide bidirectional (import/export)
indication. All voltage, current, power and energy
readings are true RMS, including harmonics.
An extensive time-of-use system allows you to configure
each day of a 2 year calendar choosing from up to 16 daily
profiles. Each profile supports up to 8 tariff changes per
day, with 15 minute resolution.
You can define 3 demand registers and 3 energy registers
which are available for use by 10 programmable tariffs. A
penalty tariff can also be activated at any time by a level
transition to one of the status inputs.
Status information includes real-time conditions for the
three on-board relays, four status/counter inputs, and
seventeen user-programmable setpoints. The scaling for
each pulse counter reading is user-definable. Also in-
cluded is internal self-diagnostic information.
Unique and Flexible User Interface
The 3720 ACM front panel features a large, high-visibility,
20-character vacuum fluorescent display. Voltage, current
and power functions can all be displayed together for the
selected phase. Very large measured values with up to 9
digits of resolution (i.e. kWh) are presented using the
entire display. Concurrent display of all three phases of
voltage and current readings is also possible.
The 3720 ACM uses four long-life, stainless steel mem-
brane switches to access all measured parameters and
status information, and for programming functions.
Using the GROUP buttons, you can define convenient custom
groupings of important parameters for quick viewing.
You can program the basic setup parameters of the
3720 ACM quickly and easily from the front panel. Basic
parameters include voltage and current scales, voltage
mode (wye, delta, etc.), baud rate, etc.
Programming for many of the advanced features of the
3720 ACM must be performed via the communications
port using a portable or remotely located computer
running POWER MEASUREMENT's SCADA software
(M-SCADA, L-SCADA or PowerView), or any compat-
ible third-party software. These parameters include
setup for waveform, data logging, and setpoint
functions. Setup for the time-of-use registers is
performed using POWER MEASUREMENT’s WinTOU Setup
utility.
Setup and other critical information is saved when
3720 ACM power is turned off. All programming is
password protected.
High-Speed Setpoint System
The comprehensive on-board setpoint system of the
3720 ACM provides extensive control over the three
on-board relay outputs, as well as triggering capabili-
ties for the waveform capture, waveform recorder, and
snapshot logging features. Setpoints can also be used
to automatically clear status input counters, or to reset
time-of-use registers or Min/Max Logs.
Seventeen user-programmable setpoints are provided,
six of which offer high-speed (67 msec / 4 cycle)
capabilities. Setpoints can be activated by a wide
variety of conditions, including
• A user-defined level on any measured param-
eter, such as voltage, current, power, harmonic
distortion (HD), demand, etc.
• Time-overcurrent characteristics.
• External equipment status (via the status
inputs).
• New hour, day, week, month or year.
An active setpoint condition can be used to trigger
simultaneously up to two separate functions. For
example you may wish to operate a relay and perform
a waveform recording when an overcurrent condition
occurs. Using predicted demand, you can apply
setpoint control of the on-board relays in effective
demand management strategies.
All setpoint activity is recorded automatically in the
on-board Event Log.
Power Quality Monitoring and Fault Recording
Beyond its on-board harmonic distortion and K-Factor
measurements, the 3720 ACM has also been equipped
with digital waveform sampling capabilities for power
quality monitoring and fault analysis. The 3720 ACM
provides two powerful methods for acquiring wave-
form data: waveform capture and waveform recording.
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Power Measurement 3720 ACM Installation and Operation Manual
1-4 Introduction
WAVEFORM CAPTURE
Waveform capture allows you to perform high-speed (128
samples/cycle) sampling of the eight voltage and current
inputs, providing high-resolution data which can be used
for detailed power quality analysis. Capture can be
triggered either through user-defined setpoint conditions,
or commands via the meter’s communications port.
Sampled waveform data is stored in on-board memory
and can be read via the communications port. POWER
MEASUREMENT's SCADA PC-based software automatically
uploads captured waveform data. You can then retrieve
the waveforms for display and analysis. The SCADA
software calculates total harmonic distortion, Crest Factor
and K-Factor for each waveform and a breakdown of
individual harmonic components (to the 63rd harmonic)
both in graphical and tabular form.
WAVEFORM RECORDER
Waveform recording allows you to analyze the conditions
occurring before, during, and after a power fluctuation or
failure and is ideal for fault and surge analysis, and to aid
in fault location.
Waveform recording runs continuously at 16 samples/
cycle on all eight voltage and current inputs. A trigger by
a user-specified setpoint condition or a command made
via the meter’s communications port freezes multiple
cycles of each waveform in memory along with a time
stamp.
The user can configure the 3720 ACM to concurrently
store on-board up to three 12-cycle events, two 18-cycle
events, or one 36-cycle event for each input. A program-
mable trigger delay allows pre-event or post-event data to
be recorded.
The recorded data is saved until uploaded to a master
station for analysis. POWER MEASUREMENT's SCADA soft-
ware can be used to display the waveforms together on
the computer screen, presenting a comprehensive picture
of the power line conditions surrounding the disturbance.
On-Board Data Logging
The 3720 ACM supports three types of on-board data
logging. Logged data can be extremely useful in the study
of growth patterns, for scheduling loads and for cost
allocation, for isolating problem sources, or for analyzing
a variety of power system operating conditions.
EVENT LOGGING
The Event Log provides 100 date and time-stamped
records. Digital input changes are recorded with 1
millisecond accuracy, ideal for sequence-of-event record-
ing. The log also records all relay operations, setpoint/
alarm conditions, setup changes, and self-diagnostic
events.
MINIMA/MAXIMA LOGGING
A Preset Min/Max Log records the extreme values for all
parameters measured by the 3720 ACM, including all
voltage, current, power, frequency, power factor, har-
monic distortion, and demand values. Minima/maxima
for each parameter are logged independently with date
and time stamp, with 1 second resolution.
16 Programmable Min/Max Logs allow you to define up
to 16 separate logs, each containing up to 16 time-stamped
parameters. Each log is triggered by the first parameter in
its list. When a new minimum or maximum for the trigger
parameter is recorded, coincident real-time values for all
other parameters in the list are simultaneously stored. For
example, you could program a log to record all per-phase
kW, kVAR, and PF demand values when total kW demand
peaks. Reset functions for the preset and programmable
Min/Max Logs are performed either from the front panel
or via communications.
HISTORICAL LOGGING
The 3720 ACM Snapshot Logs are historical or trend logs.
Up to 8 logs may be defined, each recording up to 12
channels of time-stamped data. The measured parameters
recorded by each log are user-programmable.
Each Snapshot Log can be triggered in one of three
possible ways. Trigger functions are assigned indepen-
dently for each log.
• A user-defined time interval basis provides an
interval range from 1 second to 400 days. One log
can be also configured for high-speed operation,
recording at intervals as short as 2 cycles. The high-
speed log can be useful for logging short duration
conditions, such as motor start-ups, etc.
•A1-shot method allows any standard setpoint to
automatically trigger a snapshot recording when an
active condition occurs. Setpoint conditions can
include harmonic distortion levels, status input
changes, and more.
•Agated method allows readings to be recorded on a
time interval basis only during the time that a
setpoint remains active. This method is ideal for
logging voltage and current extremes following a
breaker trip, for example.
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Power Measurement 3720 ACM Installation and Operation Manual
Introduction 1-5
ACCESS TO LOGGED DATA
Alarm conditions, events, min/max levels, and snapshot
interval readings are all automatically time-stamped and
logged into on-board nonvolatile memory and are accessible
via the communications port. Preset Min/Max Log readings
can also be viewed via the front panel display by assigning
them to either GROUP button.
POWER MEASUREMENT’s SCADA software can be used to
program all log setup parameters, and to display all logged
data. Historical snapshot data can be displayed graphically.
The SCADA software also automatically archives to disk all
logged data retrieved from each remote device. Data can be
converted into formats compatible with a wide range of third-
party database and spreadsheet applications.
RemoteCommunications
The 3720 ACM is equipped with a selectable RS-232 or RS-485
communications port which allows the 3720 ACM to be
integrated within large energy monitoring networks.
3720 ACM communications uses an advanced object and
register based open protocol which allows the 3720 ACM to be
easily adapted to third-party PLC, DCS, EMS, and SCADA
systems.
The optional multiport communications cards expand the
communications capabilities of the 3720 ACM. The MPCC
equips the 3720 ACM with one RS-232 and two RS-485 ports,
while the MPE equips the 3720 ACM with one RS-232, one
RS-485 and one Ethernet port. Refer to sections 2.6.3.a and
2.6.3.b for details.
PC-Based SCADA
The 3720 ACM maintains compatibility with POWER
MEASUREMENT’s PC-based supervisory control and data acquisition
software, M-SCADA, L-SCADA, and PowerView and the
entire family of 3000 series digital instrumentation, which
includes power meters, power demand controllers, and smart
transducer interfaces. A single M-SCADA station can
support up to 99 remote sites with a total of 3168 devices.
L-SCADA supports 1 site with 12 devices. Systems are easily
expandable, and very large systems can be built by linking
multiple master stations.
POWER MEASUREMENT’s SCADA software provides extensive
full-color data display options, automated data handling and
system control features including: real-time data display for
all or part of the power system; display of captured wave-
forms and harmonic analysis; historical trend graphing;
detection, annunciation, display and logging of alarm
conditions; and automatic retrieval and disk archival of data
logs from remote devices. With the SCADA system, power
monitoring, load trending, and harmonic or fault analysis can
be performed concurrently with other system supervisory
functions, eliminating the need for costly manual surveys
using portable instruments.
The POWER MEASUREMENT approach to SCADA guarantees
consistently accurate data retrieval by delegating extensive
data acquisition, data logging, and control capabilities to the
remote meter/RTU sites. Less processing requirements at the
master station means high reliability and performance.
Nonvolatile data logs ensure data is always retrievable
following a temporary power or communication failure.
Meter-to-Meter Time Sync
Using the global time sync broadcast capability of POWER
MEASUREMENT’s SCADA software, all 3720 ACM devices
connected on the same RS-485 bus can be time synchronized
to a typical accuracy of ±1 ms (max. ±10 ms). This allows for
1 ms time-stamp accuracy on waveform capture and recorder
data, and status input or relay activity in the 3720 ACM
Event Log. Compatible third-party systems can also take
advantage of this feature.
SystemApplications
Because of its unique measurement, storage, setpoint control
(load shedding) and display characteristics the 3720 ACM
should be considered for use in:
• Utility Installations
• Industrial Buildings
• Office Buildings
• Commercial Buildings
• Hospitals
• Telephone Exchanges
• Factories
• Pulp Mills
• Saw Mills
• Shopping Centres
• Large Stores
• Hotels
• Substation Metering
• Co-generation Systems
• Chemical Process Plants
• Multi-user sites where allocation of electrical costs is
desirable
• Any other installation which uses significant amounts
of electrical energy.
• Any other installation which is experiencing power
quality problems.
• Any other locations where remote power monitoring,
control, or analysis is needed.
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Power Measurement 3720 ACM Installation and Operation Manual
1-6 Introduction
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Power Measurement 3720 ACM Installation And Operation Manual
Installation 2-1
EnclosureConsiderations
The enclosure the 3720 ACM is mounted in (typically a
switchgear cabinet) should protect the device from atmo-
spheric contaminants such as oil, moisture, dust, and
corrosive vapors, or other harmful airborne substances.
The mounting enclosure should be positioned such that the
doors may be opened fully for easy access to the 3720 ACM
wiring and related components to allow for convenient
troubleshooting. When choosing the enclosure size, allow for
extra space for all wiring, intermediate terminal strips,
shorting blocks, or any other required components.
3720 ACM Mounting
The front bezel of the basic model is moulded plastic, while
that of the 3720 ACM-TRAN model is a flat metal plate.
Bezel dimensions differ significantly between the two models.
All other dimensions are similar.
BASIC MODEL
Appendix A provides the mounting dimensions for the
3720 ACM. The basic model 3720 ACM (i.e. with
display) may be panel mounted for easy access and
viewing, and provides four mounting studs to facilitate
this. A 5 inch depth is required behind the front panel.
WARNING
Some electrical codes may prohibit extend-
ing voltages greater than 120 VAC line-to-
neutral / 208 VAC line-to-line to the door
of the switchgear cabinet. If this is the
case, use a basic model (120 VAC input)
3720 ACM with PTs that provide 120 VAC
secondaries (see Section 2.5).
TRAN MODEL
The 3720 ACM TRAN model is a displayless version that
can be mounted flush against any flat surface using the
four mounting holes provided. The unit can also be
mounted through a panel cutout originally made for a
basic model 3720 ACM, if desired.
ENVIRONMENTALCONDITION ACCEPTABLE RANGE
3720 ACM 3720 ACM -XTEMP
OperatingTemperature 0°C (32°F) to 50°C (122°F) -20°C (-4°F) to +70°C (158°F)
Storage Temperature -30°C (-22°F) to +70°C (158°F)
RelativeHumidity 5to95%non-condensing
Figure 2.1.1 Environmental Guidelines for Installation
2 INSTALLATION
DANGER
During normal operation of this
device, hazardous voltages are
present which can cause severe injury
or death. These voltages are present
on the terminal strips of the device
and throughout the connected
potential transformer (PT), current
transformer (CT), and control power
circuits. Installation and servicing
should be performed only by quali-
fied, properly trained personnel.
CAUTION
The 3720 ACM offers a range of hardware
options that affect phase voltage, phase
current, power supply, and relay input rat-
ings. The rear panel label of the 3720 ACM
lists all equipped options. Appendices D
and E define all options and their associ-
ated ratings. This chapter provides de-
tailed installation instructions applicable to
each hardware option.
2.1 LOCATION & MOUNTING
EnvironmentalConditions
The 3720 ACM should be mounted in a dry, dirt free location
away from heat sources and very high electric fields. Once
installed, no cleaning of the device is necessary. To operate
properly and effectively, environmental conditions should fall
within the guidelines listed in Figure 2.1.1.
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Power Measurement 3720 ACM Installation And Operation Manual
2-2 Installation
CAUTION
A switch or circuit breaker should be in-
cluded in the installation, in close proxim-
ity to the unit and within easy reach to the
operator. This switch or circuit breaker
should be marked as the disconnecting
device for the unit.
2.2 GENERAL WIRING CONSIDERATIONS
Connections to the 3720 ACM are made to two terminal strips
located on the rear of the unit. Appendix A provides 3720
ACM terminal block dimensions. 12 to 14 gauge wire is
recommended for all connections. Ring or spade terminals
may be used to simplify connection.
CAUTION
1. All wiring must conform to any appli-
cable local electrical codes, and device
terminals (once installed) should not
be user accessible.
2. In applications where the on-board
relays are being used to perform criti-
cal equipment control operations (e.g.
breaker trip, etc.), special precautions
are required. See Section 2.7.
2.2.1 FIELD SERVICE
If the 3720 ACM requires servicing or field upgrading, you
may need to disconnect and remove the unit from its mount-
ing. The initial installation should be done in a way that
makes this as convenient as possible:
• All phase voltage sense leads should be protected by
breakers or fuses at their source such that the 3720
ACM can be safely disconnected.
• A CT shorting block should be provided so that the
3720 ACM current inputs can be safely disconnected
without open circuiting the CTs. The shorting block
should be wired so that protective relaying is not
affected.
• All wiring should be routed to allow easy removal of
the connections to the 3720 ACM terminal strips, the
3720 ACM cover, and the 3720 ACM itself.
2.3 POWER SUPPLY CONNECTIONS
Power Supply Options
BASIC MODEL
The basic model 3720 ACM can be powered by 100 to 240
VAC (± 10%) or 110 to 300 VDC at 0.2 Amps. Power
supply options are also available. The label on the rear
panel indicates if the unit is equipped with one of these
options.
P24/48 OPTION
This option can be powered by 20 to 60 VDC at 15 Watts.
Power Sources and Connections
The basic model can be powered from a dedicated fused feed,
or from the voltage source which it is monitoring, as long as it
is within the supply range. The P24/48 option must be
powered from a dedicated fused feed. If an AC power supply
is being used, connect the line supply wire to the 3720 ACM
L/+ terminal and the neutral supply wire to the N/- terminal.
If a DC power supply is being used, connect the positive
supply wire to the 3720 ACM L/+ terminal and the negative
(ground) supply wire to the N/- terminal.
2.4 CHASSIS GROUND CONNECTION
The chassis of the 3720 ACM must be connected to earth
ground. A good, low impedance chassis ground connection is
essential for the 3720 ACM surge and transient protection
circuitry to function effectively. It should be made to the
switchgear earth ground using a dedicated 14 gauge (or
larger) wire to a point where there will be no voltage error due
to distribution voltage drops. Do not rely on metal door
hinges as a ground path.
Ground wire connection to the chassis is made using the
supplied ground lug. For the basic model, this is attached to
one of the four mounting studs to form the protective ground
terminal . For the TRAN model, the lug is attached to one
of four mounting bolts to form the protective ground terminal
.
NOTE
The VAUX input and IOUT output operate
with reference to chassis ground. Do not
use the protective ground terminal to
connect the VAUX or IOUT functional
ground.
Ensure that the protective ground terminal screw is
tightened down securely onto the ground wire, and that the
nut has been tightened down securely onto the lug.
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Power Measurement 3720 ACM Installation And Operation Manual
Installation 2-3
CAUTION
The 3720 ACM chassis ground lug must be
connected to the switchgear earth ground
using a dedicated 14 gauge (or larger) wire
for the noise and surge protection circuitry
to function correctly. Failure to do so will
void the warranty.
2.5 PHASE VOLTAGE AND PHASE
CURRENT INPUT CONNECTIONS
2.5.1 PHASEVOLTAGE INPUTS
MaximumTerminalVoltages
The maximum constant voltage levels the phase voltage
inputs can withstand are as follows:
Voltage Option Maximum Terminal Voltage
120 150 VAC line-to-neutral, or
260 VAC line-to-line
277 346 VAC line-to-neutral, or
600 VAC line-to-line
347 434 VAC line-to-neutral, or
750 VAC line-to-line
V1 Input Connection
The 3720 ACM uses the V1 input as the reference for main-
taining phase relationships for all power and energy related
measurements. For any system configuration, the V1 input
must be connected to ensure accurate readings and the correct
operation of the 3720 ACM.
DirectConnection
Whether or not potential transformers (PTs) are required
depends on the nature of the system being monitored, the
voltage levels to be monitored, and the input option of the
3720 ACM.
BASIC MODEL
The basic model can be used for direct connection to Wye
systems up to 120 VAC line-to-neutral / 208 VAC line-
to-line or Single Phase systems up to 120 VAC line-to-
neutral / 240 VAC line-to-line.
277 OPTION
This option provides 277 VAC full scale inputs that can
be used for direct connection to Wye systems up to 277
VAC line-to-neutral / 480 VAC line-to-line or 277 VAC
line-to-neutral / 554 VAC line-to-line Single Phase
systems.
347 OPTION
Models supplied with the 347 option provide 347
VAC full scale inputs that can be used for direct
connection to 347 VAC line-to-neutral / 600 VAC
line-to-line Wye or Single Phase systems up to 347
VAC line-to-neutral / 694 VAC line-to-line.
UsingPotential Transformers
If Wye system voltages are over 347 VAC line-to-neutral /
600 VAC line-to-line or Single Phase system voltages are
over 347 VAC line-to-neutral / 694 VAC line-to-line,
potential transformers (PTs) are required.
NOTE
PTs are always required for Delta sys-
tems.
PTs are used to scale down the line-to-neutral voltage of a
Wye or Single Phase system, or the line-to-line voltage of a
Delta system to the rated input scale of the 3720 ACM.
The inputs of the basic model can be used with PTs that
have secondaries rated at 120 VAC or less. This can
include 100/√3, 110/√3, 100, 110, or 120 VAC secondar-
ies. Devices equipped with the 277 option can be used
with PTs that have secondaries rated to 277 VAC, such as
220 VAC.
For proper monitoring, correct selection of PTs is critical.
For Wye systems, the PT primary rating should equal the
system line-to-neutral voltage or nearest higher standard
size. For Delta systems, the PT primary rating should
equal the system line-to-line voltage. For all system
configurations, the PT secondary rating must be within
the rated full scale range of the 3720 ACM voltage inputs.
PT quality directly affects system accuracy. The PTs must
provide good linearity and maintain the proper phase
relationship between voltage and current in order for the
voltage, kW, and power factor readings to be valid.
Instrument Accuracy Class 1 or better is recommended.
2.5.2 PHASECURRENT INPUTS
The 3720 ACM uses CTs to sense the current in each
phase of the power feed and (optionally) in the neutral or
ground conductor. The selection of the CTs is important
because it directly affects accuracy.
Current Input Options
The 3720 ACM offers various phase current input options
to match the type of CTs being used and the desired
overrange capability. The current input ratings of all
three phase inputs and the I4 input are equivalent.
The basic model 3720 ACM is compatible with CTs with 5
Amp full scale secondaries. The 1AMP option provides
compatibility with 1 Amp CT secondaries.
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Power Measurement 3720 ACM Installation And Operation Manual
2-4 Installation
The basic model 3720 ACM provides 125% overrange capabil-
ity which allows current readings to be accurately displayed
up to 125% of full scale. For example, if the AMPS SCALE
has been set at 2000 Amps full scale, the 3720 ACM allows
for readings up to 2500 Amps.
The 3720 ACM provides three additional current input
overrange options which include 200%, 500%, and 1000%.
Note that each overrange option also affects all current-
related measurement accuracies (Amps, kW, etc.) Refer to
Appendix D for detailed specifications on each current input
option.
CAUTION
Refer to the rear panel label of the 3720
ACM to determine the equipped current
input option(s). Applying current levels
incompatible with the current input con-
figuration will permanently damage the
device.
CT Ratings
The CT secondary should have a burden capacity greater than
3 VA.
The CT primary rating is normally selected to be equal to the
current rating of the power feed protection device. However,
if the peak anticipated load is much less than the rated
system capacity, you can improve accuracy and resolution by
selecting a lower rated CT. In this case the CT size should be
the maximum expected peak current +25%, rounded up to the
nearest standard CT size.
Other factors may affect CT accuracy. The length of the CT
cabling should be minimized because long cabling contributes
to inaccuracy. Also, the CT burden rating must exceed the
combined burden of the 3720 ACM plus cabling plus any
other connected devices (burden is the amount of load being
fed by the CT, measured in Volt-Amps). The 3720 ACM
burden rating is given in Appendix D.
Overall accuracy is dependent on the combined accuracies of
the 3720 ACM, the CTs, and the PTs (if used). Instrument
accuracy Class 1 or better is recommended.
2.5.3 PT & CT CONNECTION
Figures 2.5.7a to 2.5.9 illustrate all required phase voltage and
phase current connections for various circuit configurations to
ensure correct installation. Phasing and polarity of the AC
current and voltage inputs and their relationship is critical to
the correct operation of the unit.
All phase voltage sense leads should be protected by breakers
or fuses at their source. In cases where PTs are required, if the
power rating of the PTs is over 25 Watts the secondaries
should be fused.
CTs should be connected to the device via a shorting block or
test block to facilitate the safe connection and disconnection
of the CTs.
DANGER
PT secondary circuits are capable of
generating lethal voltages and currents
with their primary circuit energized.
Standard safety precautions should be
followed while performing any
installation or service on the device
(e.g. removing PT fuses, etc.)
DANGER
CT secondary circuits are capable of
generating lethal voltages and
currents when open circuited with
their primary circuit energized.
Standard safety precautions should
be followed while performing any
installation or service on the device
(e.g. shorting CT secondaries, etc.)
Refer all questions regarding proper working procedures to
qualified personnel.
2.5.4 VOLTAGEREFERENCECONNECTION
The voltage reference terminal, VREF, of the 3720 ACM serves
as the zero voltage reference for voltage readings. A good,
low impedance VREF connection is essential for accurate
measurement. It should be made using a dedicated 14 gauge
wire to a point where there will be no voltage error due to
distribution voltage drops.
The connection point for VREF is dependent on the system
configuration. Each of the following configurations is
illustrated in Figures 2.5.7a to 2.5.9:
• If the system being monitored is 4-wire Wye or Single
Phase, VREF must be connected to the neutral conduc-
tor.
• If the system is 3-wire grounded (Delta), VREF must be
connected to the line transformer neutral.
• For 3-wire ungrounded (Open Delta) systems, and for
systems where PTs are being used, VREF must be
connected to the PT common leads.
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Power Measurement 3720 ACM Installation And Operation Manual
Installation 2-5
2.5.5 WAVEFORMCAPTURE CONNECTIONS
The 3720 ACM waveform capture feature allows signals at
each of its voltage (V1, V2, V3, VAUX) inputs and current (I1,
I2, I3, I4) inputs to be digitally sampled. The 3720 ACM uses
the V1 input as the triggering reference for waveform capture,
and to maintain phase relationships between all sampled
signals. The V1 input must be connected for waveform
capture to work. No other special wiring considerations are
necessary. The operation of the waveform capture feature is
described in detail in Chapter 6.
2.5.6 I4 CURRENT INPUT CONNECTIONS
The 3720 ACM is equipped with a fourth current input,
named I4. This input is typically used to measure the current
flow in the neutral or ground conductor. The use of this
input is optional.
The secondary rating of the CT connected to the I4 input
must be identical to that of the three phase current inputs.
This rating depends on the current input option installed in
the 3720 ACM.
The primary rating for the CT connected to the I4 input can
be different than for the three phase inputs, since the I4 input
scaling can be programmed independently.
VOLTS MODE:
4W-WYE INPUT OPTION:
≤ 120 VAC line-to-neutral / 208 VAC line-to-line Systems: Basic Model
≤ 277 VAC line-to-neutral /480 VAC line-to-line Systems: 277 Option
≤ 347 VAC line-to-neutral /600 VAC line-to-line Systems: 347 Option
FUSES
LOAD
CHASSIS
GROUND
LUG
Neutral current input
is optional.
SWITCHGEAR
CHASSIS
GROUND
N/-
L/+
VREF
V3
V2
V1
CTs
2A
IMPORT
EXPORT
ABCN
LINE
SWITCHGEAR CHASSIS
GROUND
CT SHORTING SWITCH
OR TEST BLOCK
{
SUPPLY POWER
(dependent on equipped power supply
option - see Section 2.3)
I42
I41
I12
I11
I21
I22
I31
I32
Figure 2.5.7a 4 Wire Wye: 3 Element Direct Connect
(For 120 VAC line-neutral / 208 VAC line-line to 347 VAC line-neutral / 600 VAC line-line Systems)
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