Electro Industries/GaugeTech Nexus 1250 User manual

Nexus 1250
High Performance SCADA Monitor
eElectro Industries/GaugeTech
Installation & Operation Manual
Revision 1.21
March 20, 2001
Doc #: E107-7-06-121
1800 Shames Drive
Westbury, New York 11590
Tel: [phone] u Fax: [phone]
[email protected] u www.electroind.com
“The World Leader in Power Monitoring Systems”
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Nexus 1250
Installation and Operation Manual
Revision 1.21
Published by:
Electro Industries/GaugeTech
1800 Shames Drive
Westbury, NY 11590
All rights reserved. No part of this
publication may be reproduced or
transmitted in any form or by any
means, electronic or mechanical,
including photocopying, recording,
or information storage or retrieval
systems or any future forms of
duplication, for any purpose other
than the purchaser’s use, without
the expressed written permission of
Electro Industries/GaugeTech.
© 2001
Electro Industries/GaugeTech
Printed in the United States of
America.
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eElectro Industries/GaugeTech Doc # E107-7-06-121 ii
Customer Service and SupportCustomer Service and Support
Customer support is available 9:00 am to 4:30 pm, eastern standard time, Monday through Friday.
Please have the model, serial number and a detailed problem description available. If the problem
concerns a particular reading, please have all meter readings available. When returning any merchandise
to EIG, a return materials authorization number is required. For customer or technical assistance, repair
or calibration, phone [phone] or fax [phone].
Product WarrantyProduct Warranty
Electro Industries/GaugeTech warrants all products to be free from defects in material and workmanship
for a period of four years from the date of shipment. During the warranty period, we will, at our option,
either repair or replace any product that proves to be defective.
To exercise this warranty, fax or call our customer-support department. You will receive prompt
assistance and return instructions. Send the instrument, transportation prepaid, to EIG at 1800 Shames
Drive, Westbury, NY 11590. Repairs will be made and the instrument will be returned.
Limitation of WarrantyLimitation of Warranty
This warranty does not apply to defects resulting from unauthorized modification, misuse, or use for any
reason other than electrical power monitoring. The Nexus 1250 is not a user-serviceable product.
OUR PRODUCTS ARE NOT TO BE USED FOR PRIMARY OVER-CURRENT PROTECTION. ANY
PROTECTION FEATURE IN OUR PRODUCTS IS TO BE USED FOR ALARM OR SECONDARY
PROTECTION ONLY.
THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED,
INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE. ELECTRO INDUSTRIES/GAUGETECH SHALL NOT BE LIABLE FOR
ANY INDIRECT, SPECIAL OR CONSEQUENTIAL DAMAGES ARISING FROM ANY AUTHO-
RIZED OR UNAUTHORIZED USE OF ANY ELECTRO INDUSTRIES/GAUGETECH PRODUCT.
LIABILITY SHALL BE LIMITED TO THE ORIGINAL COST OF THE PRODUCT SOLD.
Statement of CalibrationStatement of Calibration
Our instruments are inspected and tested in accordance with specifications published by Electro
Industries/GaugeTech. The accuracy and a calibration of our instruments are traceable to the National
Institute of Standards and Technology through equipment that is calibrated at planned intervals by
comparison to certified standards.
DisclaimerDisclaimer
The information presented in this publication has been carefully checked for reliability; however, no
responsibility is assumed for inaccuracies. The information contained in this document is subject to
change without notice.
This symbol indicates that the operator must refer to an explanation in the operating
instructions. Please see Chapter 3, Hardware Installation, for important safety
information regarding installation and hookup of the Nexus 1250 Monitor.
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eElectro Industries/GaugeTech Doc # E107-7-06-121 iii
About Electro Industries/GaugeTechAbout Electro Industries/GaugeTech
Electro Industries/GaugeTech was founded in 1973 by Dr. Samuel Kagan. Dr. Kagan’s first innovation,
an affordable, easy-to-use AC power meter, revolutionized the power-monitoring field. In the 1980s Dr.
Kagan and his team at EIG developed a digital multifunction monitor capable of measuring every aspect
of power.
EIG further transformed AC power metering and power distribution with the Futura+ device, which
supplies all the functionality of a fault recorder, an event recorder and a data logger in one single meter.
Today, with the Nexus 1250, EIG is a leader in the development and production of power-monitoring
products. All EIG products are designed, manufactured, tested and calibrated at our facility in Westbury,
New York.
Applications:
nMultifunction power monitoring
nSingle and multifunction power monitoring
nPower-quality monitoring
nOnboard data logging for trending power usage and quality
nDisturbance analysis
Futura+ Series Products:
nPower-quality monitoring
nHigh-accuracy AC metering
nOnboard data logging
nOnboard fault and voltage recording
DM Series Products:
nThree-phase multifunction monitoring
nWattage, VAR and amperage
nModbus, Modbus Plus, DNP 3.0 and Ethernet protocols
nAnalog retransmit signals (0–1 and 4–20mA)
Single-Function Meters:
nAC voltage and amperage
nDC voltage and amperage
nAC wattage
nSingle-phase monitoring with maximum and minimum demands
nTransducer readouts
Portable Analyzers:
nPower-quality analysis
nEnergy analysis
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EElectro Industries/GaugeTech Doc # E107-7-06-121 iv
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Table of Contents
Chapter 1: Basic Tutorial on AC Power Measurement
1.1: Single Phase Power Systems . . . . . . . . . . . . . . . . . . . . . . . .1-1
1.2: Three-Phase Systems . . . . . . . . . . . . . . . . . . . . . . . . . . .1-2
1.3: Poly Phase Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-3
1.4: Consumption, Demand and Poor Power Factor . . . . . . . . . . . . . . . .1-3
1.5: Waveform and Harmonics . . . . . . . . . . . . . . . . . . . . . . . . .1-4
Chapter 2: Nexus Overview
2.1: The Nexus System . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-1
2.2: Measurements and Calculations . . . . . . . . . . . . . . . . . . . . . . .2-3
2.3: Demand Integrators . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-6
2.4: Nexus External I/O Modules (Optional) . . . . . . . . . . . . . . . . . . .2-7
2.5: Nexus Monitor Specifications . . . . . . . . . . . . . . . . . . . . . . . .2-8
2.6: Nexus P40N External Display Specifications . . . . . . . . . . . . . . . . .2-9
2.7: Nexus P60N Touch Screen Display Specifications . . . . . . . . . . . . . . .2-9
Chapter 3: Hardware Installation
3.1: Mounting the Nexus Monitor . . . . . . . . . . . . . . . . . . . . . . . .3-1
3.2: Mounting the Nexus P40N External Display . . . . . . . . . . . . . . . . .3-3
3.3: Mounting the Nexus P60N Touch Screen External Display . . . . . . . . . . .3-4
3.4: Mounting the Nexus External I/O Modules . . . . . . . . . . . . . . . . . .3-6
Chapter 4: Electrical Installation
4.1: Wiring the Monitored Inputs and Voltages . . . . . . . . . . . . . . . . . .4-1
4.2: Fusing the Voltage Connections . . . . . . . . . . . . . . . . . . . . . . .4-1
4.3: Wiring the Monitored Inputs -VRef . . . . . . . . . . . . . . . . . . . . .4-1
4.4: Wiring the Monitored Inputs - VAux . . . . . . . . . . . . . . . . . . . . .4-1
4.5: Wiring the Monitored Inputs - Currents . . . . . . . . . . . . . . . . . . .4-1
4.6: Isolating a CT Connection Reversal . . . . . . . . . . . . . . . . . . . . .4-2
4.7: Instrument Power Connections . . . . . . . . . . . . . . . . . . . . . . .4-2
4.8: Wiring Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3
Chapter 5: Communication Wiring
5.1: Communication Overview . . . . . . . . . . . . . . . . . . . . . . . . .5-1
5.2: RS-232 Connection-Nexus Monitor to a Computer . . . . . . . . . . . . . .5-5
5.3: RS-485 Wiring Fundamentals . . . . . . . . . . . . . . . . . . . . . . . .5-5
5.4: RS-485 Connection- Nexus Monitor to a Computer or PLC . . . . . . . . . . .5-9
5.5: RJ-11 (Telephone Line) Connection- Nexus with Internal Modem Option to PC . .5-9
5.6: RJ-45 Connection- Nexus with Internal Network Option to multiple PC’s . . . . .5-9
5.7: RS-485 Connection- Nexus to an RS-485 Master (Unicom or Modem Manager) .5-10
5.8: RS-485 Connectiion- Nexus Monitor to the Nexus P40N External Display . . . .5-11
5.9: RS-485 Connectiion- Nexus Monitor to the Nexus P60N External Display . . . .5-12
5.10: Communication Ports on the Nexus I/O Modules . . . . . . . . . . . . . .5-13
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5.11: RS-485 Connection—Nexus Monitor to Nexus I/O Modules . . . . . . . . .5-14
5.12: Steps to Determine Power Needed . . . . . . . . . . . . . . . . . . . .5-15
5.13: I/O Modules’ Factory Settings and VA Ratings . . . . . . . . . . . . . . .5-15
5.14: Linking Multiple Nexus Devices in Series . . . . . . . . . . . . . . . . .5-16
5.15: Networking Groups of Nexus Monitors . . . . . . . . . . . . . . . . . .5-17
5.16: Remote Communication Overview . . . . . . . . . . . . . . . . . . . .5-18
5.17: Remote Communication- RS-232 . . . . . . . . . . . . . . . . . . . . .5-21
5.18: Remote Communication- RS-485 . . . . . . . . . . . . . . . . . . . . .5-21
5.19: Programming Modems for Remote Communication . . . . . . . . . . . . .5-22
5.20: Selected Modem Strings . . . . . . . . . . . . . . . . . . . . . . . . .5-23
5.21: High Speed Inputs Connection . . . . . . . . . . . . . . . . . . . . . .5-23
5.22: IRIG-B Connections . . . . . . . . . . . . . . . . . . . . . . . . . .5-24
Chapter 6: Using the Nexus External Displays
6.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-1
6.2: Nexus P40N External Display . . . . . . . . . . . . . . . . . . . . . . .6-1
6.3: Dynamic Readings Mode . . . . . . . . . . . . . . . . . . . . . . . . .6-2
6.4: Navigational Map of Dynamic Readings Mode . . . . . . . . . . . . . . . .6-4
6.5: Nexus Information Mode . . . . . . . . . . . . . . . . . . . . . . . . . .6-5
6.6: Navigational Map of Nexus Information Mode . . . . . . . . . . . . . . . .6-6
6.7: Display Features Mode . . . . . . . . . . . . . . . . . . . . . . . . . .6-7
6.8: Navigational Map of Display Features Mode . . . . . . . . . . . . . . . . .6-8
6.9: Nexus P60N Touch Screen External Display . . . . . . . . . . . . . . . . .6-9
6.10: Navigational Map for P60N Touch Screen External Display . . . . . . . . .6-14
Chapter 7: Transformer Loss Compensation
7.1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-1
7.2: Nexus 1250 Transformer Loss Compensation . . . . . . . . . . . . . . . . .7-2
7.3: Loss Compensation Percentages . . . . . . . . . . . . . . . . . . . . . . .7-3
7.4: Application of Load Loss Compensation Percentages . . . . . . . . . . . . .7-6
7.5: Calculating Transformer Loss Compensation Percentages (Work Sheet) . . . . .7-7
Chapter 8: Nexus Time-of-Use
8.1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-1
8.2: The Nexus TOU Calendar . . . . . . . . . . . . . . . . . . . . . . . . .8-1
8.3: TOU Prior Season and Month . . . . . . . . . . . . . . . . . . . . . . . .8-2
8.4: Updating, Retrieving and Replacing TOU Calendars . . . . . . . . . . . . . .8-2
8.5: Daylight Savings and Demand . . . . . . . . . . . . . . . . . . . . . . .8-2
Chapter 9: Nexus External I/O Modules
9.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-1
9.2: Installing Nexus External I/O Modules . . . . . . . . . . . . . . . . . . . .9-2
9.3: Using Multiple I/O Modules . . . . . . . . . . . . . . . . . . . . . . . .9-3
9.4: Factory Settings and Reset Button . . . . . . . . . . . . . . . . . . . . . .9-4
9.5: Analog Transducer Signal Output Modules . . . . . . . . . . . . . . . . . .9-5
9.6: Analog Input Modules . . . . . . . . . . . . . . . . . . . . . . . . . . .9-7
9.7: Digital Dry Contact Relay Output (Form C) Module . . . . . . . . . . . . . .9-9
9.8: Digital Solid State Pulse Output (KYZ) Module . . . . . . . . . . . . . . .9-11
9.9: Digital Status Input Module—Status Detect or Pulse Accumulation . . . . . . .9-13
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Chapter 10: Nexus Monitor with Internal Modem Option
10.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . .10-1
10.2: Hardware Connection . . . . . . . . . . . . . . . . . . . . . . . . . .10-2
Chapter 11: Nexus Monitor with Internal Network Option
11.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .11-1
11.2: Hardware Connection . . . . . . . . . . . . . . . . . . . . . . . . . .11-3
Glossary of Terms
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eElectro Industries/GaugeTech Doc #: E107-7-06-121 viii
List of FiguresList of Figures
Chapter 1: Basic Tutorial on AC Power Measurement
Figure 1.1: Single Phase Power Systems . . . . . . . . . . . . . . . . . . . . . . .1-1
Figure 1.2: Relationships Between Apparent, Real and Reactive Power . . . . . . . . . .1-2
Figure 1.3: Three Phase Power Systems . . . . . . . . . . . . . . . . . . . . . . .1-2
Figure 1.4: Poly Phase Power Systems . . . . . . . . . . . . . . . . . . . . . . . .1-3
Chapter 2: Nexus Overview
Figure 2.1: The Nexus System . . . . . . . . . . . . . . . . . . . . . . . . . . .2-1
Chapter 3: Hardware Installation
Figure 3.1: Nexus Monitor Mounting Diagram, Top View . . . . . . . . . . . . . . .3-1
Figure 3.2: Nexus Monitor Mounting Diagram, Side View . . . . . . . . . . . . . . .3-2
Figure 3.3: Nexus P40N LED External Display Mounting Diagrams . . . . . . . . . . .3-3
Figure 3.4: Nexus P60N Touch Screen Display Mounting Diagrams . . . . . . . . . . .3-4
Figure 3.5: Nexus P60N Touch Screen Display Back Detail . . . . . . . . . . . . . . .3-4
Figure 3.6: Cutout for Nexus P60N Touch Screen Display . . . . . . . . . . . . . . .3-5
Figure 3.7: Nexus P60N Touch Screen Display Bezel Mounting Diagram . . . . . . . . .3-5
Figure 3.8: Nexus I/O Modules Mounting Diagram, Overhead View . . . . . . . . . . .3-6
Figure 3.9: Nexus I/O Module Communication Ports . . . . . . . . . . . . . . . . . .3-6
Figure 3.10: Nexus I/O Modules Mounting Diagram, Front View . . . . . . . . . . . .3-7
Chapter 4: Electrical Installation
Figure 4.1: 4-Wire Wye, 3-Element Direct Voltage with 4 CTs . . . . . . . . . . . . .4-4
Figure 4.2: 4-Wire Wye, 3-Element with 3 PTs and 4 CTs . . . . . . . . . . . . . . .4-5
Figure 4.3: 3-Wire, 2-Element Open Delta with 2 PTs and 3 CTs . . . . . . . . . . . .4-6
Figure 4.4: 3-Wire, 2-Element Open Delta with 2 PT and 2 CTs . . . . . . . . . . . . .4-7
Figure 4.5: 3-Wire, 2-Element Delta Direct Voltage with 3 CTs . . . . . . . . . . . . .4-8
Figure 4.6: 3-Phase, 4-Wire Wye, 2.5 Element with 2 PTs and 3 CTs . . . . . . . . . . .4-9
Figure 4.7: 4-Wire, 3-Element Grounded Delta with 4 CTs . . . . . . . . . . . . . .4-10
Chapter 5: Communication Wiring
Figure 5.1: Communication Overview . . . . . . . . . . . . . . . . . . . . . . . .5-1
Figure 5.2: RJ-11 Communication with Internal Modem Option . . . . . . . . . . . . .5-2
Figure 5.3: RJ-45 Communication with Internal Network Option . . . . . . . . . . . .5-3
Figure 5.4: Communication Wiring . . . . . . . . . . . . . . . . . . . . . . . . .5-4
Figure 5.5: Nexus Port 1—RS-232/RS-485 Communication . . . . . . . . . . . . . .5-5
Figure 5.6: Nexus RS-485 Port (Ports 1–4) . . . . . . . . . . . . . . . . . . . . . .5-6
Figure 5.7: Straight Line and Loop Topologies . . . . . . . . . . . . . . . . . . . .5-7
Figure 5.8: Incorrect “T” and “Star” Topologies . . . . . . . . . . . . . . . . . . . .5-8
Figure 5.9: Nexus Monitor Connected to an RS-485 Master . . . . . . . . . . . . . .5-10
Figure 5.10: Nexus Monitor Connected to Nexus P40N External Display . . . . . . . .5-11
Figure 5.11: Nexus Monitor Connected to Nexus P60N Touch Screen Display . . . . . .5-12
Figure 5.12: Communication Ports on the Nexus I/O Modules . . . . . . . . . . . . .5-13
Figure 5.13: Nexus Monitor Connected to Nexus I/O Module . . . . . . . . . . . . .5-14
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Figure 5.14: Linking Multiple Nexus Devices in Series . . . . . . . . . . . . . . . .5-15
Figure 5.15: Networking Groups of Nexus Monitors . . . . . . . . . . . . . . . . .5-16
Figure 5.16: Remote Connections—RS-232/RS-485 . . . . . . . . . . . . . . . . .5-17
Figure 5.17: Remote Connections with Internal Modem Option . . . . . . . . . . . .5-18
Figure 5.18: Remote Connections with Internal Network Option . . . . . . . . . . . .5-19
Figure 5.19: Standard Null Modem Configuration . . . . . . . . . . . . . . . . . .5-20
Figure 5.20: High Speed Inputs Connection . . . . . . . . . . . . . . . . . . . . .5-22
Figure 5.21: IRIG-B Connection . . . . . . . . . . . . . . . . . . . . . . . . . .5-23
Chapter 6: Using the Nexus External Displays
Figure 6.1: Nexus P40N LED External Display . . . . . . . . . . . . . . . . . . . .6-1
Figure 6.2: Nexus P60N Touch Screen External Display . . . . . . . . . . . . . . . .6-9
Screen Captures for All Readings . . . . . . . . . . . . . . . . .6-9 - 6-13
Chapter 9: Nexus External I/O Modules
Figure 9.1: I/O Module Components . . . . . . . . . . . . . . . . . . . . . . . . .9-1
Figure 9.2: Nexus Monitor Connected to I/O Module . . . . . . . . . . . . . . . . .9-2
Figure 9.3: Multiple I/Os . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-3
Figure 9.4: I/O Port on the 4 & 8-Channel Analog Output Modules . . . . . . . . . . .9-6
Figure 9.5: I/O Port on the 8-Channel Analog Input Module . . . . . . . . . . . . . .9-8
Figure 9.6: I/O Port on the Digital Dry Contact Relay Module . . . . . . . . . . . . .9-10
Figure 9.7: I/O Port on the Digital Solid State Pulse Output (KYZ) Module . . . . . . .9-12
Figure 9.8: I/O Port on the Digital Input Module . . . . . . . . . . . . . . . . . . .9-14
Chapter 10: Nexus Monitor with Internal Modem Option
Figure 10.1: Nexus with Internal Modem Option . . . . . . . . . . . . . . . . . . .10-1
Chapter 11: Nexus Monitor with Internal Network Option
Figure 11.1: Nexus with Internal Network Option . . . . . . . . . . . . . . . . . .11-1
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eElectro Industries/GaugeTech Doc #: E107-7-06-121 1-1
Single Phase
2 Wires
Chapter 1Chapter 1
Basic Tutorial on AC Power MeasurementBasic Tutorial on AC Power Measurement
1.1: Single Phase Power Systems1.1: Single Phase Power Systems
The economics of electric power distribution networking dictate several configurations of AC power
transmission. The number of phases and voltage levels characterize these configurations.
A single phase system is the basic, two-wire system used in low-power distribution applications, such as
residential communities and offices. The voltage is typically 120VAC. For higher power requirements,
such as small commercial facilities, the typical power configuration is two lines of 120VAC opposite in
phase. This system produces 120 volts from line-to-neutral for lighting and small appliance use. The
line-to-line voltage is 240V AC, used for higher loads such as water heaters, electric dryers, ranges and
machinery.
nPower (W) in a single phase system is:
E = potential, I = current, and cos = phase difference between the potential and the current.
nPower (W) in a 120/240VAC system is:
Phase differential between the potential and the current results from a non-resistive load, either
reactive or capacitive.
nn Reactive power (VAR) is the additional power consumed that does not produce any work but must
be delivered to the load:
This is a measure of the inefficiency of the electrical system.
nn Apparent power (VA) is the total power delivered to the load, and the vector sum of real power and
reactive power.
Single Phase
3 Wires
Neutral
Line
Line 1
Neutral
Line 2
Figure 1.1: Single Phase Power Systems
È
I
E
W
cos
×
×
=
)cos()cos( 2211 Θ××+Θ××= LineLineLineLine IEIEW
Θ
×
×
=
sin
I
E
VAR
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eElectro Industries/GaugeTech Doc #: E107-7-06-121 1-2
nn Power Factor (PF) is the ratio between real power and apparent power. Ideal power distribution
should have a PF of 1. This condition can be met only if no reactive power loads exist. In real life
applications, many loads are inductive loads. Corrective capacitors are installed to correct poor Power
Factor.
1.2: Three-Phase Power Systems1.2: Three-Phase Power Systems
Athree-phase system delivers higher levels of power for industrial and commercial applications; the
three phases correspond to three potential lines. A 120° phase shift exists between the three potential
lines. A typical three-phase configuration has either a Delta connection or a Wye connection. In a three
phase system, the voltage levels between the phases and the neutral are uniform and defined by:
Real Power (W)
B
A
N
B
C
A
C
Delta Wye
Figure 1.2: Relationships Between Apparent, Real and Reactive Power
Figure 1.3: Three Phase Power Systems
22 VARW
W
VA
W
PF + ==
333 acbcab
cnbnan EEE
EEE =====
PF
=
Θ
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Voltages between the phases vary depending on loading factors and the quality of distribution
transformers. The three phase system is distributed in different voltage levels: 208VAC; 480VAC;
2,400VAC; 4,160VAC; 6,900VAC; 13,800VAC, etc.
1.3: Poly Phase Power Systems1.3: Poly Phase Power Systems
Power measurement in a poly phase system is governed by Blondel’s Theorem. Blondel’s Theorem
states that in a power distribution network that has N conductors, the number of measurement elements
required to determine power is N-1. A typical configuration of a poly phase system has either a Delta
connection or a Wye connection.
eElectro Industries/GaugeTech Doc #: E107-7-06-121 1-3
1.4: Consumption, Demand and Poor Power Factor1.4: Consumption, Demand and Poor Power Factor
nConsumption is the total electric energy usage over a time period, expressed in WH.
W = instantaneous power; T = time in hours.
WH = W x T
Consumption is typically measured in kilowatt-hours (kWh):one thousand watts consumed over one
hour. Utilities use the WH equation to determine the overall consumption in a billing period.
Delta
Wye
Figure 1.4: Poly Phase Power Systems
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nDemand is the average energy consumed over a specified time interval. The interval is determined
by the utility, typically, 15 or 30 minutes. The utility measures the maximum demand over a billing
period. This measurement exhibits a deviation from average consumption, forcing the utility to
provide generating capacity to satisfy a higher maximum consumption demand. The highest average
demand is retained in the metering system until the demand level is reset.
nPoor Power Factor results in reactive power consumption. Transferring reactive power over a
distribution network causes energy loss. To force consumers to correct their Power Factor, utilities
monitor reactive power consumption and penalize the user for poor power factor.
1.5: Waveform and Harmonics1.5: Waveform and Harmonics
Ideal power distribution has sinusoidal waveforms on voltages and currents. In real life applications,
where inverters, computers and motor controls are used, distorted waveforms are generated. These
distortions consist of harmonics of the fundamental frequency.
nSinusoidal waveform:
nDistorted waveform:
nPercent of Total harmonic distortion (% of THD):
nHarmonic distortion is a destructive force in power distribution systems. It creates safety problems,
shortens the life span of distribution transformers, and interferes with the operation of electronic
devices. The Nexus 1250 monitors the harmonic distortion to the 83rd harmonic. A waveform
capture of the distorted waveform can be read with the Nexus Communicator software.
eElectro Industries/GaugeTech Doc #: E107-7-06-121 1-4
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SignallFundamentatheofRMS SignalDistortionHarmonicTotalofRMS
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eElectro Industries/GaugeTech Doc #: E107-7-06-121 2-1
Chapter 2Chapter 2
Nexus OverviewNexus Overview
2.1: The Nexus System2.1: The Nexus System
Electro Industries’ Nexus 1250 combines high-end revenue metering with sophisticated power quality
analysis. Its advanced monitoring capabilities provide detailed and precise pictures of any metered point
within a distribution network. Extensive I/O capability is available in conjunction with all metering
functions. The optional Nexus Communicator software allows a user to poll and gather data from
multiple Nexus monitors installed at local or remote locations (see the Nexus Communicator User
Manual for details). On-board mass memory enables the Nexus to retrieve and store multiple logs. The
Nexus Monitor with Internal Modem (or Network) Option connects to a PC via standard phone line (or
MODBUS/TCP) and a daisy chain of Nexus Monitors via an RS-485 connection. See Chapters 10 and
11 for details.
Figure 2.1: The Nexus System
Computer
or SCADA
System
Nexus
Display
Expandable I/O Modules
Nexus Monitor
Modem/Ethernet
Option
Modem Gateway or
Ethernet Gateway
RS-485 Connection
Modem/Ethernet
Option
RJ-11 or RJ-45
Connection
Courtesy of NationalSwitchgear.com

eElectro Industries/GaugeTech Doc #: E107-7-06-121 2-2
nNexus 1250 Revenue Metering:
•Delivers laboratory-grade 0.04% Watt-hour accuracy in a field-mounted device.
•Auto-calibrates when there is a temperature change of more than 10 degrees centigrade.
•Exceeds all ANSI C-12 and IEC 687 specifications.
•Adjusts for transformer and line losses, using user-defined compensation factors.
•Automatically logs time-of-use for up to eight programmable tariff registers.
•Counts pulses and aggregates different loads.
nNexus 1250 Power Quality Monitoring:
•Records up to 512 samples per cycle on an event.
•Records sub-cycle transients on voltage or current readings.
•Measures and records Harmonics to the 83rd order.
•Offers inputs for neutral-to-ground voltage measurements.
•Synchronizes with IRIG-B clock signal.
nNexus 1250 Memory, Communication and Control:
•Up to 4 Meg NVRAM.
•4 High Speed Communication Ports.
•Multiple Protocols.
•Built-in RTU functionality.
•Built-in PLC functionality.
•90msec High Speed Updates for Control.
Courtesy of NationalSwitchgear.com

eElectro Industries/GaugeTech Doc #: E107-7-06-121 2-3
2.2: Measurements and Calculations2.2: Measurements and Calculations
The Nexus 1250 Monitor measures many different power parameters. The following is a list of the
formulas used to conduct calculations.
nRoot Mean Square (RMS) of Voltages:
n = number of samples
nRoot Mean Square (RMS) of Currents:
n = number of samples
nRoot Mean Square (RMS) of Phase to Phase Voltages
n = number of samples
nApparent Power (VA):
( )
n
n
ttx
v
∑
=
=1
2
RMS
( )
n
n
ttx
rms
i
I∑
=
=1
2
( ) ( )
( )
n
V
xy
n
tty
txV
∑
=−
=1
2
rmsrms IV
×
=
VA
Courtesy of NationalSwitchgear.com

eElectro Industries/GaugeTech Doc #: E107-7-06-121 2-4
nReactive Power (VAR):
nPower (Watts):
nPower Factor (PF):
nPhase Angles:
x
x
xVA
Watt
=PF
)(cos 1PF
−
=∠
Watt
VA
xx
x
22
VAR −=
samplessample IV
×
=
W
Courtesy of NationalSwitchgear.com