Megger MVCT User manual

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MEGGER VOLTAGE AND CURRENT TRANSFORMER TEST
INSTRUMENT
MVCT USER MANUAL
May 8, 2020
Part#86027R5

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Table of Contents
1.0 MVCT............................................................................................................................................. 12
1.0 Introduction...........................................................................................................................................12
1.2 Terminology...........................................................................................................................................12
1.2.1 Acronyms ....................................................................................................................12
2.0 MVCT Unpack and Preparation for Use........................................................................... 13
2.1 Contents of MVCT kit............................................................................................................................13
2.2 Assembly and Installation................................................................................................................15
2.3 Communication Ports ........................................................................................................................15
2.3.1 Ethernet Ports on MVCT .............................................................................................15
2.3.2 Ethernet Ports on Display ...........................................................................................16
2.3.3 USB 2.0 Interface on Display......................................................................................16
2.4 Supply Voltage ......................................................................................................................................16
2.5 Operating System.................................................................................................................................17
3.0 Basic Theory of Operation.................................................................................................... 17
3.1 General.....................................................................................................................................................17
3.2 CT Testing ...................................................................................................................................................17
3.2.1 Ratio Test .....................................................................................................................17
3.2.2 Polarity Test .................................................................................................................18
3.2.3 Excitation Test..............................................................................................................20
3.2.4 Insulation Resistance Test............................................................................................21
3.2.5 Burden Test..................................................................................................................22
3.2.6 Secondary Winding Resistance ....................................................................................23
4.0 Powering System ..................................................................................................................... 23
4.1. Initial Start Up.......................................................................................................................................23
5.0 User Interface ............................................................................................................................ 24
5.1 Integrated Display or Smart Touch View Interface...............................................................24
5.2 Personal Computer Interface.........................................................................................................25
5.3 Software Interface..............................................................................................................................29
5.4 Testing Mode.................................................................................................................................................32
5.4.1 CT Testing Mode –Menu Items.......................................................................................32
5.4.2 VT Testing Mode –Menu Items..................................................................................64
5.4.2.7 Self Test................................................................................................................................................72
5.4.3 Relay Testing Mode........................................................................................................................81
6.0 Testing CT with MVCT ........................................................................................................... 82
6.1 Test Plan Creation ...............................................................................................................................82
6.2 CT Saturation Test...............................................................................................................................86
6.2.1 Method 1 –Concurrent...............................................................................................86
6.2.2 Method 2 –Non Concurrent or Testing a Single Tap..................................................90
6.3 Ratio Test ................................................................................................................................................94
6.3.1 Method 1 –Concurrent...............................................................................................94
6.3.2 Method 2 –Non Concurrent or Testing a Single Tap...................................................98
6.4 CT Winding Resistance Test:........................................................................................................103
6.4.1 Method 1 –Concurrent.............................................................................................103
6.4.2 Method 2 –Non Concurrent or Testing a Single Tap................................................107

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6.5 Insulation Test:.................................................................................................................................. 111
6.6 Burden Test.........................................................................................................................................114
6.7 Manual Test......................................................................................................................................... 118
6.8 Demagnetization............................................................................................................................... 121
6.9 Self Test................................................................................................................................................. 123
7.0 Testing VT’s with MVCT ......................................................................................................125
7.1 Running a Complete Test of VT and Test Plan Creation................................................... 125
7.2 Testing VT Ratio and Phase......................................................................................................... 131
7.3 Testing Voltage Transformer –Saturation/Excitation Test............................................135
7.4 Testing Voltage Transformer Winding Resistance :..........................................................138
7.5 Testing Voltage Transformer: Secondary Short Circuit Impedance........................... 141
7.6 Testing Voltage Transformer : Demagnetization ................................................................ 145
7.7 Testing Voltage Transformer: Self Diagnostic ......................................................................147
8.0 Testing Relays with MVCT..................................................................................................149
9.0 Service Data .............................................................................................................................149
9.1 Preventive Maintenance ................................................................................................................149
9.1.1 Examine the unit every six months for: .....................................................................150
9.1.2 Upgrading Software ..................................................................................................150
9.2 Service and Repair Instructions .................................................................................................151
9.2.1 Basic Troubleshooting...............................................................................................151
10.0 Preparation for Reshipment..............................................................................................152
Appendix I CTs Mounted on Transformer Bushings............................................................154
Appendix II Testing CT in Reactor ..............................................................................................157
Appendix III CTs Inside Delta Connection ...............................................................................159

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List of Figures
Figure 1 Ethernet Ports ............................................................................................................... 16
Figure 2 Ethernet Port to Power Display...................................................................................... 16
Figure 3 USB Port......................................................................................................................... 16
Figure 4 Initial Screen................................................................................................................... 24
Figure 5 Instrument Connection Screen ....................................................................................... 25
Figure 6 Boot Up Home Screen.................................................................................................... 25
Figure 7 PowerDB Lite Initial Screen .......................................................................................... 26
Figure 8 Instrument Configuration Dialog ................................................................................... 27
Figure 9 Form Selection Dialog.................................................................................................... 27
Figure 10 Instrument Logon Screen ............................................................................................. 28
Figure 11 Connection Dialog........................................................................................................ 28
Figure 12 PowerDB Lite Home Screen ........................................................................................ 29
Figure 13 Device Settings –CT Testing....................................................................................... 33
Figure 14 Name Plate Data –CT Testing Mode........................................................................... 36
Figure 15 Home Screen CT Testing ............................................................................................. 38
Figure 16 Run All Test Screen...................................................................................................... 39
Figure 17 Manual Test Screen...................................................................................................... 40
Figure 18 Manual Test Connection Diagram................................................................................ 42
Figure 19 Manual Test Example................................................................................................... 44
Figure 20 Demagnetization Connection Diagram ........................................................................ 45
Figure 21 Demagnetization Process.............................................................................................. 46
Figure 22 Self Test Connection Diagram ..................................................................................... 47
Figure 23 Saturation Test Screen.................................................................................................. 48
Figure 24 Ratio Test Screen.......................................................................................................... 49
Figure 25 Winding Resistance Test Screen .................................................................................. 51
Figure 26 Insulation Resistance Test Screen................................................................................ 53
Figure 27 Burden Test Screen....................................................................................................... 54
Figure 28 Sample CT Test Report................................................................................................ 55
Figure 29 Sample Multi Tap Test Report .................................................................................... 57
Figure 30 Ratio and Phase Error Tables....................................................................................... 58
Figure 31 Report Tap Configuration Dialog................................................................................. 59
Figure 33 Excitation Curve Data .................................................................................................. 60
Figure 34 View Excitation Data Points ........................................................................................ 61
Figure 35 File Operation Tool Bar................................................................................................ 61
Figure 36 File Manager Screen..................................................................................................... 62
Figure 37 File Operations Using PC............................................................................................. 63
Figure 38 File Save Using PC....................................................................................................... 64
Figure 39 Device Settings –VT Testing....................................................................................... 64
Figure 40 Name Plate Data –VT Testing Mode .......................................................................... 67
Figure 41 Home Screen VT Testing Mode................................................................................... 69
Figure 42 Run All Test Screen...................................................................................................... 70
Figure 43 Demagnetization Connection Diagram ........................................................................ 71
Figure 44 Demagnetization Process.............................................................................................. 72
Figure 45 VT Ratio Test Screen ................................................................................................... 73
Figure 46 Saturation Test Screen.................................................................................................. 74

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Figure 47 VT Winding Resistance Test Screen............................................................................ 75
Figure 48 Short Circuit Impedance Test Screen........................................................................... 76
Figure 49 Sample VT Test Report................................................................................................ 77
Figure 50 Testing - File Operation Tool Bar............................................................................ 78
Figure 51 VT Testing: File Manager Screen ................................................................................ 79
Figure 52 VT Testing: File Save from PC.................................................................................... 81
Figure 53 Relay Testing System Log On...................................................................................... 81
Figure 54 Relay Testing Screen.................................................................................................... 82
Figure 55 Run All Tests –Configuration ..................................................................................... 83
Figure 56 Test Plan - Multi Tap.................................................................................................... 84
Figure 57 CT Connection Diagram Multi Tap: Concurrent ......................................................... 85
Figure 58 CT Saturation Testing Screen: Concurrent.................................................................. 85
Figure 59 CT Test Report - Concurrent........................................................................................ 86
Figure 60 CT Saturation Test Screen - Concurrent ...................................................................... 88
Figure 61 CT Saturation Connection Diagram - Concurrent........................................................ 88
Figure 62 CT Saturation Testing Screen –Concurrent................................................................. 89
Figure 63 CT Saturation Results Screen - Concurrent.................................................................. 90
Figure 64 CT Saturation Test Screen –Non Concurrent.............................................................. 91
Figure 65 CT Saturation Connection Diagram - Non Concurrent................................................ 92
Figure 66 CT Saturation Test Screen Non Concurrent................................................................. 93
Figure 67 CT Ratio Test Screen –Concurrent.............................................................................. 95
Figure 68 CT Ratio Connection Diagram - Concurrent................................................................ 96
Figure 69 CT Ratio Test Abort..................................................................................................... 97
Figure 70 CT Ratio Test Results - Concurrent ............................................................................. 98
Figure 71 CT Ratio Test Screen –Non Concurrent.................................................................... 100
Figure 72 CT Ratio Test Connection Diagram - Non Concurrent.............................................. 101
Figure 73 CT Ratio Testing Screen - Abort................................................................................ 102
Figure 74 CT Ratio Test Results –Non Concurrent................................................................... 103
Figure 75 CT Winding Test Screen –Concurrent ..................................................................... 105
Figure 76 CT Winding Connection Diagram –Concurrent........................................................ 105
Figure 77 CT Winding Test ABORT.......................................................................................... 106
Figure 78 CT Winding Results - Concurrent.............................................................................. 107
Figure 79 CT Winding Test Screen –Non Concurrent .............................................................. 108
Figure 80 CT Winding Resistance Connection Diagram Non Concurrent................................. 109
Figure 81 CT Winding Test Screen –Abort................................................................................ 110
Figure 82 CT Winding Results - Non Concurrent...................................................................... 110
Figure 83 CT Insulation Test Screen.......................................................................................... 112
Figure 84 CT Insulation Test Connection Diagram.................................................................... 113
Figure 85 CT Insulation Testing Screen..................................................................................... 113
Figure 86 CT Insulation Test Results ......................................................................................... 114
Figure 87 CT Burden Test Screen .............................................................................................. 115
Figure 88 CT Burden Test Connection Diagram........................................................................ 116
Figure 89 CT Burden Test Abort................................................................................................ 117
Figure 90 CT Burden Test Results Screen.................................................................................. 117
Figure 91 CT Manual Test Screen.............................................................................................. 119
Figure 92 CT Manual Test Connection Diagram ....................................................................... 120

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Figure 93 CT Demagnetization Connection Diagram................................................................ 122
Figure 94 CT Demagnetizing Process Screen ............................................................................ 123
Figure 95 CT Self Diagnostic Connection Diagram................................................................... 124
Figure 96 CT Self Diagnostic Test Screen ................................................................................. 125
Figure 97 VT Test Plan Screen................................................................................................... 126
Figure 98 VT Connection Diagram for Winding Resistance...................................................... 128
Figure 99 VT Winding Resistance Abort ................................................................................... 128
Figure 100 VT Demagnetization ................................................................................................ 129
Figure 101 VT Saturation/Excitation Test.................................................................................. 129
Figure 102 VT Short Circuit Impedance Connection Diagram.................................................. 130
Figure 103 VT Ratio Test Connection Diagram......................................................................... 130
Figure 104 Sample VT Test Report............................................................................................ 131
Figure 105 VT Ratio Test Screen ............................................................................................... 133
Figure 106 VT Ratio Test Connection Diagram......................................................................... 133
Figure 107 VT Ratio Testing Screen.......................................................................................... 134
Figure 108 VT Ratio Test Results .............................................................................................. 135
Figure 109 VT Saturation Test Screen........................................................................................ 136
Figure 110 VT Saturation Connection Diagram......................................................................... 137
Figure 111 VT Saturation Test Screen....................................................................................... 138
Figure 112 VT Winding Test Screen.......................................................................................... 139
Figure 113 VT Winding Resistance Connection Diagram ......................................................... 140
Figure 114 VT Winding Test Screen –Abort.............................................................................. 141
Figure 115 VT Winding Results................................................................................................. 141
Figure 116 VT Secondary Short Circuit Impedance Test Screen............................................... 142
Figure 117 VT Short Circuit Impedance Connection Diagram.................................................. 143
Figure 118 VT Short Circuit Impedance –Abort........................................................................ 144
Figure 119 VT Short Circuit Impedance Results........................................................................ 144
Figure 120 VT Demagnetization Connection Diagram.............................................................. 146
Figure 121 VT Demagnetization Screen –Abort........................................................................ 147
Figure 122 Self Diagnostic Connection Diagram....................................................................... 148
Figure 123 Self Diagnostic Test Screen...................................................................................... 149

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IMPORTANT
This manual, as well as the hardware and software described in it, is furnished under license and may be
used or copied only in accordance with the terms of such license. The content of this manual is
furnished for informational use only, is subject to change without notice. Megger assumes no
responsibility or liability for any errors or inaccuracies that may appear in this manual.
The information and data in this User Manual are proprietary. The equipment described herein may be
protected by U.S. patents. Megger specifically reserves all rights to such proprietary information as well
as rights under any patent, none of which is waived by the submission of this user manual.
Except as permitted by such license, no part of this publication may be reproduced, stored in a retrieval
system, or transmitted, in any form or by any means, electronic, mechanical, recording, or otherwise,
without the prior written permission of Megger.
Megger, the Megger logo are trademarks of Megger. All other trademarks are the property of their
respective owners.
Notice to U.S. government end users. The hardware, software and documentation are “commercial
items”, as that term is defined at 48 C.F.R. §2.101, consisting of “commercial computer software” and
“commercial computer software documentation,” as such terms are used in 48 C.F.R. §12.212 or 48
C.F.R. §227.7202, as applicable. Consistent with 48 C.F.R. §12.212 or 48 C.F.R. §§227.7202-1 through
227.7202-4, as applicable, the commercial computer software and commercial computer software
documentation are being licensed to U.S. government end users (1) only as commercial items and (2)
with only those rights as are granted to all other end users pursuant to the terms and conditions set
forth in the Megger standard commercial agreement for this software and hardware. Unpublished
rights reserved under the copyright laws of the United States. The recipient, if a Government agency,
acknowledges that this manual and the equipment described were procured with "Limited Rights" to
technical data as described in ASPR 9-203 (b).
The STVI includes an RTOS-resident computer program. This program belongs to Megger and contains
trade secret ideas and information of Megger.
Written and designed at Megger, 4271 Bronze Way, Dallas, Texas 75237.
__________________________
Printed in the USA.
2013 Megger, all rights reserved.

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SAFETY PRECAUTIONS
WARNING:
VOLTAGES GENERATED BY THIS INSTRUMENT CAN BE HAZARDOUS
This instrument has been designed for operator safety; however, no design can completely
protect against incorrect use. Electrical circuits are dangerous and can be lethal when lack of
caution and poor safety practices are used. There are several standard safety precautions that
should be taken by the operator. Where applicable, IEC safety markings have been placed on the
instrument to notify the operator to refer to the user manual for instructions on correct use or
safety related topics. Refer to the following table of symbols and definitions.
Symbol
Description
Direct Current
Alternating Current
Both direct and alternating current
Earth (ground) Terminal. There is a common chassis ground terminal
located on the front panel (see Front panel under Description of
Controls.
Protective Conductor Terminal
Frame or Chassis Terminal
On (Supply)
Off (Supply)
Caution, risk of electric shock

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Caution (refer to accompanying documents)
WARNING: Under no circumstances should the operator or technician attempt to open or
service any Megger instrument while connected to a power source. Lethal voltages are present and
may cause serious injury or death! SAFETY PRECAUTIONS (Continued)
The following are some specific safety related items associated with the MVCT test system.
Read and understand all safety precautions and operation instructions before attempting to use this
unit.
The purpose of this equipment is limited to use as described in this instruction manual. Should a
situation arise that is not covered in the general or specific safety precaution please contact Megger
regional representative or Megger, Dallas Texas.
Safety is the responsibility of the user. Misuse of this equipment can be extremely dangerous.
Always start with the power OFF, before connecting the power cord. Make sure outputs are off before
attempting to make test connections.
DO NOT attempt to connect the test set to energized equipment.
DO NOT attempt to connect the test set to Current Transformers unless the Primary Side of the Current
Transformer is grounded.
Always use properly insulated test leads. The optional test leads are rated for the continuous output
ratings of the test system, and should be properly used and cared for. DO NOT use cracked or broken
test leads.
Always turn the test system off before disconnecting the power cord.
DO NOT attempt to use the unit without a safety ground connected.
DO NOT attempt to use the unit if the power cord ground prong is broken or missing.
DO NOT use the test set in an explosive atmosphere.

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The instrument must only be used by suitably trained and competent persons.
Observe all safety warnings marked on the equipment.
For safety related or other important topics, like the statement below, will be notated with the adjoined
symbol. Read the topic carefully as it may relate either to the safe operation of the test system or the
safety of the operator.
Under no circumstances should the operator put their hand or tools inside the test system
chassis area with the test system connected to a power source. Lethal voltages are present
and may cause serious injury or death!
WEEE
The crossed out wheeled bin placed on Megger products is a reminder not to dispose of the product at
the end of its life with general waste.
Megger is registered in the UK as a Producer of Electrical and Electronic Equipment. The Registration No
is WEE/HE0146QT
IEC Enclosure Rating: IP20

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Megger

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1.0 MVCT
1.0 Introduction
The Megger MVCT test set is a lightweight, robust, portable unit used to automatically or manually test
both voltage and current transformers. For inductive VT, the MVCT is capable of performing saturation,
ratio, secondary winding resistance, secondary short circuit impedance and various insulation tests. The
MVCT is also capable of performing saturation, ratio, polarity, winding resistance, demagnetizing tests
and insulation tests on current transformers. The MVCT provides a microprocessor controlled variable
voltage and current output and precision instrumentation for automatically testing single and multi-
ratio CTs and VT’s reducing testing time and increasing productivity. The MVCT will directly connect to
multi ratio CT’s and perform all tests – saturation, ratio and polarity, winding resistance, and insulation –
on all taps with the push of a button and without changing leads. The MVCT can be controlled via an
integrated large, full color, high resolution, TFT LCD touch screen which allows the user to perform
manual and automatic testing quickly and easily using the manual test screens, as well as using pre-
constructed test routines. The large color display permits the user to easily read all pertinent data while
the test is being performed and provides the ability to view the current transformer’s saturation curve.
The MVCT can also be configured to come without a display and be controlled via a laptop.
Both current transformers and voltage transformers can be tested in their equipment configuration,
such as being mounted in transformers, oil circuit breakers or switchgear. It is necessary for the
equipment to be completely isolated from the electrical system prior to testing.
1.2 Terminology
The acronyms, terms, and definitions used throughout this manual are described below:
1.2.1 Acronyms
AC Alternating Current
CW Clockwise (rotation)
CCW Counter Clockwise (rotation)
CT Current Transformer
DC Direct Current
GPS Global Position System
GUI Graphical User Interface
Hz Hertz

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ID Identification
I/O Input/Output
kHz Kilo Hertz
LCD Liquid Crystal Display
LED Light Emitting Diode
MAG Magnitude
PC Personal Computer
ROM Read-Only Memory
STVI Smart Touch View Interface
USB Universal Serial Bus
VIGEN Voltage / Current Generator Module
VRMS Volts Root Mean Square
VT Voltage Transformer
UUT Unit Under Test
2.0 MVCT Unpack and Preparation for Use
2.1 Contents of MVCT kit
After unpacking the unit and check for evidence of any shipping damage. If there is any visual damage,
immediately notify the freight carrier to make a damage claim, and notify Megger of the damage.
Contents within the shipping container will vary depending upon how the MVCT was configured. Below
is a complete list of all accessories available with the MVCT. Please check the order and the
configuration of your MVCT to confirm which accessories should be included with your instrument.
Item (Qty.) Cat No.
MVCT Voltage and Current Transformer Test Instrument MVCT
CT Test Accessories ( Standard Leads )

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Test Lead, H1 and H2 40ft. (1ea.) 1009-515
Test Lead, X1 to X5, 20ft., (1ea.) 1009-332
VT Test Accessories (VT Leads )
VT Test Lead, Primary Side 40ft. (1ea.) 620149
Test Accessories ( Included Any Configuration )
Line cord, North America (1ea.) 90015-267
Or Line cord, International color coded wire (1ea.) 90015-267
Gnd lead, green with yellow, with large ground clip, 20ft., (1ea) 620151
Large Test clip, red, 40mm opening, (1ea.) 640266
Large Test clip, black, 40mm opening, (1ea.) 640267
Alligator clip, black, 4.1 mm, (1ea.) 9004-267
Cable Spade/Lug Adapter small ( 5 ea.) 684004
Cable Spade/Lug Adapter large ( 5 ea ) 684003
Soft side lead case 90004-427
Soft side clip case 90001-165
USB memory stick 830029
Instruction book 750025
Power DB Lite 544342
Check the equipment received against the packing list to ensure that all the materials are present. Notify
Megger of any shortages. Telephone [phone] and ask for Dallas customer service department.
Again if damage received in transit is discovered, file a claim with the carrier at once and notify Megger
or its nearest authorized sales representative, giving a detailed description of the damage.
Megger warrants the product is free of defects in material and workmanship for a period of one (1) year
from date of shipment. This warranty is non-transferable. This warranty is limited and shall not apply to
equipment that has damage, or cause of defect, due to accident, negligence, and improper operation,
faulty installation by the purchaser, or improper service or repair by any person, company or
corporation not authorized by Megger. Megger will, at its' option, either repair or replace those parts
and/or materials it deems to be defective.

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The warranty is in lieu of all other warranties, either expressed or implied on the part of Megger and in
no event shall Megger be liable for the consequential damages due to the breach thereof.
2.2 Assembly and Installation
The MVCT has been thoroughly tested and inspected to meet rigid specifications before being shipped.
The unit is ready for use without any need of assembly or any installation procedure. Follow the
instructions in this manual to understand the controls and operations of the unit before setting it up for
performing the tests.
The MVCT can be ordered either with or without an integrated display. If no display was ordered then
the unit may be controlled using a PC and the included software. The MVCT ordered with a display will
have an 10 inch TFT Color Display integrated into the lid –this touch panel display provides high
resolution, and features Wide Viewing Angle Technology with high luminance for reading in direct
sunlight. The control knob is located on the front panel. During manual testing this knob will adjust
values once the box location of the value to be changed is selected.
Power Over Ethernet Input Power
The integrated display gets Power Over Ethernet (PoE) of 48 Volts DC at 0.5 A from the MVCT.
CAUTION:
NOTE: The PoE power supply DC voltage is ON when the power supply is connected to a power
source. Connect the Ethernet cable to the Data & Power Out port of the PoE power supply to the
display Ethernet port prior to connecting to a power source.
2.3 Communication Ports
There are two types of communication ports on the MVCT, three Ethernet, and one USB ports. The
Ethernet Ports are a 10/100BaseTX port. These ports supports MDI/MDI-X auto cross over configuration,
which means both standard and “crossover” Ethernet cables
2.3.1 Ethernet Ports on MVCT
There is one Ethernet port on the MVCT for connecting the integrated display or a Megger STVI to the
unit. On the MVCT this port is labeled STVI. This port contains the PoE power supply, and will provide
power to either the display or an STVI. The IN port on the MVCT may be used to interconnect multiple
SMRT units together for synchronous multi-phase operation.. The third Ethernet port label PC is the
primary PC connection port

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Figure 1 Ethernet Ports
2.3.2 Ethernet Ports on Display
There is one Ethernet port on the display module integrated into the MVCT’s lid. This port is used to
connect the display to MVCT unit and as noted earlier this connection supplies operating voltage to the
display module. The display should be connected using the supplied cable to the STVI port located on
the MVCT unit itself.
Figure 2 Ethernet Port to Power Display
2.3.3 USB 2.0 Interface on Display
There is one USB 2.0 Interface port on the MVCT display unit mounted in the lid. This port is used for
upgrading firmware to the MVCT unit, or upgrading the PowerDB software using a USB Memory Stick. It
may also be used in conjunction with a USB mouse for ease of manual control, even a USB wireless
mouse maybe used with the display.
Figure 3 USB Port
2.4 Supply Voltage
Unit operates on a single phase AC power source .The input operating voltage should be between the
following limits.
95-265 V 50-60 Hz 15A max.

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Please refer to Input power precautions in safety section for detailed description of input power
requirements.
2.5 Operating System
Unit works on Windows operating system.
3.0 Basic Theory of Operation
3.1 General
The purpose of this section is to explain the basic theory of the following tests and to guide the operator
for making appropriate measurements with the MVCT. The following tests can be performed by the
MVCT.
3.2 CT Testing
3.2.1 Ratio Test
The ratio is defined as the number of turns in the secondary as compared to the number of turns in the
primary.
The purpose of ratio test is to prove the ratio of the CT, is as specified and also to verify the ratio at
different taps of a multi tap CT. The turns ratio is equivalent to the voltage ratio and can be expressed
as:
N2/N1=V2/V1
Where,
N2 and N1 are no. of turns of secondary and primary windings respectively
V2 and V1 are the secondary and primary side voltage readings respectively.
A suitable voltage, below saturation is applied to the secondary of the CT under test and primary side
voltage is measured to calculate the turns ratio from above expression.

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The MVCT performs the ratio test by either selecting Ratio test in the Run All test configuration or using
the ratio test screen. User can also select manual Ratio test by selecting manual option and controlling
the secondary applied voltage.
3.2.2 Polarity Test
The Polarity test proves that the predicted direction of secondary CT current (leaving) is correct for a
given direction of primary current (entering).
CAUTION
In the ratio test screen or the manual operation, do NOT apply the voltage high enough
to the secondary of CT that would cause the CT to saturate; otherwise the readings will
not be accurate.

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Polarity marks designate the relative instantaneous directions of the currents. At the same instant of
time that the primary current is entering the primary terminal the corresponding secondary current is
leaving the similarly marked secondary terminal. A CT under test is supposed to have correct polarity if
instantaneous current direction for primary and secondary current is opposite to each other.
Same connection settings as for Ratio test can be used for performing Polarity test. The two non polarity
marks are shorted together internally and potential is measured across the two polarity mark points. For
correct polarity, primary winding voltage will be in-phase with secondary winding voltage, with a phase
angle difference of zero or close to that. A CT with reverse polarity would read the sum of the two
primary and secondary voltages indicating a phase difference of approximately 180 degrees. MVCT
performs this test in automated fashion and display the result as either Polarity correct or incorrect.

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3.2.3 Excitation Test
IEEE defines the saturation as “the point where the tangent is at 45 degrees to the secondary exciting
amperes”. Also known as “knee” point.
This test verifies that the CT is of correct accuracy rating, has no shorted turns in the CT and no short
circuits are present in the primary or secondary windings of the CT under test.
A typical excitation curve for C class current transformer is shown in figure below.
An AC voltage is applied to the secondary winding of the CT. The voltage applied to the secondary
winding of the CT is increased slowly automatically by the test set. Voltage and current readings for the
secondary winding of CT are stored in the internal memory. At 300V AC the MVCT will switch to DC
voltage to finish saturating the CT. Test set automatically convert the DC voltage readings, generate an
AC excitation curve and determines the “Knee” point as per selected standard by observing a small
voltage increase causing a large increase in current. The excitation curve around the points where