8-4
T35 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
DIFFERENTIAL CHARACTERISTIC TEST EXAMPLES
CHAPTER 8: COMMISSIONING
8
Figure 8-2: Current distribution on a Y/YG0° transformer with b-c fault on LV side
Consider the above system, which illustrates the importance of CT orientation, polarity, and relay connection. These
factors also apply when performing the tests outlined in the next examples.
The transformer high voltage (HV) and low voltage (LV) side fault currents, and angles are all related. More specifically, the
HV and LV primary fault currents are displaced by 180°. The CT polarity marks point away from the protected zone and are
connected to the ~a terminals of the relay. The displayed current is what is reported by the relay.
8.2.2 Test example 1
8.2.2.1 Overview
Transformer data — 20 MVA, 115/12.47 kV, CT (HV) = 200:1, CT (LV) = 1000:1, Y/y0° with a grounded LV neutral
Test set configuration
The fault current distribution for an external b-c fault is identical for the HV and LV transformer sides and can be simulated
easily with two current sources. Connect the first current source to the relay Phase “B” and “C” terminals, corresponding to
the HV winding CTs in series, and the second source to the Phase “b” and “c” relay terminals, corresponding to the LV CTs.
Ensure that the polarity is correct and the relative phase angles are similar to that shown in the figure, that is, 180°
between IB and IC, 180° between Ib and Ic, 180° between IB and Ib, and 180° between IC and Ic. Follow the magnitudes
and angles of the injected currents from the following tables to ensure that the test performs correctly
Operating criteria
The differential element operates if the differential current (I
d
) exceeds the characteristic defined by the relay settings for
restraint current magnitude (I
r
). The differential current I
d
is the vector sum of the compensated currents, and I
r
is the
largest compensated current. Compensation refers to vector and magnitude corrections applied to the currents from the
HV and LV transformer sides.
The ~a and ~b terminal identifications are illustrative only. See the CT/VT Modules section in Chapter 3 for specific
terminal identification.
Содержание T35
Страница 9: ...TABLE OF CONTENTS T35 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL ix ABBREVIATIONS INDEX ...
Страница 10: ...x T35 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL TABLE OF CONTENTS ...
Страница 14: ...1 4 T35 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL FOR FURTHER ASSISTANCE CHAPTER 1 INTRODUCTION 1 ...
Страница 202: ...4 88 T35 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL FLEXLOGIC DESIGN USING ENGINEER CHAPTER 4 INTERFACES 4 ...
Страница 472: ...5 270 T35 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL TESTING CHAPTER 5 SETTINGS 5 ...
Страница 500: ...6 28 T35 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL PRODUCT INFORMATION CHAPTER 6 ACTUAL VALUES 6 ...
Страница 514: ...7 14 T35 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL TARGETS MENU CHAPTER 7 COMMANDS AND TARGETS 7 ...
Страница 580: ...A 16 T35 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL FLEXANALOG ITEMS APPENDIX A FLEXANALOG OPERANDS A ...
Страница 588: ...C 6 T35 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL COMMAND LINE INTERFACE APPENDIX C COMMAND LINE INTERFACE C ...
Страница 596: ...iv T35 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL ABBREVIATIONS ...