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BS EN IEC 60255-187-1:2021:2023 Edition

BS EN IEC 60255-187-1:2021:2023 Edition

$215.11

Measuring relays and protection equipment – Functional requirements for differential protection. Restrained and unrestrained differential protection of motors, generators and transformers

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BSI 2023 212
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This part of IEC 60255 specifies the minimum requirements for functional and performance evaluation of (longitudinal) differential protection designed for the detection of faults in ac motors, generators and transformers. This document also defines how to document and publish performance test results.

This document covers the differential protection function whose operating characteristic can be defined on a bias-differential plane. It includes specification of the protection function, measurement characteristics, compensation of energizing quantities, additional restraint or blocking methods (for overexcitation and magnetizing inrush), starting and time delay characteristics. This document also covers unrestrained differential protection functions traditionally combined with the restrained (biased) differential element to form a single differential relay.

This document defines the influencing factors that affect the accuracy under steady state conditions and performance characteristics during dynamic conditions. The test methodologies for verifying performance characteristics and accuracy are also included in this document.

This document also includes current transformer requirements for the protection functions.

The differential protection functions covered by this document are as follows:

This document does not specify the functional description of additional features often associated with biased differential relays such as current transformer (CT) supervision (CTS), switch onto fault (SOTF) and detection of geo-magnetically induced currents (GIC).

This document does not cover differential relays designed for bus bar protection (including high impedance differential protection and low impedance differential protection) or line protection. Additionally, this document does not explicitly cover generator incomplete longitudinal differential protection, generator split-phase transverse differential protection, self-balancing or magnetic balanced protection scheme, differential protection of phase-shifting transformers, directional restricted earth fault protection, railway transformers, convertor transformers and reactors. However, the principles covered by this document can be extended to provide guidance on these applications.

PDF Catalog

PDF Pages PDF Title
2 undefined
5 Annex ZA(normative)Normative references to international publicationswith their corresponding European publications
7 English
CONTENTS
16 FOREWORD
18 1 Scope
19 2 Normative references
3 Terms and definitions
22 Figures
Figure 1 – Explanatory diagram for start time, operate time and disengage time
23 4 Specification of the function
4.1 General
Figure 2 – Simplified biased differential functional block diagram
24 4.2 Input energizing quantities/energizing quantities
4.2.1 General
4.2.2 Connections
4.3 Binary input signals
26 Figure 3 – Primary current reference direction
27 4.4 Functional logic
4.4.1 General
4.4.2 Phase biased differential protection
28 Figure 4 – Typical restrained element (biased) characteristic
Figure 5 – Typical unrestrained element characteristic
29 4.4.3 Biased restricted earth fault protection
Figure 6 – Example of combined characteristicusing restrained and unrestrained elements
30 4.4.4 Compensation of energizing quantities
31 4.4.5 Additional restraint or blocking methods
32 4.5 Binary output signals
4.5.1 General
4.5.2 Start (pick-up) signals
4.5.3 Operate (trip) signals
4.5.4 Other output signals
4.6 Additional influencing functions and conditions
4.6.1 General
33 4.6.2 Operation during CT saturation
4.6.3 Switch onto fault
4.6.4 Energizing quantity failure (CT supervision)
4.6.5 Off-nominal frequency operation
4.6.6 Geomagnetically induced currents (GIC)
34 5 Performance specification
5.1 General
5.2 Effective and operating ranges
5.3 Steady state accuracy tests in the effective range
5.3.1 General
Tables
Table 1 – Example of effective and operating ranges of differential protection
35 5.3.2 Test related to the declared thermal withstand current
5.3.3 Basic characteristic accuracy
5.3.4 Ratio compensation accuracy
Figure 7 – Basic error of the operating characteristic
36 5.3.5 Phase (vector) compensation validity
5.3.6 Zero sequence compensation validity
5.3.7 Harmonic restraint basic accuracy
5.3.8 Basic accuracy of time delay settings
5.3.9 Disengage time
37 5.4 Dynamic performance in operating range
5.4.1 General
5.4.2 Typical operate time
5.4.3 Relay stability for external faults
38 5.4.4 Relay behaviour for internal fault preceded by an external fault
5.5 Stability during magnetizing inrush conditions
5.6 Stability during overexcitation conditions
5.7 Presence of harmonics on load
5.8 Performance during saturation of current transformers
39 5.9 Behaviour of differential protection with digital interface for the energizing quantities
6 Functional tests
6.1 General
40 6.2 Test related to the declared thermal withstand current
6.3 Steady state accuracy tests in effective range
6.3.1 General
41 Table 2 – Frequencies for steady state accuracy tests whenthe frequency effective range is equal to ±5 % of nominal frequency
Table 3 – Frequencies for steady state accuracy tests whenthe frequency effective range is larger than ±5 % of nominal frequency
Table 4 – Example frequencies for steady state accuracy tests whenthe frequency effective range is narrower than ±5 % of nominal frequency
42 6.3.2 Basic characteristic accuracy
Figure 8 – Example of an operating characteristicin the IDIFF/IREST plane with a tolerance band
43 Table 5 – Test points for differential characteristic basic accuracy
44 Figure 9 – Test cases for differential characteristic basic accuracy
Table 6 – Test lines on the differential characteristic (Figure 10)
45 Figure 10 – Example of a differential characteristic with test lines "a" to "h"
Figure 11 – Machine differential protection
47 Figure 12 – Test sequence for basic characteristic accuracy
48 Figure 13 – Machine restricted earth fault protection
Table 7 – Basic characteristic accuracy
49 6.3.3 Ratio (magnitude) compensation accuracy
Figure 14 – Example for documenting the test results for differential relay characteristic
50 6.3.4 Phase (vector) compensation validity
Figure 15 – Ratio (magnitude) compensation accuracy test
51 Figure 16 – Secondary three-phase and double-phase injection for Winding 1 (example)
52 6.3.5 Zero sequence compensation validity
Table 8 – Example of start ratios resulting from phase (vector) compensation
53 Figure 17 – Secondary single-phase and three-phase injections for Winding 1 (example)
54 Figure 18 – Zero sequence current injection on the Y side of the transformer
Figure 19 – Zero sequence current injection on the delta side of the transformer
55 6.3.6 Harmonic restraint basic accuracy test under steady state conditions at nominal frequency
Table 9 – Example of start ratios resulting from zero sequence compensation
56 Table 10 – Test points for rated frequency harmonic restraint
57 6.3.7 Accuracy related to time delay setting
Figure 20 – Example of a rated frequency harmonic restraintcharacteristic with visualization of test lines
Table 11 – Reporting example of test results for harmonic restraint basic accuracy test
58 Table 12 – Results of time delay tests
Table 13 – Reported time delay
59 6.3.8 Determination and reporting of the disengage time
Figure 21 – Sequence of events for testing the disengage time
60 6.4 Dynamic performance tests
6.4.1 General
Table 14 – Results of disengage time for all the tests
Table 15 – Frequencies for dynamic performance tests whenthe frequency operating range is equal to ±10 % of nominal frequency
Table 16 – Frequencies for dynamic performance tests whenthe frequency operating range is wider than ±10 % of nominal frequency
61 Table 17 – Example frequencies for dynamic performance tests when the frequency operating range is narrower than ±10 % of nominal frequency
62 6.4.2 Operate time for double infeed network model (restrained operation)
Figure 22 – Double infeed network model for operate time tests
63 Table 18 – Double infeed network model
64 Table 19 – Source impedances for double infeed network model –Restrained operation (e.g. 50 Hz ± 10 % operating range)
66 Figure 23 – Test sequence for double infeed network model –Restrained operation (transformer)
67 Figure 24 – Double infeed network model for operate time tests
Table 20 – Double infeed network model
68 Table 21 – Source impedances for double infeed network model –Restrained operation (e.g. 50 Hz ± 10 % operating range)
70 Figure 25 – Test sequence for double infeed network model –Restrained operation (REF)
71 Figure 26 – Double infeed network model for operate time tests
Table 22 – Double infeed network model
72 Table 23 – Source impedances for double infeed network model –Restrained operation (e.g. 50 Hz ± 10 % operating range)
73 6.4.3 Operate time for double infeed network model (unrestrained operation)
74 Figure 27 – Test sequence for double infeed network model –Restrained operation (generator)
75 Table 24 – Source impedances for double infeed network model –Unrestrained operation (e.g. 60 Hz ± 10 % operating range)
77 Figure 28 – Test sequence for double infeed network model –Unrestrained operation (transformer)
78 6.4.4 Operate time for radial single infeed network model (restrained operation)
Figure 29 – Single infeed network model for operate time tests
79 Table 25 – Single infeed network model
Table 26 – Source impedances for radial single infeed network model –Restrained operation (e.g. 50 Hz ± 10 % operating range)
82 Figure 30 – Test sequence radial single infeed network model – Restrained operation
83 Figure 31 – Single infeed network model for operate time tests
Table 27 – Single infeed network model
84 Table 28 – Source impedances for radial single infeed network model –Restrained operation (e.g. 50 Hz ± 10 % operating range)
86 Figure 32 – Test sequence for radial single infeed network –Restrained operation (generator)
87 Figure 33 – Single infeed network model for operate time tests
Table 29 – Single infeed network model
88 Table 30 – Source impedances for radial single infeed network model –Restrained operation (e.g. 50 Hz ± 10 % operating range)
90 Figure 34 – Test sequence for radial single infeed network –Restrained operation (motor)
91 6.4.5 Operate time for radial single infeed network model (unrestrained operation)
Table 31 – Source impedances for radial single infeed network model –Unrestrained operation (e.g. 60 Hz ± 10 % operating range)
93 Figure 35 – Test sequence for radial single infeed network – Unrestrained operation
94 6.4.6 Reporting of typical operate time
Table 32 – Fault statistics for typical operate time of transformer protection(nominal frequency only)
95 Table 33 – Fault statistics for typical operate time of biasedrestricted earth fault protection (nominal frequency only)
Table 34 – Fault statistics for typical operate time of generator protection(nominal frequency only)
Table 35 – Fault statistics for typical operate time of motor protection(nominal frequency only)
96 Table 36 – Operate time classes
Table 37 – Corresponding operate time classes
97 Figure 36 – Example of distribution of the operate time for one application
Table 38 – Number of operate times and percentage
98 Table 39 – Example of typical operate time at nominal frequency (mode, median, mean)
99 Figure 37 – Operate time as a function of the off-nominal frequency values(effective range is the specified range of ±10 % of nominal frequency)
Table 40 – Examples of operate times (50 Hz nominal, CT configuration 500 A/1 Aand 1 000 A/1 A, power transformer protection)
100 6.4.7 Stability for external faults
Figure 38 – Operate time as a function of the off-nominal frequency values(accuracy range beyond the specified range of ±10 % of nominal frequency
101 Figure 39 – Double infeed network model for stability tests
Table 41 – Double infeed network model
102 Table 42 – Source impedances for double infeed network model stability tests(e.g. 50 Hz ± 10 % operating range)
104 Figure 40 – Sequence of fault injection for stability due to external faults (transformer)
105 Figure 41 – Double infeed network model for stability tests
Table 43 – Double infeed network model
106 Table 44 – Source impedances for double infeed network model stability tests(e.g. 50 Hz ± 10 % operating range)
108 Figure 42 – Sequence of fault injection for stability due to external faults (REF)
109 Figure 43 – Double infeed network model for stability tests
Table 45 – Double infeed network model
110 Table 46 – Source impedances for double infeed network model stability tests(e.g. 50 Hz ± 10 % operating range)
112 Figure 44 – Sequence of fault injection for stability due to external faults (generator)
113 Figure 45 – Double infeed network model for stability tests
Table 47 – Double infeed network model
114 Table 48 – Source impedances for double infeed network model stability tests(e.g. 50 Hz ± 10 % operating range)
116 Figure 46 – Sequence of fault injection for stability due to external faults (motor)
117 6.5 Relay behaviour for internal fault preceded by an external fault
6.5.1 General
6.5.2 Application specific considerations: transformer differential
Figure 47 – Double infeed network model for internal fault preceded by an external fault
118 Table 49 – Double infeed network model
Table 50 – Source impedances, fault resistances and pre-fault conditions for internal fault preceded by an external fault (e.g. for 50 Hz power system frequency)
120 6.5.3 Application specific considerations: biased restricted earth fault
121 Figure 48 – Double infeed network model for internal faultpreceded by an external fault test
Table 51 – Double infeed network model
122 Table 52 – Source impedances, fault resistances and pre-fault conditions for internal fault preceded by an external fault tests (e.g. for 50 Hz power system frequency)
124 6.5.4 Application specific considerations: generator differential
Figure 49 – Double infeed network model for internalfault preceded by an external fault test
125 Table 53 – Double infeed network model
Table 54 – Source impedances, fault resistances and pre-fault conditions for internal fault preceded by an external fault tests (e.g. for 50 Hz power system frequency)
127 6.5.5 Reporting
Table 55 – Operate time for internal fault preceded by an external faultand for internal fault when the relay always operated
128 6.6 Stability during inrush conditions
6.6.1 General
6.6.2 Application specific considerations: transformer differential
Table 56 – Operate time for internal fault preceded by an external faultand for internal fault when the relay did not always operate
129 Figure 50 – Power transformer inrush current waveform
Table 57 – Coefficients of the inrush current waveforms
130 Figure 51 – Comparison of waveforms
Table 58 – Nameplate data for test-transformers
Table 59 – Parameter k values
131 Figure 52 – Connection for the relay when current is injected from Y winding
132 Figure 53 – Connection for the relay when current is injected from delta winding
133 6.7 Stability during overexcitation conditions
6.7.1 General
6.7.2 Application specific considerations: transformer differential
134 Figure 54 – Power transformer overexcitation current waveform injected from Y winding
Figure 55 – Overexcitation current waveform injected from delta winding
135 Figure 56 – Comparison of the waveforms injected from Y winding
Table 60 – Coefficient of the overexcitation waveforms
136 Figure 57 – Comparison of the waveforms injected from delta winding
Table 61 – Test data for the transformer
137 Figure 58 – Three-phase overexcitation current waveform injected from Y winding
138 6.8 Performance with load harmonics
6.8.1 General
6.8.2 Application specific considerations: transformer differential
Figure 59 – Three-phase overexcitation current waveform injected from delta winding
Figure 60 – Test with superimposed harmonics on load – Transformer protection
139 Table 62 – Transformer data for the superimposed harmonics on load test
Table 63 – Fundamental component of load current in pu
Table 64 – Harmonic content for superimposed harmonics on load test
Table 65 – Harmonic phase angles for superimposed harmonics on load test
142 6.8.3 Application specific considerations: generator or motor differential
Figure 61 – Three-phase load current waveform on the Y sideof the transformer with superimposed harmonics
Figure 62 – Three-phase load current waveforms on the delta side ofthe YNd1 transformer with superimposed harmonics
143 Figure 63 – Test with superimposed harmonics on load
Table 66 – Generator or motor data for the superimposed harmonics on load test
144 Table 67 – Harmonic phase angles for superimposed harmonics on load test
145 6.8.4 Application specific considerations: biased restricted earth fault
Figure 64 – Test with superimposed harmonics on load –Restricted earth fault protection
146 Table 68 – Transformer data for the superimposed harmonics on load test
Table 69 – Harmonic phase angles for superimposed harmonics on load test
147 6.8.5 Reporting
148 7 Documentation requirements
7.1 Type test report
7.2 Other user documentation
149 Annex A (informative)Examples of phase (vector) compensationand zero sequence compensation schemes
A.1 General
Figure A.1 – Example of a transformer
Table A.1 – Transformer data
150 A.2 Y→d conversion
A.2.1 Current conversion
Figure A.2 – Current vectors
151 A.2.2 Three-phase fault at Y (star/wye) side
152 A.2.3 Phase-phase fault at Y (star/wye) side
A.2.4 Single-phase fault at Y (star/wye) side
Figure A.3 – Three-phase injection at Y (star/wye) side
Figure A.4 – Phase-phase injection at Y (star/wye) side
153 A.2.5 Three-phase fault at delta side
Figure A.5 – Single-phase injection at Y (star/wye) side
154 A.2.6 Phase-phase fault at delta side
A.2.7 Single-phase fault at delta side
Figure A.6 – Three-phase injection at delta side
Figure A.7 – Phase-phase injection at delta side
155 Figure A.8 – Internal single-phase fault at delta sidewith neutral grounding transformer in the system
Figure A.9 – Single-phase injection at delta side
156 Figure A.10 – External single-phase fault at delta sidewith neutral grounding transformer inside protected zone
157 A.2.8 Ratio between start currents under different fault types
A.3 d→Y conversion
A.3.1 Current conversion
Table A.2 – Start currents under different fault types
158 A.3.2 Three-phase fault at Y (star/wye) side
A.3.3 Phase-phase fault at Y (star/wye) side
A.3.4 Single-phase fault at Y (star/wye) side
159 A.3.5 Three-phase fault at delta side
A.3.6 Phase-phase fault at delta side
160 A.3.7 Single-phase fault at delta side
A.3.8 Ratio between start currents under different fault types
Table A.3 – Start currents under different fault types
161 Annex B (normative)Calculation of mean, median and mode
B.1 Mean
B.2 Median
B.3 Mode
B.4 Example
162 Annex C (normative)CT requirements
C.1 General
164 Table C.1 – Levels of remanent or remaining flux to be considered for external faults
Table C.2 – Levels of remanent or remaining flux to be considered for external faultswhen the difference of size between the CTs is limited
165 Figure C.1 – Fault positions to be considered for specifying the CT requirements
166 C.2 Transformer differential protection
C.2.1 General
C.2.2 Fault 1
Figure C.2 – Fault positions to be considered for transformer differential protection
167 C.2.3 Fault 2
C.2.4 Fault 3
168 C.3 Transformer restricted earth fault protection
C.3.1 General
C.3.2 Fault 1
Figure C.3 – Fault positions to be considered for the restricted earth fault protection
169 C.3.3 Fault 2
C.3.4 Fault 3
170 C.4 Generator differential protection
C.4.1 General
C.4.2 Fault 2
Figure C.4 – External fault position to be consideredfor the generator differential protection
171 C.4.3 Criteria and additional conditions
C.5 Motor differential protection
C.5.1 General
C.5.2 Fault 1
C.5.3 Criteria and additional conditions
Figure C.5 – Internal fault position to be considered for the motor differential protection
172 C.5.4 Start of motor, security case
C.5.5 Criteria and additional conditions
C.6 Reporting
173 Annex D (informative)CT saturation and influence on the performance of differential relays
175 Figure D.1 – Fault positions to be considered for specifying the CT requirements
Figure D.2 – Additional fault position to be considered in case of summation of currents
178 Annex E (informative)Guidance on dimensioning of CTs for transformer differential protection
E.1 General
179 E.2 Example 1
E.2.1 General
Figure E.1 – Transformer differential relay example 1
Table E.1 – Fault currents
180 E.2.2 Verification of CT1 – Internal fault
E.2.3 Verification of CT1 – External fault
181 E.2.4 Verification of CT2
182 E.3 Example 2
E.3.1 General
Figure E.2 – Transformer differential relay example 2
Table E.2 – Fault currents
183 E.3.2 Dimensioning of CT1
184 E.3.3 Dimensioning of CT2
186 Annex F (informative)Examples of test procedures to determine CT sizingrequirements for differential protection
F.1 General
188 F.2 Test data
F.2.1 General
F.2.2 Network model for CT requirement tests for the transformer differential protection
189 Figure F.1 – Network models and fault positions for transformer differential protection
190 Table F.1 – Specification of test cases for the transformer differential protection –Internal and external faults with one saturated CT
191 Table F.2 – Specification of test cases for the transformer differential protection –External faults with two saturated CTs
Table F.3 – Example time constants with corresponding R/X ratios
192 F.2.3 Network model for CT requirement tests for the transformer restricted earth fault protection
Figure F.2 – Network models and fault positions for transformerrestricted earth fault protection
193 Table F.4 – Specification of test cases for the transformer restricted earth fault protection – Internal and external faults with one saturated CT
Table F.5 – Specification of test cases for the transformer restricted earth fault protection – External faults with two saturated CTs
194 F.3 CT data and CT models
195 Table F.6 – Excitation characteristic data for the high-remanence basic CT
196 Figure F.3 – Excitation characteristic for the high-remanence basic CT
198 Figure F.4 – Magnetization curve for the high-remanence type basic CT
Table F.7 – Magnetization curve data for the high-remanence type basic CT
199 Figure F.5 – Secondary current at the limit of saturation causedby the AC component with no remanent flux in the CT
Figure F.6 – Secondary current in case of maximum DC offset
201 Figure F.7 – Excitation characteristics for non-remanenceand high-remanence type basic CTs
Table F.8 – Excitation characteristic datafor the non-remanence type basic CT
202 F.4 Test summary
Figure F.8 – Magnetization curve for non-remanence type basic CTs
Table F.9 – Magnetization curve data for non-remanence type CT
204 Annex G (normative)Ramping methods for testing basic characteristic accuracy
G.1 General
G.2 Pre-fault condition
G.3 Pseudo-continuous ramp
205 Figure G.1 – Secondary injected currents for the simulation of a through load of 30 %
Table G.1 – Restraining and differential currents for differentdefinitions of the restraining current
206 G.4 Ramp of shots
Figure G.2 – Pseudo-continuous ramp in the restraining current –Differential current plane in the time domain
207 Figure G.3 – Ramp of shots showing differential step change and the time step
Figure G.4 – Ramp of shots with binary search algorithm
208 Annex H (informative)Example of COMTRADE file for an evolving fault test case
209 Annex I (normative)Definition of fault inception angle
Figure I.1 – Graphical definition of fault inception angle
Table I.1 – Fault type and reference voltage
210 Bibliography

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