IEC 60255-121:2014 specifies minimum requirements for functional and performance evaluation of distance protection function typically used in, but not limited to, line applications for effectively earthed, three-phase power systems. This standard also defines how to document and publish performance tests. This standard covers distance protection function whose operating characteristic can be defined on an impedance plane and includes specification of the protection function, measurement characteristics, phase selection, directionality, starting and time delay characteristics. The test methodologies for verifying performance characteristics and accuracy are included in this standard. The standard defines the influencing factors that affect the accuracy under steady state conditions and performance characteristics during dynamic conditions. It also includes the instrument transformer requirements for the protection function. The general requirements for measuring relays and protection equipment are defined in IEC 60255-1.

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PDF Pages	PDF Title
4	Foreword Endorsement notice
6	English CONTENTS
13	1 Scope 2 Normative references
14	3 Terms and definitions
15	4 Specification of the function 4.1 General 4.2 Input energizing quantities/energizing quantities
16	4.3 Binary input signals Figures Figure 1 – Simplified distance protection function block diagram
17	4.4 Functional logic 4.4.1 Faulted phase identification 4.4.2 Directional signals 4.4.3 Distance protection function characteristics
18	4.4.4 Distance protection zone timers 4.5 Binary output signals 4.5.1 General 4.5.2 Start (pickup) signals
19	4.5.3 Operate signals 4.5.4 Other binary output signals 4.6 Additional influencing functions/conditions 4.6.1 General 4.6.2 Inrush current 4.6.3 Switch onto fault/trip on reclose 4.6.4 Voltage transformer (VT) signal failure (loss of voltage)
20	4.6.5 Power swings 4.6.6 Behavior during frequencies outside of the operating range 5 Performance specifications 5.1 General 5.2 Effective and operating ranges Tables Table 1 – Example of effective and operating ranges of distance protection
21	5.3 Basic characteristic accuracy under steady state conditions 5.3.1 General 5.3.2 Determination of accuracy related to time delay setting Figure 2 – Basic accuracy specification of an operating characteristic
22	5.3.3 Disengaging time 5.4 Dynamic performance 5.4.1 General 5.4.2 Transient overreach (TO) Figure 3 – Basic angular accuracy specifications of directional lines
23	5.4.3 Operate time and transient overreach (SIR diagrams) 5.4.4 Operate time and transient overreach (CVT-SIR diagrams). 5.4.5 Typical operate time
24	5.5 Performance with harmonics 5.5.1 General Figure 4 – SIR diagram – Short line average operate time
25	5.5.2 Steady-state harmonics tests 5.5.3 Transient LC oscillation tests 5.6 Performance during frequency deviation 5.6.1 General 5.6.2 Steady state testing during frequency deviation 5.6.3 Transient testing during frequency deviation
26	5.7 Double infeed tests 5.7.1 General 5.7.2 Single line, double infeed system 5.7.3 Double line, double infeed system
27	5.8 Instrument transformer (CT, VT and CVT) requirements 5.8.1 General 5.8.2 CT requirements
28	Figure 5 – Fault positions to be considered for specifying the CT requirements
29	Table 2 – Recommended levels of remanence in the optional cases when remanence is considered
31	6 Functional tests 6.1 General 6.2 Rated frequency characteristic accuracy tests 6.2.1 General
32	6.2.2 Basic characteristic accuracy under steady state conditions
33	Figure 6 – Test procedure for basic characteristic accuracy
34	Figure 7 – Calculated test points A, B and C based on the effective range of U and I Figure 8 – Modified points B’ and C’ based on the limited setting range
35	Figure 9 – Position of test points A, B, C, D and E in the effective range of U and I Figure 10 – Position of test points A, B’, C’, D and E in the effective range of U and I
36	Figure 11 – Quadrilateral characteristic showing ten test points
37	Figure 12 – Quadrilateral characteristic showing test ramps
38	Figure 13 – Quadrilateral characteristic showing accuracy limits
39	Figure 14 – Quadrilateral/polygonal characteristic showing accuracy limits Figure 15 – MHO characteristic showing nine test points
40	Figure 16 – MHO characteristic showing test ramps
41	Figure 17 – Accuracy limits for MHO characteristic
44	Table 3 – Basic characteristic accuracy for various points (quadrilateral/polygonal) Table 4 – Overall basic characteristic accuracy (quadrilateral/polygonal) Table 5 – Basic characteristics accuracy for various points (MHO) Table 6 – Overall basic characteristic accuracy (MHO)
45	6.2.3 Basic directional accuracy under steady state conditions
46	Figure 18 – Basic directional element accuracy tests
47	Figure 19 – Directional element accuracy tests in the second quadrant
48	Figure 20 – Directional element accuracy tests in the second quadrant Figure 21 – Directional element accuracy tests in the fourth quadrant
49	Figure 22 – Directional test accuracy lines in the fourth quadrant Table 7 – Basic directional accuracy for various fault types Table 8 – Basic directional accuracy eαX
50	6.2.4 Determination of accuracy related to time delay setting 6.2.5 Determination and reporting of the disengaging time
51	Figure 23 – Position of the three-phase fault for testing the disengaging time
52	6.3 Dynamic performance 6.3.1 General Figure 24 – Sequence of events for testing the disengaging time Table 9 – Results of disengaging time for all the tests
53	6.3.2 Dynamic performance: operate time and transient overreach (SIR diagrams) Figure 25 – Power system network with zero load transfer
55	Table 10 – Short line SIR and source impedance for selected ratedcurrent and frequency
56	Table 11 – Short line SIR and source impedances for other rated current and frequency
57	Figure 26 – Dynamic performance: operate time and dynamic overreach (SIR diagram)
58	Figure 27 – SIR diagram for short line: minimum operate time
59	Figure 28 – SIR diagram for short line: average operate time Figure 29 – SIR diagram for short line: maximum operate time
61	Figure 30 – Dynamic performance tests (SIR diagrams) Table 12 – Long line SIR and source impedances for selected rated current and frequency
62	Table 13 – Long line SIR and source impedances for other rated current and frequency
63	6.3.3 Dynamic performance: operate time and transient overreach (CVT-SIR diagrams) Figure 31 – SIR diagram for long line: minimum operate time
64	Figure 32 – SIR diagram for long line: average operate time Figure 33 – SIR diagram for long line: maximum operate time
65	Table 14 – Short line CVT-SIR source impedance
66	Figure 34 – Dynamic performance: operate time and dynamic overreach(CVT-SIR diagram)
67	6.3.4 Dynamic performance: transient overreach tests
68	Figure 35 – CVT-SIR diagram for short line: minimum operate time Figure 36 – CVT-SIR diagram for short line: average operate time
69	Figure 37 – CVT-SIR diagram for a short line: maximum operate time
70	Table 15 – Transient overreach table for short line Table 16 – Transient overreach table for long line
71	6.3.5 Dynamic performance: typical operate time Table 17 – Transient overreach table for short line with CVTs
72	Figure 38 – Fault statistics for typical operate time
73	Table 18 – Typical operate time Table 19 – Typical operate time
74	Table 20 – Typical operate time
75	Figure 39 – Frequency distribution of operate time Table 21 – Typical operate time (mode, median, mean)
76	6.4 Performance with harmonics 6.4.1 Steady state harmonics tests
77	6.4.2 Transient oscillation tests (network simulation L-C) Figure 40 – Ramping test for harmonics Table 22 – Steady state harmonics test
79	Figure 41 – Steady-state harmonics test
80	Figure 42 – Simulated power system network Table 23 – Capacitance values
81	Figure 43 – Flowchart of transient oscillation tests
83	Figure 44 – Simulated voltages (UL1, UL2, UL3) and currents (IL1, IL2, IL3)
84	6.5 Performance during off-nominal frequency 6.5.1 Steady state frequency deviation tests Figure 45 – Transient oscillation tests – Operate time
85	Figure 46 – Test points for quadrilateral characteristics Figure 47 – Test points for MHO characteristic Figure 48 – Test ramp direction for quadrilateral characteristic
86	Figure 49 – Test ramp direction for MHO characteristic
87	6.5.2 Transient frequency deviation tests Table 24 – Quadrilateral/polygonal basic characteristic accuracy at fmin and fmax Table 25 – MHO basic characteristic accuracy at f min and f max
88	Figure 50 – Steady-state frequency deviation tests
89	Figure 51 – Short line model for frequency deviation test
91	Figure 52 – Flowchart of transient frequency deviation tests
92	6.6 Double infeed tests 6.6.1 Double infeed tests for single line Figure 53 – SIR diagrams for frequency deviation tests – average operate time
93	Figure 54 – Network model for single line tests
94	Figure 55 – Line to earth fault Figure 56 – Line to line fault Figure 57 – Line to line to earth fault
95	Figure 58 – Three-phase fault
96	Table 26 – Tests without pre-fault load
97	Table 27 – Tests with pre-fault load
98	6.6.2 Double infeed tests for parallel lines (without mutual inductance)
100	Figure 59 – Network model for parallel lines tests Table 28 – Current reversal test
101	Figure 60 – Network model for current reversal test Table 29 – Evolving faults (only one line affected)
102	6.6.3 Reporting of double infeed test results Table 30 – Evolving faults (both lines affected)
103	7 Documentation requirements 7.1 Type test report 7.2 Documentation Table 31 – Double infeed test results
104	Annex A (informative) Impedance characteristics A.1 Overview A.1.1 General A.1.2 Non-directional circular characteristic A.1.3 MHO characteristic Figure A.1 – Non-directional circular characteristic with directional supervision
105	Figure A.2 – MHO characteristic
106	A.1.4 Quadrilateral/polygonal Figure A.3 – Quadrilateral/polygonal characteristics
108	A.2 Example characteristics A.2.1 General A.2.2 Non-directional circular characteristic (ohm) A.2.3 Reactive reach line characteristic Figure A.4 – Non-directional circular characteristic (ohm)
109	A.2.4 MHO characteristic A.2.5 Resistive and reactive intersecting lines characteristic Figure A.5 – Reactive reach line characteristic Figure A.6 – MHO characteristics
110	A.2.6 Offset MHO characteristic. Figure A.7 – Resistive and reactive intersecting lines characteristics Figure A.8 – Offset MHO
112	Annex B (informative) Informative guide for the behaviour of timers in distance protection zones for evolving faults Figure B.1 – The same fault type evolving from time delayed zone 3 (position 1) into time delayed zone 2 (position 2) after 200 ms
113	Figure B.2 – Phase to earth fault in time delayed zone 3 (position 1) evolving into three-phase fault in the same zone (position 2) after 200 ms
114	Annex C (normative) Setting example Figure C.1 – Setting example for a radial feeder
115	Figure C.2 – Phase to earth fault (LN)
116	Figure C.3 – Phase to phase fault (LL)
117	Annex D (normative) Calculation of mean, median and mode D.1 Mean D.2 Median D.3 Mode D.4 Example
118	Annex E (informative) CT saturation and influence on the performance of distance relays
119	Figure E.1 – Fault positions to be considered for specifying the CT requirements
121	Annex F (informative) Informative guide for testing distance relays based on CT requirements specification F.1 General Figure F.1 – Fault positions to be considered
122	F.2 Test data Figure F.2 – Double source network
123	F.3 CT data and CT model
124	Figure F.3 – Magnetization curve for the basic CT Table F.1 – Magnetization curve data
125	Figure F.4 – Secondary current at the limit of saturation caused by AC component with no remanent flux in the CT Figure F.5 – Secondary current in case of maximum DC offset
127	Annex G (informative) Informative guide for dimensioning of CTs for distance protection G.1 General
128	G.2 Example 1 Figure G.1 – Distance relay example 1
129	Table G.1 – Fault currents
130	G.3 Example 2 Figure G.2 – Distance relay example 2 Table G.2 – Fault currents
133	Annex H (normative) Calculation of relay settings based on generic point P expressed in terms of voltage and current H.1 Settings for quadrilateral/polygonal characteristic Figure H.1 – Quadrilateral/polygonal characteristic showing test point P on the reactive reach line
134	Figure H.2 – Quadrilateral distance protection function characteristic showing test point P on the resistive reach line.
135	H.2 Settings for MHO characteristic Figure H.3 – MHO characteristic showing test point P
136	Annex I (normative) Ramping methods for testing the basic characteristic accuracy I.1 Relationship between simulated fault impedance and analog quantities I.2 Pre-fault condition I.3 Phase to earth faults
137	Figure I.1 – Three-line diagram showing relay connections and L1N fault Figure I.2 – Voltage and current phasors for L1N fault
138	I.4 Phase to phase faults. Figure I.3 – Voltages and currents for L1N fault, constant fault current Figure I.4 – Voltages and currents for L1N fault, constant fault voltage
139	Figure I.5 – Three-line diagram showing relay connections and L1L2 fault
140	Figure I.6 – Voltage and current phasors for L1L2 fault Figure I.7 – Voltages and currents for L1L2 fault, constant fault current
141	I.5 Ramps in the impedance plane I.5.1 Pseudo-continuous ramp Figure I.8 – Voltages and currents for L1L2 fault, constant fault voltage
142	I.5.2 Ramp of shots Figure I.9 – Pseudo-continuous ramp distance relay characteristic on an impedance plane Figure I.10 – Pseudo-continuous ramp showing impedance step change and the time step
143	Figure I.11 – Ramp of shots distance relay characteristic on an impedance plane
144	Figure I.12 – Ramp of shots showing impedance step change and the time step Figure I.13 – Ramp of shots with binary search algorithm
145	Annex J (normative) Definition of fault inception angle Figure J.1 – Graphical definition of fault inception angle
146	Table J.1 – Fault type and reference voltage
147	Annex K (normative) Capacitive voltage instrument transformer model K.1 General K.2 Capacitor voltage transformer (CVT) Figure K.1 – CVT equivalent electrical circuit
148	Table K.1 – Parameter values for the 50 Hz version of the CVT model Table K.2 – Parameter values for the 60 Hz version of the CVT model
149	Figure K.2 – Transient response of the 50 Hz version of the CVT model

Published By	Publication Date	Number of Pages
BSI	2014	152


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Status	Definitive
Pages	152
Publication Date	2014-07-31
ISBN	978 0 580 70318 8
Standard Number	BS EN 60255-121:2014
Title	Measuring relays and protection equipment – Functional requirements for distance protection
Identical National Standard Of	EN 60255-121 (IEC 60255-121:2014) AS, IEC 60255-121:2014
Descriptors	Transient response, Length, Instrument transformers, Electromagnetic compatibility, Measuring relays, Electrical protection equipment, Voltage regulators
Publisher	BSI
Committee	PEL/95
ICS Codes	29.120.70 - Relays

BS EN 60255-121:2014

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