IEC 61400-21-2:2023

IEC 61400-21-2 ®
Edition 1.0 2023-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 21-2: Measurement and assessment of electrical characteristics – Wind
power plants
Systèmes de génération d'énergie éolienne –
Partie 21-2: Mesurage et évaluation des caractéristiques électriques – Centrales
éoliennes
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IEC 61400-21-2 ®
Edition 1.0 2023-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –

Part 21-2: Measurement and assessment of electrical characteristics – Wind

power plants
Systèmes de génération d'énergie éolienne –

Partie 21-2: Mesurage et évaluation des caractéristiques électriques – Centrales

éoliennes
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.180 ISBN 978-2-8322-6648-9

– 2 – IEC 61400-21-2:2023 © IEC 2023
CONTENTS
FOREWORD . 9
INTRODUCTION . 11
1 Scope . 13
2 Normative references . 14
3 Terms and definitions . 15
4 Symbols and abbreviated terms . 25
4.1 Symbols . 25
4.2 Abbreviated terms . 27
5 Power plant specifications . 27
6 Overall test and documentation requirements . 29
6.1 General . 29
6.2 Test conditions, monitoring and reporting requirements . 31
6.3 Test conditions in the case of external influences . 33
6.4 Test and measurement equipment . 33
6.4.1 General . 33
6.4.2 Voltage, current and power calculations . 33
6.4.3 Measurement equipment . 33
6.4.4 Existing measurement equipment for power control tests . 34
6.4.5 Optional measurements . 34
6.5 Functional and performance test . 34
6.6 Power plant controller . 35
6.6.1 General . 35
6.6.2 Definition and requirements . 35
6.6.3 Measurement points . 36
6.6.4 Measurement data . 37
6.6.5 Test setup . 37
6.6.6 Documentation . 38
7 Measurement and test of electrical characteristics . 39
7.1 General . 39
7.2 Power quality aspects . 39
7.2.1 General . 39
7.2.2 Flicker during continuous operation . 39
7.2.3 Rapid voltage changes due to switching operations . 40
7.2.4 Harmonics . 41
7.3 Steady state operation . 43
7.3.1 General . 43
7.3.2 Unbalance . 43
7.4 Dynamic performance . 44
7.4.1 Undervoltage and overvoltage ride-through (UVRT and OVRT)
capability . 44
7.4.2 Test setup and test conditions . 44
7.4.3 Test and measurement procedure . 44
7.4.4 Documentation . 46
7.5 Disconnection from grid . 47
7.5.1 Grid protection . 47
7.5.2 Requirements of test devices . 48

7.5.3 Grid protection test – PP level . 48
7.5.4 Grid protection test – PGU level . 49
7.5.5 RoCoF . 49
8 Control performance . 49
8.1 General . 49
8.2 Performance test . 49
8.2.1 General . 49
8.2.2 Active power control tests . 50
8.2.3 Controlled shutdown . 52
8.2.4 Synthetic inertia response . 54
8.2.5 Reactive power control . 57
8.2.6 Reactive power capability . 60
8.3 Functionality tests . 63
8.3.1 General . 63
8.3.2 Active power ramp rate limitation test . 63
8.3.3 Priority of setpoints . 65
8.3.4 Frequency control . 67
8.3.5 Reactive power ramp rate limitation . 72
8.3.6 Voltage control Q(U)-characteristic . 76
8.3.7 Power factor control . 78
8.3.8 Communication error/fallback scenarios . 81
9 Assessment of power quality of power plants (PP) . 84
9.1 General . 84
9.2 Voltage fluctuations . 84
9.2.1 Voltage change . 84
9.2.2 Flicker in continuous operation . 85
9.2.3 Voltage change and flicker during switching operations . 86
9.3 Current harmonics, interharmonics and higher frequency components . 87
Annex A (informative) Report template . 89
A.1 Overview. 89
A.2 Power plant specification and test conditions . 89
A.3 Power plant controller . 90
A.4 Power quality aspects . 91
A.5 Steady state operation . 120
A.6 Dynamic performance . 121
A.7 Disconnection from grid (grid protection) . 122
A.8 Performance test . 122
A.8.1 General . 122
A.8.2 Static error test . 122
A.8.3 Dynamic response test . 123
A.8.4 Controlled shutdown . 123
A.8.5 Synthetic inertia response . 124
A.8.6 Reactive power control . 126
A.8.7 Reactive power capability . 127
A.9 Functionality tests . 128
A.9.1 Active power ramp rate limitation test . 128
A.9.2 Priority of setpoints . 129
A.9.3 Frequency control . 130
A.9.4 Reactive power ramp rate limitation . 131

– 4 – IEC 61400-21-2:2023 © IEC 2023
A.9.5 Voltage control Q(U)-characteristic . 132
A.9.6 Power factor control . 133
A.9.7 Communication error / fallback scenarios . 135
Annex B (informative) Harmonic evaluation . 137
B.1 Harmonic estimation at the point of interest . 137
B.2 Background harmonic distortion . 137
B.3 Harmonic summation . 138
B.4 Harmonic propagation studies . 138
B.5 PP harmonic contribution evaluation . 139
B.5.1 General . 139
B.5.2 Incremental PP harmonic contribution based on simulations . 139
B.5.3 PP electromagnetic compatibility analysis based on simulations . 139
B.5.4 Harmonic measurements at the POC . 140
Annex C (informative) Validation procedure for PP . 141
Annex D (informative) Measurement accuracy . 143
Bibliography . 146

Figure 1 – Example of step response . 19
Figure 2 – Example of a PP setup . 29
Figure 3 – General structure of a PPC for reactive power control within a power plant . 35
Figure 4 – General structure of a PPC for active power control within a power plant . 36
Figure 5 – Illustration of the PPC as a black box with in- and outputs . 36
Figure 6 – Illustration of the PPC with the internal system data . 37
Figure 7 – Illustration of a complete test setup . 38
Figure 8 – Example of time series for the active and reactive current measured (M)
and simulated (S) active and reactive current [1]. 47
Figure 9 – Adjustment of active power reference value . 51
Figure 10 – Example of active power response step . 51
Figure 11 – Example of controlled shutdown . 54
Figure 12 – Synthetic inertia – example response and definitions . 56
Figure 13 – Test for static error . 59
Figure 14 – Example of test of dynamic response . 59
Figure 15 – Example of test of reactive power capability QP-chart . 62
Figure 16 – Example of reactive power capability UP-chart corresponding to the QP-
chart . 62
Figure 17 – Example of available active power and active power in ramp rate limitation
mode . 64
Figure 18 – Example of active power setpoint prioritization test . 66
Figure 19 – PPC measured frequency feedback is replaced by a simulated frequency . 69
Figure 20 – Example of an active power control function P = f(f), with the different
measurement points and related steps of frequency . 70
Figure 21 – Example of reactive power ramp rate limitation test . 75
Figure 22 – Example of the Q(U) characteristic with a 4 % slope . 76
Figure 23 – Example of possible PP communication faults . 81
Figure 24 – Example of graph for communication error test. 83
Figure A.1 – Figure 25 – Voltage flicker P versus active power for normal operation . 91
st
Figure A.2 – Voltage flicker P for background level . 92
st
Figure A.3 – Time series of three-phase voltages as RMS of PP starting . 92
Figure A.4 – Time series of three-phase currents as RMS of PP starting. 92
Figure A.5 – Time series of active and reactive power of PP starting . 92
Figure A.6 – Time series of three-phase voltages as RMS of PP stopping. 93
Figure A.7 – Time series of three-phase currents as RMS of PP stopping . 93
Figure A.8 – Time series of active and reactive power of PP stopping . 93
th
Figure A.9 – Maximum of the 99 percentiles of integer harmonic currents versus
harmonic order . 117
th
Figure A.10 – Maximum of the 99 percentiles of interharmonic currents versus
frequency . 117
th
Figure A.11 – Maximum of the 99 percentiles of higher frequency current
components versus frequency . 117
th
Figure A.12 – Maximum of the 95 percentiles of integer harmonic currents versus
harmonic order . 117
th
Figure A.13 – Maximum of the 95 percentiles of interharmonic currents versus
frequency . 118
th
Figure A.14 – Maximum of the 95 percentiles of higher frequency current
components versus frequency . 118
th
Figure A.15 – Maximum of the 99 percentiles of integer harmonic voltages versus
harmonic order . 118
th
Figure A.16 – Maximum of the 99 percentiles of interharmonic voltages versus
frequency . 118
th
Figure A.17 – Maximum of the 99 percentiles of higher frequency voltage
components versus frequency . 119
th
Figure A.18 – Maximum of the 95 percentiles of integer harmonic voltages versus
harmonic order . 119
th
Figure A.19 – Maximum of the 95 percentiles of interharmonic voltages versus
frequency . 119
th
Figure A.20 – Maximum of the 95 percentiles of higher frequency voltage
components versus frequency . 119
Figure A.21 – Current unbalance factor as a function of active power . 120
Figure A.22 – Voltage unbalance factor as a function of active power . 120
Figure A.23 – Time series: Instantaneous three-phase currents and voltages at the
POC . 121
Figure A.24 – Time series: Positive and negative sequence of the active and reactive
current . 121
Figure A.25 – Time series: Positive and negative sequence of the active and reactive
power . 121
Figure A.26 – Time series: Positive and negative sequence grid voltage at the POC . 122
Figure A.27 – Time series of available active power, measured active power output
and reference values . 122
Figure A.28 – Time series of available active power, measured active power output

and reference values . 123
Figure A.29 – Time series of available active power, measured active power output
and reference values . 123

– 6 – IEC 61400-21-2:2023 © IEC 2023
Figure A.30 – Time-series of available active power, measured active power and
reference value of the grid frequency for (test 1 and test 2) 0,25 × P < P < 0,5 × P . 124
n n
Figure A.31 – Time-series of available active power, measured active power and

reference value of the grid frequency for (test 3 and test 4) P > 0,8 × P . 124
n
Figure A.32 – Time-series of available active power, measured active power and
reference value of the grid frequency for (test 5 and test 6) v > v . 124
n
Figure A.33 – Time-series of reactive power reference values and measured reactive
power and grid voltage during the test of reactive power control . 126
Figure A.34 – Time-series of reactive power reference values and measured reactive

power, grid voltage during the test of reactive power control . 126
Figure A.35 – Zoom of step response (for all three-step responses) in the time-series
of reactive power reference values and measured reactive power, grid voltage during
the test of reactive power control . 127
Figure A.36 – Test of reactive power capability QP-chart . 127
Figure A.37 – Reactive power capability UP-chart corresponding to the QP-chart. 128
Figure A.38 – Time-series of available active power and active power in ramp rate
limitation mode – Slow ramp rate . 128
Figure A.39 – Time-series of available active power and active power in ramp rate
limitation mode – Fast ramp rate . 129
Figure A.40 – Time-series of active power setpoints, available power and active power . 129
Figure A.41 – Time-series of active power setpoints, available power and active power . 130
Figure A.42 – Time-series of simulated frequency . 130
Figure A.43 – Time series of reactive power setpoint, reactive power . 131
Figure A.44 – Time series of voltage – Reactive power, expected reactive power for a
given slope . 132
Figure A.45 – Time series of active power, reactive power, power factor and power
factor reference . 133
Figure A.46 – Time-series of active power setpoint, active power and available power
and failure time point (case 1 to case 3) . 135
Figure A.47 – Graph for communication error test (example) . 136
Figure B.1 – Simplified representation for the PP connected to the external grid used
for the estimation of incremental harmonic contribution at POC or any other point of
interest . 139
Figure B.2 – Simplified representation of the PP for harmonic propagation studies
including the harmonic background and PGU’s non-ideal harmonic voltage source . 140

Table 1 – Overview of measurements and their requirements . 30
Table 2 – Description and general requirements of the HIL test functional . 38
Table 3 – List of recorded signals . 45
Table 4 – List of electrical signals to be monitored for the evaluation of events . 45
Table 5 – Maximum measurement uncertainties for the grid simulator . 48
Table 6 – List of signals during test . 50
Table 7 – Accuracy of the active power control values . 52
Table 8 – Results from the active power dynamic response test . 52
Table 9 – Example of list of signals during test . 53
Table 10 – Results of the emergency shutdown test. 54
Table 11 – List of signals during test . 55

Table 12 – Synthetic inertia settings . 57
Table 13 – Synthetic inertia test results . 57
Table 14 – List of signals during test . 58
Table 15 – Test for static error . 60
Table 16 – Test for dynamic response . 60
Table 17 – List of signals during test . 61
Table 18 – Example of reactive power capability QP-chart . 63
Table 19 – List of signals during test . 63
Table 20 – Active power ramp rate calculation . 65
Table 21 – List of signals during test . 66
Table 22 – Test results priority of setpoints . 67
Table 23 – List of signals during test . 68
Table 24 – Example of test sequence for the frequency dependent active power
function . 72
Table 25 – List of signals during test . 73
Table 26 – Test procedure reactive power ramp rate limitation test . 74
Table 27 – Reactive power ramp rate calculation . 75
Table 28 – List of signals during test . 77
Table 29 – Voltage control Q(U) – slope test . 78
Table 30 – List of signals during test . 79
Table 31 – Example of power factor control test . 80
Table 32 – List of signals during test . 82
Table 33 – Example of communication error test – Failure on external interface . 83
Table 34 – Example of failure of PPC or communication between PPC and PGUs . 83
Table 35 – Example of failure of grid data measurement . 84
Table 36 – Specification of exponents according to IEC TR 61000-3-6. 88
Table A.1 – General and nominal data . 89
Table A.2 – General power plant capabilities and control functions . 90
Table A.3 – General test and report information . 90
Table A.4 – General test conditions and grid data . 90
Table A.5 – General test conditions and test setup . 91
Table A.6 – Flicker values . 91
Table A.7 – Rapid voltage changes due to switching operations . 92
Table A.8 – General test information . 93
th
Table A.9 – 99 percentile of 10 min harmonic magnitudes per week. 94
th
Table A.10 – 99 percentile of 10 min harmonic magnitudes per week . 95
th
Table A.11 – 99 percentile of 10 min harmonic magnitudes per week . 97
th
Table A.12 – 95 percentile of 10 min harmonic magnitudes per week . 98
th
Table A.13 – 95 percentile of 10 min harmonic magnitudes per week . 99
th
Table A.14 – 95 percentile of 10 min harmonic magnitudes per week . 101
th
Table A.15 – 99 percentile of 10 min harmonic magnitudes per week . 102
th
Table A.16 – 99 percentile of 10 min harmonic magnitudes per week . 103

– 8 – IEC 61400-21-2:2023 © IEC 2023
th
Table A.17 – 99 percentile of 10 min harmonic magnitudes per week . 105
th
Table A.18 – 95 percentile of 10 min harmonic magnitudes per week . 106
th
Table A.19 – 95 percentile of 10 min harmonic magnitudes per week . 107
th
Table A.20 – 95 percentile of 10 min harmonic magnitudes per week . 108
th
Table A.21 – 99 percentile of 3 s harmonic magnitudes per week . 109
th
Table A.22 – 99 percentile of 3 s harmonic magnitudes per week . 111
th
Table A.23 – 99 percentile of 3 s harmonic magnitudes per week . 112
th
Table A.24 – 99 percentile of 3 s harmonic magnitudes per week . 113
th
Table A.25 – 99 percentile of 3 s harmonic magnitudes per week . 114
th
Table A.26 – 99 percentile of 3 s harmonic magnitudes per week . 116
Table A.27 – Unbalance . 120
Table A.28 – General fault information of undervoltage and overvoltage ride-through
a
(UVRT and OVRT) events/record . 121
Table A.29 – Accuracy of the active power control values . 122
Table A.30 – Accuracy of the active power control values . 123
Table A.31 – Results of the emergency shutdown test . 123
Table A.32 – Synthetic inertia test results . 125
Table A.33 – Test for static error. 126
Table A.34 – Test for dynamic response . 127
Table A.35 – PQ-diagram . 128
Table A.36 – Active power ramp rate calculation – Slow ramp rate . 129
Table A.37 – Active power ramp rate calculation – Fast ramp rate . 129
Table A.38 – Test results priority of setpoints . 130
Table A.39 – Frequency dependent active power function results . 131
Table A.40 – Reactive power ramp rate calculation . 132
Table A.41 – Voltage control Q(U) – slope test. 133
Table A.42 – Power factor control test . 134
Table A.43 – Communication error test – Failure on external interface (example) . 135
Table A.44 – Failure of PPC or communication between PPC and PGUs (example) . 135
Table A.45 – Failure of grid data measurement (example) . 135
Table A.46 – Communication error test – Failure on external interface (example) . 136
Table A.47 – Failure of PPC or communication between PPC and PGUs (example) . 136
Table A.48 – Failure of grid data measurement (example) . 136
Table C.1 – Recommended assessment methods for the validation of the electrical
capabilities of the PP . 141
Table D.1 – Voltage transducer (VT) in MV, HV and EHV. 143
Table D.2 – Current transducer (CT) in MV, HV und EHV. 144

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
WIND ENERGY GENERATION SYSTEMS –

Part 21-2: Measurement and assessment of electrical characteristics –
Wind power plants
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