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BSI PD IEC/TR 61869-100:2017

BSI PD IEC/TR 61869-100:2017

$215.11

Instrument transformers – Guidance for application of current transformers in power system protection

Published By Publication Date Number of Pages
BSI 2017 140
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This part of IEC 61869 is applicable to inductive protective current transformers meeting the requirements of the IEC 61869-2 standard.

It may help relay manufacturers, CT manufacturers and project engineers to understand how a CT responds to simplified or standardized short circuit signals. Therefore, it supplies advanced information to comprehend the definition of inductive current transformers as well as their requirements.

The document aims to provide information for the casual user as well as for the specialist.

Where necessary, the level of abstraction is mentioned in the document. It also discusses the question about the responsibilities in the design process for current transformers.

PDF Catalog

PDF Pages PDF Title
4 CONTENTS
9 FOREWORD
11 INTRODUCTION
12 1 Scope
2 Normative references
3 Terms and definitions and abbreviations
3.1 Terms and definitions
14 3.2 Index of abbreviations
Figures
Figure 1 – Definition of the fault inception angle γ
16 4 Responsibilities in the current transformer design process
4.1 History
4.2 Subdivision of the current transformer design process
17 5 Basic theoretical equations for transient designing
5.1 Electrical circuit
5.1.1 General
18 Figure 2 – Components of protection circuit
19 Figure 3 – Entire electrical circuit
20 5.1.2 Current transformer
Figure 4 – Primary short circuit current
21 Figure 5 – Non-linear flux of Lct
22 5.2 Transient behaviour
5.2.1 General
Figure 6 – Linearized magnetizing inductance of a current transformer
23 Figure 7 – Simulated short circuit behaviour with non-linear model
24 5.2.2 Fault inception angle
25 5.2.3 Differential equation
Figure 8 – Three-phase short circuit behaviour
26 Figure 9 – Composition of flux
27 6 Duty cycles
6.1 Duty cycle C – O
6.1.1 General
28 Figure 10 – Short circuit current for two different fault inception angles
Figure 11 – ψmax as the curve of the highest flux values
29 6.1.2 Fault inception angle
Figure 12 – Primary current curves for the 4 cases for 50 Hz and ϕ = 70°
Tables
Table 1 – Four significant cases of short circuit current inception angles
30 6.1.3 Transient factor Ktf and transient dimensioning factor Ktd
Figure 13 – Four significant cases of short circuit currents with impact on magnetic saturation of current transformers
33 Figure 14 – Relevant time ranges for calculation of transient factor
34 Figure 15 – Occurrence of the first flux peak depending on Tp, at 50 Hz
35 Figure 16 – Worst-case angle θtf,ψmax as function of Tp and t’al
36 Figure 17 – Worst-case fault inception angle γtf,ψmax as function of Tp and t’al
Figure 18 – Ktf,ψmax calculated with worst-case fault inception angle θψmax
37 Figure 19 – Polar diagram with Ktf,ψmax and γtf,ψmax
42 Figure 20 – Determination of Ktf in time range 1
43 Figure 21 – Primary current curves for 50Hz, Tp = 1 ms, γψmax = 166° for t’al = 2 ms
44 Figure 22 – worst-case fault inception angles for 50Hz, Tp = 50 ms and Ts = 61 ms
45 Figure 23 – transient factor for different time ranges
46 Figure 24 – Ktf in all time ranges for Ts = 61 ms at 50 Hz with t’al as parameter
Figure 25 – Zoom of Figure 24
47 Figure 26 – Primary current for a short primary time constant
48 Figure 27 – Ktf values for a short primary time constant
49 Figure 28 – Short circuit currents for various fault inception angles
50 Figure 29 – Transient factors for various fault inception angles (example)
Figure 30 – Worst-case fault inception angles for each time step (example for 50 Hz)
51 Figure 31 – Primary current for two different fault inception angles(example for 16,67 Hz)
52 6.1.4 Reduction of asymmetry by definition of the minimum current inception angle
Figure 32 – Transient factors for various fault inception angles(example for 16,67 Hz)
Figure 33 – Worst-case fault inception angles for every time step(example for 16,67 Hz)
53 Figure 34 – Fault occurrence according to Warrington
54 Figure 35 – estimated distribution of faults over several years
55 6.2 Duty cycle C – O – C – O
6.2.1 General
Figure 36 – Transient factor Ktf calculated with various fault inception angles γ
56 6.2.2 Case A: No saturation occurs until t’
Figure 37 – Flux course in a C-O-C-O cycle of a non-gapped core
57 Figure 38 – Typical flux curve in a C-O-C-O cycle of a gapped core,with higher flux in the second energization
58 6.2.3 Case B: Saturation occurs between t’al and t’
Figure 39 – Flux curve in a C-O-C-O cycle of a gapped core, with higher flux in the first energization
59 Figure 40 – Flux curve in a C-O-C-O cycle with saturation allowed
60 6.3 Summary
Figure 41 – Core saturation used to reduce the peak flux value
61 Figure 42 – Curves overview for transient designing
62 Table 2 – Equation overview for transient designing
63 7 Determination of the transient dimensioning factor Ktd by numerical calculation
7.1 General
7.2 Basic circuit
64 7.3 Algorithm
Figure 43 – Basic circuit diagram for numerical calculation of Ktd
65 7.4 Calculation method
66 7.5 Reference examples
Figure 44 – Ktd calculation for C-O cycle
67 Figure 45 – Ktd calculation for C-O-C-O cyclewithout core saturation in the first cycle
68 Figure 46 – Ktd calculation for C-O-C-O cycleconsidering core saturation in the first cycle
69 Figure 47 – Ktd calculation for C-O-C-O cycle with reduced asymmetry
70 Figure 48 – Ktd calculation for C-O-C-O cycle with short t’al and t’’al
71 8 Core saturation and remanence
8.1 Saturation definition for common practice
8.1.1 General
8.1.2 Definition of the saturation flux in the preceding standard IEC 60044-1
Figure 49 – Ktd calculation for C-O-C-O cycle for a non-gapped core
72 Figure 50 – Comparison of the saturation definitionsaccording to IEC 60044-1 and according to IEC 61869-2
73 8.1.3 Definition of the saturation flux in IEC 61869-2
Figure 51 – Remanence factor Kr according to the previous definition IEC 60044-1
74 8.1.4 Approach “5 % – Factor 5”
Figure 52 – Determination of saturation and remanenceflux using the DC method for a gapped core
Figure 53 – Determination of saturation and remanence flux using DC method for a non-gapped core
75 8.2 Gapped cores versus non-gapped cores
Table 3 – Comparison of saturation point definitions
76 Table 4 – Measured remanence factors
77 8.3 Possible causes of remanence
78 Figure 54 – CT secondary currents as fault records of arc furnace transformer
79 Figure 55 – 4-wire connection
80 Figure 56 – CT secondary currents as fault records in the second fault of auto reclosure
81 9 Practical recommendations
9.1 Accuracy hazard in case various PR class definitions for the same core
9.2 Limitation of the phase displacement ∆ϕ and of the secondary loop time constant Ts by the transient dimensioning factor Ktd for TPY cores
Table 5 – Various PR class definitions for the same core
82 10 Relations between the various types of classes
10.1 Overview
10.2 Calculation of e.m.f. at limiting conditions
Table 6 – e.m.f. definitions
Table 7 – Conversion of e.m.f. values
83 10.3 Calculation of the exciting (or magnetizing) current at limiting conditions
10.4 Examples
Table 8 – Conversion of dimensioning factors
Table 9 – Definitions of limiting current
84 10.5 Minimum requirements for class specification
10.6 Replacing a non-gapped core by a gapped core
Table 10 – Minimum requirements for class specification
85 11 Protection functions and correct CT specification
11.1 General
11.2 General application recommendations
11.2.1 Protection functions and appropriate classes
Table 11 – Effect of gapped and non-gapped cores
86 Table 12 – Application recommendations
87 11.2.2 Correct CT designing in the past and today
89 11.3 Overcurrent protection: ANSI code: (50/51/50N/51N/67/67N); IEC symbol: I>
11.3.1 Exposition
90 Figure 57 – Application of instantaneous/time-delay overcurrent relay (ANSI codes 50/51) with definite time characteristic
Figure 58 – Time-delay overcurrent relay, time characteristics
91 11.3.2 Recommendation
11.3.3 Example
11.4 Distance protection: ANSI codes: 21/21N, IEC code: Z<
11.4.1 Exposition
Figure 59 – CT specification example, time overcurrent
92 Figure 60 – Distance protection, principle (time distance diagram)
93 11.4.2 Recommendations
11.4.3 Examples
Figure 61 – Distance protection, principle (R/X diagram)
94 Figure 62 – CT Designing example, distance protection
98 Figure 63 – Primary current with C-O-C-O duty cycle
Figure 64 – Transient factor Ktf with its envelope curve Ktfp
99 Figure 65 – Transient factor Ktf for CT class TPY with saturation in the first fault
Figure 66 – Transient factor Ktf for CT class TPZ with saturation in the first fault
100 11.5 Differential protection
11.5.1 Exposition
Figure 67 – Transient factor Ktf for CT class TPX
101 11.5.2 General recommendations
11.5.3 Transformer differential protection (87T)
Figure 68 – Differential protection, principle
102 Figure 69 – Transformer differential protection, faults
103 Figure 70 – Transformer differential protection
105 Table 13 – Calculation results of the overdimensioning of a TPY core
Table 14 – Calculation results of overdimensioning as PX core
106 11.5.4 Busbar protection: Ansi codes (87B)
Figure 71 – Busbar protection, external fault
109 11.5.5 Line differential protection: ANSI codes (87L) (Low impedance)
Figure 72 – Simulated currents of a current transformerfor bus bar differential protection
110 Figure 73 – CT designing for a simple line with two ends
111 11.5.6 High impedance differential protection
Table 15 – Calculation scheme for line differential protection
112 Figure 74 – Differential protection realized with a simple electromechanical relay
113 Figure 75 – High impedance protection principle
114 Figure 76 – Phasor diagram for external faults
115 Figure 77 – Phasor diagram for internal faults
116 Figure 78 – Magnetizing curve of CT
119 Figure 79 – Single-line diagram of busbar and high impedance differential protection
Table 16 – Busbar protection scheme with two incoming feeders
121 Figure 80 – Currents at the fault location (primary values)
122 Figure 81 – Primary currents through CTs, scaled to CT secondary side
Figure 82 – CT secondary currents
123 Figure 83 – Differential voltage
Figure 84 – Differential current and r.m.s. filter signal
124 Figure 85 – Currents at the fault location (primary values)
Figure 86 – Primary currents through CTs, scaled to CT secondary side
125 Figure 87 – CT secondary currents
Figure 88 – Differential voltage
126 Figure 89 – Differential current and r.m.s. filtered signal
Figure 90 – Currents at the fault location (primary values)
127 Figure 91 – Primary currents through CTs, scaled to CT secondary side
Figure 92 – CT secondary currents
128 Figure 93 – Differential voltage
Figure 94 – Differential current and r.m.s. filtered signal
129 Figure 95 – Differential voltage without varistor limitation
130 Annex A (informative)Duty cycle C – O software code
132 Annex B (informative)Software code for numerical calculation of Ktd
137 Bibliography

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BSI PD IEC/TR 61869-100:2017
$215.11