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 |
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 |
Related products
-
BSI PD IEC/TR 61869-100:2017
Instrument transformers – Guidance for application of current transformers in power system protection Published By…
-
BSI PD IEC/TR 61869-100:2017
Instrument transformers – Guidance for application of current transformers in power system protection Published By…
