The approach with older electromechanical high impedance relays was to use an universally safe K factor of 1.0,
but the older relays operated quickly with a lower V
K
/V
s
ratio. With more modern IEDs, it is desirable to identify the
optimum K factor for stability, so that the required V
K
/V
s
ratio for stability and operating speed will not make CT
kneepoint voltage requirements worse than traditional requirements.
The high impedance REF CT requirements are shown in the following figure. They are valid for:
5
£
X/R
£
120 and 0.5In
£
40In
V00752
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0
0.01
0.02
0.03
0.04
0.05
0.06
Av
er
ag
e
op
er
at
in
g
tim
e
V
K
/V
S
K
Stable
Unstable
K (blue curve)
Average operating time (red curve)
Figure 90: High Impedance REF CT requirement
Using the above graphical tool:
1.
Locate the required average operation time on the right-hand side of the vertical axis.
2.
Draw a horizontal line across until it intersects the red curve
3.
Draw a vertical line from the above intersection point
4.
Read off the the Vk/Vs value from the horizontal axis
5.
Where this vertical line intersects the blue curve, read off the K value on the left hand side of the vertical
axis
If we take the example where the average operating time is 38 ms, the above graphical operations reveal that
Vk/Vs = 4 and K = 0.95.
For best accuracy we recommend class X or class 5P current transformers (CTs). The CT requirements for high
impedance REF protection are generally lower than those for differential protection. If the line CTs for high
impedance REF protection are the same as those used for differential protection, the differential CT requirements
cover both differential and high impedance REF applications. However if the line CTs for high impedance REF are
not the same as those used for differential protection, the high impedance REF CT requirements can be obtained
by using the graph shown above.
Chapter 8 - Restricted Earth Fault Protection
P64x
190
P64x-TM-EN-1.3
Summary of Contents for P642
Page 2: ......
Page 18: ...Contents P64x xvi P64x TM EN 1 3 ...
Page 24: ...Table of Figures P64x xxii P64x TM EN 1 3 ...
Page 25: ...CHAPTER 1 INTRODUCTION ...
Page 26: ...Chapter 1 Introduction P64x 2 P64x TM EN 1 3 ...
Page 36: ...Chapter 1 Introduction P64x 12 P64x TM EN 1 3 ...
Page 37: ...CHAPTER 2 SAFETY INFORMATION ...
Page 38: ...Chapter 2 Safety Information P64x 14 P64x TM EN 1 3 ...
Page 50: ...Chapter 2 Safety Information P64x 26 P64x TM EN 1 3 ...
Page 51: ...CHAPTER 3 HARDWARE DESIGN ...
Page 52: ...Chapter 3 Hardware Design P64x 28 P64x TM EN 1 3 ...
Page 87: ...CHAPTER 4 SOFTWARE DESIGN ...
Page 88: ...Chapter 4 Software Design P64x 64 P64x TM EN 1 3 ...
Page 98: ...Chapter 4 Software Design P64x 74 P64x TM EN 1 3 ...
Page 99: ...CHAPTER 5 CONFIGURATION ...
Page 100: ...Chapter 5 Configuration P64x 76 P64x TM EN 1 3 ...
Page 121: ...CHAPTER 6 TRANSFORMER DIFFERENTIAL PROTECTION ...
Page 122: ...Chapter 6 Transformer Differential Protection P64x 98 P64x TM EN 1 3 ...
Page 165: ...CHAPTER 7 TRANSFORMER CONDITION MONITORING ...
Page 166: ...Chapter 7 Transformer Condition Monitoring P64x 142 P64x TM EN 1 3 ...
Page 189: ...CHAPTER 8 RESTRICTED EARTH FAULT PROTECTION ...
Page 190: ...Chapter 8 Restricted Earth Fault Protection P64x 166 P64x TM EN 1 3 ...
Page 215: ...CHAPTER 9 CURRENT PROTECTION FUNCTIONS ...
Page 216: ...Chapter 9 Current Protection Functions P64x 192 P64x TM EN 1 3 ...
Page 249: ...CHAPTER 10 CB FAIL PROTECTION ...
Page 250: ...Chapter 10 CB Fail Protection P64x 226 P64x TM EN 1 3 ...
Page 259: ...CHAPTER 11 VOLTAGE PROTECTION FUNCTIONS ...
Page 260: ...Chapter 11 Voltage Protection Functions P64x 236 P64x TM EN 1 3 ...
Page 274: ...Chapter 11 Voltage Protection Functions P64x 250 P64x TM EN 1 3 ...
Page 275: ...CHAPTER 12 FREQUENCY PROTECTION FUNCTIONS ...
Page 276: ...Chapter 12 Frequency Protection Functions P64x 252 P64x TM EN 1 3 ...
Page 286: ...Chapter 12 Frequency Protection Functions P64x 262 P64x TM EN 1 3 ...
Page 287: ...CHAPTER 13 MONITORING AND CONTROL ...
Page 288: ...Chapter 13 Monitoring and Control P64x 264 P64x TM EN 1 3 ...
Page 306: ...Chapter 13 Monitoring and Control P64x 282 P64x TM EN 1 3 ...
Page 307: ...CHAPTER 14 SUPERVISION ...
Page 308: ...Chapter 14 Supervision P64x 284 P64x TM EN 1 3 ...
Page 322: ...Chapter 14 Supervision P64x 298 P64x TM EN 1 3 ...
Page 323: ...CHAPTER 15 DIGITAL I O AND PSL CONFIGURATION ...
Page 324: ...Chapter 15 Digital I O and PSL Configuration P64x 300 P64x TM EN 1 3 ...
Page 336: ...Chapter 15 Digital I O and PSL Configuration P64x 312 P64x TM EN 1 3 ...
Page 337: ...CHAPTER 16 COMMUNICATIONS ...
Page 338: ...Chapter 16 Communications P64x 314 P64x TM EN 1 3 ...
Page 397: ...CHAPTER 17 CYBER SECURITY ...
Page 398: ...Chapter 17 Cyber Security P64x 374 P64x TM EN 1 3 ...
Page 415: ...CHAPTER 18 INSTALLATION ...
Page 416: ...Chapter 18 Installation P64x 392 P64x TM EN 1 3 ...
Page 431: ...CHAPTER 19 COMMISSIONING INSTRUCTIONS ...
Page 432: ...Chapter 19 Commissioning Instructions P64x 408 P64x TM EN 1 3 ...
Page 460: ...Chapter 19 Commissioning Instructions P64x 436 P64x TM EN 1 3 ...
Page 461: ...CHAPTER 20 MAINTENANCE AND TROUBLESHOOTING ...
Page 462: ...Chapter 20 Maintenance and Troubleshooting P64x 438 P64x TM EN 1 3 ...
Page 477: ...CHAPTER 21 TECHNICAL SPECIFICATIONS ...
Page 478: ...Chapter 21 Technical Specifications P64x 454 P64x TM EN 1 3 ...
Page 507: ...APPENDIX A ORDERING OPTIONS ...
Page 508: ...Appendix A Ordering Options P64x P64x TM EN 1 3 ...
Page 512: ...Appendix A Ordering Options P64x A4 P64x TM EN 1 3 ...
Page 513: ...APPENDIX B SETTINGS AND SIGNALS ...
Page 515: ...APPENDIX C WIRING DIAGRAMS ...
Page 516: ...Appendix C Wiring Diagrams P64x P64x TM EN 1 3 ...
Page 590: ......
Page 591: ......