CTs may be close to saturation so a high bias current is needed. More differential current is then needed to trip the
circuit breakers, allowing greater security from external faults and less risk of maloperation.
This is achieved by defining an operating current characteristic. Often a triple slope characteristic is used as shown
below.
K1
K2
Restraint region
Operate region
Is2
Is1
Ibias
Idiff
V00664
High Set Threshold
Figure 35: Compensation using biased differential characteristic
Idiff is the differential current, which is the vector sum of all the current inputs. Ibias is a current which is
proportional to the scalar sum of all currents entering and leaving the zone. The bias current is used to calculate
an operating current. If the differential current calculated by the IED is above the operation current, then the
device will trip (providing no blocking signals are asserted).
The characteristic can be defined by setting certain parameters such as the minimum operating current Is1 (Iset
1), Is2 (Iset 2), K1 and K2. Is1 sets the minimum operating current. Is2 sets the level of bias current at which the
steeper slope sets in. Constants K1 and K2 define the slopes. A High Set Threshold is usually defined, which ensures
the device will operate for very high currents, even if blocking signals are present.
The slope parts of the characteristic curve provide stability for external faults that cause CT saturation. The high
bias current region of the characteristic curve has a steeper slope than the low bias current region in order to
improve the stability even further for high-current external faults. The first slope, K1, compensates for CT errors
and tap changer errors. The second slope, K2, compensates for CT saturation. Is1 should be set above transient
overfluxing and Is2 should be considered as the transformer full load current. The CTs are sized according to the
transformer full load current.
2.3
THREE-PHASE TRANSFORMER CONNECTION TYPES
There are two ways of connecting a three-phase transformer winding:
●
Star-connected (sometimes known as Y, or Wye)
●
Delta-connected (sometimes known as
D
or D)
In some transformers, the windings are split at the centre point and terminals are brought out so that they can
also be interconnected. These windings can be zig-zag connected (Z-connected).
The more common connection types are:
●
Y-y
●
Y-d
●
Y-z
●
D-d
●
D-y
●
D-z
To differentiate between the low and high voltage sides of the transformer, a standard convention has been
adopted whereby lower case is used for the low voltage side and upper case is used for the high voltage side.
P64x
Chapter 6 - Transformer Differential Protection
P64x-TM-EN-1.3
101
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: ......