005 Busbar Protection Concepts by Siemens.pptx

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1. Busbar Protection Concepts Power Academy India siemens.com Restricted © Siemens 2020

2. Power System General Table of content Busbar Protection Concepts Busbar Introduction Need of Busbar Protection Busbar Arrangement Blockable O/C relays High Impedance Bus Differential Low Impedance Bus Differential Bus Zones Requirements on the Isolator Auxiliary Contacts End Fault Protection Breaker Failure Protection Busbar Architecture

3. Frequency of faults Type of fault Percentage occurrence L-g 85 L-L 8 L-L-g 5 L-L-L 2 or less Equipment Percentage of total faults Overhead lines 50 Cables 10 Switchgears 15 Transformers 12 CT’s and PT’s 2 Control equipment 3 Miscellaneous 8 Transmission lines 85 Busbars 12 Generators/Transformers 3 Electrical faults in the power system

4. Busbars are very critical elements in a power system, since they are the points of coupling of many circuits, transmission, generation, or loads. A single bus fault can cause damage equivalent to many simultaneous faults and such faults usually draw large currents. So a high-speed bus protection is often required to limit the damage on equipment and system stability or to maintain service to as much load as possible. The term “bus protection” refers to protection at the bus location, independent of equipment at remote locations . Busbar Introduction

5. Why do we need to Protect Busbar?

6. In its absence fault clearance takes place in Zone-II of distance relay by remote end tripping This means slow and unselective tripping and wide spread black out Effect of delayed clearance Greater damage at fault point Indirect shock to connected equipment's like shafts of Generator and windings of transformer. Need for Bus bar protection

7. Human injuries for station personnel Damage to substation equipment Disturbance in power system (power quality) Power system transient instability Power system blackout (if not cleared quickly) Consequence of Bus Faults

8. Speed Dependability Security Requirements on Bus Protection

9. What are the requirements of Busbar Protection?

10. Short tripping time Detect internal faults Stable at external faults Disconnect only faulty part of bus Secure against maloperation due to Auxiliary contact failure, Human mistakes & Faults in secondary circuits Requirements of Busbar Protection

11. High Speed Tripping for All Internal Faults Trip for any internal faults with high speed The tripping speed for bus protection should be around half cycle (normally less then a cycle required from the utilities) Switching on to the bus fault after maintenance must be cleared quickly The fault detection time must be within 1-3 ms (possible CT explosion for heavy internal fault) Simultaneous/Evolving faults should be detected and cleared The fault between bay CT and CB should be cleared by BF protection or end fault protection (transfer trip command) Speed & Dependability Requirement:

12. Fully Stable for External Faults Heavy CT saturation during external fault conditions might cause m al operation of bus protection Different CT ratios connected to a bus will easily produce heavy CT saturation conditions once the external fault occurs in the bay with smallest CT ratio CT secondary burden also can cause heavy CT saturation Power system dc time constant will influence saturation Fully Stable for Open CT Condition Open CT condition can be easily detected Switching between bus zones can be properly arranged so that each protection zone can have correct measuring inputs Overall zone checking criteria or under voltage starting criterion are required by utilities in order to provide second operating condition Security Requirement:

13. Open-air switchgear Air-insulated Metal enclosed switchgear SF6-insulated or Gas Insulated Types of Switchgear

14. Single bus single breaker Single bus with bus Sectionalizer Main and transfer bus Double bus single breaker with bus coupler Double bus double breaker Double bus one and a half breaker One and Half Breaker Ring busbar Busbar arrangements

15. FEEDER1 MAIN BUSBAR FEEDER2 T/F-1 T/F-2 FEEDER3 FEEDER4 BAY1 BAY2 BAY3 BAY4 BAY5 BAY6 Single Bus System

16. Single Bus System Advantage Simple in Design Easy Maintenance Less Expenditure Good Appearance Disadvantage In case of bus fault or bus bar isolator fault or maintenance Total Substation is out of service. In case of maintenance of transformer circuit breaker the associated transformer has also to be shut-down. Similarly for Line also.

17. FEEDER1 MAIN BUSBAR FEEDER2 T/F-1 T/F-2 FEEDER3 FEEDER4 BAY1 BAY2 BAY3 BAY4 BAY5 BAY6 CB SECTIONALISER Single Bus System with CB Sectionalizer System

18. In this, main bus is divided into two sections with a circuit breaker and isolators in between the adjoining sections. One complete section can be taken out for maintenance without disturbing the continuity of other section. Even if a fault occurs on one section of the bus, that faulty section along will be isolated while the other section continues to be in service. Single Bus System with CB Sectionalizer System

19. FEEDER1 BUS-1 TRANSFER BUS FEEDER2 TRANSFER BUS COUPLER T/F-1 T/F-2 FEEDER3 FEEDER4 BAY1 BAY2 BAY3 BAY4 BAY5 BAY6 BAY7 Single Main and Transfer Bus System

20. With this arrangement, all the feeders are normally on the main bus. If at any time, a line breaker maintenance is required, that particular feeder, can be transferred on to the transfer bus. The feeder protection thus gets transferred to trip bus couple breaker. On fault occurrence or maintenance, entire bus becomes de-energised. Salient features: Only one line at a time can be transferred on the transfer bus For maintenance or on fault occurrence, total bus becomes dead. Single Main and Transfer Bus System

21. FEEDER1 BUS-2 BUS-1 FEEDER2 T/F-1 T/F-2 BUS COUPLER FEEDER3 FEEDER4 BAY1 BAY2 BAY3 BAY4 BAY5 BAY7 BAY8 Double Main Bus System

22. Salient features: This has got flexibility of transferring any line to any of the buses. For maintenance or on fault occurrence only one bus becomes dead while the other bus remains in service. For maintenance of a breaker, that particular line has to be taken out of service. To overcome this, an additional bypass isolator is provided as indicated in figure below. Double Main Bus System

23. FEEDER1 BUS-2 BUS-1 T/F-1 BUS COUPLER FEEDER2 T/F-2 FEEDER3 FEEDER4 BAY1 BAY2 BAY3 BAY4 BAY5 BAY6 BAY7 When any CB problem or for preventive maintenance then all other feeders shifted to another bus of faulted CB Bus and close the Bypass Isolator, then protection is shifted to bus coupler and open the faulty CB Double Main Bus & CB Bypass Isolator System

24. FEEDER1 BUS-2 BUS-1 FEEDER2 TRANSFER BUS COUPLER T/F-1 T/F-2 BUS COUPLER TRANSFER BUS FEEDER3 FEEDER4 BAY1 BAY2 BAY3 BAY4 BAY5 BAY6 BAY7 BAY8 Double Main Bus & Transfer Bus System

25. This is combination of main and transfer bus and double bus arrangement. Salient features: This has got flexibility of transferring any line to any of the main buses. For maintenance or any fault occurrence, only one bus becomes dead while other bus continues to be in service. Any line breaker can be taken out for maintenance by transferring it to transfer bus, transferring its protection to transfer bus coupler breaker. Double Main Bus & Transfer Bus System

26. FEEDER1 BUS-2 BUS-1 T/F-1 T/F-2 FEEDER2 BAY1 BAY3 BAY6 BAY8 BUS COUPLER BAY2 BUS COUPLER BAY7 BAY4 BAY5 BUS SECTIONALISER This is an improvement over the double bus bar arrangement. For maintenance or an occurrence of a fault, only one section of the faulty bus only becomes dead while the rest continues to be in service. Double Bus with Sectionalizer System

27. FEEDER2 FEEDER4 FEEDER6 FEEDER8 FEEDER10 FEEDER12 FEEDER1 FEEDER3 FEEDER5 FEEDER7 FEEDER9 FEEDER11 BUS-2 BUS-1 BAY1 BAY2 BAY3 BAY4 BAY5 BAY6 BAY7 BAY8 BAY9 BAY10 BAY11 BAY12 BAY13 BAY14 BAY15 BAY16 BAY17 BAY18 DIA1 DIA2 DIA3 DIA4 DIA5 DIA6 One and Half Circuit Breaker System (I-CONFIGUARATION)

28. BUS-2 BUS-1 FEEDER3 FEEDER4 FEEDER7 FEEDER8 FEEDER11 FEEDER12 FEEDER1 FEEDER2 FEEDER5 FEEDER6 FEEDER9 FEEDER10 BAY1 BAY2 BAY3 BAY4 BAY5 BAY6 BAY7 BAY8 BAY9 BAY10 BAY11 BAY12 BAY13 BAY14 BAY15 BAY16 BAY17 BAY18 DIA1 DIA2 DIA3 DIA4 DIA5 DIA6 One and Half Circuit Breaker System (D-CONFIGUARATION)

29. Salient features: It has 3 breakers for two circuits. No changeover of line from one bus to the other is required. For breaker maintenance of any line, the load gets transferred to the other bus. For maintenance or an occurrence of a bus fault, all the interconnections will be on healthy bus. Even if both buses become dead, lines can still be in service through the tiebreaker. This has got many such advantages to maintain the system stability. Drawbacks Two CBs have to be tripped at a primary fault Autoreclosing of two CBs in sequence Summation of CTs necessary One and Half Circuit Breaker System

30. FEEDER1 BAY1 BAY2 BAY3 BAY4 FEEDER2 FEEDER3 BAY5 BAY6 BAY7 BAY8 FEEDER4 FEEDER1 BUS-2 BUS-1 BAY1 BAY2 BUS-2 BUS-1 FEEDER2 BAY3 BAY4 FEEDER3 BAY5 BAY6 BAY7 BAY8 FEEDER4 FOR ECONOMICAL& RELIABULITY PURPOSE THIS SYSTEM ADOPTED IN 800KV SYSTEM Double Bus & Double Breaker System Advantages Busbar fault will not disturb operation Maintenance of one CB without load interruption Drawbacks Two CBs have to be tripped at a primary fault Autoreclosing of two CBs in sequence Summation of CTs necessary

31. Ring Bus System Advantages Operation can be maintained with 1 circuit breaker (CB) out of service Simple interlocking Drawbacks Two CBs have to be tripped at a primary fault Autoreclosing of two CBs in sequence Summation of CTs required Switching in VT circuits

32. Blockable O/C relay ( For radial systems in distribution systems) Differential Protection High impedance Differential Low impedance or Percentage Biased Differential Types of BB Protections

33. Reverse Interlocking x x O/C O/C x UMZ x O/C t= 50ms t= xxxms Pick - up Pick - up + + Blocking 1 power direction 2 Pick - up + Reverse Interlocking x x M O/C O/C x O/C x O/C t= 50ms t= xxxms Pick - up Pick - up 1 1 1 + + Blocking 1 1 1 power direction power direction 2 2 2 2 2 2 Pick - up + Line protection trips and blocks 50ms Stage in incoming - feeder protection Incoming - feeder protection trips in 50ms, because no feeder protection picked up Blocking Scheme typically Used Short coordination time required Care must be taken with possible saturation of feeder CTs This Technique is limited to Simple one incomer distribution buses Blockable O/C relays

34. In theory, bus protection is a straight forward application of Kirchhoff's first law All current differential protection have problems to overcome if the CTs saturate (and they often do) on external faults There are some practical problems associated with complex bus configurations requiring CT switching I 4 I 3 I 2 I 1 Principle : First Kirchhoff - law Fault - free operation : I 1 +I 2 +....I n Fault in busbar - area : I 1 +I 2 +....I n I 4 I 3 I 2 I 1 Principle : First Kirchhoff - law Fault - free operation : I 1 +I 2 +....I n Fault in busbar - area : I 1 +I 2 +....I n  Current differential protection principle = Bus Differential Protection

35. Id> Id> Id> Phase segregated busbar protection

36. Id> Non Phase segregated busbar protection

37. Sensitive, stable and fast protection for single busbar arrangements and 1 ½ breaker systems. The system has limits when used in complex Busbar configurations. However, special CT requirements, additional high voltage device protection, Demanding maintenance, etc put restrictions in its application. High Impedance Differential Protection

38. Requirements on the CT used for High-impedance Protection be dedicated to the High-impedance Busbar Protection Scheme (i.e. cannot be shared with other protection relays) Must have identical turns-ratio (CT Ratio) ( Aux.CT for ratio corrections unacceptable) Have a low resistance of the secondary windings Have a minimum knee-point voltage of approx. 300-500V. Should have a low magnetizing current (few milliamps) High Impedance Differential Protection

39. Check-Zone Feature For a double busbar arrangement, two different high impedance units are required. In this case, the current must be switched between the two different measuring units By connecting auxiliary switches to the busbar isolator contacts. In some cases the auxiliary switches did not operate correctly. This caused the busbar Protection to trip the busbar. For this reason, a safety precaution was introduced: An overall Check-Zone unit, fed from individual CT cores. This overall scheme does not Include any switching of CT and therefore is more secure. The TRIP command is only given when both a discriminating and check-zone system Operates. High Impedance Differential Protection

40. Sensitive and stable scheme for simple buses CT’s class X required, all with identical ratio Extensions done easy? Basic features SETTING V R > I F ( R CT + 2 R L ) V K > 2 V R High Impedance Differential Protection

41. R2 I3 3 I2 2 Ik=I2+I3 1 R2 R2 87 Ur Xm=0 i2 i3 ik ir is Rs Rr ik Fig 1: External Faults Condition for Stability During External Faults: Ur1 > ik1 R2 or ir1 Rr > ik1 R2 ie Rr > ik1/ir1 * R2 Where: ir1 = Current setting of the diff. relay Ur1 = Voltage setting of relay ckt. ik1 = Maximum secondary fault current on external faults SETTING V R > I F ( R CT + 2 R L ) V K > 2 V R High Impedance Differential Protection

42. Fig 2: Internal Faults Rct I3 3 I2 2 I1 1 Rct Rct 87 Ur i2 i3 i1 ir is Rs Rr ir Operation on Internal Faults Ir1 = q (ir1 + n . im + is) Where: Ir1 = Primary fault current required for operation of protection q = CT turns ratio ir1 = Current setting diff.relay n = total No. of CTs per phase, inclusive the CTs of feeders temporarily disconnected. im = CT secondary magnetising current at Ur1 volts. is = Current drawn by the voltage limiting resistor Rs at Ur1 volts. SETTING VR > IF ( RCT + 2 RL) VK > 2 VR High Impedance Differential Protection

43. Disadvantages The same CT ratio, magnetizing features are needed to secure the stability and sensitivity. Need dedicated CT Cores Aux CTs for ration corrections unacceptable The nonlinear resistance is required to reduce the secondary voltage. CT core can not be shared by other relays Uset / Uext_max >2.0 is necessary CT knee point voltage to be larger than 2xUset High Impedance Differential Protection

44. Low Impedance Protection is preferable for the protection of double and multiple busbars systems. Advantage od Percentage biased differential Relay Free of any need for matched CT Characteristics or ratios Other Protective relays can be included in the same circuit.. Stable for infinite fault levels In sensitive to CT Saturation. Detects fault within 1-2ms and initiates tripping within 5-7ms . Low Impedance Differential Protection Bus Protection

45. Used over wide range of bus configurations With all types of CT’s, free nominal current, tolerant to saturation Special treatment of CT saturation is needed Low Impedance Differential Protection

46. BUS DIFF ZONE Diff Relay BUS Bus Differential Zone for Single Busbar System

47. # SINGLE ZONE INTERCONNECTION Diff Relay A Diff Relay B BUS DIFF ZONE B BUS-A BUS-B BUS DIFF ZONE A Bus Differential Zone for Single Busbar with Sectionalizing Isolator When both the buses are coupled through isolators I.e. when both the Bus isolators of any feeder is closed during bus change over, both the Bus bars will act as single bus bar and bus coupler gets bypassed. In the event of fault on any one of the buses during this condition, feeders Connected to both the buses will be tripped. In the case of bus bar Protection, this logic is achieved through a separate bus Interconnection unit or Single zone reconnection unit.

48. BUS DIFF ZONE A Diff Relay A Diff Relay B BUS DIFF ZONE B BUS-A BUS-B Bus Differential Zone for Single Busbar with Sectionalizing Breaker

49. BUS - A BUS - B AUX. BUS Bus Differential Zone for Double Busbar with Transfer Bus

50. Isolator Aux. Contact ‘a’ should close before the primary contact closes and Aux contact’ b’ closes after the primary contact opens. Busbar Zone assignment will be based this isolator status Throw-over relay 100% 0% Main contact Aux. Contact a Aux. Contact b a b O C Requirements on the Isolator Auxiliary Contacts

51. Where there is only one CT in the bus coupler bay, there will be a blind Zone or dead zone between the breaker and the CT, and for a fault in this zone the selectivity of the busbar protection is lost resulting in Mal-operation and unwanted operation of wrong bus bar protection and Non-operation of the required busbar protection. If this is allowed to persist, it will result in tripping of remote end feeders in Zone-II. Further, when both the buses are coupled through bus coupler and if the bus coupler breaker fails to trip for a fault on any of the buses, the Other bus continue to feed the fault till all the feeders connected to that Bus trip at remote end in Zone-II or by LBB of bus coupler breaker. To take care of this type of faults, the bus bar protection is provided with a feature called bus coupler CT disconnection , which shorts the bus Coupler CT after a preset time after the operation any of the bus barProtections irrespective of the status of bus coupler breaker. Blind Zone – CT Disconnection Requirement One CT in one side of BC Two CTs are available in both sides of BC

52. Blind Zone – Feeder bay with EFP Busbar-Side Current Transformer For current transformers installed on the busbar side, end-fault protection with an open circuit breaker extends the protection range to the circuit breaker. Through this, the actual external Fault become one internal Fault, which can be switched off in the shortest time by the busbar protection function. Without end-fault protection, feeder protection does recognize the fault but cannot clear it. Only the active Circuit-breaker failure protection function can clear the fault with the corresponding time delay.

53. Line-Side Current Transformer With line-side current transformers, end-fault protection with an open circuit breaker prevents over function of the busbar protection. Without end-fault protection, a fault between an open circuit breaker and a current transformer results in unwanted tripping of the busbar protection. In the event of this error, only the circuit breaker at the opposite end can disconnect the fault current. This is possible by routing the inter-tripping command. Feeder protection considers this situation to be a fault in the reverse direction and trips with the set delay. If no transmission channels are present at the opposite end of the line, the fault is not cleared until the set grading time of the opposite end. Blind Zone – Feeder bay with EFP

54. Stability In modern networks the critical fault clearing time may be less than 200 ms. Hence, if the fault is not cleared due to failure of the primary protective relays or their associated circuit breaker, a fast - acting back - up protective relay must clear the fault There are two basic forms Remote back - up Local back - up G G Breaker Failure Protection

55. Local back - up protection can be divided into two categories Relay back - up Breaker back - up 87BB Breaker Failure Protection – Local back up

56. Basic Principle of Breaker Failure Protection

57. Breaker Failure Protection

58. ­ 30 ms ­ 60 ms Fault occurs Normal clearing time Current detector drop-out Margin Breaker interrupting time Protection time Start BFP BFP timer t2 BFP Trip Breaker time Back-up breaker Breaker failure total clearing time Time Chart

59. Busbar Protection Architecture Centralized Architecture Distributed Architecture

60. Published by Siemens Power Academy Goa India E-mail: For technical support easupport.in@ @siemens.com Siemens Power Academy TD India Contact page siemens.com The image is a placeholder (non-exclusive for Siemens) and should be changed if desired.