Presentation is loading. Please wait.

Presentation is loading. Please wait.

Fundamentals of Bus Bar Protection GE Multilin. 2 GE Consumer & Industrial Multilin 2-Jun-14 Outline Bus arrangements Bus components Bus protection techniques.

Similar presentations


Presentation on theme: "Fundamentals of Bus Bar Protection GE Multilin. 2 GE Consumer & Industrial Multilin 2-Jun-14 Outline Bus arrangements Bus components Bus protection techniques."— Presentation transcript:

1 Fundamentals of Bus Bar Protection GE Multilin

2 2 GE Consumer & Industrial Multilin 2-Jun-14 Outline Bus arrangements Bus components Bus protection techniques CT Saturation Application Considerations: High impedance bus differential relaying Low impedance bus differential relaying Special topics

3 3 GE Consumer & Industrial Multilin 2-Jun-14 Distribution and lower transmission voltage levels No operating flexibility Fault on the bus trips all circuit breakers Single bus - single breaker

4 4 GE Consumer & Industrial Multilin 2-Jun-14 Distribution and lower transmission voltage levels Limited operating flexibility Multiple bus sections - single breaker with bus tie

5 5 GE Consumer & Industrial Multilin 2-Jun-14 Transmission and distribution voltage levels Breaker maintenance without circuit removal Fault on a bus disconnects only the circuits being connected to that bus Double bus - single breaker with bus tie

6 6 GE Consumer & Industrial Multilin 2-Jun-14 Increased operating flexibility A bus fault requires tripping all breakers Transfer bus for breaker maintenance Main and transfer buses

7 7 GE Consumer & Industrial Multilin 2-Jun-14 Very high operating flexibility Transfer bus for breaker maintenance Double bus – single breaker w/ transfer bus

8 8 GE Consumer & Industrial Multilin 2-Jun-14 High operating flexibility Line protection covers bus section between two CTs Fault on a bus does not disturb the power to circuits Double bus - double breaker

9 9 GE Consumer & Industrial Multilin 2-Jun-14 Used on higher voltage levels More operating flexibility Requires more breakers Middle bus sections covered by line or other equipment protection Breaker-and-a-half bus

10 10 GE Consumer & Industrial Multilin 2-Jun-14 Higher voltage levels High operating flexibility with minimum breakers Separate bus protection not required at line positions Ring bus

11 11 GE Consumer & Industrial Multilin 2-Jun-14 Bus components breakers SF6, EHV & HV - Synchropuff Low Voltage circuit breakers

12 12 GE Consumer & Industrial Multilin 2-Jun-14 Disconnect switches & auxiliary contacts

13 13 GE Consumer & Industrial Multilin 2-Jun-14 Current Transformers Oil insulated current transformer (35kV up to 800kV) Gas (SF6) insulated current transformer Bushing type (medium voltage switchgear)

14 14 GE Consumer & Industrial Multilin 2-Jun-14 Protection Requirements High bus fault currents due to large number of circuits connected: CT saturation often becomes a problem as CTs may not be sufficiently rated for worst fault condition case large dynamic forces associated with bus faults require fast clearing times in order to reduce equipment damage False trip by bus protection may create serious problems: service interruption to a large number of circuits (distribution and sub- transmission voltage levels) system-wide stability problems (transmission voltage levels) With both dependability and security important, preference is always given to security

15 15 GE Consumer & Industrial Multilin 2-Jun-14 Bus Protection Techniques Interlocking schemes Overcurrent (unrestrained or unbiased) differential Overcurrent percent (restrained or biased) differential Linear couplers High-impedance bus differential schemes Low-impedance bus differential schemes

16 16 GE Consumer & Industrial Multilin 2-Jun-14 Interlocking Schemes Blocking scheme typically used Short coordination time required Care must be taken with possible saturation of feeder CTs Blocking signal could be sent over communications ports (peer-to-peer) This technique is limited to simple one-incomer distribution buses

17 17 GE Consumer & Industrial Multilin 2-Jun-14 Overcurrent (unrestrained) Differential Differential signal formed by summation of all currents feeding the bus CT ratio matching may be required On external faults, saturated CTs yield spurious differential current Time delay used to cope with CT saturation Instantaneous differential OC function useful on integrated microprocessor-based relays

18 18 GE Consumer & Industrial Multilin 2-Jun Linear Couplers Z C = 2 – 20 - typical coil impedance (5V per 1000Amps => 60Hz ) If = 8000 A 40 V10 V 0 V20 V 2000 A 4000 A0 A 0 V External Fault

19 19 GE Consumer & Industrial Multilin 2-Jun Linear Couplers E sec = I prim *X m - secondary voltage on relay terminals I R = I prim *X m /(Z R + Z C ) – minimum operating current where, I prim – primary current in each circuit X m – liner coupler mutual reactance (5V per 1000Amps => 60Hz ) Z R – relay tap impedance Z C – sum of all linear coupler self impedances If = 8000 A 0 A 0 V10 V 0 V20 V 40 V 2000 A 4000 A0 A Internal Bus Fault

20 20 GE Consumer & Industrial Multilin 2-Jun-14 Fast, secure and proven Require dedicated air gap CTs, which may not be used for any other protection Cannot be easily applied to reconfigurable buses The scheme uses a simple voltage detector – it does not provide benefits of a microprocessor-based relay (e.g. oscillography, breaker failure protection, other functions) Linear Couplers

21 21 GE Consumer & Industrial Multilin 2-Jun-14 High Impedance Differential Operating signal created by connecting all CT secondaries in parallel o CTs must all have the same ratio o Must have dedicated CTs Overvoltage element operates on voltage developed across resistor connected in secondary circuit o Requires varistors or AC shorting relays to limit energy during faults Accuracy dependent on secondary circuit resistance o Usually requires larger CT cables to reduce errors higher cost Cannot easily be applied to reconfigurable buses and offers no advanced functionality

22 22 GE Consumer & Industrial Multilin 2-Jun-14 Percent Differential Percent characteristic used to cope with CT saturation and other errors Restraining signal can be formed in a number of ways No dedicated CTs needed Used for protection of re- configurable buses possible

23 23 GE Consumer & Industrial Multilin 2-Jun-14 Low Impedance Percent Differential Individual currents sampled by protection and summated digitally o CT ratio matching done internally (no auxiliary CTs) o Dedicated CTs not necessary Additional algorithms improve security of percent differential characteristic during CT saturation Dynamic bus replica allows application to reconfigurable buses o Done digitally with logic to add/remove current inputs from differential computation o Switching of CT secondary circuits not required Low secondary burdens Additional functionality available o Digital oscillography and monitoring of each circuit connected to bus zone o Time-stamped event recording o Breaker failure protection

24 24 GE Consumer & Industrial Multilin 2-Jun-14 Digital Differential Algorithm Goals Improve the main differential algorithm operation o Better filtering o Faster response o Better restraint techniques o Switching transient blocking Provide dynamic bus replica for reconfigurable bus bars Dependably detect CT saturation in a fast and reliable manner, especially for external faults Implement additional security to the main differential algorithm to prevent incorrect operation o External faults with CT saturation o CT secondary circuit trouble (e.g. short circuits)

25 25 GE Consumer & Industrial Multilin 2-Jun-14 Low Impedance Differential (Distributed) Data Acquisition Units (DAUs) installed in bays Central Processing Unit (CPU) processes all data from DAUs Communications between DAUs and CPU over fiber using proprietary protocol Sampling synchronisation between DAUs is required Perceived less reliable (more hardware needed) Difficult to apply in retrofit applications

26 26 GE Consumer & Industrial Multilin 2-Jun-14 Low Impedance Differential (Centralized) All currents applied to a single central processor No communications, external sampling synchronisation necessary Perceived more reliable (less hardware needed) Well suited to both new and retrofit applications.

27 27 GE Consumer & Industrial Multilin 2-Jun-14 CT Saturation

28 28 GE Consumer & Industrial Multilin 2-Jun-14 CT Saturation Concepts CT saturation depends on a number of factors o Physical CT characteristics (size, rating, winding resistance, saturation voltage) o Connected CT secondary burden (wires + relays) o Primary current magnitude, DC offset (system X/R) o Residual flux in CT core Actual CT secondary currents may not behave in the same manner as the ratio (scaled primary) current during faults End result is spurious differential current appearing in the summation of the secondary currents which may cause differential elements to operate if additional security is not applied

29 29 GE Consumer & Industrial Multilin 2-Jun-14 CT Saturation No DC Offset Waveform remains fairly symmetrical With DC Offset Waveform starts off being asymmetrical, then symmetrical in steady state

30 30 GE Consumer & Industrial Multilin 2-Jun-14 External Fault & Ideal CTs Fault starts at t 0 Steady-state fault conditions occur at t 1 t0t0 t1t1 Ideal CTs have no saturation or mismatch errors thus produce no differential current

31 31 GE Consumer & Industrial Multilin 2-Jun-14 External Fault & Actual CTs Fault starts at t 0 Steady-state fault conditions occur at t 1 t0t0 t1t1 Actual CTs do introduce errors, producing some differential current (without CT saturation)

32 32 GE Consumer & Industrial Multilin 2-Jun-14 External Fault with CT Saturation Fault starts at t 0, CT begins to saturate at t 1 CT fully saturated at t 2 t0t0 t1t1 t2t2 CT saturation causes increasing differential current that may enter the differential element operate region.

33 33 GE Consumer & Industrial Multilin 2-Jun-14 Some Methods of Securing Bus Differential Block the bus differential for a period of time (intentional delay) o Increases security as bus zone will not trip when CT saturation is present o Prevents high-speed clearance for internal faults with CT saturation or evolving faults Change settings of the percent differential characteristic (usually Slope 2) o Improves security of differential element by increasing the amount of spurious differential current needed to incorrectly trip o Difficult to explicitly develop settings (Is 60% slope enough? Should it be 75%?) Apply directional (phase comparison) supervision o Improves security by requiring all currents flow into the bus zone before asserting the differential element o Easy to implement and test o Stable even under severe CT saturation during external faults

34 34 GE Consumer & Industrial Multilin 2-Jun-14 High-Impedance Bus Differential Considerations

35 35 GE Consumer & Industrial Multilin 2-Jun-14 High Impedance Voltage-operated Relay External Fault 59 element set above max possible voltage developed across relay during external fault causing worst case CT saturation For internal faults, extremely high voltages (well above 59 element pickup) will develop across relay

36 36 GE Consumer & Industrial Multilin 2-Jun-14 High Impedance Voltage Operated Relay Ratio matching with Multi-ratio CTs Application of high impedance differential relays with CTs of different ratios but ratio matching taps is possible, but could lead to voltage magnification. Voltage developed across full winding of tapped CT does not exceed CT rating, terminal blocks, etc.

37 37 GE Consumer & Industrial Multilin 2-Jun-14 High Impedance Voltage Operated Relay Ratio matching with Multi-ratio CTs Use of auxiliary CTs to obtain correct ratio matching is also possible, but these CTs must be able to deliver enough voltage necessary to produce relay operation for internal faults.

38 38 GE Consumer & Industrial Multilin 2-Jun-14 Electromechanical High Impedance Bus Differential Relays Single phase relays High-speed High impedance voltage sensing High seismic IOC unit

39 39 GE Consumer & Industrial Multilin 2-Jun-14 Operating time: 20 – I > 1.5xPKP P -based High-Impedance Bus Differential Protection Relays

40 40 GE Consumer & Industrial Multilin 2-Jun-14 R ST = stabilizing resistor to limit the current through the relay, and force it to the lower impedance CT windings. MOV – Metal Oxide Varistor to limit the voltage to 1900 Volts 86 – latching contact preventing the resistors from overheating after the fault is detected High Impedance Module for Digital Relays

41 41 GE Consumer & Industrial Multilin 2-Jun-14 High-Impedance Module + Overcurrent Relay

42 42 GE Consumer & Industrial Multilin 2-Jun-14 Fast, secure and proven Requires dedicated CTs, preferably with the same CT ratio and using full tap Can be applied to small buses Depending on bus internal and external fault currents, high impedance bus diff may not provide adequate settings for both sensitivity and security Cannot be easily applied to reconfigurable buses Require voltage limiting varistor capable of absorbing significant energy May require auxiliary CTs Do not provide full benefits of microprocessor-based relay system (e.g. metering, monitoring, oscillography, etc.) High Impedance Bus Protection - Summary

43 43 GE Consumer & Industrial Multilin 2-Jun-14 Low-Impedance Bus Differential Considerations

44 44 GE Consumer & Industrial Multilin 2-Jun-14 P-based Low-Impedance Relays No need for dedicated CTs Internal CT ratio mismatch compensation Advanced algorithms supplement percent differential protection function making the relay very secure Dynamic bus replica (bus image) principle is used in protection of reconfigurable bus bars, eliminating the need for switching physically secondary current circuits Integrated Breaker Failure (BF) function can provide optimal tripping strategy depending on the actual configuration of a bus bar

45 45 GE Consumer & Industrial Multilin 2-Jun-14 Up to 24 Current Inputs 4 Zones Zone 1 = Phase A Zone 2 = Phase B Zone 3 = Phase C Zone 4 = Not used Different CT Ratio Capability for Each Circuit Largest CT Primary is Base in Relay 2-8 Circuit Applications Small Bus Applications

46 46 GE Consumer & Industrial Multilin 2-Jun-14 Relay Current Inputs 4 Zones Zone 1 = Phase A (12 currents) Zone 2 = Phase B (12 currents) Zone 3 = Not used Zone 4 = Not used CB 12CB 11 Different CT Ratio Capability for Each Circuit Largest CT Primary is Base in Relay Relay Current Inputs 4 Zones Zone 1 = Not used Zone 2 = Not used Zone 3 = Phase C (12 currents) Zone 4 = Not used 9-12 Circuit Applications Medium to Large Bus Applications

47 47 GE Consumer & Industrial Multilin 2-Jun-14 Large Bus Applications 87B phase A 87B phase B 87B phase C Logic relay (switch status, optional BF)

48 48 GE Consumer & Industrial Multilin 2-Jun-14 Large Bus Applications For buses with up to 24 circuits

49 49 GE Consumer & Industrial Multilin 2-Jun-14 Summing External Currents Not Recommended for Low-Z 87B relays Relay becomes combination of restrained and unrestrained elements In order to parallel CTs: CT performance must be closely matched o Any errors will appear as differential currents Associated feeders must be radial o No backfeeds possible Pickup setting must be raised to accommodate any errors

50 50 GE Consumer & Industrial Multilin 2-Jun-14 Definitions of Restraint Signals maximum of geometrical average scaled sum of sum of

51 51 GE Consumer & Industrial Multilin 2-Jun-14 Sum Of vs. Max Of Restraint Methods Sum Of Approach More restraint on external faults; less sensitive for internal faults Scaled-Sum Of approach takes into account number of connected circuits and may increase sensitivity Breakpoint settings for the percent differential characteristic more difficult to set Max Of Approach Less restraint on external faults; more sensitive for internal faults Breakpoint settings for the percent differential characteristic easier to set Better handles situation where one CT may saturate completely (99% slope settings possible)

52 52 GE Consumer & Industrial Multilin 2-Jun-14 Bus Differential Adaptive Approach

53 53 GE Consumer & Industrial Multilin 2-Jun-14 Bus Differential Adaptive Logic Diagram DIF L DIR SAT DIF H OR AND OR 87B BIASED OP AND

54 54 GE Consumer & Industrial Multilin 2-Jun-14 Phase Comparison Principle Internal Faults: All fault (large) currents are approximately in phase. External Faults: One fault (large) current will be out of phase No Voltages are required or needed Secondary Current of Faulted Circuit (Severe CT Saturation)

55 55 GE Consumer & Industrial Multilin 2-Jun-14 Phase Comparison Principle Continued…

56 56 GE Consumer & Industrial Multilin 2-Jun-14 CT Saturation Fault starts at t 0, CT begins to saturate at t 1 CT fully saturated at t 2 t0t0 t1t1 t2t2

57 57 GE Consumer & Industrial Multilin 2-Jun-14 CT Saturation Detector State Machine NORMAL SAT := 0 EXTERNAL FAULT SAT := 1 EXTERNAL FAULT & CT SATURATION SAT := 1 The differential characteristic entered The differential- restraining trajectory out of the differential characteristic for certain period of time saturation condition The differential current below the first slope for certain period of time

58 58 GE Consumer & Industrial Multilin 2-Jun-14 CT Saturation Detector Operating Principles The 87B SAT flag WILL NOT be set during internal faults, regardless of whether or not any of the CTs saturate. The 87B SAT flag WILL be set during external faults, regardless of whether or not any of the CTs saturate. By design, the 87B SAT flag WILL force the relay to use the additional 87B DIR phase comparison for Region 2 The Saturation Detector WILL NOT Block the Operation of the Differential Element – it will only Force 2-out-of-2 Operation

59 59 GE Consumer & Industrial Multilin 2-Jun-14 CT Saturation Detector - Examples The oscillography records on the next two slides were captured from a B30 relay under test on a real-time digital power system simulator First slide shows an external fault with deep CT saturation (~1.5 msec of good CT performance) o SAT saturation detector flag asserts prior to BIASED PKP bus differential pickup o DIR directional flag does not assert (one current flows out of zone), so even though bus differential picks up, no trip results Second slide shows an internal fault with mild CT saturation o BIASED PKP and BIASED OP both assert before DIR asserts o CT saturation does not block bus differential More examples available (COMTRADE files) upon request

60 60 GE Consumer & Industrial Multilin 2-Jun-14 Despite heavy CT saturation the external fault current is seen in the opposite direction CT Saturation Example – External Fault time, sec current, A ~1 ms

61 61 GE Consumer & Industrial Multilin 2-Jun-14 CT Saturation – Internal Fault Example

62 62 GE Consumer & Industrial Multilin 2-Jun-14 Applying Low-Impedance Differential Relays for Busbar Protection Basic Topics Configure physical CT Inputs Configure Bus Zone and Dynamic Bus Replica Calculating Bus Differential Element settings Advanced Topics Isolator switch monitoring for reconfigurable buses Differential Zone CT Trouble Integrated Breaker Failure protection

63 63 GE Consumer & Industrial Multilin 2-Jun-14 Configuring CT Inputs For each connected CT circuit enter Primary rating and select Secondary rating. Each 3-phase bank of CT inputs must be assigned to a Signal Source that is used to define the Bus Zone and Dynamic Bus Replica Some relays define 1 p.u. as the maximum primary current of all of the CTs connected in the given Bus Zone

64 64 GE Consumer & Industrial Multilin 2-Jun-14 Per-Unit Current Definition - Example Current Channel PrimarySecondaryZone CT-1 F13200 A1 A1 CT-2 F22400 A5 A1 CT-3 F31200 A1 A1 CT-4 F43200 A1 A2 CT-5 F51200 A5 A2 CT-6 F65000 A5 A2 For Zone 1, 1 p.u. = 3200 AP For Zone 2, 1 p.u. = 5000 AP

65 65 GE Consumer & Industrial Multilin 2-Jun-14 Configuration of Bus Zone Dynamic Bus Replica associates a status signal with each current in the Bus Differential Zone Status signal can be any logic operand o Status signals can be developed in programmable logic to provide additional checks or security as required o Status signal can be set to ON if current is always in the bus zone or OFF if current is never in the bus zone CT connections/polarities for a particular bus zone must be properly configured in the relay, via either hardwire or software

66 66 GE Consumer & Industrial Multilin 2-Jun-14 Configuring the Bus Differential Zone 1. Configure the physical CT Inputs o CT Primary and Secondary values o Both 5 A and 1 A inputs are supported by the UR hardware o Ratio compensation done automatically for CT ratio differences up to 32:1 2. Configure AC Signal Sources 3. Configure Bus Zone with Dynamic Bus Replica Bus Zone settings defines the boundaries of the Differential Protection and CT Trouble Monitoring.

67 67 GE Consumer & Industrial Multilin 2-Jun-14 Dual Percent Differential Characteristic High Breakpoint Low Breakpoint Low Slope High Slope High Set (Unrestrained) Min Pickup

68 68 GE Consumer & Industrial Multilin 2-Jun-14 Calculating Bus Differential Settings The following Bus Zone Differential element parameters need to be set: o Differential Pickup o Restraint Low Slope o Restraint Low Break Point o Restraint High Breakpoint o Restraint High Slope o Differential High Set (if needed) All settings entered in per unit (maximum CT primary in the zone) Slope settings entered in percent Low Slope, High Slope and High Breakpoint settings are used by the CT Saturation Detector and define the Region 1 Area (2-out-of-2 operation with Directional)

69 69 GE Consumer & Industrial Multilin 2-Jun-14 Calculating Bus Differential Settings – Minimum Pickup Defines the minimum differential current required for operation of the Bus Zone Differential element Must be set above maximum leakage current not zoned off in the bus differential zone May also be set above maximum load conditions for added security in case of CT trouble, but better alternatives exist

70 70 GE Consumer & Industrial Multilin 2-Jun-14 Calculating Bus Differential Settings – Low Slope Defines the percent bias for the restraint currents from I REST =0 to I REST =Low Breakpoint Setting determines the sensitivity of the differential element for low-current internal faults Must be set above maximum error introduced by the CTs in their normal linear operating mode Range: 15% to 100% in 1%. increments

71 71 GE Consumer & Industrial Multilin 2-Jun-14 Calculating Bus Differential Settings – Low Breakpoint Defines the upper limit to restraint currents that will be biased according to the Low Slope setting Should be set to be above the maximum load but not more than the maximum current where the CTs still operate linearly (including residual flux) Assumption is that the CTs will be operating linearly (no significant saturation effects up to 80% residual flux) up to the Low Breakpoint setting

72 72 GE Consumer & Industrial Multilin 2-Jun-14 Calculating Bus Differential Settings – High Breakpoint Defines the minimum restraint currents that will be biased according to the High Slope setting Should be set to be below the minimum current where the weakest CT will saturate with no residual flux Assumption is that the CTs will be operating linearly (no significant saturation effects up to 80% residual flux) up to the Low Breakpoint setting

73 73 GE Consumer & Industrial Multilin 2-Jun-14 Calculating Bus Differential Settings – High Slope Defines the percent bias for the restraint currents I REST High Breakpoint Setting determines the stability of the differential element for high current external faults Traditionally, should be set high enough to accommodate the spurious differential current resulting from saturation of the CTs during heavy external faults Setting can be relaxed in favour of sensitivity and speed as the relay detects CT saturation and applies the directional principle to prevent maloperation Range: 50% to 100% in 1%. increments

74 74 GE Consumer & Industrial Multilin 2-Jun-14 Calculating Unrestrained Bus Differential Settings Defines the minimum differential current for unrestrained operation Should be set to be above the maximum differential current under worst case CT saturation Range: 2.00 to p.u. in 0.01 p.u. increments Can be effectively disabled by setting to p.u.

75 75 GE Consumer & Industrial Multilin 2-Jun-14 Dual Percent Differential Characteristic High Breakpoint Low Breakpoint Low Slope High Slope High Set (Unrestrained) Min Pickup

76 76 GE Consumer & Industrial Multilin 2-Jun-14 Protecting re-configurable buses Reconfigurable Buses

77 77 GE Consumer & Industrial Multilin 2-Jun-14 Protecting re-configurable buses Reconfigurable Buses

78 78 GE Consumer & Industrial Multilin 2-Jun-14 Protecting re-configurable buses Reconfigurable Buses

79 79 GE Consumer & Industrial Multilin 2-Jun-14 Protecting re-configurable buses Reconfigurable Buses

80 80 GE Consumer & Industrial Multilin 2-Jun-14 Isolators Reliable Isolator Closed signals are needed for the Dynamic Bus Replica In simple applications, a single normally closed contact may be sufficient For maximum safety: o Both N.O. and N.C. contacts should be used o Isolator Alarm should be established and non-valid combinations (open-open, closed-closed) should be sorted out o Switching operations should be inhibited until bus image is recognized with 100% accuracy o Optionally block 87B operation from Isolator Alarm Each isolator position signal decides: o Whether or not the associated current is to be included in the differential calculations o Whether or not the associated breaker is to be tripped

81 81 GE Consumer & Industrial Multilin 2-Jun-14 Isolator – Typical Open/Closed Connections

82 82 GE Consumer & Industrial Multilin 2-Jun-14 Isolator Open Auxiliary Contact Isolator Closed Auxiliary Contact Isolator PositionAlarmBlock Switching OffOnCLOSEDNo Off LAST VALIDAfter time delay until acknowledged Until Isolator Position is valid On CLOSED OnOffOPENNo NOTE: Isolator monitoring function may be a built-in feature or user- programmable in low impedance bus differential digital relays Switch Status Logic and Dyanamic Bus Replica

83 83 GE Consumer & Industrial Multilin 2-Jun-14 Differential Zone CT Trouble Each Bus Differential Zone may a dedicated CT Trouble Monitor Definite time delay overcurrent element operating on the zone differential current, based on the configured Dynamic Bus Replica Three strategies to deal with CT problems: 1. Trip the bus zone as the problem with a CT will likely evolve into a bus fault anyway 2. Do not trip the bus, raise an alarm and try to correct the problem manually 3. Switch to setting group with 87B minimum pickup setting above the maximum load current.

84 84 GE Consumer & Industrial Multilin 2-Jun-14 Strategies 2 and 3 can be accomplished by: Using undervoltage supervision to ride through the period from the beginning of the problem with a CT until declaring a CT trouble condition Using an external check zone to supervise the 87B function Using CT Trouble to prevent the Bus Differential tripping (2) Using setting groups to increase the pickup value for the 87B function (3) Differential Zone CT Trouble

85 85 GE Consumer & Industrial Multilin 2-Jun-14 Differential Zone CT Trouble – Strategy #2 Example CT Trouble operand is used to rise an alarm The 87B trip is inhibited after CT Trouble element operates The relay may misoperate if an external fault occurs after CT trouble but before the CT trouble condition is declared (double-contingency) 87B operates Undervoltage condition CT OK

86 86 GE Consumer & Industrial Multilin 2-Jun-14 Example Architecture for Large Busbars Dual (redundant) fiber with 3msec delivery time between neighbouring IEDs. Up to 8 relays in the ring Phase A AC signals and trip contacts Phase B AC signals and trip contacts Phase C AC signals and trip contacts Digital Inputs for isolator monitoring and BF

87 87 GE Consumer & Industrial Multilin 2-Jun-14 Phase A AC signals wired here, bus replica configured here Phase B AC signals wired here, bus replica configured here Phase C AC signals wired here, bus replica configured here Auxuliary switches wired here; Isolator Monitoring function configured here Isolator Position Example Architecture – Dynamic Bus Replica and Isolator Position

88 88 GE Consumer & Industrial Multilin 2-Jun-14 Phase A AC signals wired here, current status monitored here Phase B AC signals wired here, current status monitored here Phase C AC signals wired here, current status monitored here Breaker Failure elements configured here BF Initiate & Current Supv. Example Architecture – BF Initiation & Current Supervision

89 89 GE Consumer & Industrial Multilin 2-Jun-14 Phase A AC signals wired here, current status monitored here Phase B AC signals wired here, current status monitored here Phase C AC signals wired here, current status monitored here Breaker Fail Op command generated here and send to trip appropriate breakers Breaker Fail Op Trip Example Architecture – Breaker Failure Tripping Trip

90 90 GE Consumer & Industrial Multilin 2-Jun-14 IEEE Guide for Protective Relay Applications to Power System Buses is currently being revised by the K14 Working Group of the IEEE Power System Relaying Committee.

91 91 GE Consumer & Industrial Multilin 2-Jun-14

92


Download ppt "Fundamentals of Bus Bar Protection GE Multilin. 2 GE Consumer & Industrial Multilin 2-Jun-14 Outline Bus arrangements Bus components Bus protection techniques."

Similar presentations


Ads by Google