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Bus Differential Protection Applications Using the GE B30 and B90
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Presentation Outline Introduction to Bus Protection CT Saturation
GE Multilin Bus Protection Offering B30 & B90 Application Considerations Advanced Application Topics B90 Application Examples B30 & B90 User Software Conclusions
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Introduction to Bus Protection
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Challenges to Bus Zone Protection
High Fault Current Levels Large dynamic forces can place mechanical stress on busbars and result in physical damage to equipment therefore fast clearing times are required. High fault currents can lead to CT saturation, particularly for external faults, which may lead to mal-operation of the bus protection. Mal-Operation of Bus Protections Have Significant Impact Loss of customer loads may damage both customer assets as well as customer perception of the utility. System voltage levels and corresponding system stability may be adversely affected. Best Case: Remedial Action Schemes (load shedding) Worst Case: Partial or Total System Collapse (wide-spread blackout) Bus Protection Must be Dependable and Secure, With Emphasis on Security…
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Challenges to Bus Zone Protection Continued…
Many Different Bus Topologies Many switchyard configurations possible. Many different CT placements possible. Single Bus, Double Bus (Single and Double Breaker), Main and Transfer Bus, Breaker-and-a-Half and hybrids Buses may Reconfigure at Any Time Different apparatus may be connected/disconnected from a given bus. Switching may happen from any number of sources Manually from human operator action (e.g. equipment maintenance) Automatically from other protections, Wide-Area Special Protections, Remedial Action Schemes, Auto-Restoration/Auto-Transfer Schemes… Bus Protection Must Adapt Automatically (No User Intervention) and in Real-Time, Based on Bus Configuration…
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Re-Configurable Bus Zones
Different Currents May Need to be Added/Removed from Each Bus Zone Dynamically, Depending on Switch Status.
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Bus Zone Protection Techniques
All Bus Zone protections essentially operate based on Kirchoff’s Law for Currents: ‘The sum of all currents entering a node must equal zero.’ The only variation is on how this is implemented. Unrestrained Differential Interlocking/Blocking Schemes High Impedance Differential Low Impedance Percent Differential
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Unrestrained Differential (Overcurrent)
Differential current created by physically summing CTs CT ratio matching required (auxiliary CTs) External faults may cause CT saturation, leading to spurious differential currents in the bus protection Intentional time delay added to cope with CT saturation effects Unrestrained differential function useful for microprocessor-based protections (check zone) Intentional Time Delay means No Fast Zone Clearance
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Interlocking/Blocking Schemes
Blocking signals generated by downstream protections (usually instantaneous overcurrent) Simple inst. overcurrent protection with short intentional time delay Need to wait for blocking signals Usually inverse timed backup provided Timed backup may be “tricked” by slow clearance of downstream faults. Blocking can be done via communications (e.g GSSE/GOOSE, dedicated communications) Technique Limited to Radial Circuits with Negligible Backfeed
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High Impedance Differential (Overvoltage)
Operating signal created by connecting all CT secondaries in parallel CTs must all have the same ratio Must have dedicated CTs Overvoltage element operates on voltage developed across resistor connected in secondary circuit Requires varistors or AC shorting relays to limit energy during faults Accuracy dependent on secondary circuit resistance Usually requires larger CT cables to reduce errors » higher cost Cannot Easily be Applied to Reconfigurable Buses and Offers no Advanced Functionality (Oscillography, Breaker Fail).
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Low Impedance Percent Differential
Individual currents sampled by protection and summated digitally CT ratio matching done internally (no auxiliary CTs) Dedicated CTs not necessary Additional algorithms improve security of percent differential characteristic during CT saturation Dynamic bus replica allows application to reconfigurable buses Done digitally with logic to add/remove current inputs from differential computation Switching of CT secondary circuits not required Low secondary burdens Additional functionality available without additional devices Digital oscillography Time-stamped event recording Breaker Failure Can be Applied to Reconfigurable Buses and Secure from CT Saturation, with Additional Useful Functionality.
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Microprocessor-Based 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
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Microprocessor-Based 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.
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Digital Differential Algorithm Goals
Improve the main differential algorithm operation Better filtering Faster response Better restraint techniques Switching transient blocking Provide dynamic bus replica for reconfigurable busbars Dependably detect CT saturation in a fast and reliable manner, especially for external faults Apply additional security to the main differential algorithm to prevent incorrect operation External faults with CT saturation CT secondary circuit trouble (e.g. short circuits)
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CT Saturation
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CT Saturation Concepts
CT saturation depends on a number of factors Physical CT characteristics (size, rating, winding resistance, saturation voltage) Connected CT secondary burden (wires + relays) Primary current magnitude, DC offset (system X/R) 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
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CT Saturation No DC Offset With DC Offset
Waveform remains fairly symmetrical With DC Offset Waveform starts off being asymmetrical, then symmetrical in steady state
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CT Saturation – External Fault with Ideal CTs
Fault starts at t0 Steady-state fault conditions occur at t1 Ideal CTs have no saturation or mismatch thus produce no differential current
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CT Saturation – External Fault with Actual CTs
Fault starts at t0 Steady-state fault conditions occur at t1 Actual CTs do introduce errors thus produce some differential current (without CT saturation)
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CT Saturation – External Fault with CT Saturation
Fault starts at t0, CT begins to saturate at t1 CT fully saturated at t2 CT saturation causes increasing differential current that may enter the differential element operate region.
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Some Methods of Securing Bus Differential
Block the bus differential for a period of time (intentional delay) Increases security as bus zone will not trip when CT saturation is present Prevents high-speed clearance for internal faults with CT saturation or evolving faults Change settings of the percent differential characteristic (usually Slope 2) Improves security of differential element by increasing the amount of spurious differential current needed to incorrectly trip Difficult to explicitly develop settings (Is 60% slope enough? Should it be 75%?) Apply directional (phase comparison) supervision Improves security by requiring all currents flow into the bus zone before asserting the differential element Easy to implement and test Stable even under severe CT saturation during external faults
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GE Multilin Bus Protection Offering
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GE Multilin Bus Differential Relays
High Impedance Differential PVD (Electromechanical) MIB II (single function digital relay) HID (high impedance module for UR-series) Solid-State Bus Differential BUS1000/2000 Low Impedance Digital Differential B30 B90 Both the B30 and B90 have a great deal in common, but do have some significant differences as well
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B30 & B90 – What is the Same Proven Hardware. Proven Algorithms.
Both are members of the Universal Relay (UR) family Common hardware & software Common added features Common communications interfaces & protocols User Programmable Logic (FlexLogic™) High Performance Typical Response Time: 12 msec + output contact Max. Response Time: 16 msec + output contact Secure for external faults with severe CT saturation Both use the same proven algorithms for ratio compensation, dynamic bus replication, differential calculations, CT saturation detection and differential element security UR Common Features Modular hardware design allows for greater flexibility in I/O configuration Time Synchronisation via IRIG-B or SNTP Multiple communications ports and protocols to interface with SCADA Modbus, DNP3, IEC 61850, IEC RS-232, RS-485, Ethernet (10/100 Base-T, 10 Base-FL, 100 Base-FX) Inter-relay communications using Direct I/O over various media Advance Sequential Event Recording 1024 Event record (per chassis with the B90) Any binary state can be configured for event recording (self-test errors automatically recorded) Contact Inputs/Outputs Protection Elements Logic Elements Communications Signals 1 microsecond timestamps on events Advanced Oscillography/Disturbance Recording (per chassis with B90) Configurable sampling rates: 8, 16, 32, 64 samples/cycle All AC quantities automatically recorded Programmable analog content: phasor magnitudes, angles, differential quantities, frequency (up to 16) Programmable digital content: any digital state (up to 64) Programmable trigger & pre/post fault Settable Number of records, treatment of old records (preserve/overwrite). User-programmable Fault Reports User-programmable LEDs and optional Pushbuttons for Front Panel Interface Universal voltage inputs (24 VDC – 250 VDC) Universal current inputs (1 A and 5 A secondaries in the same hardware) Universal power supplies (HI: VDC/ Vac, LO: VDC) Proven Hardware. Proven Algorithms.
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B30 & B90 – What is Different B30 provides three-phase bus differential protection in a single hardware chassis All three phase currents from all feeders are connected to a single chassis with multiple DSPs (1 zone), with phase segregation done in software only. Limited to 6 three-phase current sources (or five current sources and one three-phase voltage source) Up to six breaker failure elements included B90 provides hardware-segregated bus differential protection in one or more hardware chassis DSP modules configured for up to 8 currents (7 currents & 1 voltage) for a single phase Phase segregation by hardware and software configuration Minimum configuration: 8 feeders in a single chassis with three DSP modules (4 zones) Maximum configuration: 24 feeders in three chassis, each with 3 DSPs (4 zones) Additional I/O, additional Logic, optional breaker failure available B30 – Cost effective protection & metering. B90 – Comprehensive and scalable protection.
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Configuring the Bus Differential Zone
Bus Zone settings defines the boundaries of the Differential Protection and CT Trouble Monitoring. Configure the physical CT Inputs CT Primary and Secondary values Both 5 A and 1 A inputs are supported by the UR hardware Ratio compensation done automatically for CT ratio differences up to 32:1 Configure AC Signal Sources (B30 only) Configure Bus Zone with Dynamic Bus Replica
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The Dynamic Bus (Example 1)
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The Dynamic Bus Replica – B30 Configuration (Example 1)
Bus Zone Source A CT-1 Bus Zone Status A On (Always Included in Bus Zone) Bus Zone Source B CT-2 Bus Zone Status B S-1 (Only Included in Bus Zone if S-1 Closed) Bus Zone Source C CT-3 Bus Zone Status C S-3 Bus Zone Source D CT-4 Bus Zone Status D S-5 Bus Zone Source E CT-5 Bus Zone Status E On Bus Zone Source F CT-8 Bus Zone Status F
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Summing External Currents Not Recommended
Relay becomes combination of restrained and unrestrained elements In order to parallel CTs: CT performance must be closely matched Any errors will appear as differential currents Associated feeders must be radial No backfeeds possible Pickup setting must be raised to accommodate any errors
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Bus Differential Block Diagram
The currents are digitally pre-filtered (Block 1) in order to remove the decaying DC components and other signal distortions. The filtered input signals are brought to a common scale taking into account the transformation ratios of the connected CTs (Block 2). Phasors of the differential zone currents are estimated digitally (Block 3) and the differential (Block 4) and restraining (Block 5) signals are calculated. The magnitude of the differential signal is compared with a threshold and an appropriate flag indicating operation of the unbiased bus differential protection is produced (Block 6). The magnitudes of the differential and restraining currents are compared and two auxiliary flags that correspond to two specifically shaped portions of the differential operating characteristic (DIF1 and DIF2) are produced (blocks 7 and 8). The characteristic is split in order to enhance performance of the relay by applying diverse security measures for each of the regions. The directional element (Block 10) supervises the biased differential characteristic when necessary. The current directional comparison principle is used that processes phasors of all the input currents as well as the differential and restraining currents. The saturation detector (Block 9) analyzes the differential and restraining currents as well as the samples of the input currents. This block sets its output flag upon detecting CT saturation. The output logic (Block 11) combines the differential, directional and saturation flags into the biased differential operation flag. The applied logic enhances performance of the relay while keeping an excellent balance between dependability/speed and security.
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Definitions of Restraint Signals
“sum of” “scaled sum of” “geometrical average” “maximum of”
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“Sum Of” Versus “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) B30, B90 (and UR in General) Use the “Max Of” Definition for Restraint Quantities.
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Bus Differential Adaptive Approach
Region 1 Low current magnitudes CT saturation possible due to DC offset CT saturation difficult to detect More security required Use 2-out-of-2 Operating Mode Region 2 High current magnitudes Quick CT saturation possible CT saturation easy to detect Security required only if CT saturation detected Dynamically decide if 1-out-of-2 or 2-out-of-2 Operating Mode
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Bus Differential Adaptive Logic Diagram
DIFL DIR SAT DIFH OR AND 87B BIASED OP
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Phase Comparison Principle
Internal Faults: All fault (“large”) currents are approximately in phase. External Faults: One fault (“large”) current will be out of phase Secondary Current of Faulted Circuit (Severe CT Saturation) No Voltages are required or needed
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Phase Comparison Principle Continued…
Implementation Select n fault “Contributors” A contributor is a feeder carrying a significant amount of current (above load) A feeder is a contributor if it’s current magnitude is: Above the high breakpoint setting of the bus differential element Above a certain portion of the restraint current Determine the angle between each Contributor and the sum of the remaining n-1 Contributors. Determine the maximum of the angles and compare with the directional threshold Threshold is set at 90o For external faults, the maximum of the angles should be greater than 90o An angle of more than 90o for an internal fault due to CT saturation is not physically possible.
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CT Saturation Redux Fault starts at t0, CT begins to saturate at t1
CT fully saturated at t2
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CT Saturation Detector State Machine
NORMAL SAT := 0 EXTERNAL FAULT SAT := 1 FAULT & CT SATURATION The differential characteristic entered The differential- restraining trajectory out of the differential characteristic for certain period of time saturation condition current below the first slope for certain period of time The CT saturation condition is declared when the magnitude of the restraining signal becomes larger than the higher breakpoint and at the same time the differential current is below the first slope. As the phasor estimator in the main differential algorithm introduces a processing delay that may cause fast CT saturation to be missed, a similar procedure is done using the relations between the signals at the waveform level to catch fast CT saturation. Additionally, the sample-based stage of the saturation detector uses the time derivative of the restraining signal (di/dt) to better trace the saturation pattern shown in the above diagram. The CT saturation condition is of a transient nature and requires a seal-in, therefore the CT saturation detector state machine is used. The saturation detector is capable of detecting saturation occurring in approximately 2 ms into a fault. It should be emphasized that the saturation detector has no dedicated settings, but does rely on settings for the main differential characteristic for proper operation.
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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
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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) SAT saturation detector flag asserts prior to BIASED PKP bus differential pickup 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 BIASED PKP and BIASED OP both assert before DIR asserts CT saturation does not block bus differential More examples available (COMTRADE files) upon request
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CT Saturation Example – External Fault
0.06 0.07 0.08 0.09 0.1 0.11 0.12 -200 -150 -100 -50 50 100 150 200 time, sec current, A ~1 ms Despite heavy CT saturation the external fault current is seen in the opposite direction Two examples of relay operation are presented: an external fault with heavy CT saturation and an internal fault with mild CT saturation. The protected bus includes six circuits connected to CT banks F1, F5, M1, M5, U1 and U5, respectively. The circuits F1, F5, M1, M5 and U5 are capable of feeding some fault current; the U1 circuit supplies a load. The F1, F5 and U5 circuits are significantly stronger than the F5 and M1 connections. The M5 circuit contains the weakest (most prone to saturation) CT of the bus. The Figure presents the bus currents and the most important logic signals for the case of an external fault. Despite very fast and severe CT saturation, the B30 remains stable.
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CT Saturation – Internal Fault Example
The Figure presents the same signals but for the case of an internal fault. The B30 trips in 10 ms (fast form-C output contact).
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Digital Phase-Segregated Bus Differential
n·iA, vA Phase A Protection TRIPA n· iB, vB Phase B Protection TRIPB n· iC, vC Phase C Protection TRIPC Isolator Monitoring, Bkr. Fail Phase-segregated multi-IED protection system Large number of AC inputs, digital inputs and outputs possible Digital communications between IEDs allow sharing digital states Expanded Oscillography, Event Recording, Programmable Logic
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B90 Architecture Phase A Protection PS B90 #1 CPU COMMS Phase-segregated multi-IED protection system built on UR platform Up to 24 AC Inputs per chassis Up to 24 single phase currents 12 single phase currents & 12 single phase voltages per chassis Variety of digital inputs and output contacts available via modular configuration Digital communications between IEDs for sharing digital states PS CPU B90 #2 Phase B Protection DSP I/O COMMS PS CPU B90 #3 Phase C Protection DSP I/O COMMS
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B90 Components: Protection
Power Supply CPU DSP 1 I/O DSP 2 DSP 3 Comms 8 AC single-phase inputs Other UR-based IEDs Up to 24 AC inputs per chassis with 3 DSP modules Up to 3 digital I/O modules per chassis for contact outputs and digital inputs Analog signal processing: Differential calculations, IOC, TOC, UV, BF current supervision Three-phase protection for busbars with up to 8 feeders or single-phase protection for busbars with up to 24 feeders.
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B90 Components: Logic Up to 96 digital inputs or
Power Supply CPU Other UR-based IEDs I/O Comms Up to 96 digital inputs or Up to 48 output contacts or Any combination of the above. Up to 24 breaker failures for the associated bus zone Logic processing: Breaker Failure logic and timers, isolator monitoring and alarming for dynamic bus replication
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B90 Architecture for Large Busbars
Dual (redundant) fiber with 3msec delivery time between neighbouring IEDs. Up to 8 B90s/URs 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
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B90 Architecture – Dynamic Bus Replica and Isolator Position
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 Up to 96 auxuliary switches wired here; Isolator Monitoring function configured here Isolator Position
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B90 Architecture – BF Initiation & Current Supervision
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 Up to 24 BF elements configured here BF Initiate & Current Supv.
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B90 Architecture – Breaker Failure Tripping
Phase A AC signals wired here, current status monitored here Breaker Fail Op Breaker Fail Op Trip Trip Phase B AC signals wired here, current status monitored here Phase C AC signals wired here, current status monitored here Breaker Fail Op Breaker Fail Op Trip Breaker Fail Op command generated here and send to trip appropriate breakers
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B90 Applications for Large Busbars
B90-B B90-C Single Bus Single Breaker B90-A B90-B B90-C B90-Logic Double Bus Single Breaker
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B90 Applications for Large Busbars Continued
Single Bus Single Breaker with Bus Tie B90-A B90-B B90-C Double Bus Double Breaker B90-A B90-B B90-C
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B30 & B90 Application Considerations
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Applying the B30 or B90 for Busbar Protection
Basic Topics Configure physical CT Inputs Configure Bus Zone and Dynamic Bus Replica Calculating Bus Differential Element settings Advanced Topics Isolator Monitoring More on Dynamic Bus Replica – Blind Spots & End Fault Protection Differential Zone CT Trouble Additional Security for the Bus Differential Zone B90 Application Example
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Configuring CT Inputs For each connected CT circuit enter Primary rating and select Secondary rating. For the B30, each 3-phase bank of CT inputs must be assigned to a Signal Source (SRC1 through SRC6) which are then assigned to the Bus Zone and Dynamic Bus Replica For the B90, the CT channels are assigned directly to the Bus Zone and Dynamic Bus Replica (no Signal Sources) For B30, CTs are connected in 3-phase sets For B90, CTs are connected as individual single phases UR hardware is built to support combinations of both 1 A and 5 A secondaries within the same DSP module Both the B30 and B90 define 1 p.u. as the maximum primary current of all of the CTs connected in the given Bus Zone
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B90 Per-Unit Current Definition - Example
DSP Channel Primary Secondary Zone CT-1 F1 3200 A 1 A 1 CT-2 F2 2400 A 5 A CT-3 F3 1200 A CT-4 F4 2 CT-5 F5 CT-6 F6 5000 A For Zone 1: 1.00 ASEC injected on F1 is 1.00 p.u. 6.67 ASEC injected on F2 is 1.00 p.u. 2.67 ASEC injected on F3 is 1.00 p.u. For Zone 2: 1.56 ASEC injected on F4 is 1.00 p.u. 20.83 ASEC injected on F5 is 1.00 p.u. 5.00 ASEC injected on F6 is 1.00 p.u. For Zone 1, 1 p.u. = 3200 Apri For Zone 2, 1 p.u. = 5000 A pri
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Configuration of Bus Zone (Dynamic Bus Replica)
Dynamic Bus Replica associates a status signal with each current in the Bus Differential Zone Status signal can be any FlexLogic™ operand Status signals can be developed in FlexLogic™ to provide additional checks or security as required 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 For the B30, each Signal Source (SRC1 – SRC6) must be assigned a status signal to be included in the three-phase Bus Zone For the B90, the CT channels are assigned status inputs directly in the respective Bus Zone(s) and the CT direction must also be configured for all current inputs in each bus zone In or Out, depending on CT polarity
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Bus Differential Characteristic
High Set (Unrestrained) High Slope Low Slope High Breakpoint Low Breakpoint
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Calculating Bus Differential Settings
The following Bus Zone Differential element parameters need to be set: Differential Pickup Restraint Low Slope Restraint Low Break Point Restraint High Breakpoint Restraint High Slope 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)
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Calculating Bus Differential Settings - 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 (VTs for example) May also be set above maximum load conditions for added security in case of CT trouble, but better alternatives exist Range: p.u. to p.u. in p.u. increments
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Calculating Bus Differential Settings – Low Slope
Defines the percent bias for the restraint currents from IREST=0 to IREST=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
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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 Range: 1.00 to 4.00 p.u. in 0.01 p.u. increments
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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 Range: 4.00 to p.u. in 0.01 p.u. increments
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Calculating Bus Differential Settings – High Slope
Defines the percent bias for the restraint currents IRESTHigh 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
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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.
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Advanced Topics
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Advanced Topics Isolators and Isolator Monitoring
More on Dynamic Bus Replicas Blind Spots End Fault Protection Differential Zone CT Trouble Additional Security for the Bus Differential Zone External Check Zone Undervoltage Supervision Overcurrent Supervision B90 Application Examples
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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: Both N.O. and N.C. contacts should be used Isolator Alarm should be established and non-valid combinations (open-open, closed-closed) should be sorted out Switching operations should be inhibited until bus image is recognized with 100% accuracy Optionally block 87B operation from Isolator Alarm Each isolator position signal decides: Whether or not the associated current is to be included in the differential calculations Whether or not the associated breaker is to be tripped
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Isolator – Typical Open/Closed Connections
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Full-Featured Isolator Monitoring
Isolator Open Aux. Contact Isolator Closed Aux. Contact Isolator Position Isolator Alarm Block Switching Off On CLOSED No LAST VALID After time delay until reset Until isolator position valid OPEN For the B30, this needs to be implemented using FlexLogic™ For the B90 (Logic), there are 48 dedicated Isolator Position monitoring elements
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Switching An Isolator – Closing Sequence
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Isolator Monitoring Scheme – B90
B90 Isolator Position Logic Open Position Input Closed Position Input Isolator n Position On Off On (Closed) Off On Off (Open) On On On (Closed)* Off Off Use Last Valid* *Invalid states will assert the ISOLATOR n ALARM & ISOLATOR n BLOCK operands
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Dynamic Bus Replica – Changing the Bus Zone
Bus Tie Breaker with Two CTs TB Z1 Z2 Overlapping zones – no blind spots Both zones trip the Tie-Breaker No special treatment of the TB required in terms of its status for Dynamic Bus Replica (treat as regular breaker)
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Dynamic Bus Replica – Changing the Bus Zone
Bus Tie Breaker with Single CTs TB Z1 Z2 Both zones trip the Tie-Breaker Blind spot between the TB and the CT Fault between TB and CT is external to Z2 Z1: no special treatment of the TB required (treat as regular CB) Z2: special treatment of the TB status required: The CT must be excluded from calculations after the TB is opened Z2 gets extended (opened entirely) onto the TB
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Dynamic Bus Replica – Changing the Bus Zone
expand Z1 Z2 TB Sequence of events: Z1 trips and the TB gets opened After a time delay the current from the CT shall be removed from Z2 calculations As a result Z2 gets extended up to the opened TB The Fault becomes internal for Z2 Z2 trips finally clearing the fault
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Dynamic Bus Replica – Changing the Bus Zone
CT CB Blind spot for bus protection Blind spot exists between the CB and CT CB is going to be tripped by line protection After the CB gets opened, the current shall be removed from differential calculations (expanding the differential zone up to the opened CB) Identical to the Single-CT Tie-Breaker
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Dynamic Bus Replica – Changing the Bus Zone
contract CB CT “Over-trip” spot for bus protection “Over-trip” spot between the CB and CT when the CB is opened When the CB opens, the current shall be removed from differential calculations (contracting the differential zone up to the opened CB) Identical as for the Single-CT Tie-Breaker, but…
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Dynamic Bus Replica – Changing the Bus Zone
Blind spot for bus protection CB CT but… A blind spot created by contracting the bus differential zone End Fault Protection required to trip remote end circuit breaker(s)
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End Fault Protection (EFP)
Instantaneous overcurrent element enabled when the associated CB is open to cover the blind spot between the CB and line-side CT Pickup delay should be long enough to ride-through the ramp down of current interruption (1.3 cycles maximum) EFP inhibited from circuit breaker manual close command For the B30, the End Fault Protections need to be implemented using FlexLogic™ For the B90, there are 24 dedicated End Fault Protection elements
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End Fault Protection – B90 EFP Element Logic
(2) Excessive current … (3) Causes the EFP to operate (1) The EFP gets armed after the breaker is open
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End Fault Protection – Special Consideration
BUS SECTION TRANSFER BUS CB BYPASS selective "dead-zone" only if the isolator is open High currents may not be caused by a fault in the EFP “dead zone” With By-pass Isolator closed, a fault on the transfer bus will cause current to flow through the EFP CT EFP element must be disabled (Blocked) when the By-pass Isolator is closed.
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Differential Zone CT Trouble
Each Bus Differential Zone (1 for the B30, 4 for the B90) has 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: Trip the bus zone as the problem with a CT will likely evolve into a bus fault anyway Do not trip the bus, raise an alarm and try to correct the problem manually Switch to setting group with 87B minimum pickup setting above the maximum load current.
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Differential Zone CT Trouble
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) DO NOT use the Bus Differential element BLOCK input: The element traces trajectory of the differential-restraining point for CT saturation detection and therefore must not be turned on and off dynamically Supervise the trip output operand of the 87B in FlexLogic™ instead
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Differential Zone CT Trouble – Strategy #2 Example
87B operates Undervoltage condition CT OK 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)
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Additional Security for The Bus Differential Zone
No matter how high the reliability, any relay may fail. For bus applications, any MTBF will never be high enough Consider securing the application against reasonable contingencies CT problems, AC wiring problem Problems with aux. switches for breakers, isolators DC wiring problems involving the Dynamic Bus Replica Failure of relay hardware (single current input channel, single digital input) Security above and beyond inherent security mechanisms in the B30/B90 CT Saturation Detector Directional (Phase) Comparison Isolator monitoring
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External Check Zone Principle: Guards against:
Develop an independent copy of the differential current for the entire bus regardless of dynamic zones for individual bus sections Use the check zone to supervise the tripping zone(-s) Use independent CTs / CT cores if possible to guard against CT and wiring problems Use independent relay current inputs to guard against relay problems Alarm on spurious differential Guards against: CT problems AC wiring problems Problems with aux switches for breakers and disconnectors DC wiring problems for dynamic bus replica Failures of current inputs
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Application of the External Check Zone to the B30
With only six 3-phase inputs the B30 handles 1 zone of protection Actual (tripping) zone shall be configured to reflect dynamic image of the bus External check zone can be configured in some circumstances as an unrestrained zone that (ideally) uses separate CTs or CT cores An IOC function may be configured if needed to operate on the externally summated currents For external zone identical CT ratios or matching transformers are required Make use of three ground CT inputs (IG) and Ground IOC or unused 3-phase bank & Phase IOC elements to provide check zone
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Application of the External Check Zone to the B30 - Example
RED BUS BLUE BUS All isolators All breakers All currents BLUE B30 RED B30 Prior to tripping a given section, it is beneficial to check if the plain sum of all the currents is excessive indicating on a fault either in section RED or BLUE. Each relay uses appropriate information to detect faults in each zone of protection. Both relays monitor the overall differential current supplied externally and use it to supervise their 87B functions. This brings extra immunity to CT failures and problems with isolator positions. Ideally external check zone shall be built using separate cores or CTs. Ratio matching may be a problem for the external check zone.
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Application of the External Check Zone to the B30
87B phase A supervised by IOC1 phase A; the IOC responds to the externally formed differential current Three-phase trip command
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Application of the External Check Zone to the B90
Version 1 Use two different CTs / CT cores Place the supervising zone in a different chassis Strong security bias, practically a 2-out-of-2 independent relay scheme Use fail-safe output to substitute for the permission if the supervising relay fails / is taken out of service
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Application of the External Check Zone to the B90
Version 2 Use two different CTs / CT cores Place the supervising zone in the same chassis, different DSP module Strong security bias, almost 2-out-of-2 independent relay scheme Simpler panel wiring compared with version 1 (No inter chassis wiring needed)
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Application of the External Check Zone to the B90
Version 3 Use a single CT (simpler wiring) Place the supervising zone in a different chassis Guards against relay problems and bus replica problems Use fail-safe output to substitute for the permission if the supervising relay fails / is taken out of service
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Application of the External Check Zone to the B90
Version 4 Use a single CT Place the supervising zone in the same chassis, different DSP module Guards against relay problems and bus replica problems No inter chassis wiring needed
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Undervoltage Supervision
Principle: Supervise all differential trips with undervoltage Set high ( pu) for speed and sensitivity Need 3 UV elements per bus per phase (undervoltage functions AG, AB, CA supervise differential trip for phase A) Alarm on spurious differential Guards against: CT problems AC wiring problems Problems with aux switches for breakers and disconnectors DC wiring problems for dynamic bus replica Failures of current inputs
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Application of Undervoltage Supervision to the B90
Version 1 Place the supervising voltage inputs in a different chassis Guards against relay problems and bus replica problems Does not need any extra ac current wiring Use fail-safe output to substitute for the permission if the supervising relay fails / is taken out of service
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Application of Undervoltage Supervision to the B90
Version 2 Place the supervising voltage inputs in the same chassis Guards against relay problems and bus replica problems Does not need any extra ac current wiring No inter chassis wiring needed
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Overcurrent Supervision
Principle: Supervise trips to breakers with OC condition set above maximum load Loads will not get tripped; facilitates bus transfer applications With a single CT / wiring / relay input problem, only up to one breaker will get tripped, not the entire bus Danger that very weak sources feeding a bus fault will not get tripped, solution possible via logic Guards against: CT problems AC wiring problems Problems with aux switches for breakers and disconnectors DC wiring problems for dynamic bus replica Failures of current inputs Typically, no trip will occur on CT and wiring problems A single CB may get tripped on specific relay problems (sees spuriously high current)
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Application of Overcurrent Supervision to the B90
Version 1 Use the same relay inputs as for the main differential, otherwise check zone should be used as a better solution Does not need any extra ac current wiring
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Application of Overcurrent Supervision to the B90
Version 2 Select strong sources and wire them to different DSPs Use k-out-of-N (2-out-of-3, for example) to facilitate trips on weak sources A given breaker gets tripped if it is sees a high current, or any k out of N strong sources see high currents
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Application of Overcurrent Supervision to the B90
Version 3 Select strong sources and wire them to different DSPs Use k-out-of-N (2-out-of-3, for example) to facilitate trips on weak sources A given breaker gets tripped if any k out of N strong sources see high currents In this example, 2 current inputs would have to fail “high” to cause misoperation
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B90 Application Examples
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B90 Example – Reconfigurable Bus
Double bus, single breaker with bus-tie 10 feeders with single CT Circuit breaker bypass switches per feeder CB Current inclusion in bus zone depends on isolator switch position (ISO x) Bus Tie (CB1-2) Closed: Include L8 in Zone 1 and L7 in Zone 2 Include F1 (CB1) in Zone 1 Include F2 (CB2) in Zone 2 Include F3 (CB3) in Zone 1 Include F4 (CB4) in Zone 2 Include F5 (CB5) in Zone 2 Include F6 (CB6) in Zone 2 Include F7 (CB7) in Zone 2 Include F8 (CB8) in Zone 1 Include L1 (CB9) in Zone 2 Include L2 (CB10) in Zone 1
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B90 Example – Architecture
Breaker Failure inputs and outputs Phase A AC signals and trip contacts Phase B AC signals and trip contacts Phase C AC signals Digital Inputs for isolators and breakers monitoring Tx Rx Direct I/O Ring (Ch. 1) Direct I/O Ring (Ch. 2)
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B90 Example – Dynamic Bus Replica Logic
INCLUSION OF FEEDER CTs INTO BUS 1(ZONE 1), OR BUS 2(ZONE 2) PROTECTION Feeder 1 will be included into Bus 1, if ISOLATOR 1 POSITION is “ON”, or the two buses are paralleled, and ISOLATOR 2 POSITION is “ON” Feeder 1 will be included into Bus 2, if ISOLATOR 2 POSITION is “ON”, or the two buses are paralleled, and ISOLATOR 1 POSITION is “ON” The logic provides for inclusion of the feeders into the two buses, upon detection of bus parallel path(VO63 = “ON”). In this case the input currents for ZONE 1, ZONE 2, CHECK ZONE 3 become the same: Z1 = Z2 = Z3. The logic also provides that the feeder CT will not be included into any of the two buses(zones), should both isolators ISO1, and ISO2 are declared “OPEN”
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B90 – Bus Zone Definitions (Dynamic Bus Replica)
DIFFERENTIAL ZONE 1 (BUS 1) Differential current: Id = F1 + F3 + F8 + L2 + L8 Restraint current: Ir = max(F1, F3, F8, L2, L8) DIFFERENTIAL ZONE 2 (BUS 2) Differential current: Id = F2 + F4 + F5 +F6 +F7 +L1 + L7 Restraint current: Ir = max(F2, F4, F5, F6, F7, L1, L7) DIFFERENTIAL ZONE 3 (CHECK ZONE = BUS 1 + BUS 2) Differential current: Id = F1 +F2 + F3 +F4 +F5 +F6 +F7 + F8 + L1 +L2 + + (L7 OR L8) WHEN FEEDER CT BY-PASSED Restraint current: Ir = max(F1, F2, F3, F4, F5, F6, F7, F8, L1, L2, (L7 OR L8) WHEN FEEDER CT BY-PASSED)
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B90 – Direct I/O Communications Configuration
B90-1 A PHASE B90-5 BKR FAIL B90-2 B PHASE B90-3 C PHASE Isolators and breakers positions B90-4 STATUS Fiber Optic channels Direct outputs on IED4 Direct inputs on IED1, 2, and 3 ZONE 1 ZONE 2 ZONE 3 Differential zones configuration on IED1, 2, and 3
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B90 Example – AG Fault on Bus 1
Bus Tie (CB1-2) Closed: Include L8 in Zone 1 and L7 in Zone 2 Include F1 (CB1) in Zone 1 Include F2 (CB2) in Zone 2 Include F3 (CB3) in Zone 1 Include F4 (CB4) in Zone 2 Include F5 (CB5) in Zone 2 Include F6 (CB6) in Zone 2 Include F7 (CB7) in Zone 2 Include F8 (CB8) in Zone 1 Include L1 (CB9) in Zone 2 Include L2 (CB10) in Zone 1
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B90 Example – AG Fault on Bus 1 Trip Logic
* Denotes a binary signal received from an external B90 via communications (Direct I/O, GOOSE/GSSE) * Denotes a binary signal received from an external B90 via communications (Direct I/O, GOOSE/GSSE)
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B90 Example – AG Fault on Bus 1 Trip Logic
* Denotes a binary signal received from an external B90 via communications (Direct I/O, GOOSE/GSSE)
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B90 Example – Bus 2 Fault With Buses Paralleled
Bus Tie (CB1-2) Closed: Include L8 in Zone 1 and L7 in Zone 2 Include F1 (CB1) in Zone 1 Include F2 (CB2) in Zone 2 Include F3 (CB3) in Zone 1 Include F4 (CB4) in Zone 2 Include F5 (CB5) in Zone 2 Include F6 (CB6) in Zone 2 Include F7 (CB7) in Zone 2 Include F8 (CB8) in Zone 1 Include L1 (CB9) in Zone 2 Include L2 (CB10) in Zone 1
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B90 Example – Buses Paralleled Logic
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B90 Example – Dynamic Bus Replica (Paralleled Buses)
BUS ZONE 1 BUS ZONE 2
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B90 Example – Dynamic Bus Replica (Paralleled Buses)
ISO19 & ISO20 CLOSED PARALLEL PATH DETECTED INCLUDE ALL FEEDERS IN BOTH ZONE 1 & ZONE 2 ZONE 1 = ZONE 2 = ZONE 3 A Bus Fault on Either Bus 1 or Bus 2 will result in both Bus Differential Zones Tripping
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B90 Example – Paralleled Buses Trip Logic
* Denotes a binary signal received from an external B90 via communications (Direct I/O, GOOSE/GSSE) Both Zone 1 and Zone 2 operate and…
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B90 Example – Paralleled Buses Trip Logic
…trip all breakers in Zone 1 and Zone 2. * Denotes a binary signal received from an external B90 via communications (Direct I/O, GOOSE/GSSE)
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B90 Example – External Fault on F4 with Breaker Fail
Feeder Protection detects fault and sends trip command to CB4 After a time, current flow is detected in F4 Breaker Failure for CB4 is declared and signal sent to B90-5 B90-5 sends signals to Protection B90s to trip appropriate breakers Bus Tie (CB1-2) Closed: Include L8 in Zone 1 and L7 in Zone 2 Include F1 (CB1) in Zone 1 Include F2 (CB2) in Zone 2 Include F3 (CB3) in Zone 1 Include F4 (CB4) in Zone 2 Include F5 (CB5) in Zone 2 Include F6 (CB6) in Zone 2 Include F7 (CB7) in Zone 2 Include F8 (CB8) in Zone 1 Include L1 (CB9) in Zone 2 Include L2 (CB10) in Zone 1
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B90 Example – Breaker Fail Zone Trip Logic
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B90 Example – Breaker Failure Trip Logic
* Denotes a binary signal received from an external B90 via communications (Direct I/O, GOOSE/GSSE)
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B90 Example – Breaker Failure Trip Logic
* Denotes a binary signal received from an external B90 via communications (Direct I/O, GOOSE/GSSE)
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B30 & B90 User Software
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B30 & B90 – Software UR Setup – Universal configuration software for the entire Universal Relay (UR) family Free download from GEMultilin.com B30 Differential Phasor Model Simulator – Simulate B30 operation offline using virtual B30 model Enervista Viewpoint Software Suite Engineer – Graphical Logic Designer, Real-Time Logic Monitor, Advanced COMTRADE Viewer Monitoring – Simplified Monitoring, Data Logging & Event Retrieval for Small Systems Maintenance – Automatic report generation for Relay Health and Relay & Settings Security
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UR Setup – Universal Relay Configuration Software
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UR Setup – COMTRADE Viewer
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B30 Differential – Phasor Model
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B30 Differential – Phasor Display
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B30 Differential – Operating Characteristic
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EnerVista Viewpoint Engineer Graphical FlexLogic™ Designer
Design Control Logic in this intuitive, easy to use IEC 1131 Graphical Logic Designer Simplify the process of creating complex control logic for Substation Automation such as advanced Tripping, Reclosing and Transfer Schemes. Design Logic with drag and drop ease using a library of inputs, outputs, logic gates, symbols and configuration tools Document actual setting file with text to make it easier for others to understand Create settings offline without having to communicate with the relay Powerful Intuitive Logic Compiler Analyses logic for potential problems in logic such as: detecting infinite loops in logic using inputs and outputs, or protection, control and monitoring elements that have not been configured properly using Virtual Outputs that have not been assigned using inputs for hardware or features that is not available on your relay Optimizes control logic equations to obtain maximum efficiency and to use the fewest possible lines of logic
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EnerVista Viewpoint Engineer Real-Time FlexLogic™ Analyzer
Analyze the Status of each component of your UR Flexlogic in Real-Time Identify which inputs are triggering and enabling each logic gate Ascertain why your control logic is not operating as you expected Quickly detect any wiring problems Determine which control interlocks are causing your breaker from operating
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EnerVista Viewpoint Engineer
IEC System/Substation Designer Device Logic Designer System/Substation Designer Create Logic in an Graphical IEC Editor Analyze status of logic in Real-Time Link Control Logic from multiple UR Devices Create Setting Files for multiple UR’s Analyze the status of Peer-to-Peer messages in Real-Time Shipping Q1, 2006 Link Control Logic from multiple UR Devices Create Setting Files for multiple UR’s in IEC format Analyze the status of Peer-to-Peer messages in Real-Time Shipping Q4, 2006
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EnerVista Viewpoint Monitoring Easy to use Monitoring & Data Recording for Small Systems
PLUG-AND-PLAY MONITORING GLOBAL COMTRADE VIEWER Pre-configured screens for instant monitoring View Waveforms Recorded From your Devices SINGLE-LINE MONITORING AND CONTROL TRENDING REPORTS View Single-Line monitoring screens in minutes Historical Record of Monitored Data AUTOMATIC EVENT AND WAVEFORM RETRIEVAL AUTOMATIC EVENT AND WAVEFORM RETRIEVAL Effortless Data Archiving Instant Alarm Notification
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Device Status and Health
EnerVista Viewpoint Maintenance Reports to Simplify all Maintenance Tasks Viewpoint Maintenance will provide the following reports to simplify all maintenance tasks Fault Diagnostics Report Device and Equipment Status Report Settings Security Report Fault Diagnostics Device Status and Health Settings Security
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Conclusions
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Conclusions B30 B90 For smaller busbars (up to 6 feeders)
Single chassis providing three-phase bus differential protection, logic and I/O capabilities Isolator monitoring may be done in FlexLogic™ if required End Fault Protection may be provided using FlexLogic™ if required Additional security can be provided (fewer feeders in zone) Inter-relay communications supported for additional I/O B90 For large, complex busbars (up to 24 feeders) Multiple chassis for single-phase bus differential, plus extra IEDs for dynamic bus replica, breaker fail… Internal full-feature isolator monitoring provided (B90-Logic) 24 End Fault Protection elements provided (B90-Protection) Additional security can be provided (fewer feeders in zone) Inter-relay communications supported for additional I/O
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Conclusions B30 is limited in scope to small busbars, therefore application is fairly simple and straightforward B90 designed to be applied to large complex busbars, therefore application can be quite complicated: Multiple B90s: Protection Algorithm processing Dynamic Bus Replica logic Isolator monitoring Breaker Failure Inter-relay Communication schemes for I/O transfer, inter-tripping GE Multilin can provide a complete engineered B90 System Solution, based on specific customer application & requirements
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Conclusions Both B30 and B90 provide secure, high performance bus differential protection for reconfigurable busbars using the same proven algorithms Both B30 and B90 are members of the Universal Relay (UR) family, with common configuration and management tools for all relays: EnerVista UR Setup: Universal configuration tool EnerVista ViewPoint: software suite for all GE Multilin IEDs Launchpad: Device Setup & Document Management Engineer: Advanced Logic Design & Monitoring (Optional) Maintenance: Troubleshooting & Reporting Tools (Optional) Monitoring: Monitoring & Data Recording for Small Systems (Optional) EnerVista Launchpad: Easily launch configuration tools for any GE Multilin Device from a single Application Manage your Support Documents and Software Tools Receive Automatic Notification or new updates as soon as they are available EnerVista Viewpoint Engineer: Design Logic with Drag-and-Drop ease Real-time feedback of FlexLogic™ states Documentation of Logic Commissioning Procedures and Tools EnerVista Viewpoint Maintenance: Single click retrieval of Fault Data Setting Security Report showing history of setting changes Health Report showing status of Protective Devices Track Firmware Configuration changes to GE Multilin devices EnerVista Viewpoint Monitoring: Pre-configured screens for Instant Monitoring Single-Line monitoring Annunciator Alarms Trending Reports Automatic Fault Data Collection
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Q & A
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