Ieee transfer schemes for M-T-M distribution systems
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The document discusses the design of a transfer scheme for a secondary selective substation with two busses that can each be supplied by an incoming line circuit breaker, connected by a normally open bus tie breaker. It outlines the equipment arrangement, existing system loading conditions, and final configuration. Key aspects of designing the transfer scheme are discussed, including conditions for transfer, safety concerns, implementation methods, testing procedures, and maintenance. Logic diagrams of the main breaker and tie breaker are presented, showing how the transfer is initiated and blocked under various conditions.
Ieee transfer schemes for M-T-M distribution systems
- 1. Secondary Selective Substation Transfer Scheme April 2013 Industrial Power System Design
- 2. Presentation Outline • Definition – Secondary Selective Substation • Equipment Arrangement • Discussion Topics – How do you design a transfer scheme? • Existing System Description Normal System Loading Abnormal System Loading • Final System Configuration • Transfer Scheme Definitions • Implementation
- 3. Definition Secondary Selective Substation • Substations having two busses, each supplied by a normally-closed incoming line circuit breaker and connected together by a normally-open bus tie circuit breaker.
- 6. Discussion Topics How do you design a transfer scheme? • What conditions are required for transfer? Breaker positions? Breaker status? Voltage conditions? Make before break or break before make? Do we need to know about one side or both sides of switchgear to initiate transfer? Flow Chart, Logic Chart or if then statements? • What is the equipment arrangement? Where are current transformers going to be placed? Why? Where are potential transformers going to be placed? Why?
- 7. Discussion Topics How do you design a transfer scheme? • Safety concerns? Electrical protection requirements? Re-energizing bus with fault present? What do I do with downstream power sources (i.e. generators or synchronous motors)? Sources synchronized? How do you know? • Motor spin down complete • How will the system be implemented? Mechanical relays/hardwired Electronic relays/hardwired Electronic relays/communication
- 8. Discussion Topics How do you design a transfer scheme? • How do you recover from automatic transfer? Automatic or Manual? • If electronic relays, which ones? Pros and Cons for each Do you want to program the scheme or do you want to work within an existing framework? Typical: SEL or MULTILIN Does one give you an advantage in terms of end of project paperwork? Will final implementation be “black box” approach or will there be certain outputs that can be checked to tell you where you are in the transfer initiation by technician?
- 9. Discussion Topics How do you design a transfer scheme? • Communication between team members? No two engineers will design the system the same way. What are common assumptions? • Single mode of failure or multiple? • Will additional failure modes be handled with internal programming or procedural changes to the operation of the equipment. • What ranges or setpoints will be utilized? Why? • What requires an alarm to be sent? • What requires the automatic system to be disabled?
- 10. Discussion Topics How do you design a transfer scheme? • How do you test the system? What equipment is needed? If doors are stand alone • Where do you test the system? Factory Office/Lab In the field • Who should be involved in final testing? • Who decides on final testing methodology?
- 11. Discussion Topics How do you design a transfer scheme? • How do you know if your system is working properly? • Maintenance What needs to be done on a periodic basis? • Software updates, how do they effect the current system? • Who maintains programming files? • Standard breaker maintenance and time testing? • Relay testing to validate accuracy? • Training Who gets trained? What material is provided to make that individual successful?
- 12. 52-A 52-B 52-T 50P/N, 51P/N, 25, 27 51P/N, 25, 27 PT-1 PT-2 PT-4 PT-3 50P/N, 51P/N, 25, 27 Single Tie Arrangement
- 13. 52-A 52-B 52-T 50P/N, 51P/N, 25, 27 PT-1 PT-350P/N, 51P/N, 25, 27 Single Tie Arrangement
- 14. Flow Chart
- 15. Flow Chart
- 16. Flow Chart
- 17. One-Line Depiction • 27I-1, 27I-2 Instantantaneous under voltage relay • 27R-1, 27R-2 Residual voltage relay, 3 phase • 50/51-1, 2 Instantaneous and time overcrurrent relay • 50N/51N-1, 2 Residually connected instantaneous and time overcurrent relay • 51G-1, 2 Transformer X0 connection overcurrent relay
- 18. One-Line Depiction • 63 - Transformer fault pressure relay, rate-of-rise type or Buchholz relay • 63X - Auxiliary seal in relay • 86T- Hand reset transformer lockout relay • 25- Synchronism check relay
- 19. One-Line Depiction • 27I Relays 27I prevent an automatic transfer from occurring upon simultaneous loss of both sources, or loss of one source and low voltage on the other. Relays 27I operate through auxiliary relay 96. Because relays 96 are time delay type, an automatic transfer is also prevented upon simultaneous restoration of both sources after a double outage. Relays 27I also seal in relays 97 to prevent transfer if the supply breaker should trip first on overcurrent faults in the secondary selective substation.
- 20. Main Breaker Schematic 27I Relays 27I prevent an automatic transfer from occurring upon simultaneous loss of both sources, or loss of one source and low voltage on the other. Relays 27I operate through auxiliary relay 96. Because relays 96 are time delay type, an automatic transfer is also prevented upon simultaneous restoration of both sources after a double outage. Relays 27I also seal in relays 97 to prevent transfer if the supply breaker should trip first on overcurrent faults in the secondary selective substation.
- 21. Main Breaker Schematic 50/50N Relays 50 and 50N operate through the 97 relay, and are used to block transfer during overcurrent faults until the fault is cleared by the feeder breaker or incoming line breaker. When the settings are properly set they permit relay 27 to time out faster under fault conditions. The backup to this scheme includes time current/voltage coordination between the 51 overcurrent relay and the 27 undervoltage relay. The 51 relay should trip before the 27 sends the tripping signal.
- 22. Main Breaker Schematic •83- Auxiliary relay used in the transfer initiation from the main breaker to the tie breaker via the following functions: Trips the main breaker Closes the tie once the main breaker opens, and the bus voltage is 25% of it nominal value to prevent out of phase re-closer
- 23. Main Breaker Schematic • Auxiliary relay, instantaneous pickup, adjustable time delay drop out TDDO- time delay dropout, TDC- time delay closing, TDO-time delay opening
- 24. Main Breaker Schematic • 52LS-1 contact closes when incomer No. 1 is in the racked in position. • 52LS-2 contact closes when incomer No. 2 is in the racked in position. • 24LS contact closes when the tie breaker is in the racked in position. • 52-2/a contact closes when incomer No. 2 breaker is closed. • 10 trip selector switch used in manual transfers.
- 25. Main Breaker Schematic • 24/a contact closes when the tie breaker is closed. • 52-1/a contact closes when incomer No. 1 breaker is closed. • 96-1/TDC blocks the automatic transfer if the incomer No. 2 bus voltage is not healthy. • 97-1/TDC blocks the automatic transfer if the 50 instantaneous current relay detects flow of fault current. The block doesn't clear until the 50 relay clears and there is no longer a depressed undervoltage condition caused by the fault condition.
- 26. Main Breaker Schematic • 24/b breaks the transfer system seal in rung when the tie breaker closes. • 83-1 auxiliary relay that initiates the automatic transfer.
- 27. Tie Breaker Schematic 24LS D-C BUS NO.3 (+) 8-T 27R-1 27R-2 24CS C 83-1 83-2 52-1 b 52-2 b 24 b (1) 52LS-1 (4) 52LS-2 (4) 10 T 52-1 a 52-2 a (4) (4) 24CS TRLGL (8) (8) (8) 24 a 24 TC (1) 24 CC (-) 8-T D-C BUS NO.3 25Y (2) 27R Relays protect the motors which carry through automatic transfer, against overvoltage and instantaneous tripping of their circuit breakers due to closing in out of phase with residual voltage. Protection is achieved by delaying transfer until residual voltage drops to a safe level. Motors will generate a decaying residual voltage if source power is interrupted under load with no fault to dissipate magnetic energy stored in the motors.
- 28. Tie Breaker Schematic 24LS D-C BUS NO.3 (+) 8-T 27R-1 27R-2 24CS C 83-1 83-2 52-1 b 52-2 b 24 b (1) 52LS-1 (4) 52LS-2 (4) 10 T 52-1 a 52-2 a (4) (4) 24CS TRLGL (8) (8) (8) 24 a 24 TC (1) 24 CC (-) 8-T D-C BUS NO.3 25Y (2) 27R-1 contact closes when the residual bus voltage decays to 25% of the rated bus voltage in order to prevent an out of phase reclosure between the motor back emf and the new source voltage when the tie breaker is closed.
- 29. Normal Operating Condition SCE Owned/ Operated XOM Owned/ Operated Cable Capacity Transformer Capacity Switchgear Capacity 18 Air Cooled Fan Cooled 15 22.4 Power MVA 21.6 Normal Load 12.5 MVA Normal Load 15.5 MVA Cable Capacity Transformer Capacity Air Cooled Fan Cooled Switchgear Capacity 18 Power MVA 15 22.4 21.6 Normal Flow Normal Flow 12.5 MVA 15.5 MVA Percent Capacity Utilized 86 103 69 72 Total Load 28 MVA Breaker Open Breaker Closed Breaker Closed 69 83 56 58 Percent Capacity Utilized Bus 1 Bus 2
- 30. Abnormal Operating Condition SCE Owned/ Operated XOM Owned/ Operated Cable Capacity Transformer Capacity Switchgear Capacity 18 Air Cooled Fan Cooled 15 22.4 Power MVA 21.6 Normal Load 12.5 MVA Normal Load 15.5 MVA Cable Out of Service Transformer Out of Service Switchgear Breaker Out of Service Abnormal Flow Abnormal Flow 0 MVA 28 MVA Percent Capacity Utilized 156 187 123 130 Total Load 28 MVA Breaker Closed Breaker Closed Breaker Open Bus 1 Bus 2
- 38. Final System Logic Diagrams
- 39. Final System Logic Diagrams
- 40. Final System Logic Diagrams
- 41. Final System Logic Diagrams
- 42. Final System Logic Diagrams
- 43. Final System Logic Diagrams
- 44. Final System Logic Diagrams
- 45. Final System Logic Diagrams
- 46. Final System Logic Diagrams
- 47. Final System Logic Diagrams
- 48. Final System Logic Diagrams
- 49. Final System Logic Diagrams
- 50. Final System Logic Diagrams
- 51. Final System Logic Diagrams
- 52. Final Discussion
Editor's Notes
- #13: Permissives: MOC (Both Mains Closed and Tie Open/Dummy Tie Closed) TOC (Both Mains and Tie/Dummy Tie Racked In) No 86 Lockouts (M, L, T, or B) Good Voltage on alternate incomer for a minimum of X seconds. On fault block transfer and allow for downstream coordinated fault clearing