Downloaded 107 times
Uploaded byRabah Zaimeddine
Time current curves
A protective device coordination study involves organizing the time-current characteristics of protective devices from the utility to downstream devices. The study determines device ratings, settings, and ensures minimum load is interrupted during faults while protecting devices. Results include instrument transformer ratios, relay settings, fuse ratings, and circuit breaker ratings. The study should be revised every 5 years or when devices are added or modified.
More Related Content
![protection of transmission lines[distance relay protection scheme]](https://cdn.slidesharecdn.com/ss_thumbnails/os-exe3-23-may2011-sr-i-776s21tr-lineprotection-120425095503-phpapp02-thumbnail.jpg?width=640&height=640&fit=bounds)
Time current curves
- 1.
- 2. Protective Device Coordination ProtectiveDevice Coordination Study- Description: • An organized time-current study of protective devices from the utility to a device. • A comparison of the time it takes protective devices to operate when certain levels of normal or abnormal current pass through them. 2
- 3. Protective Device Coordination ProtectiveDevice Coordination Study- Objective: • Determine the characteristics, ratings, and settings of overcurrent protective devices • Ensure that the minimium, un-faulted load is interrupted when the protective devices isolate a fault or overload anywhere in the system. 3
- 4. Protective Device Coordination ProtectiveDevice Coordination Study- Results: • Selection of instrument transformers ratios • Protective relay characteristics and settings • Fuse ratings • LV circuit breaker ratings, characteristics, and settings. 4
- 5. Protective Device Coordination ProtectiveDevice Coordination Study- Frequency: • This study should be revised as new protective are added or as existing devices are modified. • At a minimum, it is recommended that this study be performed every 5 years. 5
- 6. Protective Device Coordination ProtectiveDevice Coordination Study- Frequency: • This study should be revised as new protective are added or as existing devices are modified. • At a minimum, it is recommended that this study be performed every 5 years. 6
- 7. (b) Electric powerand lighting circuits. (1) Routine opening and closing of circuits. Load rated switches, circuit breakers, or other devices specifically designed as disconnecting means shall be used for the opening, reversing, or closing of circuits under load conditions. Cable connectors not of the load break type, fuses, terminal lugs, and cable splice connections may not be used for such purposes, except in an emergency. OSHA 1910.334 Use of Equipment 7
- 8. OSHA 1910.334 Use ofEquipment (b) Electric power and lighting circuits. (2) Reclosing circuits after protective device operation. After a circuit is de-energized by a circuit protective device, the circuit protective device, the circuit may not be manually reenergized until it has been determined that the equipment and circuit can be safely energized. The repetitive manual reclosing of circuit breakers or reenergizing circuits through replaced fuses is prohibited. Note: When it can be determined from the design of the circuit and the overcurrent devices involved that the automatic operation of a device was caused by an overload rather than a fault condition, no examination of the circuit or connected equipment is needed before the circuit is reenergized. 8Cargill Electrical Team Meeting
- 9. (b) Electric powerand lighting circuits. (3) Overcurrent protection modification. Overcurrent protection of circuits and conductors may not be modified, even on a temporary basis, beyond that allowed by 1910.304(e), the installation safety requirements for overcurrent protection. OSHA 1910.334 Use of Equipment 9Cargill Electrical Team Meeting
- 10.
- 11. Time-Current Curves Cables The Time-CurrentCurves for cables are also known as “Damage” curves. 11Cargill Electrical Team Meeting
- 12. Cargill Electrical TeamMeeting 12 Time Current Curves Motor The Time-Current Curves for motors are also known as “Damage” curves.
- 13. 13 Time-Current Curves Protective Relays 50– Instantaneous Overcurrent Relay 51 – AC Time Overcurrent Relay 67 – AC Directional Overcurrent Relay
- 14.
- 15. Time-Current Curves Fuses 800 A Fuse Rating Whatwould cause a fuse to blow? 1. Inappropriate Sizing 2. Inappropriate Type for application 3. Fault 15
- 16.
- 17.
- 18. Time-Current Curves Circuit Breakers Noaction to left of curve Trip or clear on and to right of curve All devices should be considered at same voltage 18
- 19. Short Time (i.e., motorstarts/stops) Long Time (i.e., TOL) Instantaneous (i.e., Faults) Time-Current Curves Circuit Breakers 19
- 20. Time-Current Curves Circuit Breakers 20CargillElectrical Team Meeting
- 21. Manufacturer Model No. Trip Unit Rating FaultDuty Time-Current Curves Circuit Breakers 21Cargill Electrical Team Meeting
- 22. Available Settings LTPU –Long Time Pickup LTD - Long Time Delay STPU – Short Time Pickup STD – Short Time Delay INST – Instantaneous GF – Ground Fault GFD – Ground Fault Delay L S I G Time-Current Curves Circuit Breakers 22Cargill Electrical Team Meeting
- 23. LTPU Setting Time-Current Curves CircuitBreakers 23Cargill Electrical Team Meeting
- 24. STPU Setting Time-Current Curves CircuitBreakers 24Cargill Electrical Team Meeting
- 25. STD Setting Time-Current Curves CircuitBreakers 25
- 26. INST Setting Time-Current Curves CircuitBreakers 26
- 27.
- 28. Time-Current Curves Thermal-Mag Breakers Thermalportion (usually fixed) “Mag” portion (usually adjustable) “Mag” Setting – Equates to INST 28
- 29. Transformer Protection Point < 2500 kVA> 2500 kVA ANSI 17.6 x Ifl x 58% 16.6 x Ifl x 58% Inrush (for 0.1 sec) 8 x Ifl 12 x Ifl NEC Rule (6 x Ifl) 6 x Ifl 6 x Ifl Time-Current Curves Transformers 29
- 30. 30 Time-Current Curves Transformers Transformer Inrush mustbe left of curve
- 31. 31 Time Current Curves MotorProtection Refer to NEC Article 430.52, “Rating or Setting for Individual Motor Circuit” and manufacturer recommendations for determining appropriate motor protection.
- 32. 32 Time Current Curves MotorProtection
- 33. 33 Time Current Curves MotorProtection
- 34. 34 Time Current Curves MotorProtection Motor protection relays are typically programmed to operate approximately halfway between Load Current Curve and the Motor Damage Curve.
- 35. 35 Time Current Curves MotorProtection
- 36. 36 Time-Current Curves Questions orComments?
- 37.
- 38. 38 Troubleshooting Troubleshooting Tools: • DesignInformation: — One-Line Diagrams — Time-Current Curves — Manufacturer Literature — Operating History • Maintenance Information: — Visual Inspection — IR Surveys — Oil Sample Reports — UE/PD Surveys — Testing Data Sheets — Protective Relays — Power Monitors
- 39. • Scheduled PMOverdue (Needed Cleaning) • High Humidity compounded problem • Expulsion Type Fuse failed to operate correctly Troubleshooting 39
- 49. 49 Time-Current Curves Transformers Transformer Inrush mustbe left of curve
- 50. Control Power Transformer (CPT) BreakerTrip: Cause - Rodent Troubleshooting 50
- 51. Note: First indication providedthrough IR Survey. High Resistance Fuse Extenuating Circumstances: •Inadequate spare parts •Production pressure Troubleshooting 51
- 52. Note: First indication providedthrough IR Survey. HV Bushing Repair Required • Jumpers undersized • Heating resulted in gasket failure • Oil contamination resulted in flashover at bushing. Troubleshooting 52
- 53.
- 54. HV Insulated Bus InsulationTracking (Carbon Treeing) Troubleshooting 54
- 55. HV Jumper Cable InsulationTracking (Corona Damage Due to Improper Installation) Troubleshooting 55
- 56. Tap Changer Eminent ConnectionFailure Note: First indication provided through Oil Sampling. Troubleshooting 56
- 59. Cargill Electrical TeamMeeting 59 October 2007 Event: Fault (~8,000A) resulted in switchgear lineup burning without fuses clearing. Cause: Only one of nine 4/0 ground cables was connected. Cable burned through, effectively “protecting” fuse. X Troubleshooting
- 60. 60 December 2011 Event: Fuse(HS0202A) and Utility relay (50/51) cleared, shutting plant down. Cause: TBD. Troubleshooting
- 61.
- 62.
- 63. 63 HS0202A feeds thefollowing: TH0202B thru HS0202B (65A) TH0202C thru HS0202C (100A) TH0202D thru HS0202D (100A) TH0202E thru HS0202E (200A) Apparent fault on B and/or C phase below HS0202A Troubleshooting X
- 64. OSHA 1910.334 Use ofEquipment (b) Electric power and lighting circuits. (2) Reclosing circuits after protective device operation. After a circuit is de-energized by a circuit protective device, the circuit protective device, the circuit may not be manually reenergized until it has been determined that the equipment and circuit can be safely energized. The repetitive manual reclosing of circuit breakers or reenergizing circuits through replaced fuses is prohibited. Note: When it can be determined from the design of the circuit and the overcurrent devices involved that the automatic operation of a device was caused by an overload rather than a fault condition, no examination of the circuit or connected equipment is needed before the circuit is reenergized. 64
- 65.