1 / 53

Power System Protection

Power System Protection. Dr. Ibrahim El-Amin. Protective Device Coordination. Definition. Overcurrent Coordination A systematic study of current responsive devices in an electrical power system. Objective. To determine the ratings and settings of fuses, breakers, relay, etc.

issac
Download Presentation

Power System Protection

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Power System Protection Dr. Ibrahim El-Amin

  2. Protective Device Coordination

  3. Definition • Overcurrent Coordination • A systematic study of current responsive devices in an electrical power system.

  4. Objective • To determine the ratings and settings of fuses, breakers, relay, etc. • To isolate the fault or overloads.

  5. Criteria • Economics • Available Measures of Fault • Operating Practices • Previous Experience

  6. Design • Open only PD upstream of the fault or overload • Provide satisfactory protection for overloads • Interrupt SC as rapidly (instantaneously) as possible • Comply with all applicable standards and codes • Plot the Time Current Characteristics of different PDs

  7. Analysis When: • New electrical systems • Plant electrical system expansion/retrofits • Coordination failure in an existing plant

  8. Protection vs. Coordination • Coordination is not an exact science • Compromise between protection and coordination • Reliability • Speed • Performance • Economics • Simplicity

  9. Protection • Prevent injury to personnel • Minimize damage to components • Quickly isolate the affected portion of the system • Minimize the magnitude of available short-circuit

  10. Spectrum Of Currents • Load Current • Up to 100% of full-load • 115-125% (mild overload) • Overcurrent • Abnormal loading condition (Locked-Rotor) • Fault Current • Fault condition • Ten times the full-load current and higher

  11. Coordination • Limit the extend and duration of service interruption • Selective fault isolation • Provide alternate circuits

  12. C D A B t A C D B I Coordination

  13. Equipment • Motor • Transformer • Generator • Cable • Busway

  14. I2t I2t I2t t I22t Motor Xfmr Cable Gen I Capability / Damage Curves

  15. Transformer CategoryANSI/IEEE C-57.109

  16. FLA 200 Thermal (D-D LL) 0.87 Infrequent Fault (D-R LG)0.58 Frequent Fault Mechanical 2 Inrush Isc 2.5 25 Transformer t (sec) I2t = 1250 K=(1/Z)2t I (pu)

  17. Transformer Protection

  18. Protective Devices • Fuse • Relay (50/51 P, N, G, SG, 51V, 67, 46, 79, 21, …) • Thermal Magnetic • Low Voltage Solid State Trip • Electro-Mechanical • MCP • Overload Heater

  19. Fuse • Non Adjustable Device • Continuous and Interrupting Rating • Voltage Levels • Characteristic Curves • Min. Melting • Total Clearing • Application

  20. Total Clearing Time Curve Minimum Melting Time Curve

  21. Current Limiting Fuse(CLF) • Limits the peak current of short-circuit • Reduces magnetic stresses (mechanical damage) • Reduces thermal energy

  22. 100,000 Let-Through Chart 15% PF (X/R = 6.6) 230,000 300 A 100 A 12,500 Peak Let-Through Amperes 60 A 5,200 Symmetrical RMS Amperes

  23. Fuse Generally: • CLF is a better short-circuit protection • Non-CLF (expulsion fuse) is a better Overload protection

  24. Typically: Non-CLF: 140% of full load CLF: 150% of full load Selectivity Criteria

  25. Thermal-Magnetic Magnetic Only Integrally Fused Current Limiting High Interrupting Capacity Types Frame Size Trip Rating Interrupting Capability Voltage Molder Case CB

  26. Thermal Maximum Thermal Minimum Magnetic (instantaneous)

  27. LVPCB • Voltage and Frequency Ratings • Continuous Current / Frame Size • Override (12 times cont. current) • Interrupting Rating • Short-Time Rating (30 cycle) • Fairly Simple to Coordinate

  28. LT PU CB 2 CB 1 CB 2 LT Band ST PU CB 1 480 kV IT If =30 kA ST Band

  29. Motor Protection • Motor Starting Curve • Thermal Protection • Locked Rotor Protection • Fault Protection

  30. Motor Overload Protection (NEC Art 430-32) • Thermal O/L (Device 49) • Motors with SF not less than 1.15 • 125% of FLA • Motors with temp. rise not over 40 • 125% of FLA • All other motors • 115% of FLA

  31. Locked Rotor Protection • Thermal Locked Rotor (Device 51) • Starting Time (TS < TLR) • LRA • LRA sym • LRA asym (1.5-1.6 x LRA sym) + 10% margin

  32. Fault Protection (NEC Art 430-52) • Non-Time Delay Fuses • 300% of FLA • Dual Element (Time-Delay Fuses) • 175% of FLA • Instantaneous Trip Breaker • 800% of FLA* • Inverse Time Breakers • 250% of FLA *MCPs can be set higher

  33. (49) I2T tLR O/L MCP (51) ts 200 HP Starting Curve MCP (50) LRAs LRAasym

  34. Overcurrent Relay • Time-Delay (51 – I>) • Short-Time Instantaneous ( I>>) • Instantaneous (50 – I>>>) • Electromagnetic (induction Disc) • Solid State (Multi Function / Multi Level) • Application

  35. IL CT IR 51 Time-Overcurrent Unit • Ampere Tap Calculation • Ampere Pickup (P.U.) = CT Ratio x A.T. Setting • Relay Current (IR) = Actual Line Current (IL) / CT Ratio • Multiples of A.T. = IR/A.T. Setting = IL/(CT Ratio x A.T. Setting)

  36. IL CT IR 50 Instantaneous Unit • Instantaneous Calculation • Ampere Pickup (P.U.) = CT Ratio x IT Setting • Relay Current (IR) = Actual Line Current (IL) / CT Ratio • Multiples of IT = IR/IT Setting = IL/(CT Ratio x IT Setting)

  37. Relay Coordination • Time margins should be maintained between T/C curves • Adjustment should be made for CB opening time • Shorter time intervals may be used for solid state relays • Upstream relay should have the same inverse T/C characteristic as the downstream relay (CO-8 to CO-8) or be less inverse (CO-8 upstream to CO-6 downstream) • Extremely inverse relays coordinates very well with CLFs

  38. Fixed Points Points or curves which do not change regardless of protective device settings: • Motor starting curves • Transformer damage curves & inrush points • Cable damage curves • SC maximum fault points • Cable ampacities

  39. 4.16 kV Relay: IFC 53 CT 800:5 50/51 CB Cable CU - EPR 1-3/C 500 kcmil Isc = 30,000 A 5 MVA DS 6 % Situation Calculate Relay Setting (Tap, Inst. Tap & Time Dial) For This System

  40. Transformer: IL IR Set Relay: CT R Solution

  41. What is ANSI Shift Curve? Question

  42. Answer • For delta-delta connected transformers, with line-to-line faults on the secondary side, the curve must be reduced to 87% (shift to the left by a factor of 0.87) • For delta-wye connection, with single line-to-ground faults on the secondary side, the curve values must be reduced to 58% (shift to the left by a factor of 0.58)

  43. What is meant by Frequent andInfrequent for transformers? Question

  44. Answer

  45. Question What T/C Coordination interval should be maintained between relays?

  46. A B t CB Opening Time + Induction Disc Overtravel (0.1 sec) + Safety margin (0.2 sec w/o Inst. & 0.1 sec w/ Inst.) I Answer

More Related