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5010566.ppt

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Nafir Anas

The document discusses power system protection and protective device coordination. It defines overcurrent coordination as the systematic study of current responsive devices in an electrical power system to determine ratings and settings to isolate faults and overloads. The objective is to open only protective devices upstream of the fault or overload. Analysis is needed for new or expanded electrical systems. Protective device coordination requires compromises between protection, speed, reliability and economics.

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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. To isolate the fault or overloads.
Criteria Economics Available Measures of Fault Operating Practices Previous Experience
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
Analysis When: New electrical systems Plant electrical system expansion/retrofits Coordination failure in an existing plant
Protection vs. Coordination Coordination is not an exact science Compromise between protection and coordination Reliability Speed Performance Economics Simplicity
Protection Prevent injury to personnel Minimize damage to components Quickly isolate the affected portion of the system Minimize the magnitude of available short-circuit
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
Coordination Limit the extend and duration of service interruption Selective fault isolation Provide alternate circuits
Coordination t I C B A C D D B A
Equipment Motor Transformer Generator Cable Busway
Capability / Damage Curves t I I2 2 t Gen I2 t Motor Xfmr I2 t Cable I2 t
Transformer Category ANSI/IEEE C-57.109 Minimum nameplate (kVA) Category Single-phase Three-phase I 5-500 15-500 II 501-1667 501-5000 III 1668-10,000 5001-30,000 IV above 1000 above 30,000
Infrequent Fault Incidence Zones for Category II & III Transformers * Should be selected by reference to the frequent-fault-incidence protection curve or for transformers serving industrial, commercial and institutional power systems with secondary-side conductors enclosed in conduit, bus duct, etc., the feeder protective device may be selected by reference to the infrequent-fault-incidence protection curve. Source: IEEE C57 Source Transformer primary-side protective device (fuses, relayed circuit breakers, etc.) may be selected by reference to the infrequent-fault- incidence protection curve Category II or III Transformer Fault will be cleared by transformer primary-side protective device Optional main secondary side protective device. May be selected by reference to the infrequent-fault- incidence protection curve Feeder protective device Fault will be cleared by transformer primary-side protective device or by optional main secondary- side protection device Fault will be cleared by feeder protective device Infrequent-Fault Incidence Zone* Feeders Frequent-Fault Incidence Zone*
Transformer t (sec) I (pu) Thermal 200 2.5 I 2 t = 1250 2 25 Isc Mechanical K=(1/Z) 2 t (D-D LL) 0.87 (D-R LG) 0.58 Frequent Fault Infrequent Fault Inrush FLA
5010566.ppt
Transformer Protection MAXIMUM RATING OR SETTING FOR OVERCURRENT DEVICE PRIMARY SECONDARY Over 600 Volts Over 600 Volts 600 Volts or Below Transformer Rated Impedance Circuit Breaker Setting Fuse Rating Circuit Breaker Setting Fuse Rating Circuit Breaker Setting or Fuse Rating Not more than 6% 600 % 300 % 300 % 250% 125% (250% supervised) More than 6% and not more than 10% 400 % 300 % 250% 225% 125% (250% supervised) Table 450-3(a) source: NEC
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
Fuse Non Adjustable Device Continuous and Interrupting Rating Voltage Levels Characteristic Curves Min. Melting Total Clearing Application
Minimum Melting Time Curve Total Clearing Time Curve
Current Limiting Fuse (CLF) Limits the peak current of short-circuit Reduces magnetic stresses (mechanical damage) Reduces thermal energy
5010566.ppt
Symmetrical RMS Amperes Peak Let-Through Amperes 100 A 60 A 15% PF (X/R = 6.6) 12,500 5,200 230,000 300 A 100,000 Let-Through Chart
Fuse Generally: CLF is a better short-circuit protection Non-CLF (expulsion fuse) is a better Overload protection
Selectivity Criteria Typically: Non-CLF: 140% of full load CLF: 150% of full load
Molder Case CB Thermal-Magnetic Magnetic Only Integrally Fused Current Limiting High Interrupting Capacity Types Frame Size Trip Rating Interrupting Capability Voltage
Thermal Minimum Thermal Maximum Magnetic (instantaneous)
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
480 kV CB 2 CB 1 CB 2 CB 1 IT ST PU ST Band LT PU LT Band If =30 kA
Motor Protection Motor Starting Curve Thermal Protection Locked Rotor Protection Fault Protection
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
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
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
200 HP MCP O/L Starting Curve I 2 T (49) MCP (50) (51) ts tLR LRAs LRAasym
Overcurrent Relay Time-Delay (51 I>) Short-Time Instantaneous ( I>>) Instantaneous (50 I>>>) Electromagnetic (induction Disc) Solid State (Multi Function / Multi Level) Application
5010566.ppt
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) IL IR CT 51
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) IL IR CT 50
41 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
Fixed Points Motor starting curves Transformer damage curves & inrush points Cable damage curves SC maximum fault points Cable ampacities Points or curves which do not change regardless of protective device settings:
Situation Calculate Relay Setting (Tap, Inst. Tap & Time Dial) For This System 4.16 kV DS 5 MVA Cable 1-3/C 500 kcmil CU - EPR CB Isc = 30,000 A 6 % 50/51 Relay: IFC 53 CT 800:5
Solution A Inrsuh 328 , 8 694 12 I A 338 . 4 800 5 I I L R Transformer: A kV kVA L 694 16 . 4 3 000 , 5 I IL CT R IR Set Relay: A 55 1 . 52 800 5 328 , 8 ) 50 ( 1 ) 38 . 1 (6/4.338 0 . 6 4 . 5 338 . 4 % 125 緒 A Inst TD A TAP A
Question What is ANSI Shift Curve?
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)
Question What is meant by Frequent and Infrequent for transformers?
Answer Infrequent Fault Incidence Zones for Category II & III Transformers Source Transformer primary-side protective device (fuses, relayed circuit breakers, etc.) May be selected by reference to the infrequent-fault- incidence protection curve Category II or III Transformer Fault will be cleared by transformer primary-side protective device Optional main secondary side protective device. May be selected by reference to the infrequent-fault- incidence protection curve Feeder protective device Fault will be cleared by transformer primary-side protective device or by optional main secondary- side protection device Fault will be cleared by feeder protective device Infrequent-Fault Incidence Zone* Feeders Frequent-Fault Incidence Zone*
Question What T/C Coordination interval should be maintained between relays?
Answer A t I B CB Opening Time + Induction Disc Overtravel (0.1 sec) + Safety margin (0.2 sec w/o Inst. & 0.1 sec w/ Inst.)
Question What is Class 10 and Class 20 Thermal OLR curves?
Answer Class 10 for fast trip, 10 seconds or less Class 20 for, 20 seconds or less There is also a Class 30 for long trip time
Answer

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5010566.ppt

  • 1. Power System Protection Dr. Ibrahim El-Amin
  • 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
  • 13. Equipment Motor Transformer Generator Cable Busway
  • 14. Capability / Damage Curves t I I2 2 t Gen I2 t Motor Xfmr I2 t Cable I2 t
  • 15. Transformer Category ANSI/IEEE C-57.109 Minimum nameplate (kVA) Category Single-phase Three-phase I 5-500 15-500 II 501-1667 501-5000 III 1668-10,000 5001-30,000 IV above 1000 above 30,000
  • 16. Infrequent Fault Incidence Zones for Category II & III Transformers * Should be selected by reference to the frequent-fault-incidence protection curve or for transformers serving industrial, commercial and institutional power systems with secondary-side conductors enclosed in conduit, bus duct, etc., the feeder protective device may be selected by reference to the infrequent-fault-incidence protection curve. Source: IEEE C57 Source Transformer primary-side protective device (fuses, relayed circuit breakers, etc.) may be selected by reference to the infrequent-fault- incidence protection curve Category II or III Transformer Fault will be cleared by transformer primary-side protective device Optional main secondary side protective device. May be selected by reference to the infrequent-fault- incidence protection curve Feeder protective device Fault will be cleared by transformer primary-side protective device or by optional main secondary- side protection device Fault will be cleared by feeder protective device Infrequent-Fault Incidence Zone* Feeders Frequent-Fault Incidence Zone*
  • 17. Transformer t (sec) I (pu) Thermal 200 2.5 I 2 t = 1250 2 25 Isc Mechanical K=(1/Z) 2 t (D-D LL) 0.87 (D-R LG) 0.58 Frequent Fault Infrequent Fault Inrush FLA
  • 19. Transformer Protection MAXIMUM RATING OR SETTING FOR OVERCURRENT DEVICE PRIMARY SECONDARY Over 600 Volts Over 600 Volts 600 Volts or Below Transformer Rated Impedance Circuit Breaker Setting Fuse Rating Circuit Breaker Setting Fuse Rating Circuit Breaker Setting or Fuse Rating Not more than 6% 600 % 300 % 300 % 250% 125% (250% supervised) More than 6% and not more than 10% 400 % 300 % 250% 225% 125% (250% supervised) Table 450-3(a) source: NEC
  • 20. 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
  • 21. Fuse Non Adjustable Device Continuous and Interrupting Rating Voltage Levels Characteristic Curves Min. Melting Total Clearing Application
  • 22. Minimum Melting Time Curve Total Clearing Time Curve
  • 23. Current Limiting Fuse (CLF) Limits the peak current of short-circuit Reduces magnetic stresses (mechanical damage) Reduces thermal energy
  • 25. Symmetrical RMS Amperes Peak Let-Through Amperes 100 A 60 A 15% PF (X/R = 6.6) 12,500 5,200 230,000 300 A 100,000 Let-Through Chart
  • 26. Fuse Generally: CLF is a better short-circuit protection Non-CLF (expulsion fuse) is a better Overload protection
  • 27. Selectivity Criteria Typically: Non-CLF: 140% of full load CLF: 150% of full load
  • 28. Molder Case CB Thermal-Magnetic Magnetic Only Integrally Fused Current Limiting High Interrupting Capacity Types Frame Size Trip Rating Interrupting Capability Voltage
  • 30. 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
  • 31. 480 kV CB 2 CB 1 CB 2 CB 1 IT ST PU ST Band LT PU LT Band If =30 kA
  • 32. Motor Protection Motor Starting Curve Thermal Protection Locked Rotor Protection Fault Protection
  • 33. 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
  • 34. 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
  • 35. 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
  • 36. 200 HP MCP O/L Starting Curve I 2 T (49) MCP (50) (51) ts tLR LRAs LRAasym
  • 37. Overcurrent Relay Time-Delay (51 I>) Short-Time Instantaneous ( I>>) Instantaneous (50 I>>>) Electromagnetic (induction Disc) Solid State (Multi Function / Multi Level) Application
  • 39. 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) IL IR CT 51
  • 40. 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) IL IR CT 50
  • 41. 41 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
  • 42. Fixed Points Motor starting curves Transformer damage curves & inrush points Cable damage curves SC maximum fault points Cable ampacities Points or curves which do not change regardless of protective device settings:
  • 43. Situation Calculate Relay Setting (Tap, Inst. Tap & Time Dial) For This System 4.16 kV DS 5 MVA Cable 1-3/C 500 kcmil CU - EPR CB Isc = 30,000 A 6 % 50/51 Relay: IFC 53 CT 800:5
  • 44. Solution A Inrsuh 328 , 8 694 12 I A 338 . 4 800 5 I I L R Transformer: A kV kVA L 694 16 . 4 3 000 , 5 I IL CT R IR Set Relay: A 55 1 . 52 800 5 328 , 8 ) 50 ( 1 ) 38 . 1 (6/4.338 0 . 6 4 . 5 338 . 4 % 125 緒 A Inst TD A TAP A
  • 45. Question What is ANSI Shift Curve?
  • 46. 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)
  • 47. Question What is meant by Frequent and Infrequent for transformers?
  • 48. Answer Infrequent Fault Incidence Zones for Category II & III Transformers Source Transformer primary-side protective device (fuses, relayed circuit breakers, etc.) May be selected by reference to the infrequent-fault- incidence protection curve Category II or III Transformer Fault will be cleared by transformer primary-side protective device Optional main secondary side protective device. May be selected by reference to the infrequent-fault- incidence protection curve Feeder protective device Fault will be cleared by transformer primary-side protective device or by optional main secondary- side protection device Fault will be cleared by feeder protective device Infrequent-Fault Incidence Zone* Feeders Frequent-Fault Incidence Zone*
  • 49. Question What T/C Coordination interval should be maintained between relays?
  • 50. Answer A t I B CB Opening Time + Induction Disc Overtravel (0.1 sec) + Safety margin (0.2 sec w/o Inst. & 0.1 sec w/ Inst.)
  • 51. Question What is Class 10 and Class 20 Thermal OLR curves?
  • 52. Answer Class 10 for fast trip, 10 seconds or less Class 20 for, 20 seconds or less There is also a Class 30 for long trip time