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(manual operated) (reclosing relay)
"" (OCB) (CT) (PT)
Overcurrent
Overcurrent relay fault Breaker fault fault fault
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fault fault fault impedance (source) fault fault
fault
fault breaker setting B fault F2 fault F1 F2 B F1 F2 fault level source : 2:1 fault fault fault level
fault fault level fault fault level ( source) fault level
Note: definite time/independent time (thermal rating)
fault Inverse Definite Time Characteristic (IDMT)
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Plug Setting Multiplier (PSM) Time Multiplier Setting (TMS) (time multiplier setting) TMS 7 CT CT % secondary CT CT 5 A secondary 50-200% setting 2.5-10 A CT secondar, 10-40% 0.5-2 A CT primary norminal full load % setting norminal full load 400 A CT ratio 500/5 50-200% 5A 100% full load 125% full load log/log x y PSM ( error ) : CT ratio 500/5 resetting range 50-200% (2.5-10A) primary current 5000 A curve standard inverse 100% 5A secondary CT = 5000/500 x5 = 50A 50A 10 setting Plug setting multiplier PSM = 50/5 = 10 curve standard inverse 10 3 ( TMS unity) primary 2500A (25A secondary) 50% 2.5A PMS 10 ( 25/2.5) 3 (TMS=1)
load CT ratio () overload relay Resetting time Reseting time ( setting 90% 95% setting TMS 0.1-1.0 contact 10 PSM TMS trip
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3 10 PMS TMS=1, TMS=0.5 setting 1.5 , TMS=1 0.3 , 10 x PSM PSM curve microprocessor based TMS TMS
operating time (grading intervals or Margin) a) () b) Overshoot c) d) circuit breaker Circuit Breaker breaker 1000 volt 1. Molded case circuit breaker (MCCB) breaker mold 2 phenolic breaker 2 - breaker trip ON OFF reset OFF ON quick make , quick break breaker
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molded case circuit breaker 2 Thermal magnetic CB. Solid state trip CB. Thermal magnetic molded case circuit breakerbreaker 2 Thermal unit bimetal ( 2 ) bimetal CB. trip bimetal
Magnetic unit 8-10 breaker
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Solid state trip or Electronic trip molded case circuit breaker breaker diagram CT breaker CT microprocessor tripping coil soliniod coil CB.
breaker , amp meter & fault indicator fault name plate , , 3 ampere trip , ampere frame interrupting capacity arcing chamber arc chute (contact) (contact) fixed contact movable contact bimetal
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