201.32 Non-Class 480 Flashcards
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Functions of 480V Non-Class 1E Electrical Dist. System
Provides reliable AC power to balance of plant 480V loads
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Functions of a Load Center (LC).
Electrical distribution supply points for motors >= 100 HP, static loads >= 100 KW, and Motor Control Centers (MCC)
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What is a double-ended Load Center?
Two separate transformers ,supply two separate buses, which can be connected with a cross-tie breaker. Each end normally supplied from separate Aux buses.
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Interlock for Double-ended LCs
To prevent inadvertent paralleling of buses that could be powered from different offsite AC sources, only two of the three breakers (2 feeder, 1 X-tie) can be closed at a time.
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What is a single ended load center?
One transformer feeds the LC.
(1N, 1P, 1R, 1S, 1T, 12L, and 1W)
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Function of Motor Control Center
Power distribution point for motors of less than 100 HP and static loads 100 KW or less.
Exception is IA Compressor 14(24). 200 HP powered from 1(2)G5. Has soft start to limit current.
Magnetic trip elements and thermal overloads
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Which Non-Class MCCs are fed from Class-1E MCCs?
1A5, 1B5, 1C5.
NOT safety-related, but supply safety-related support systems.They are shed during emergencies by the sequencer.
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Function of 208/120 VAC Distribution Panels (DPs)
Located at MCC’s as well as throughout the plant Typical Loads: Space heaters, AFW sample pump, Cold Chem Lab toilet exhaust fan
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Selective Tripping
Isolate branch circuit breaker closest to fault first.
Load supply breaker should trip first protecting MCC. If it fails to trip, then MCC feeder breaker would be next to trip
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How are 480 V LC transformers cooled?
Forced air from fans. Inside transformers are dry, outside are oil filled.
Local amber light when fan is running
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What are the MCCs that are diesel backed and where are they located?
1G5 - SE TGB 29’ (actually 31’)
12K3 - south yard, next to LTG Diesel Bldg
1G8 - EAB penthouse 83’
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Which LC is diesel backed and where is it located?
LC 1W - EAB penthouse 83’
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Normal and Emergency power for MCC 1G5
LC 1U
BOP Diesel
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Normal and Emergency power for MCC 1G8
LC 1W
TSC Diesel
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Normal and Emergency power for 12K3
LC 12L
LTG Diesel
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BOP Diesel Generator Electrical Ratings
700 KW
480 V
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LTG Diesel Generator Electrical Ratings
700 KW
480 V
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TSC Diesel Generator Electrical Ratings
1200 KW
4160 V
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Automatic start for BOP diesel
UV on MCC 1G5, will start and load w/in 15 secs (unless feeder tripped on over current to prevent energizing a faulted bus)
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Automatic start for LTG Diesel
UV on MCC 12K3, will start and load w/in 15 secs (unless feeder tripped on over current to prevent energizing a faulted bus)
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Automatic start on TSC Diesel
UV on LC 1W , will start and load w/in 15 secs (unless feeder tripped on over current to prevent energizing a faulted bus)
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Source of control power for LCs
125 VDC control power
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Source of control power for MCCs
Small transfomer downstream of each load breaker inside cubicle provides 125 VAC control power
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Causes for “480V LC Trouble”
CP010
Bus Ground Fault (except 12H)
Bus Undervoltage
Feeder breaker status (breaker alignment abnormal)
Transformer high temperature
