Non Class 480 Load Centers& MCC (NG/NH) Flashcards
What’re load centers for ?
Transforms 13.8kv(NA) power to 480VAC powering:
Non class loads >50HP
480VAC MCC <50HP
Describe flow path of 480VAC(NG)(NH)
From13.8(NA)
Transformed to 480vac
Distributed to >50HP load
Also distributed to MCC(NH) for <50HP loads
MCC steps down 480VAC->120VAC for distribution panel
What is the disconnect switch inside load center cubicle for ?
To be able to isolate power from NA system, without losing power to the other load centers
What components inside the load center interface with Kirk key interlock ?
The disconnect switch & the B2 main feeder breaker
What is the Kirk Key interlock for ?
Safety feature to prevent disconnect switch from being opened under load
How does Kirk Key Interlock work ?
Requires B2 break to be TRIPPED open to allow you access to a key. The key allows you to operate the disconnect switch
Major operating steps to operate Kirk key interlock ?
.Open B2 Breaker
.press breakers trip button and pull o it locking hasp
.press plunger below key lock
.turn key and remove it
.insert key below disconnect and turn
.rotate disconnect switch handle down 180 degrees
What voltages does load center transformer to?
13.8KV —>480KV
What’re the load center transformers cooled with ?
Natural circulation of air from vents on the cubicle
What’re the load center transformers located by cooling towers cooled by ?
Cooled from natural circ. Through cooling fins
What happens on a over current trip on ?
It will trip 13.8kv supply breakers on NAN-S01/S02 and the 480Main Feeder breaker
What’re circuit breakers meant for ?
To break circuit on a fault isolating equipment from power source
What’re Motor Feeder Breakers for ?
They’re equipped with longtime/instantaneous overcurrent for tripping & must be reset locally after trip
What is the control power for loadcenters ?
125DC (NK)
When are the closing springs charged on 480Load Center ?
Closing springs recharge upon OPENING of breaker
What does RED light mean on breaker ?
Breakers closed and trip circuit has continuity
What does GREEN light mean on breaker ?
Breaker is open (If light shines brighter there is a fault)
What does the blue light mean on the Cooling tower Load Centers breakers ?
Will trip due to high vibration of the fan
What control power do MCC’s use ?
It uses its own power for control power; it sends its 480VAC power through transformer that steps it down to 120VAC for control power
What happens to MCC control power if 480VAC to the MCC is lost ?
The MCC will lose control power because it will be unable to supply itself
How does NH system interface with class 480VAC load centers (PG) system
PG system supplies power to non class SIAS load shed MCCs:
NHN-M19
NHN-M20
NHN-M71
NHN-M72
What indication will Control Room get on a Load Center fault?
Control room will receive a trouble alarm
