Systems Exam 1 - DC Electrical Distribution Flashcards
How are parallel operations of BCs prevented?
Mechanical interlock on DC bus end prevents aligning oncoming and off-going BCs.
What is the only trip for DC BKRs?
Overcurrent
High discharge rate on the batteries can occur if…
…the battery charger loses power, usually from a loss of the bus.
uD1 Major Loads (24/48 VDC)
“uD1, Turbine Fun”
→EHC Controller
→Extended Turbine Protection Cabinet
(Also includes auto turbine tester cabinet, TSE, seal steam controller, vibration monitoring, electrical generator protection cabinet, hydraulic control equipment rack)
uD2 Major Loads (125/250 VDC)
“uD2 does its duty (emergency pumps)”
→Main Turbine Emergency LO Pump (250VDC)
→MFP Emergency LO Pumps (250VDC)
→Main Generator Emergency Seal Oil Pump (250VDC)
→uD2-1, uD2-2, uD2-3
→XD2-1 (U1 preferred source), XD2-2 (U1 preferred source), XD2-3 (U1 preferred source)
uD3 Major Loads (125 VDC)
“uD3, RCP”
→Plant Computer through IV uC5, IV uC6
→DC Control power to RCP breakers via uD3-1 (RCP breakers provide primary overcurrent protection for Containment Penetration with Normal and Alternate feeder breakers on the associated bus acting as secondary overcurrent protection)
→MFP Digital Controls
→Condensate Polishing Digital Controls
DC Bus Operability
For a DC Bus to be considered operable it must have the following:
→Operable battery charger connected to the bus (each bus has installed spared)
→Operable battery connected to the bus
→Maximum of 2 inverters per DC Bus
→Batteries are rated for 4 hours at full load
125 VDC Control Room Emergency Lighting
1200 amp-hour rating
150 amps for 8 hours
List the MCC feeds for the following BCs:
-uD1
-uD2
-uD3
-uD4
→uD1 = MCC uB1-3, supplies positive bus
→uD2 = MCC uB2-3, supplies negative bus
→uD3 = MCC uB2-1, supplies positive bus
→uD4 = MCC uB4-1, supplies negative bus
Why are the 125 VDC Safeguards Batteries located in separate rooms?
To limit potential H2 ignition.
Effects of Loss of Train “A” 125 VDC:
NOTE: Effects are similar for Loss of Train “B”.
→Train A Rx Trip and Bypass Breaker shunt trips not available/ UV available
→Feedwater valves fail closed
→Train A EDG will not start and cannot flash field/ can’t stop from CR if running
→Steam Dumps fail closed
→TDAFWP speed indication lost
→PZR Aux Spray fails closed
→PORV 455A fails closed
→VCT Level control lost
→Letdown isolates
→SGBD and Sample valves close
→TDAFWP Train Steam Supply fails open
→Train A MDAFWP flow control and recirc valves fail open
→Loss of control power to Train A 6.9kV and 480 LC breakers
What does the float charge do?
What does the equalize charge do?
→Float: maintains battery at capacity
→Equalize: equalizes voltage across all cells in battery
Battery Operability
→For a battery to be considered operable then its Float Voltage must be between 128 VDC and 140 VDC.
→Placing a charger in Equalize does not inop the battery if its float voltage was within spec initially and the equalize voltage does not exceed the upper limit
What is the thumb rule for which side of a circuit contains a ground.
“Dimmer is grimmer.”
The side with the dimmer light contains the ground.
Which battery chargers can be supplied by outage power?
→BCuED1-2
→BCuED2-2
→BCuED3-1
→BCuED4-1
→BCuD4
(Plant Support AC, a.k.a. outage power, can’t be used in Modes 1-4 because Safeguards equipment on outage power is NOT considered OPERABLE.)
What color is the Equalize light on the battery chargers?
The float light?
The alarm lights?
→amber
→green
→red
What do the DC buses do for the EDG controls?
What happens if we lose the DC buses?
→field flash
→the diesel won’t start on either normal or emergency start signals
→if diesel already running, it could no longer be remotely shutdown from CR
What can inverter IVuEC1/3 supply?
Panels:
→uPC1
→uPC3
→uEC1
→uEC5
What can inverter IVuEC2/4 supply?
Panels:
→uPC2
→uPC4
→uEC2
→uEC6
What is important to know about these keyed mechanical interlocks?
The key can’t be removed until the mechanical bar is in the upward blocking position.
Ensure an operable battery charger is aligned to panel uD2 during EOP-2.0 to….
…prevent the MSIVs from re-opening
→a steam leak in the MSIV room(s) could cause the hydraulic dump solenoid valves to fail closed
→as a result, if the oil pump were to supply oil to the MSIV in those conditions, the valve would open
