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SBK NLO N8021I - 13.8 kV Distribution System
Terms in this set (13)
The function of the 13.8 kV distribution system is to provide 13.8 kV electrical power to the 13.8 kV auxiliary equipment within Seabrook Station.
STATE the function of the 13.8 kV Distribution System.
Review slide 28 and be able to draw it.
DRAW and LABEL a simplified diagram of the 13.8 kV distribution system showing the power sources, transformers, and interconnecting breakers.
UATs and Rats are located north of the turbine building between the GSUs and the switchyard.
13.8 kV buses are located in the non-essential switchgear.
STATE the physical location of the following components:
13.8 kV Buses
Review drawings on slides 29 - 31.
Normally the 13.8 kV buses are powered by the UATs while at 100% power or at 0% power (when at 0% power the main generator breaker is opened and power is back fed through the GSUs to the UATs). UAT 2A feeds bus 1 and UAT 2B feeds bus 2.
If there is an issue with the GSUs, UATs, or switchyard Bus 6 then the 13.8 kV busses will be powered by the RATs. The system would also be aligned this way for maintenance on the GSUs, UATs, or switchyard bus 6.
DESCRIBE the flowpath of electrical power to the 13.8 kV system with the unit in the following conditions:
High side voltage is 25 kV
Low side voltage is 13.8 kV and 4.16 kV
High side voltage is 345 kV
Low side voltage is 13.8 kV and 4.16 kV
STATE the high side and low side voltages for the following:
Oil in tank is circulated through an oil to air heat exchangers via pump to cool the transformer.
2 sets of 8 oil-to-air heat exchangers (radiators)
2 fans circulate air across each set of heat exchangers.
16 total radiators
4 total fans
Fans & Pump on @ 65° C
12 fans with 2 sets of 4 radiators in parallel
Auto on @ 70 °C (158° F) / Off < 70 °C
All fans run in manual ON
Powered from 480 V stepped down to 230 V ABT (MCC-131/261)
Auxiliaries tripped by 86 RP/RB
COMPARE the cooling system construction for the following: (include a description of the heat transfer fluids, mechanical equipment, and control features.)
Accommodates seasonal & operational changes in temperature/gas space pressure - 1.15 inches per 10 °C (50 °F) change in temperature
If pressure in tank increases to 7.5 psig the bleeder valve operates to relieve pressure
If a vacuum (5 psig) is created, the valve will open to allow air into the tank. The dielectric oil will absorb the air
11.5 psig relief valve at the top of the tank. Reseats at 8 psig
The UAT also has has sudden pressure relays that will isolate the transformers if a pressure rise is sensed as caused by an internal fault.
"Inertaire" oil preservation system supplied by 2000 psig nitrogen cylinder maintains 0.5 psig overpressure
A relief valve installed downstream of the regulator relieves pressure greater that 6.5 psig
Secondary relief in 3rd stage of regulator > 8 psig
High press blowout port on regulator
A 10 psig relief valve located in the top of tank is in case of excessive heat near the nitrogen cylinder
DESCRIBE the transformer gas control system for the following:
Oil will burn when heated to 300 °F
Dry pipe, open head sprinkler system
7 zones total - one per transformer with each zone having an auto/manual deluge valve in TB
A dual wire type detector (2 wires separated by foam) surrounds each transformer
A high temperature of 190 °F melts foam allowing 2 wires to short which will activate the detection circuit, operating the associated deluge valve
DESCRIBE the operation of the UAT/RAT transformer fire protection system.
13.8 kV Bus 1
UAT 2A(norm) / RAT 3A(alt)
Reactor Coolant Pumps 1A/B
Circulating Water Pumps 39A/C
480V Unit Substations 11-17
13.8 kV Bus 2
UAT 2B (norm) / RAT 3B (alt)
Reactor Coolant Pumps 1C/D
Circulating Water Pump 39B
480V Unit Substations 21-28
Given a list of the 13.8 kV motor loads, IDENTIFY their correct bus power supply system.
86UP/86UB protective actions (trips)
Opens Main Generator breaker
Open exciter field breaker
Isolate 13.8 & 4.16 kV Buses 1-6 (UAT supply)
Isolates 345 kV Bus 6 (PCB 11 & 12)
Isolates UAT cooling auxiliaries
(This should result in a fast transfer to the RAT on 13.8 kV buses 1 and 2)
DESCRIBE how an electrical fault within a UAT will affect the station electrical distribution alignment.
Opens all 13.8 kV and 4.16 kV bus RAT supply breakers
Opens 345 kV PCBs 695 and 52 (Bus 5)
Isolates affected RAT cooling fans
DESCRIBE how an electrical fault within a RAT will affect the station electrical distribution system alignment.
Red - Breaker Closed
Green - Breaker Open
Amber - Breaker disagreement (control switch in a position other than actual breaker position)
White Light on RAT supply breakers indicate that they are ready for auto closure.
White light on the 86 relays indicate that the relay is reset and that the coil is good.
DESCRIBE the meaning of each of the indicating lights associated with the MCB and local control switches for the 13.8 KV UAT and RAT incoming supply breakers.
Review slide 84. The actual prints are 1-NHY-310101 Sheets A01b, A01c, and A01d (Bus 1) and A16b, A16c, and A16d (Bus 2).
Review slide 102. The actual prints are 1-NHY-310101 Sheets A02b and A02c (Bus 1) and A17b and A17c (Bus 2).
Given a schematic for a 13.8 KV UAT/RAT incoming supply breaker, TRACE the path of control power necessary to open or shut the breaker.
THIS SET IS OFTEN IN FOLDERS WITH...
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SBK NLO N1900I - Seabrook Systems Overview
SBK NLO N8011 - 345 kV Distribution System
SBK NLO N8015I - 480 VAC Distribution System
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