13.8kv Flashcards
13.8kV
State the function of the 13.8kV Distribution System
Supply power to various non-vital 13.8 kV station auxiliaries
Draw and label a simplified diagram of the 13.8 kV distribution system showing power sources, transformers and interconnecting breakers
State the physical location of the UAT/RAT transformers and 13.8 kV buses
• UATs located in the transformer yard, north of Turbine Building , next to GSUs • RATs located in the transformer yard, north of the Turbine Building, facing the 345 kV switchyard • 13.8 kV buses located in the Non-essential switchgear (Turbine Building west wall & Control Building north wall)
Describe the flowpath of electrical power to the 13.8 kV system with the unit operating and shutdown
• Operating flowpath: – 13.8 kV buses are supplied by the main generator via the UATs. – 25 kV stepped down to 13.8 kV – RATs receive 345 kV power directly from 345 kV Bus 5 and stepped down to 13.8 kV • Shutdown flowpath: – power is supplied by offsite 345 kV bus, and stepped down to 13.8 at the UAT • RATs from 345 kV bus 5 stepped down to 13.8 kV
State the high and low side voltages for UATs and RATs
The Unit Auxiliary Transformer (UAT) High side voltage is 25 kV Low side voltage is 13.8 kV and 4.16 kV • The Reserve Auxiliary Transformer (RAT) High side voltage is 345 kV Low side voltage is 13.8 kV and 4.16 kV
Compare the cooling system construction for the UATs and RATs (including heat transfer fluids, mechanical equipment and controls
UAT Powered from 480 V ABT (MCC131-preferred/261-standby) Tripped by 86 UP/UB Oil in tank is circulated through an oil to air heat exchanger 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 & Pumps on @ 70° C • RAT 12 fans with 2 sets of 4 radiators in parallel Auto on @ 70 °C (158° F) / Off 65 °C All fans run in manual ON Powered from 480 V stepped down to 230 V ABT (MCC131/261) Normal power seeking Auxiliaries tripped by 86 RP/RB
Describe the transformer gas control for UATs and RATs
UAT • 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 RAT • “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 operation of the transformer fire protection system
• 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
Identify Power Supplies for 13.8 kV motor loads
• Bus 1: RCP’s: A/B, CWP’s: A/C, US:11-17 • Bus 2: RCP’s: C/D, CWP: B, US 21-28
Describe how an electrical fault within a UAT will affect the station electrical distribution alignment
Trips turbine, exciter field breaker, generator breaker, all 13.8 kV and 4.16kV incoming supply breakers, affected UAT cooling fans and 345 kV breakers, and actuates failure circuits Auto transfers to RAT’s if conditions are met
Describe how an electrical fault within a RAT will affect the station electrical distribution alignment
Trips: 13.8 kV incoming supply line breakers, 4160 incoming supply breakers, rats colling fans, 345kV SWYD breakers and actuates failure circuits
Describe the meaning of the indicating lights associated with the UAT and RAT incoming supply breakers
MCB: green -> open, Red -> closed, Amber -> open with switch in NAC
Local: green -> open, Red -> closed, White -> ready for auto close, White above 86 relay -> no 86 lockout active
