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Systems > 25 kV Electrical System > Flashcards

25 kV Electrical System Flashcards

1
Q

Why is the output of the Generator split into its 3 individual phases?

A

Output is relatively low so current is very high (30,000 amps)( high heat )

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2
Q

How is iso phase bus cooled? What are auto features of the cooling system?

A

Hollow conductor, air flow through middle and opposite direction on outside of conductor between guard pipe (cooled by SCW) Auto start of stby fan - loss running fan (in on position) - hi ISO phase bus temp 155 deg - other fan off and 25 kv energized - exc field bkr closed - one output bkr closed

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3
Q

What interlocks must be met to operate the MOD?

A
  • mn gen UV relay actuated - exciter field breaker open - both output breakers open - all aux xfr feeder breakers open - 25 kV ground switch open
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4
Q

What interlocks prevent energizing a grounded 25 kV system? (Can’t close ISO phase bus ground switch)

A
  • MOD must be fully open
  • exciter field breaker must be open (FCB)
  • aux xfr feeder breakers open
  • output breakers open (PCB)
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5
Q

What is the danger of manually isolating a sudden pressure relay on 25 kv XFMR? When should isophase bus blower be in service, other than normal ops (generator carrying load on grid)?

A
  • w/unit trip cutin……may result in Unit Trip (normal ops slow transient, catasrophic failure=> rapid press rise - if available isophase bus blower should be in service when back feeding from 500 kV
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6
Q

Describe U-1 Main XFMR (25->500 kv)

A
  • head tank - contains oil, maintains pressure inside xfmr, small amount air in air bladder
  • radiator - six systems, each has (1 pump, 1 hx, 4 fans), fans pull air through hx cooling oil, pump moves oil
  • oil - electrical insulator and cooling medium
  • gas detector - oil breaks down or winding insulation breaks down, creates H2

half of cooling systems start when xfmr energized, other half start on high oil temp

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7
Q

Describe U-2 main XFMR (25->500 kv)

A
  • head tank - contains oil, maintains pressure inside xfmr, small amount air in air bladder
  • radiator - 3 systems, each has (1 pump, 1 hx, 3 fans), fans pull air through hx cooling oil, pump moves oil
  • oil - electrical insulator and cooling medium
  • gas detector - oil breaks down or winding insulation breaks down, creates H2

sequential starting of cooling systems: (3 possible seq)

  • 1st group start when xfmr energized
  • 2nd group start on oil temp of 50 /65 hot spot
  • 3rd group start on oil temp of 70 /85 hot spot
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8
Q

Describe Aux XFMR 1-2 (25->4 kv)

A
  • XFM shell - kept at positive pressure N2
  • radiator - 2 systems, each has (2 hx, 6 fans), fans pull air through hx cooling oil, natural circ moves oil
  • oil - electrical insulator and cooling medium

half of cooling systems start hot spot therm 80

other half start hot spot therm 85

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9
Q

Describe Aux XFMR 1-1 (25->12 kv)

A
  • XFM shell - kept at positive pressure N2
  • radiator - 10hx, 16 fans pull air through hx cooling oil
  • oil - electrical insulator and cooling medium, circulated by natrual circ and pump
  • oil pump - starts when second group fans start

1st group cooling - 12 fans starts 80 ºC

2nd group cooling - 4 fans and pump 85 ºC

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10
Q

what are the protection relays for the following XFMR’s

Main XFMR (25->500 kv)

Aux XFMR 1-1 (25->12 kv)

Aux XFMR 1-2 (25->4 kv)

A

Main:

  • o.c. (open PCB’s)
  • over voltage open (open PCB’s)
  • line directional o.c. phase (open PCB’s)
  • line directional o.c. ground (open PCB’s)
  • line pilot wire diff (open PCB’s)
  • sudden pressure (unit trip)

1-1

  • o.c. (unit trip)
  • sudden pressure (unit trip)
  • diff (unit trip)

1-2

  • x-winding ground o.c. (alarm)
  • y-winding groud o.c. (alarm)
  • sudden pressure (unit trip)
  • diff (unit trip)
  • o.c. (unit trip)
  • lockout (unit trip)
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11
Q

The ground switch must be open to do what?

A

Close FCB
Close aux transformer feeder breakers
Close 500kv PCBs

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12
Q

The MOD must be fully open to close what?

A

The ground switch

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13
Q

What is the Sudden pressure relay and what will it cause?

A

A catastrophic fault will result in a rapid pressure rise

Causes a unit trip
-Trips turbine
-Opens 500kv
-opens FCB
-opens aux feeder breakers
-transfers to startup

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14
Q

What kind of windings are on the 25kv, 500kv

A

25kv are the primary windings (DELTA)
500kv are the secondary windings (WYE)

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15
Q

What is the hydran monitor monitoring and what is considered a bad value?

A

It is looking for gases that are formed due to oil breakdown and insulation breakdown

High numbers are bad

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16
Q

What are the p/s for the cooling groups on the Unit 1 MBTs? What happens if power is lost?

A

Group 1=11D
Group 2=11E

If power is lost to either bus, it will result in loss of half of the cooling capability, but not a complete loss.

17
Q

How are the Unit 1 MBTs alarms detected? How does reflash work?

A

It will alarm in the CR
Other alarms from same phase will reflash, but other alarms from other phases will be blocked
-this will require a 4hr como measure to check the other 2 phases

18
Q

Unit 2 fan and pump power supply. What happens if power is lost?

A

Power seeking power supply for all cooling fans and pumps. Automatically switches back to normal power supply when it returns

19
Q

How are the Unit 2 MBTs alarms detected? Reflash capabilities?

A

Alarms In the CR. Alarms on other phases will reflash if there is an alarm on 1 phase.

20
Q

What do the aux transformers have to keep the air out?

A

Have N2 to keep air out.

21
Q

Aux Transformers #1 25kv to 12kv cooling and auto starts

A

2 banks of cooling with an auto start of bank 1 @80degC and bank 2 @85degC

22
Q

Aux transformers 1 protections and actions?

A

-sudden pressure relay-> unit trip
-differential->unit trip
-overcurrent->unit trip
-ground overcurrent (no auto trips) alarm only

23
Q

Aux trans #2 cooling?

A

Natural circulation

24
Q

How many secondary windings does the #2 aux trans have and why?

A

2 secondary
The Y windings only serve the 4kv bus E due to two condensate/ booster pump sets and the heater drain tank pump (equal to 11,500hp) the X winding powers 4kv busses D,F,G, and H

25
Q

Aux transformer #2 protection relay and actuations

A

Overcurrent ->unit trip
Differential-> unit trip
Sudden pressure -> unit trip

26
Q

Why should the isophase cooling be kept on while back feeding?

A

To help prevent accumulation of debris in ducting

27
Q

What must you do if you get a high temperature alarm in a MBT?

A

It must be locally reset

Systems (89 decks)

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