125vdc Flashcards
125VDC
STATE the functions of the Vital, Non-Vital, and Switchyard Distribution Systems
Vital: Supply / distribute 125 V DC control power to vital plant equipment, including:
• Backup power for vital and non-vital instrumentation Uninterruptible Power Supplies (UPSs).
• Tripping and closing power for essential 4160 and 480 loads
• Emergency DG and Emergency Power Sequencer control power
Non-vital: Supply and distribute 125 V DC control power power to non-vital plant equipment, including:
o Backup power for several non-vital instrumentation Uninterruptible Power Supplies (UPSs).
o Tripping and closing power for non-essential 4160 and 480 loads
o Power to various emergency components in plant secondary systems used in the event of a loss of all AC power (i.e., DC pumps).
SWYD: Primary function:
o supply and distribute 125 V DC control power to the 345 kV breakers, motor-operated disconnects (MODs), and the protective relaying systems.
• Secondary functions:
o Provide power to instrumentation and alarms associated with the 345 kV distribution system.
o Provide power to emergency DC lighting in the switchyard and relay room during a loss of the normal AC lighting.
STATE the location for the following Vital, Non-Vital, and Switchyard DC Busses:
Vital: Essential switchgear
Non-vital: TB-21’ south
SWYD: relay room
STATE the Vital and Non-Vital bus numbers
Vital: Buses 11A thru 11D
Non-vital: 12A and 12B
STATE the normal and backup power supplies to the Vital, Non-Vital, and Switchyard DC busses
Vital: Normal: Charger Back-up: Vital batteries Non-vital: Normal: Charger Back-up: US-53 SWYD: Normal: Charger Back-up: US-53
DESCRIBE the purpose of the interlock between the normal and alternate battery supplies on a Vital DC bus
Prevents paralleling vital batteries
DESCRIBE which busses each portable battery charger can supply
Train “A” normally has BC-1P. Vital Bus 11A, 11C and Non-Vital Buses 12A & 12B Train “B” normally has BC-2P. Vital Bus 11B, 11D
DESCRIBE the circumstance(s) under which two vital battery chargers may be operated in parallel
never
DESCRIBE the meaning of the statement “normally the battery is float charged”
Normally the battery charger is in service maintaining the battery fully charged
STATE the approximate numerical value of the float and equalize charge voltages
Normal: 131.5V
Equaliziing: 137.5V
EXPLAIN how to determine the amount of current going to a vital battery during a charge
Look at the battery ammeters outside of the vital battery room
DESCRIBE the expected result of placing the FLOAT/EQUALIZE switch in the EQUALIZE position
The charger output should increase to 137.5V
When placing the charger in service, DESCRIBE which breaker on a battery charger must be closed first in order to avoid damage to the charger.
Care must be taken when starting or securing the battery charger to prevent damage, to its solid state components. Before starting the battery charger, place the ECT in the OFF position. Close the DC output breaker and then the AC input breaker
DISCUSS the events that led to Bus 11B being isolated form the Battery Charger on June 21, 2006.
Electricians did not understand how to secure the battery charger. Additionally the CRO assumed that the resultant alarms were “expected” from the maintenance activities
STATE the reading on a Vital D.C. Bus Ground Detector Ammeter with no grounds present.
Zero
EXPLAIN why battery ventilation must be operating when batteries are being charg
Battery charging generates Hydrogen which can cause a flammable environment and then an explosive environment
