ELEC_001
Location and function of the ground service switch:
MD-88:
- APU PWR switch and EXT PWR switch, both located on overhead panel, remove and select their respective power to ground service bus.
MD-90:
- Ground Service Power Switch, located on ovhd panel, performs following functions:
- OFF - Disconnects APU or external power from AC tie bus to ground service bus.
- ON - Connects APU or external power from AC tie bus to ground service bus, provided right generator bus is not powered. APU power has priority over external power for powering ground service bus.
ELEC_002
Recall the essential electrical equipment that may be powered during a complete loss of normal electrical power when positioning EMER PWR switch to ON or ARM (90):
- Captain’s PFD, ND, Airspeed, Altimeter, TA/VSI
- # 1 VHF COMM/NAV
- Interphone
- PA
- FGCP course/heading bugs (course/hdg displayed on ND)
- APU and Engine fire detection/protection
- Capt/FO/Cockpit white flood lights
- Cockpit thunderstorm lights
ELEC_003
Recall when the battery charger will operate?
- BATT switch ON
- EMER PWR switch OFF
- Ground service bus powered
ELEC_004
Understand that on initial electrical power up (MD-90), you must wait 90 seconds before starting APU. Why?
This will allow EPCU built-in-test to finish and prevents an ELEC SYS BIT FAIL message on the OAP. (Requires maintenance action to clear)
ELEC_005
Explain how to connect the APU generator to electrical system:
- Check APU voltage and frequency: 115 ± 3 volts, 396 ± 8 Hz (ground), 400 ± 10 Hz (air)
- MD-88 - Placing L/R APU BUS Switch to ON selects APU power to respective buses. They are left in the ON position in-flight unless a non-normal checklist calls for them to be off)
- MD-90 – APU GEN switch is normally left on to supply power to the respective generator bus provided all protection circuits are satisfied and generator is operating.
ELEC_006
Explain the meaning of each blue light on the electrical panel:
MD-88:
- APU PWR AVAIL Light: Indicates APU generator power available.
- EXT PWR AVAIL Light: Indicates external power available.
- POWER IN USE Light: Indicates selected power source connected to respective bus.
MD-90
- EXT PWR AVAIL Light: - Indicates external power switch ON and external power frequency and voltage are within required limits.
- APU POWER AVAIL Light: Indicates APU generator switch is ON, APU generator frequency and voltage are within the required limits.
ELEC_007
Know where to read voltage, frequency and amps:
AC VOLTS Meter, FREQUENCY Meter, and AC LOAD Meter are located on Electrical Power Panel of Forward Overhead Panel. DC Volts, Amps and Loads are adjacent to AC indicators.
ELEC_008
List the components powered by the ground service bus:
Ground service bus provides power to only those circuits necessary for ground servicing.
ELEC_009
Recall how long the batteries will last on emergency power:
MD-88:
- In the event of a complete loss of normal electrical power, ship’s batteries will provide both AC and DC emergency power when EMER PWR switch is ON for approx 30 min.
- MD-90 - Ship’s batteries will provide both AC and DC emergency power when EMER PWR switch is in ARM or ON for approximately 45 minutes.
ELEC_010
(88) Recall the function of the A/C BUS X TIE Switch:
- OPEN - Opens AC crosstie relay, isolates left and right generator buses. Prevents closing of relay.
- AUTO - AC crosstie relay will operate automatically.
The AC Crosstie system has 3 functions:
- Prevents paralleling.
- Powers unpowered generator bus.
- Isolates generator bus faults.
NOTE: Under certain fault conditions, AC crosstie relay will lock open.
ELEC_011
(90) Recall the function of the BUS TIE switches on MD-90:
- OPEN – Isolates the L/R generator bus from the tie bus.
- AUTO – (Normal position) Electrical Power Control Unit (EPCU) automatically opens and closes bus tie relays as required to maintain elecrical power to respective buses.
ELEC_012
Recall the function of the DC BUS X TIE Switch:
- CLOSE - Closes DC cross-tie relay and connects left & right DC buses. Supplies DC power from one side to the other in case both transformer rectifiers fail on either left or right system.
- OPEN - (Normal position) Left and right DC buses are isolated.
ELEC_013
Recall the function of the EMER PWR switch:
MD-88
- OFF - Removes batteries as a source of emergency power.
- ON - Connects batteries as source of emergency AC and DC power. Power to DC emergency bus is now supplied from battery direct bus. AC power is supplied to AC emergency bus by emergency inverter. Inverter is powered from the battery direct bus, standby lights illuminate (Battery switch ON).
MD-90
- OFF - Disarmed and resets the Automatic Emergency Power System.
- ARM - (Normal position) Emergency power relay is placed in the standby mode for automatic activation (requires at least one FUEL switch ON) when the electrical power control unit(EPCU) detects a power loss to the emergency AC, DC, or DC transfer bus.
- ON - Emergency power is energized, prevents battery charger operation. The battery supplies power for AC emergency bus and DC transfer bus.
ELEC_014
Explain the function of the BATT switch:
- OFF - Removes batteries from battery bus, battery charger, and DC transfer bus.
- ON - Connects battery direct bus to battery bus. Selects batteries to battery charger and DC transfer bus. White line, positioned horizontally, indicates locked.
ELEC_016
Recall normal AC power voltage and frequency for the engine driven generators:
- Voltage: 115 ± 3 Volts
- Frequency: 400 ± 4 Hz
