Electrical

Question 1

When will the battery charger operate

Answer 1

1. BATT switch ON
2. EMER PWR switch is OFF
3. Ground service bus is powered

Question 2

Normal AC power voltage and frequency for the engine driven generators

Answer 2

Voltage - 115 +/-3 V

Frequency - 400 +/-4 Hz

Question 3

Identify the location and function of the ground service switch
MD88
MD90

Answer 3

MD88:
The APU PWR switch and EXT PWR switch, both located on the overhead panel, remove and select their respective power to the ground service bus

MD90
1. Ground service power switch located on the overhead panel performs the following functions:
A. OFF - disconnects APU or external power from the AC tie bus to the ground service bus
B. ON - connects APU or external power from the AC tie bus to the ground service bus provided the right generator bus is not powered. APU Power has priority over external power for powering the ground service bus

Question 4

What are the essential electrical equipment that may be powered during a complete loss of normal electrical power when positioning the EMER PWR switch ON or ARM(90)

Answer 4

1. Captains PFD, ND, Airspeed, altimeter, TA/VSI
2. # 1 VHF COM/NAV
3. Interphone
4. PA
5. FGCP course/heading bugs(displayed on ND)
6. APU and Eng. fire detection/protection
7. Capt/FO/Cockpit flood lights
8. Cockpit thunderstorm lights

Question 5

On the MD90 how long must you wait before starting APU and why

Answer 5

90 seconds
This allows the EPCU built in test to finish and prevents an ELEC SYS BIT FAIL message on the OAP which requires maint action to clear

Question 6

How do you connect the APU generator to the electrical system?
What values do you check first
88
90

Answer 6

BOTH - check voltage and frequency: 115 +/-3 V, 396+/-8 Hz(ground) 400 +/-10(air)
MD88:
Placing the L/R APU BUS switch to ON selects APU Power to the respective buses. they are left in the ON position in flight unless a non-normal checklist calls for them to be off

MD90:
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

Question 7

Explain the meaning of each blue light on the electrical panel
MD88
APU PWR AVAIL
EXT PWR AVAIL
PWR IN USE

MD90
EXT PWR AVAIL
APU PWR AVAIL

Answer 7

MD88

1. APU PWR AVAIL light - indicates APU generator power is available
2. EXT PWR AVAIL light- external power available
3. POWER IN USE light - selected power source is connected to respective bus

MD90

1. EXT PWR AVAIL light - external power switch is ON and frequency and voltage in limits
2. APU PWR AVAIL - APU generator is ON and freq and volts within limits

Question 8

Where do you read voltage frequency and amps

Answer 8

The AC VOLTS meter, FREQUENCY meter, and AC LOAD meter, located on the electrical power panel of the forward overhead panel

D.C. Volts, amps and loads are adjacent to the AC indicators

Question 9

List the components powered by the ground service bus

Answer 9

The ground service bus provides power to only those circuits necessary for ground servicing

Question 10

How long will be batteries last on emergency power
MD88
MD90

Answer 10

MD88: both AC and D.C. Emergency power when the EMER PWR switch is ON for approximately 30 minutes

MD90: with EMER PWR switch IN or ARM, both AC and DC power for 45 minutes

Question 11

Recall the function of the A/C BUS X TIE switch

OPEN
AUTO

Answer 11

OPEN - opens AC crosstie relay, isolates left and right generator busses, prevents closing of relay

AUTO - The AC crosstie relay will operate automatically

Question 12

What are the 3 functions of the AC crosstie relay

Answer 12

1. Prevents paralleling
2. Powers on powered generator bus
3. Isolates generator plus faults

Under certain fault conditions AC crosstie relay will lock open

Question 13

What’s the function of the BUS TIE switches on the MD90

OPEN
AUTO

Answer 13

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 electrical power to respective busses

Question 14

What’s the function of the D.C. BUS TIE switch

CLOSE
OPEN

Answer 14

CLOSE - closes DC cross tie relay and connects the left and right DC buses. supplies DC power from one side to the other in case both transformer rectifiers fail on either the left or right system

OPEN - (normal position) left and right DC buses are isolated

Question 15

Explain the function of the BATT switch

OFF
ON

Answer 15

OFF - remove batteries from battery bus, battery charger and DC transfer bus

ON - Connects battery direct bus to battery bus.
Select some batteries to battery charger and DC transfer bus
White line, position horizontally, indicates locked

Question 16

What’s the function of the EMaeR PWR switch
MD88
MD90

Answer 16

MD88:
OFF - remove batteries as source of emergency power
ON - K’NEX batteries as source of emergency AC and DC power. Power to DC emergency boss 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(Batt switch on)

MD90
OFF - this armed 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(through the emergency inverter), DC emergency boss and DC transfer bus

Question 17

ESV Prep question. It may not be all inclusive

What is provided when the emergency power switch is in the ON position

Answer 17

AC power is supplied to the AC emergency bus through the emergency inverter

STandby lights illuminate

AIrcraft batteries are the source of Emergency AC and D.C. Power