Aircraft Electrical Systems

Alternators and Generators

1. Alternators vs. DC Generators

Alternators produce a usable voltage level at lower RPMs than DC generators because alternators have more field poles.

2. Delta Wound Three-Phase Alternator Stator

The windings wired in relation to each other in a delta-wound three-phase alternator stator are in series.

3. Generator Output

Generator output is expressed in the number of amps at rated voltage.

4. AC 43.13 Electrical System Design

The AC 43.13 suggests that the electrical system of an aircraft be designed so that when all systems are operating, no more than 80% of generator capacity can be exceeded.

5. Reverse Current Cutout Relay

The main function of a reverse current cutout relay in a generator system is preventing motoring of the generator.

6. Increasing Induced Current in a Coil

The three main ways to increase an induced current in a coil from an electromagnet are to:

• Increase the number of turns of the coil
• Increase current flow
• Increase RPM

7. Vibrating Contacts in a Voltage Regulator

Vibrating contacts are used as a variable resistor in a three-unit type voltage regulator.

8. Three-Unit Voltage Regulator

The three-unit voltage regulator will limit the voltage and protect the circuit from overloads.

9. Carbon-Pile Voltage Regulator

In a carbon-pile type voltage regulator, if the pressure on the carbon pile is increased, the resistance will decrease.

10. Three-Unit Type Regulator Components

The three units in a three-unit type regulator include the reverse current cutout relay.

11. Carbon Pile Voltage Regulator Operation

When the pressure applied to the carbon stacks is varied in a carbon pile voltage regulator, current is directly changed because of the distance between the disks.

Electrical System Components and Practices

12. Bonding Jumper Resistance

The maximum allowable resistance through bonding jumpers connected on the aircraft is 0.003 ohms.

13. Solid State Inverter

A solid-state inverter is another name for a static inverter.

14. Aircraft Electrical Switch Orientation

Aircraft electrical switches are typically oriented in the cockpit for installation as follows: ON - forward/up, OFF - down/backwards.

15. Constant Speed Drive (CSD)

The main purpose of the constant speed drive (CSD) is to maintain constant frequency.

16. Reverse Current Cutout Relay in Alternator Systems

A reverse current cutout relay is not necessary in an alternator system because diodes prevent reverse current flow.

17. Advantages of AC over DC

Advantages of AC over DC for large aircraft include that AC is easily stepped up or down with less line loss.

18. AC Generator Operation

When operating an AC generator, the frequency and voltage must be constant.

19. Low Voltage Output in a Single Generator System

If a single generator system shows a low voltage output, the voltage regulator may be out of adjustment.

20. Generator Motoring

A generator may be motored by the battery if the reverse current cutout relay points are open.

21. Equalizing Current Loads Between Generators

Current loads are equalized between two generators when they are adjusted in parallel.

22. Vibrator Type Voltage Regulator

The amount of time that the points will remain open in a vibrator-type voltage regulator depends on the load.

23. Automatic Reset Circuit Breakers

Automatic reset type circuit breakers are not permitted as circuit protection devices.

24. Switch Selection for High Inrush Current

Choosing a switch able to handle high inrush current is done by applying a derating factor.

25. Ground Resistance Measurement

A resistance measurement of 0.005 ohms from a ground point of a battery to the ground terminal or ground point of a generator or electrical device is considered satisfactory.

26. Ammeter Redline

An ammeter can be "redlined" at 100% of the alternator rating and is referred to as an overload condition.

27. AN/MS Electrical Connector Pin Side

The negative (-) connection is the pin side of an AN or MS electrical connector.

28. Stud/Nut Terminal Block Connections

When using a stud/nut combination for bonding terminals to a terminal block, the number of terminals should be limited to 4 (with no bus bar or jumper strip).

29. Stud/Nut Terminal Block Connections with Bus Bar

When using a stud/nut combination for bonding terminals to a terminal block, the number of terminals should be limited to 4 (with a bus bar or jumper strip installed).