LEC Electrical & Electronic Systems 2 — Questions and Answers
Question 1: What is the primary function of the main reservoir in a locomotive's pneumatic/electrical control system?
- Store compressed air for brakes and controls (Correct answer)
- Cool the traction motors
- Regulate voltage to cab electronics
- Filter electrical surges from the power grid
Correct answer: Store compressed air for brakes and controls
The main reservoir stores compressed air used to operate brakes, whistles, and various pneumatic controls on the locomotive.
Question 2: Which component converts AC power from the alternator into DC power for traction motors on a diesel-electric locomotive?
- Transformer
- Rectifier (Correct answer)
- Inverter
- Regulator
Correct answer: Rectifier
A rectifier converts alternating current (AC) produced by the main alternator into direct current (DC) used by the traction motors.
Question 3: A locomotive's cab signals display a 'Restricting' aspect. What does this indicate to the engineer?
- Proceed at track speed
- Stop immediately
- Proceed prepared to stop short of a train, obstruction, or switch (Correct answer)
- Increase speed to clear the block
Correct answer: Proceed prepared to stop short of a train, obstruction, or switch
A Restricting cab signal indicates the engineer must proceed prepared to stop short of any obstruction, typically requiring reduced speed.
Question 4: What is the purpose of a ground relay on a locomotive?
- Prevent overvoltage to cab lighting
- Detect and isolate electrical faults to ground in traction circuits (Correct answer)
- Regulate battery charging current
- Protect the radio from static discharge
Correct answer: Detect and isolate electrical faults to ground in traction circuits
A ground relay detects unintended electrical paths to ground in the high-voltage traction circuit and isolates the affected circuit to prevent damage.
Question 5: When a locomotive experiences a 'wheel slip' indication, which system is primarily responding?
- Brake pipe pressure control
- Wheel slip detection and correction system (Correct answer)
- Dynamic brake blending unit
- Fuel injection controller
Correct answer: Wheel slip detection and correction system
The wheel slip detection and correction system monitors axle speed differentials and reduces tractive effort to restore adhesion when slipping is detected.
Question 6: What does the term 'notch' refer to in relation to locomotive throttle operation?
- A brake application increment
- A discrete throttle position that controls engine power output (Correct answer)
- A speed restriction zone marker
- A coupling mechanism setting
Correct answer: A discrete throttle position that controls engine power output
A notch is a discrete throttle position on the controller that corresponds to a specific power output level, typically ranging from idle to Notch 8.
Question 7: Which type of braking uses the traction motors as generators to slow the train?
- Pneumatic braking
- Dynamic braking (Correct answer)
- Emergency braking
- Hand braking
Correct answer: Dynamic braking
Dynamic braking reconnects the traction motors as generators, converting kinetic energy into electrical energy (dissipated as heat) to slow the locomotive.
LEC Electrical & Electronic Systems 2
What is the primary function of the main reservoir in a locomotive's pneumatic/electrical control system?