LEC Electrical & Electronic Systems 3 — Questions and Answers
Question 1: What is the voltage range typically used for battery systems on a modern diesel-electric freight locomotive?
- 12 volts DC
- 24 volts DC
- 64–74 volts DC (Correct answer)
- 110 volts AC
Correct answer: 64–74 volts DC
Most diesel-electric freight locomotives use a 64–74 volt DC battery system to power starting circuits, control systems, and lighting when the engine is off.
Question 2: An engineer notices the 'low oil pressure' light illuminating while running at full throttle. What is the correct initial response?
- Increase throttle to build more pressure
- Reduce throttle and notify dispatch while monitoring the situation (Correct answer)
- Apply emergency brakes immediately
- Switch to dynamic braking to reduce engine load
Correct answer: Reduce throttle and notify dispatch while monitoring the situation
Reducing throttle decreases engine load while monitoring oil pressure; the engineer should notify dispatch and follow railroad procedures to protect the prime mover.
Question 3: What is the function of the load regulator on a diesel-electric locomotive?
- Controls fuel delivery to maintain constant engine RPM under varying loads (Correct answer)
- Regulates brake pipe pressure
- Adjusts cab temperature automatically
- Monitors axle bearing temperatures
Correct answer: Controls fuel delivery to maintain constant engine RPM under varying loads
The load regulator adjusts the electrical load on the main alternator to maintain constant engine RPM regardless of traction power demands.
Question 4: Which system on a locomotive continuously monitors axle bearing temperatures and alerts the crew to overheating?
- Hot bearing detector (HBD) wayside system
- Onboard bearing temperature monitoring system (Correct answer)
- Locomotive Event Recorder (LER)
- Wheel profile sensor
Correct answer: Onboard bearing temperature monitoring system
The onboard bearing temperature monitoring system uses sensors on each axle to detect abnormal heat and alert the engineer before a hotbox failure occurs.
Question 5: A locomotive's electrical system shows repeated tripping of the same circuit breaker. What should the engineer do?
- Continuously reset the breaker until arrival
- Reset once; if it trips again, leave it open and report it (Correct answer)
- Bypass the breaker using a jumper wire
- Increase battery voltage to overcome the fault
Correct answer: Reset once; if it trips again, leave it open and report it
Resetting a circuit breaker once is permitted; if it trips again, leaving it open prevents fire or further damage, and the fault must be reported.
Question 6: What does 'MU (multiple unit) operation' require regarding electrical connections between locomotives?
- Only mechanical couplings are needed
- A 27-point electrical MU cable connecting control circuits between units (Correct answer)
- A separate radio link for each locomotive cab
- Direct wiring of traction motors across units
Correct answer: A 27-point electrical MU cable connecting control circuits between units
MU operation uses a 27-point electrical cable (jumper) to connect the control circuits of multiple locomotives so one engineer can control all units simultaneously.
Question 7: What is the purpose of the event recorder (black box) on a locomotive?
- Record audio conversations in the cab
- Capture operational data such as speed, brake applications, and throttle position (Correct answer)
- Monitor fuel consumption in real time
- Control automatic speed restrictions
Correct answer: Capture operational data such as speed, brake applications, and throttle position
The locomotive event recorder captures data including speed, throttle position, brake pipe pressure, and other operational parameters for accident investigation and compliance.
LEC Electrical & Electronic Systems 3
What is the voltage range typically used for battery systems on a modern diesel-electric freight locomotive?