LEC Mechanical and Electrical Systems 2

Question 1

What is the primary function of the dynamic brake grid resistors on a diesel-electric locomotive?

Accepted Answer

Dissipate heat produced by dynamic braking current

Answer

Grid resistors convert electrical energy from dynamic braking into heat, which is then dissipated into the atmosphere.

Question 2

On a modern AC traction locomotive, what device converts the alternator's AC output to DC before inverters redistribute power to the traction motors?

Accepted Answer

Rectifier

Answer

A rectifier converts the main alternator's AC output to DC, which inverters then convert back to variable-frequency AC for the AC traction motors.

Question 3

A locomotive's air compressor fails to build pressure. Which system is most immediately affected?

Accepted Answer

Automatic and independent brakes

Answer

The automatic and independent brake systems rely on compressed air; without adequate pressure, brakes cannot be applied or released properly.

Question 4

What does the term 'transition' refer to in the context of diesel-electric locomotive operation?

Accepted Answer

Changing traction motor electrical connections to optimize power at different speeds

Answer

Transition changes traction motor connections (series to parallel or changes in field strength) to deliver optimum tractive effort across different speed ranges.

Question 5

Which safety device prevents a locomotive engine from overspeeding?

Accepted Answer

Engine overspeed governor

Answer

The overspeed governor shuts down the engine if RPM exceeds a safe limit, preventing mechanical damage to the prime mover.

(LEC) Locomotive Engineer Certification Practice Test

(LEC) Locomotive Engineer Certification Practice Test

LEC Mechanical and Electrical Systems 2