EGSA Load Bank Testing 5 — Questions and Answers
Question 1: What is the purpose of a 'block load' test during generator commissioning?
- To test the generator at zero load for 30 minutes
- To apply a large percentage of rated load in a single step to test transient performance (Correct answer)
- To run the generator at 50% load indefinitely
- To test only the reactive load capacity
Correct answer: To apply a large percentage of rated load in a single step to test transient performance
A block load test applies a significant load step (often 100% rated load) at once to evaluate the generator's worst-case transient response.
Question 2: When connecting portable load bank cables to a generator output panel, which safety step must be performed first?
- Start the generator at no load
- Verify the generator is de-energized and locked out/tagged out (Correct answer)
- Set the load bank to maximum load
- Check the exhaust temperature
Correct answer: Verify the generator is de-energized and locked out/tagged out
LOTO (lockout/tagout) procedures must be completed before making any electrical connections to prevent electrocution.
Question 3: A generator's fuel consumption during a load bank test is significantly higher than the manufacturer's published rating at full load. This most likely indicates:
- The load bank is drawing less than rated kW
- An engine performance problem such as injector wear or turbocharger inefficiency (Correct answer)
- The AVR is set too high
- The coolant temperature is too low
Correct answer: An engine performance problem such as injector wear or turbocharger inefficiency
Excessive fuel consumption at rated load suggests combustion inefficiency caused by worn injectors, a failing turbocharger, or compression loss.
Question 4: What is the function of the load bank's cooling fan during resistive load testing?
- To cool the generator alternator windings
- To dissipate heat generated by the resistive elements (Correct answer)
- To provide combustion air to the engine
- To circulate coolant through the radiator
Correct answer: To dissipate heat generated by the resistive elements
Resistive load bank elements convert electrical energy to heat, and the internal cooling fan removes that heat to prevent element damage.
Question 5: During a load bank test at a facility, the utility power is accidentally restored while the generator is supplying the load bank. What is the most critical hazard?
- The load bank will overheat
- Out-of-phase paralleling can cause severe mechanical and electrical damage to the generator (Correct answer)
- The generator fuel consumption will increase
- The load bank circuit breakers will trip on overload
Correct answer: Out-of-phase paralleling can cause severe mechanical and electrical damage to the generator
If utility and generator are connected out of phase, the resulting torque and current surge can destroy the generator's windings and crankshaft.
Question 6: What is the recommended minimum warm-up period before applying load bank load to a cold diesel generator during formal testing?
- No warm-up is required; load can be applied immediately
- 3 to 5 minutes at no load to allow oil to circulate and temperatures to stabilize (Correct answer)
- 30 minutes at full load
- 1 hour at 50% load
Correct answer: 3 to 5 minutes at no load to allow oil to circulate and temperatures to stabilize
A 3–5 minute warm-up period ensures oil has reached operating viscosity and engine temperatures have stabilized before load is applied.
Question 7: Which load bank test result would indicate that a generator's alternator has a shorted field winding?
- Frequency hunting above and below 60 Hz
- Inability to build or maintain rated output voltage under load (Correct answer)
- Excessive coolant temperature at rated load
- High fuel consumption at partial load
Correct answer: Inability to build or maintain rated output voltage under load
A shorted field winding reduces magnetic field strength, preventing the alternator from generating or sustaining rated output voltage.
EGSA Load Bank Testing 5
What is the purpose of a 'block load' test during generator commissioning?