⚡ Generator & Switchboard

Oral Questions & Practical Answers

Part 2 – Emergency Generator & Blackout Scenarios

Real onboard situations explained the way examiners expect — and ships actually work.

1. What is a blackout?

A blackout is the total loss of electrical power on the main switchboard.

It may be caused by:

• Generator trip
• Fuel failure
• Overload
• Short circuit
• Human error

2. What happens immediately after a blackout onboard?

1. Main generators trip
2. Main switchboard becomes dead
3. Emergency generator starts automatically
4. Emergency switchboard is energized
5. Only essential emergency loads are supplied

3. How does the emergency generator start automatically?

By an under-voltage relay.

• Relay senses loss of voltage on the main switchboard
• Sends start signal to emergency generator
• Generator starts and breaker closes automatically

4. Why is synchronisation not required when restoring power after blackout?

Because:

• Emergency generator is electrically isolated
• Bus tie breaker between main and emergency switchboard is open

There is no paralleling, so synchronisation is unnecessary.

5. What loads are supplied by the emergency generator?

Typical emergency loads:

• Emergency lighting
• Navigation equipment
• Communication systems
• Steering gear (if required)
• Fire pumps / alarms

Non-essential loads are not connected.

6. What is the purpose of the bus-tie breaker between MSB and ESB?

It ensures:

• No paralleling between emergency and main generators
• Safe isolation during blackout
• Smooth restoration of normal power

7. What is the correct sequence to restore normal power after blackout?

1. Start main generator
2. Stabilize voltage and frequency
3. Close main generator breaker
4. Ensure emergency generator breaker opens
5. Restore normal loads gradually

8. Why should loads be restored gradually after blackout?

• Prevent overload
• Avoid frequency drop
• Avoid generator trip
• Protect sensitive equipment

Sudden load application may cause repeat blackout.

9. What happens if all starting air bottles are empty during blackout?

Emergency procedures:

1. Use emergency air bottle to start generator
2. If empty, start emergency air compressor
3. Emergency compressor is powered by emergency generator
4. Fill emergency air bottle
5. Start main generator

10. What is an emergency air compressor?

• Powered by emergency generator
• Used only during blackout
• Supplies air for starting main engines / generators

11. What is a shaft generator?

A shaft generator:

• Is driven by main engine
• Produces electrical power at sea speed
• Uses frequency converter to maintain constant output frequency

12. Why is shaft generator not used during maneuvering?

Because:

• Main engine speed varies
• Output frequency becomes unstable
• Frequency converter cannot compensate fully at low speed

13. How is constant frequency maintained in a shaft generator?

By using:

• Thyristor controlled frequency converters
• Power electronics

These convert variable speed input into stable electrical output.

14. What is the difference between blackout and preferential trip?

15. What action will you take if blackout occurs during your watch?

• Stay calm
• Check emergency power supply
• Inform engine control room / bridge
• Assist restoration as per checklist
• Monitor voltage and frequency

16. Why is emergency generator located outside engine room?

• Fire safety
• Flood safety
• Must operate independently from engine room conditions

17. What is the minimum time emergency generator must start after blackout?

Within 45 seconds (as per SOLAS requirements)