Generator Synchronization on Ships

Generator Synchronization on Ships

Onboard a ship, uninterrupted power isn’t a luxury — it’s a necessity. From the bridge to the engine room, everything relies on a stable electrical supply. That’s where synchronized generators step in. Whether we’re switching between engines or sharing the load, synchronization is the unsung hero keeping everything running smoothly.

Let’s break down what synchronization is, why it matters, and how it’s done on real ships — with no jargon, just solid seamanship.

What is Generator Synchronization?

In simple terms, synchronizing means matching a standby generator’s output with the ship’s main bus bar — so that when we connect it, there are no surges, sparks, or damage.

Before flipping the breaker to connect a second generator, we need to ensure:

  • Voltage is equal
  • Frequency is the same (or slightly higher)
  • Phase sequence is identical
  • Phase angle is aligned

Do it wrong, and you’ll face reverse power, electrical arcs, or a blackout. Do it right, and your generators will share the load like a well-trained team.

Pre-Synchronization Checks: What Must Match?

1. Voltage

The incoming generator’s voltage must match the main bus bar. If it’s too high, it’ll dump reactive power. Too low? It’ll start absorbing it.

2. Frequency

Frequencies should be equal — or the incoming generator should be slightly faster. Usually 0.2–0.3 Hz higher.

3. Phase Sequence

R, Y, B — the phase order must match. A mismatch means the generator is essentially fighting the system.

4. Phase Angle

Voltage waveforms need to rise and fall together. If the waves aren’t in sync, it can cause electrical shock during closing.

Synchronizing Methods Used at Sea

There are a few tools we use onboard to match everything up:

1. Synchroscope Method

This is the most accurate method used during normal operations.

Here’s how we do it:

  • Start the standby generator (let’s say D/G 2) and let voltage stabilize.
  • Use the synchroscope to check phase angle difference between D/G 2 and the running generator (D/G 1).
  • The pointer will rotate:

    • Clockwise: D/G 2 is fast
    • Anticlockwise: D/G 2 is slow

We aim for a slow clockwise rotation. As the pointer nears the 12 o’clock position, we close the breaker.

Why 12 o’clock? That’s when the voltages are in phase — perfect timing.

2. Three Lamp Method (Emergency)

No synchroscope? No problem. This method works when you connect three lamps across the phases:

  • Lamps flicker slowly = Almost synchronized
  • All lamps go dark at once = That’s your cue — close the breaker

Clockwise flicker = generator fast; anticlockwise = slow. It’s simple but effective.

3. Two Bright, One Dark Method

A more precise lamp method:

  • L1 and L3 connected with reversed polarity; L2 normal
  • When L1 and L3 are bright, and L2 is dark, you’re at synchronis

Again, close the breaker right at that moment.

Step-by-Step: Parallel Operation of Generators

Let’s say you want to put D/G 2 online with D/G 1 already running. Here’s what happens:

1. Start the Engine

Start D/G 2 and allow voltage to stabilize (usually handled by the AVR).

2. Compare Parameters

Use selector switches to check D/G 2’s voltage and frequency. Compare it with the bus bar. Adjust frequency using the governor motor.

3. Check Synchronism

Watch the synchroscope:

  • Clockwise rotation = Generator is fast (good)
  • Wait till pointer nears 12 o’clock
  • Confirm phase angle alignment

Or if using lamps: look for uniform flicker or the correct bright/dark combination.

4. Close the Breaker

When synchronism is achieved, close the generator breaker just before the pointer hits 12. This compensates for contactor delay.

5. Load Sharing

Once connected, adjust the governor to let D/G 2 take on load. Balance load between D/G 1 and D/G 2 proportionally.

6. Monitor Frequency

Keep a close watch on the bus frequency — adjust governor as needed to keep it steady at 60 Hz (or 50 Hz, depending on the ship).

Removing a Generator (Load Shift)

To take one generator offline:

  • Use the governor to reduce its load
  • When output drops to about 5% of rated load, open the breaker

Important: Don’t let load go negative — if reverse power relay trips, it’ll shut down the breaker automatically after a delay.

Cautions During Synchronization

  • Never rush the process — wait for the right phase alignment
  • Watch out for large frequency variations
  • Never overload the online generator(s) during load shift

  • Keep the synchronization panel clean and functioning — emergency methods only work when tested and understood

A Quick Recap on Synchronous Speed

In case you’re brushing up:
Ns = (120 × f) / P

  • Ns = Speed in RPM
  • f = Frequency
  • P = Number of poles

This formula helps you understand how fast your generator should be spinning under ideal sync conditions.

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