Overspeed in diesel genset: causes and solutions

Solutions for diesel genset overspeed fault

Step 1: Forced shutdown

Activate the emergency shutdown button if it is safe to do so.

For fuel injection pumps with exposed or toothed rods, pull the rods back to the stop position.

For engines with decompression devices, pull the decompression handle to release uncompressed gas and shut down the engine.

If a shut-off device is installed on the intake pipe, immediately turn it off or block the air filter intake with a cloth to cut off fuel and air. Also, close the tank and block the oil and gas supply, causing the cylinders to stop.

For gensets with a transmission, shift into high gear while pressing the brake pedal, then slowly lift the clutch to force the engine to stop.

Step 2: Diagnosis after shutdown

If the engine doesn’t accelerate normally when the pedal is raised quickly, the accelerator pedal stick or arm may be jammed.

If engine speed cannot be reduced immediately after shutdown, the governor may not be functioning correctly.

If lifting the accelerator pedal increases engine speed, the fuel injection pump may be faulty.

If the fuel supply system is normal but an overspeed occurred, excess fuel or oil may have entered the cylinders.

Review the fault log, check the control panel data, alarm messages, and sensor readings to determine the cause of the overspeeding.

Inspect the engine, alternator, and protection systems for any apparent damage.

Signs and effects of diesel genset overspeed

1. Warning alarms and shutdown systems

Most BISON diesel gensets are equipped with alarms and automatic shutdown systems that activate when engine speed exceeds safe limits. Audible or visual alerts warn operators of overspeed conditions, while shutdown systems disconnect the genset to prevent further damage.

2. Increased stress on engine components

Excessive speed puts extreme stress on critical engine parts, accelerating wear and tear and reducing performance. The signs include:

Pistons and valves: may bend, break, or collide.

Crankshaft and bearings: can crack or seize.

Flywheel: high-speed rotation may cause cracks or shattering.

3. Risk of catastrophic engine failure

If overspeed continues unchecked, it can push the engine beyond its mechanical limits, causing severe internal damage such as:

Broken connecting rods or crankshaft failure

Piston and valve damage

Alternator windings burned due to over-frequency

Damage to the AVR and connected electrical equipment

It emits a roaring sound, and a large amount of black or blue smoke comes out of the exhaust pipe.

4. Safety hazards

• Fire: Sparks or excess fuel may ignite.
• Flying debris: broken engine parts can cause injury.

5. Operational and financial impacts

• Downtime: operations may stop until repairs are completed.
• Repair or replacement costs: engine damage can be expensive to fix.
• Connected equipment damage: over-frequency and voltage spikes can harm devices, increasing financial loss.

Preventive measures and best practices

1. Routine maintenance

1. Governor and actuator checks: inspect and adjust the governor and fuel actuators to ensure correct response to engine speed changes.
2. Electrical system inspection: maintain secure, corrosion-free connections and verify that speed sensors and relays provide accurate readings.
3. Fuel system maintenance: clean and inspect fuel pumps, injectors, and filters to prevent over-fueling or clogs. Ensure fuel quality meets manufacturer recommendations.
4. Lubrication and component inspection: replace worn or damaged engine parts and ensure proper lubrication.

2. Testing safety systems

Periodically test overspeed shutdown systems to confirm proper operation. And, verify that emergency shutdown valves or flaps operate correctly during overspeed events.

3. Load bank testing

Use a load bank to simulate real operating conditions and confirm that the governor prevents overspeed. And run the genset to rated speed and adjust the overspeed setting to confirm the system trips correctly.

4. Operator training

Train operators to react quickly to overspeed alarms and conduct regular standard operating procedures (SOPs) and safety drills to ensure operators are prepared for safe responses.