Analysis of The Main Causes of Abnormal Frequency in Diesel Generator Sets

The frequency of diesel generator sets is generally 50Hz or 60Hz, subject to local power grid standards. Frequency stability is determined by engine speed and load variations, which should remain constant under ideal operating conditions.

50Hz regions: Most countries in Europe and Asia

60Hz regions: North America and parts of South America

Speed correspondence:

1500 rpm for 50Hz (4-pole generator)

1800 rpm for 60Hz

1) Fuel System Failures (Most Common Cause)

The fuel system delivers diesel steadily. Any fluctuation in fuel supply directly causes unstable engine speed and frequency deviation.

Substandard fuel quality: Diesel containing water, impurities, colloids or improper grade leads to incomplete combustion and uneven power output, resulting in fluctuating engine speed. Failure to use low-freezing diesel in low-temperature environments will cause wax deposition and block oil pipelines.

Air intrusion in oil circuits: Loose pipe joints, poor sealing or excessively low fuel level allow air to enter the pipeline. Compressible air causes unstable fuel injection volume and severe frequency fluctuation.

Clogged fuel filters: Long-term unreplaceable primary and fine fuel filters get blocked by impurities, leading to insufficient and unstable fuel supply, accompanied by speed drop, frequency swing and black exhaust smoke.

Fuel injection system malfunctions: Worn or clogged fuel injectors cause poor atomization and uneven fuel supply among cylinders. Worn plungers and poorly sealed delivery valves of high-pressure fuel pumps result in unstable oil supply pressure, further triggering unbalanced engine speed and power frequency.

2) Governing Control System Malfunctions (Core Control Failure)

The governing system acts as the core command center for frequency stability. It adjusts fuel injection volume in real time via closed-loop feedback to maintain constant engine speed.

Mechanical governor faults: Worn flyweights, fatigued springs and stuck levers of traditional mechanical governors fail to accurately sense speed changes, causing delayed or excessive fuel regulation and frequency instability.

Electronic governor abnormalities: Parameter drift, loose or dirty speed sensors and poor wire connection distort speed signals, leading to inaccurate fuel injection control and unstable power frequency.

Main control module faults: Abnormal programs and aging components of PLC or main controller disable automatic frequency modulation and load distribution functions, making frequency unable to stay within standard range.

3) Mechanical System Defects (Power Transmission & Structural Issues)

Worn, loose or unbalanced mechanical parts cause unstable power transmission, which further leads to speed fluctuation and frequency errors.

Engine internal wear: Worn cylinders and pistons, poorly sealed valves and excessive connecting rod bearing clearance reduce compression pressure, cause uneven combustion power and unstable rotation speed.

Transmission component faults: Loose couplings, aging shock pads and slipping drive belts between engine and generator result in distorted speed transmission and abnormal frequency.

Excessive unit vibration: Loose anchor bolts, unlevel installation and failed shock absorption system generate fierce vibration, interfere with normal operation of governing components and cause frequency drift.

4) Electrical Load & External Environmental Influences

Sudden load change & unbalanced load: Frequent start-stop of high-power equipment and unbalanced three-phase load (single-phase load exceeding 30% of rated load) trigger sharp speed change and frequency fluctuation.

Harsh operating environment: High temperature and humidity weaken heat dissipation and reduce output power; low temperature increases engine oil viscosity, causing difficult startup and unstable speed; dust-clogged air filters reduce air intake, lower combustion efficiency and cause frequency instability.