The Risks of High-power Inductive Loads To Small Air-cooled Diesel Generators

Using a small air-cooled diesel generator set to forcibly start a high-power inductive load that exceeds its carrying capacity (such as a large motor, air compressor, etc.) is very likely to cause the generator to burn out. The following are three major risks:

1. Stator winding overheating
When the inductive load starts, it generates an impact of 5 to 7 times the rated current (such as a 7.5kW motor starting current ≈ 45kW), which far exceeds the overload capacity of a small generator (usually only 110% load is allowed). Copper loss (I^2R) increases sharply → Winding temperature rise exceeds the insulation level (such as H level 180℃) → Insulation carbonization short circuit. Typical case: A 10kVA generator forcibly starts a motor of more than 3kW, and smoke appears within 30 seconds.

2. Rotor excitation out of control
The large current impact causes the generator terminal voltage to drop instantly (>20%), and the AVR (automatic voltage regulator) forcibly increases the excitation current to maintain the voltage. The rotor excitation winding overheats → rotor interturn short circuit → magnetic field distortion → stator current imbalance.

3. Permanent magnet demagnetization (permanent magnet generator)
The impact current causes a strong reverse magnetic field in the stator → irreversible demagnetization of the rotor permanent magnet → the generator power permanently decreases by 30%~50%.