Short Circuit in a Power Generator

A power generator may experience a short circuit. Unlike the power grid, such a system is considered a so-called soft source. This means that the impedance of the short-circuit circuit changes dynamically during the fault. In this situation, magnetic flux distribution occurs.

At the initial stage of a short circuit, the damper cage causes the main flux generated by the fault currents to be pushed out of the rotor. At this point, the generator’s reactance is low – around 10–15% of the steady-state value. This state is called transient for a reason – it lasts very briefly. This is because the electromagnetic time constant is quite small, averaging about 0.01 s.

When this phenomenon subsides, the main flux gradually enters the rotor. At that point, the generator’s reactance rises – reaching 20–40% of the generator’s steady-state value.

The next stage is the steady-state short circuit condition. It is characterized by a further increase in the short-circuit reactance. At this moment, the main flux closes through the rotor of the generator. As a result, the reactance increases even more – reaching up to 200–300% of the steady-state value.

Systems Used in Modern Power Generators

Modern devices designed to supply electricity in the event of a failure are equipped with a special excitation current regulator with a forcing system. During a short circuit, it can maintain the generator’s reactance at the appropriate level – characterized by a multiple of the generator’s rated current, sustained for no longer than 10 seconds.

The time limitation for maintaining a given reactance value during faults is related to the thermal durability of the winding insulation. If this period is extended, it may cause damage to these components. Such issues are found primarily in older generator models that are not equipped with adequate protections.

Short Circuits and Generator Location

When installing a power generator, it is crucial to choose the proper location. Authorized personnel know very well that a short circuit may occur during use. They understand the consequences of such an event and can select the right installation site. Generators must not be placed in areas exposed to moisture or near flammable materials.

How to Prevent a Power Generator Short Circuit?

A short circuit can occur in any device. However, there are practices that can minimize the risk of such an event. These include:

  • regular maintenance and inspections – a generator should be regularly checked and serviced by qualified personnel, including inspection of wires, connections, plugs, engine, alternator, etc.,
  • choosing the right location and ventilation – the generator should be placed in a proper area, away from heat sources and moisture, with efficient ventilation provided,
  • using appropriate electrical protections – the generator should have adequate protections such as fuses, residual-current devices (RCDs), and cable shielding. Proper protection against electric shock is also crucial,
  • correct device connection – connecting the generator must follow the manufacturer’s instructions, paying attention to the voltage and power of devices to avoid overloading,
  • selecting the appropriate load level – the generator’s maximum load must not be exceeded. Each unit has a defined safe output. Exceeding it may cause overheating and damage, while also negatively affecting connected devices,
  • avoiding untested or damaged cables – generator wires must be fully functional and of high quality, preferably certified,
  • protecting against moisture – the generator must be shielded from rain, damp, or other atmospheric factors that may impact its performance.

All generator users should be properly trained in its operation. If any faults are noticed, they must be promptly repaired to prevent a short circuit from occurring at the moment the generator is most needed.