Types Of Generator Faults & Way To Protect A DG Set

The different types of generator faults can be categorized into two parts, the internal fault & the external fault. The internal fault in DG Set occurs due to problems in the DG Set components & external faults due to abnormal Genset operational conditions or any external network issue. Most of the time the fault comes in the prime mover mechanical components of diesel generator, gas, or any other fuel DG Set. Prime mover is nothing but the components which are responsible for the drive of the generator & its combustion engine (diesel engine).

Due to the fault in the generator, you have to face unwanted current flow which is more dangerous for the operator. Also, the fault cause number of problems such as current loss, overheating, interruption of power delivery & many more. The proper care of the generator reduces the priority of problems in the DG Set. The Genset protection system detects the fault & after that, the circuit has tripped which fault occurs. Lastly, the physical location of the fault will be identified. Here in this article, we have shared the knowledge for various types of generator faults, how to identified them & ways to protect your home or industrial generator against those faults.

Common faults in DC generator

As previously we cleared that a DG Set mainly facing two types of generator faults internal & external. Also, the reasons behind these faults are always different. Here get the detailed information for the different types of internal generator fault.

1. Stator winding fault in the generator

The stator fault mainly occurs due to the insulation failure of the stator coils. The problem in stator winding is more expensive for the user because that is responsible for the high damage in the Genset. So it this very necessary to have automatic generator protection to avoid such types of problems. The major sorts of such types faults are:

  •  Phase-to-phase
  •  Phase-to-earth
  •  Windings overheating
  •  Inter-turn

2. Rotor circuit fault in DG Set

Due to the severe mechanical errors, your DG Set is facing rotor circuit fault. The result of this fault is overheating which may damage the Genset rotor. The unbalanced currents can cause severe vibration and acute overheating problems. Rotor overheating caused due to the unbalanced loading of the generator is easily detected by rotor temperature indicators. The major types of rotor faults are:

  • Earth fault
  • Winding short-circuit of a rotor
  • Overheating

3. Loss of field

The loss of field in DG Set occurs due to the failure of excitation. That will arise the failure of the auxiliary supply & the driving of motor also one of the major responsible reason for the loss of excitation in a generator. As we know the field in the AC generator consists of a coil within the Genset which is responsible to receive voltage from excitation & produce magnetic flux.

4. Vibration in DG Set

Due to the rotor imbalance, we are facing high vibration issue in the power DG Set. Because of coupling, components non-connectivity, oil issue, rubbing, misalignment, or other journal issues. Continuous vibration in DG Set may be damage internal parts of the generator during the operation, To avoid this problem you need to do a proper inspection 

5. The operational issue in the DG Set motor

To get the continuous power supply during the main grid failure, generator components running functionality in a proper manner are very important, especially the motor of DG Set. Most of the time due to continuous running hours your power generator gets overheating. And you facing an unwanted shutdown. So this is very important to check water level or other generator cooling method during the operation of DG Set.

6. The generator is out of step

Generator out of step or  Loss of Synchronism occurs when a generator experiences a large increase in the angular difference of the ElectroMotive Force. That issue will occur when other generators to which it is connected, usually following a major power system disturbance. To avoid this problem in DG Set you need to check the connection between both DG Set, operational condition & performance of Genset.

7. Overheating in bearing & pressure in the lubrication

As we previously explained, the overheating in the DG Set is one of the main reasons for the auto shut down of the standby generator. Also, the bearing can be expected to fail and cause other equipment to fail without lubricants. Overheating of the generator is the result of improper lubrication.

Types of External Faults in a Generator

Types of external faults in a generator are due to abnormal operating conditions and external power system faults. Here get the list of a few common external faults that occur in the generator for home or any industrial DG Set.

  • External short-circuit
  • Non-synchronized connection
  • Out-of-step
  • Overload
  • Cummins generator Overspeed fault
  • Phase unbalance and negative phase sequence
  • Frequency fluctuations
  • Voltages fluctuation

This is the list of various external faults in the DG Set that occurs due to further reasons. There is no matter which type of DG Set you are using either 3 phase or single-phase generator. The problem you are facing due to any of these reasons in your different type of Genset.

How to protect a DG Set- Generator protection tips

The generators are connected to an electrical power system, hence any fault in the power system should be eliminated from the generator to avoid severe damages. Many varieties of faults occur in the system, that is why generators are protected with full protective schemes. The risk of a fault cannot be eliminated even after ensuring efficient construction, design, operations, and preventive means of protection. The device used in the generator ensures the elimination of faults that occur as quickly as possible.

There are mainly two type of possibility to protect a Genset, the first one Protective relays to detect fault that occurs outside the DG Set & the another one is Protective relays to detect fault that occurs inside the DG Set. Here get the list of the best way to protect your generator against any problem.

1. Insulation failure protection

The longitudinal differential protection of the generator is provided in the stator winding against phase to phase or phase to earth fault. The second protection scheme for stator winding is inter-turn fault protection. This form of protection is essential for all large generating units with increasing size and voltage as a generator produces a relatively high voltage in comparison to its output, which contains a large number of conductors per slot.

2. Stator earth fault protection

Stator earth protection is one of the major protections provided to generators. The capacity of generators has increased by more than 500MW so it is crucial to reduce the outage time. Short circuits between the stator winding and stator core are the common electrical faults in the generators. Inter turn faults, which are difficult to detect, will quickly develop into the ground and will be tripped by the stator earth fault protection. A current transformer is mounted in the neutral-to-earth connection when the stator neutral is earthed through a resistor.

3. Unbalanced stator loading protection

The unbalancing which occurs due to fault in the stator winding itself can be cleared instantaneously by the differential protection provided in the generator. The unbalancing occurring due to external faults, might remain undetected or may persist for a significant period of time, depending on the protection coordination of the generator. These types of faults are cleared by installing a  negative phase sequence relay to match the withstand curve of the machine.

4. Stator overheating protection

The overheating is detected by embedded temperature detectors which are caused by overloading. The temperature detector coils form a Wheatstone bridge circuit and are arranged to measure the current flowing in the stator winding. You need to do special observation when you choose any used Genset for the power backup service.

5. Low vacuum protection

This protection is in the form of a regulator which compares the vacuum against the atmospheric pressure. The stop valves are closed and the main circuit breaker is tripped if the vacuum conditions do not improve below 21 inches.

6. Protection against lubrication oil failure

The lubrication oil is obtained from the same pump as governor oil and failure of the governor oil will automatically stop the valve from closing.

7. Loss of boiler Firing Protection

The protection against loss of boiler firing is obtained by providing contacts with the fan motors which may trip the generator and by using boiler pressure contacts that unload the generator if boiler pressure falls.

8. Protection against prime mover failure

The generator will continue to rotate in motoring mode if the prime mover fails to supply mechanical energy to the generator. It takes electrical energy from the system instead of supplying it to the system.

9. Protection against rotor distortion

To minimize the disruption, the rotor is turned at a low speed during the cool-down process. It is standard practice to fit shaft eccentricity detectors as uneven temperature distribution can destroy the rotor.

10. Protection against vibration

The vibration detectors which are mounted on the bearing pedestals consist of a coil on springs between U-shaped permanent magnets. The output voltage is passed from the coil into integrating circuits and then into intervals indicating the instrument. Also, by using a silent enclosure for DG Set, you can easily reduce the noise & vibration of the diesel generator.

11. Back up protection

Backup protection should always be given to the generator as if the faults that occurred may not have been cleared by the appropriate protection scheme, then backup protection relays should be operated to clear the previous fault. It is very desirable to apply an overcurrent relay in combination with the under voltage relay, controlling the fault settings.


Prevention against the various problem in DG Set is helpful to increase the shelf life & the performance of Genset. But to get a continuous power supply from your industrial portable Genset, the proper care & maintenance are mandatory. The prevention against overloads and abnormal conditions of the machine to avoid severe damages. Electrical generators are subjected to an internal fault or external fault. The fault that occurred in the generator should be cleared as soon as possible, as they may create damages. Great care should be taken in coordinating the system used, to ensure that a sensitive, selective, and discriminative generator protection scheme is obtained. Also, when you choose a rental generator service for temporary power needs, maintenance will be offered by the service provider.

Here in this blog, we have shared the information for various types of generator faults including external & internal faults. I hope this article will help you a lot more to understand better & the major prevention to get optimal power output from Genset.

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