Types of Faults in an Alternator

An alternator is an electromechanical energy conversion device that converts mechanical energy into alternating current electrical energy. An alternator is basically a synchronous generator that produces electricity at a certain frequency.

To drive the alternator, a prime mover is used. Some commonly used prime movers are steam turbine, water turbine, gas turbine, and diesel engine. Like any other rotating electrical machine, different types of faults can also occur in an alternator. Due to these faults, we get a reduced efficiency and performance of the alternator. Further, these faults can cause malfunctioning or complete failure of the alternator that imposes a significant maintenance cost.

In this article, you will learn about different types of faults that occur in an alternator so that you can take prevent action and reduce the down time as well as maintenance cost.

Types of Faults in Alternator

In an alternator, a fault is nothing but any abnormal functioning that affects the operation and reduces the efficiency and performance.

There could be several different types of faults occur in an alternator. These faults can be due to either electrical issues or mechanical issues or any other operational issues.

A list of faults that can occur in alternator is given below −

• Prime mover failure fault

• Field failure fault

• Over current fault

• Over voltage fault

• Over speed fault

• Unbalanced loading

• Stator winding faults

Let us discuss about each type of fault that occur in an alternator in detail.

(1) Prime Mover Failure Fault

The prime mover failure fault occurs when the source of input mechanical energy fails or malfunctions. Some common reasons of prime mover failure are mechanical damages and fuel delivery interruption.

The common consequence of the prime mover failure is that the alternator starts working as a synchronous motor and takes current from the supply system. This effect is known as inverted running.

(2) Field Failure Fault

In an alternator, an excitation system is provided to produce required magnetic field for the operation.

When there is a problem in the field excitation system of the alternator and it is unable to setup sufficient magnetic field required for operation of the alternator. This condition is called field failure fault.

The main reasons behind the failure of field system are lose or broken connections, damaged brushes, short-circuiting of rotor winding, etc.

The major consequences of the failure of field system include output voltage drop, complete loss of electrical output, etc. However, it is also important to note that the field failure fault in alternator occurs very rarely.

(3) Overcurrent Fault

An undesirable condition in which an electric current of a value greater than rated current flows through the windings of the alternator is known as overcurrent fault.

The overcurrent fault can damage the alternator’s windings permanently.

The primary reasons behind the overcurrent fault are excessive loading, short-circuited windings, insultation failure, etc.

Due to overcurrent fault, overheating and permanent damage to the windings can occur.

(4) Overvoltage Fault

When the output voltage of an alternator becomes greater than the rated output voltage, then such a fault is known as overvoltage fault.

The overvoltage fault in an alternator mainly occurs when the speed of the prime mover increases due to sudden loss of the electrical load on the alternator.

The overvoltage fault can result in damage of electrical components like sensors or cause electric fire.

(5) Overspeed Fault

When the rotational speed of rotor of the alternator becomes greater than the rated operating speed, then this condition is called overspeed fault.

The overspeed fault can damage the mechanical structure and components of the alternator and can pose safety hazards.

The major reason of the overspeed fault in an alternator is the sudden loss of electrical loss or failure of prime mover speed control system.

(6) Fault Due to Unbalanced Loading

A condition when there are different currents in different phases of the alternator is termed as unbalanced loading of the alternator.

The primary causes of unbalanced loading are faults to earth and faults between phases in the external circuit of the alternator.

The unbalanced currents can result in overheating, voltage fluctuation, damage to the field winding of the alternator.

(7) Stator Winding Faults

Any kind of fault that occurs within the stator windings of the alternator is termed as a stator winding fault. In other words, the damage that occurs in stator windings of the alternator is called stator winding fault.

Some common types of faults that occur in stator winding are short circuit, open circuit, inter-turn fault, earth fault, phase-to-phase fault, etc.

The stator winding faults can result in reduced voltage output, overheating of the machine, and voltage fluctuations.

Conclusion

This is all about different types of faults that occur in an alternator. There can also be several other mechanical faults like bearing damage, rotor unbalancing, loosening of components, cooling fan failure, etc.

The faults in an alternator can interrupt its operation or reduce the efficiency and performance. Therefore, we need to regularly inspect and test the alternator for any kind of fault so that we can ensure its reliable operation.

FAQs Related to Faults in Alternator

The following section is meant for answering some commonly asked question related to faults in an alternator.

1. What are the probable faults in the alternator?

The following are some most probable faults in an alternator −

• Prime mover failure

• Excitation field failure

• Overcurrent and overvoltage fault

• Overspeed fault

• Unbalanced loading fault

• Stator and rotor winding faults

All these faults are explained in detail above in this article.

2. What are rotor faults in an alternator?

The common faults that occur in rotor of an alternator are given below −

• Short-circuit fault of rotor winding

• Open-circuit fault of rotor winding

• Earth fault of rotor winding

• Inter-turn fault of rotor winding

• Rotor unbalance fault

• Rotor misalignment fault

• Bearing damage

3. What is a turn-to-turn fault on an alternator?

In an alternator, the turn-to-turn fault occurs when two or more turns of a coil are short-circuited. It is also known as inter-turn fault.

4. Which fault is more severe in alternator?

In context to this article, the short-circuit fault is the most severe fault among all the faults discussed above.

5. What happens when alternator is faulty?

A faulty alternator results in the following major issues −

• Degraded performance

• Decreased efficiency

• Reduced voltage output

• Discontinuous power supply

• Malfunctioning of complete electrical system

• Unstable grid operation

• Damage to sensitive appliances and equipment, etc.

6. What is the most common fault with an alternator?

The most common fault that occurs in an alternator is unbalance loading fault.

7. How do I know if my alternator is faulty?

The following are some major indications/ behaviors which show our alternator is faulty −

• Warning lights or alarms

• Voltage fluctuation

• Abnormal noises from the alternator

• Overheating of the alternator

• Burning smell

• Malfunctioning of electrical equipment, etc.