9 Issues On Voltage Of AC Generator

Voltage stability can be of different types depending on the external circumstances. Because the device might have to stabilize the voltage for the short or long term. Also, the disturbance level of the voltage plays an important part. It let us know if the amount is large enough to be overcoming.

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Proper functioning of an AC generator is what one expects from quality generators. This includes the voltage of the generator is stable enough not to burn the appliances. Because the constant fluctuations of the voltage prove disastrous for your electric devices. As a result, you might have to change the devices due to them getting burned down.

So let us discuss what it means by voltage stability and how you can keep your voltage stable in an AC generator.

What is voltage stability?

Voltage stability is the ability of the power system to sustain a fixed voltage. The voltage remains fixed under tolerable conditions and even under disruption (Kundur, 2019). Because that is the purpose of designing a voltage stability framework.

Voltage stability can be of different types depending on the external circumstances. Because the device might have to stabilize the voltage for the short or long term. Also, the disturbance level of the voltage plays an important part. It let us know if the amount is large enough to be overcoming.

We classify voltage stability into the following types:

In how many types can voltage stability be classified?

We can classify voltage stability into two main types based on:

  • The amount of disturbance.
  • The time for which the disturbance is being done.

We can further divide them into two more types. Those are a small and large amount of disturbance and less and more time of disturbance.

What do you mean by small and large disturbance voltage stability?

When a small amount of load rises on the generator, the internal mechanism of the generator readjusts itself. This happens due to the additional load of the attached appliances. This readjustment ensures that the system keeps the voltage within an acceptable range. We call this small disturbance voltage stability.

There are two reasons for this small disturbance:

  • Due to the load characteristics
  • The continuous/discontinuous control within the mechanism.

While large disturbance voltage stability is a more complex process.

What do you mean by Bus voltage? How it relates to large disturbance voltage stability?

A bus voltage is the same as the battery voltage that varies by 20% from the stable value of voltage. It can be a regulated or an unregulated one. In the end, despite fluctuation, it remains almost constant.

Large disturbance voltage stability means the ability of the generator to keep the bus voltage within an acceptable range. The causes of large disturbance include:

  • Short circuit
  • Line outage
  • System failure

The system’s framework and its load conditions tell large disturbance voltage stability. Also, the control and protection of the two combined affect large disturbance too.

What do you mean by long-term and short-term voltage stability?

As per the period and the length of time, we divide voltage stability into two types:

As the name implies, long-term voltage stability lasts for a long time. Usually, it lasts for several minutes to even dozens of minutes.

While short-term voltage stability lasts for short time. It lasts usually for a few seconds.

What is the difference between a voltage regulator and a voltage stabilizer?

Both regulator and the stabilizer work to adjust the output to a normal level. The difference between them comes with the input. The voltage regulator stabilizes the load current giving a constant output. While the stabilizer gives a constant output. It does this by reducing the fluctuations in load voltage (Kebo, 2020).

What are the factors that affect the voltage in an AC generator?

Following factors affect the voltage in an AC generator:

a) The number of turns on the stator windings:

The more the number of turns on the windings more is the voltage produced. Because the output voltage is proportional to the number of turns in the windings. We can manually adjust this only if we supply the windings with fixed taps.

The number of windings is usually fixed at the design stage of the alternator.

b) Magnetic field strength:

If the magnetic field is strong, it helps in creating more flux. The strength of the magnetic field develops in the rotor. It cuts the stator windings. More the flux density more is the voltage.

You should note that you cannot increase the maximum strength on an infinite level. There comes a point when the iron reaches a saturation point. This means that despite you provide more excitation, the flux density will not further increase. Instead, this might negatively affect the windings in creating winding ad iron losses.

c) The rotational speed of rotor:

If we increase the speed of the rotor, more flux will be produced. As a result, the output voltage will increase. If we decrease the speed of the rotor, the output voltage will be decreased.

Changing the rotational speed of the rotor is not a preferred option. Because it will change output frequency too. So we prefer regulated rotational speed to maintain constant output.

d) Output load on the generator:

When the load current increases, the windings internal resistance also increases. This results in a drop in the output voltage.

e) Load impedance:

Capacitance increases the output voltage of the generator. While inductance decreases it.

How to keep the voltage stable in an AC generator?

You can keep the voltage stable in an AC generator by adjusting the direct current supply to the rotor.

You can do this by utilizing an Automatic Voltage Regulator (AVR). The automatic voltage regulator controls the direct current field to regulate the output voltage. In spite of the change in load current, the AVR trims output voltage and keeps it constant (Mckenzie, 2018). This maintains the load. As a result, it meets the load requirements.

No manual ways are suggested to keep the voltage stable. Although, you can do this by:

  • Keeping the number of turns on the stator windings the same throughout the time of use.
  • Keeping the field strength of the magnet the same.
  • By maintaining the constant speed of the rotor.
  • By keeping the external load on the generator the same.
  • By carefully adjusting the capacitance and inductance of the generator.

As these manual ways include working with the internal mechanism of the generator, they can prove hazardous. This may prove detrimental to the life-span of the generator. So you should better leave it to the professionals.

Although we recommend you to prefer buying a good quality generator. A good quality generator surely includes an AVR. Because constant fluctuation can adversely affect the generator windings.

What are the advantages of keeping voltage stable in an AC generator?

By keeping voltage stable in an AC generator you can:

  • Increase the life of the generator.
  • Protect yourself from any hazardous moment that might occur due to voltage fluctuations.
  • You get to experience less to no power losses.
  • The power shift from the grid to the generator becomes significantly easy.


After reading this article, you must have understood voltage stability. Classifying voltage stability into large, small, and on period bases makes the problem easy to solve. After identification, we can ask for an AVR that entirely fits the framework.

Although it’s always better to never compromise on quality. But if you have bought one, just don’t replace it in one instant.
You should better get advice from the professional. As manual working with internal mechanisms can prove hazardous to the health of the generator for various reasons.

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Hey all, I'm Baymax Yan, working at a generator manufacturer and Having more than 15 years of experience in this field, and I belives that “learn and lives.” The sure thing is that I can often help my work. So I have created the blog to share all my knowledge with you. Hope my sharing helps!

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