How to manage transformer inrush current?

Electrical
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                     TRANSFORMER INRUSH CURRENT

Transformer inrush current is due to the energization of the transformer and it is usually seen in one winding of the transformer and mostly it would be the primary winding this situation arises when the primary of the transformer draws maximum instantaneous current, when the secondary of the transformer is open circuit (not connected to the load) this inrush current won’t produce any permanent faults but it will cause the unnecessary switching in the circuit breaker.

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There are several methods to reduce the inrush current, the conventional methods can’t be used because of the high value of resistances, so newer methods are used, by using power quality standards and the reconstruction of the power system will enforce the electric utilities to decrease the amount of inrush current

DISADVANTAGES OF INRUSH CURRENT

  • Failures and incorrect operation of electrical machines and relay system
  • Electrical and mechanical vibrations among the winding of the transformer
  • Irregular voltage distribution along the transformer windings
  • Voltage drop will be high at the power system at the energization time
  • Harmonics and current disturbance in the system and lower power quality characteristics
  • Due to the various frequency of inrush current there is a possibility for resonance

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REDUCTION OF INRUSH CURRENT BY USING STARTING RESISTANCES

The inrush current will flow to the transformer neutral point due to the unbalanced feature of inrush current, by using a series resistance in the neutral point of the transformer it will behave as starting series resistance, and it will improve the inrush current reduction

A great reduction of the inrush current can be seen when the three phases of the transformer are switched on simultaneously and it decreases greatly when it is switched on non-simultaneously.

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Inrush currents are due to the flux variation in the transformer core which is dependent to network voltage we can use some parameters like inductance, resistance, to reduce the transient flux of the transformer and it will result in a reduction of the inrush current

Some common solutions for reducing the inrush current

  • Hysteresis flux of the transformer can be reduced
  • Switching on the transformer at the voltage peak
  • Increasing the frequency at the switching time
  • Reducing the voltage at the switching time
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What Are the Effects of Inrush Current?

Inrush current, if not managed, can put your transformer & power system at risk. This could involve two (or) more of the following:

Voltage Drop

When the voltage decreases dramatically, all portions of the system must work harder than usual, perhaps causing the system to burn out. This can also lead to power disruptions and supply instabilities.

Mechanical Stress

Certain levels of inrush current might result in excessive mechanical stress, reducing the lifespan of the transformer, electronics, and other system components.

Triggered Switches

Circuit breakers & other switches may detect inrush current as an anomaly, causing them to trip inadvertently. This causes unwanted interruptions, which have a significant impact on the system’s overall efficiency. As a result, some steps must be made, such as increasing the breaker size.

Increase Downtime

If the inrush current is not effectively managed, it can cause repeated transformer breakdowns or, worse, total system failure, resulting in shorter operations and more time allocated for maintenance and repair.

Vibrations

The large surge in inrush current can cause the transformer’s windings and other components to vibrate. These vibrations can also produce noises, which are a strong indication that there is a problem with the system.

Overloading

Inrush current can exceed the transformer’s designed capacity. Ultimately, the transformer becomes overloaded, overheats, & eventually fails. More than time restrictions, this may cause damage to insulation & other thermal components, reducing the life of your transformer.[quote=“Rabert, post:2, topic:6441, full:true”]

Voltage Drop

When the voltage decreases dramatically, all portions of the system must work harder than usual, perhaps causing the system to burn out. This can also lead to power disruptions and supply instabilities.

Mechanical Stress

Certain levels of inrush current might result in excessive mechanical stress, reducing the lifespan of the transformer, electronics, and other system components.

Triggered Switches

Circuit breakers & other switches may detect inrush current as an anomaly, causing them to trip inadvertently. This causes unwanted interruptions, which have a significant impact on the system’s overall efficiency. As a result, some steps must be made, such as increasing the breaker size.

Increase Downtime

If the inrush current is not effectively managed, it can cause repeated transformer breakdowns or, worse, total system failure, resulting in shorter operations and more time allocated for maintenance and repair.

Vibrations

The large surge in inrush current can cause the transformer’s windings and other components to vibrate. These vibrations can also produce noises, which are a strong indication that there is a problem with the system.

Overloading

Inrush current can exceed the transformer’s designed capacity. Ultimately, the transformer becomes overloaded, overheats, & eventually fails. More than time restrictions, this may cause damage to insulation & other thermal components, reducing the life of your transformer.

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