No more worries about inrush current

No more worries about inrush current
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Dimensioning is crucial in order to ensure that a circuit breaker doesn’t trip due to a transformer's inrush current. Discover here how to choose the correct type of transformer and what other solutions EREA have to offer.

Connecting a transformer draws a high current from the network for a fraction of a second. This is such a brief event that it does not cause heating of the cables. Nevertheless the inrush current can cause a circuit breaker to trip if it is not correctly dimensioned .

Solution 1: circuit breakers

The first option to prevent tripping is to select the correct fuses or circuit breakers protecting the installation's cabling. A type D circuit breaker or an aM type fuse can handle a higher inrush current. Take a fuse where the current is 1.5x to 2x the value of the maximal primary line current in the transformer. This will perform even under the most difficult circumstances.

In some cases a C-type circuit breaker or a gG fuse may be used. In order to ensure a dependable installation you will, however, have to select a higher nominal value.

This does have two consequences however:

  • The copper section is larger, resulting in increased cost
  • It is possible that the entire electrical network will need to be upgraded.

The EREA catalogue has tables with recommended safety devices . Turn to page 10 and 32 for single-phase transformers, or pages 8, 18 and 22 for three-phase transformers.

Solution 2: reduce the inrush current with IRC transformers

For applications where higher inrush currents are not manageable EREA also have options to reduce the inrush current: IRC transformers with a reduced InRushCurrent. 

These transformers can be used with a non-overdimensioned C-type circuit breaker: Protection on the basis of the nominal current.

The downside, however, is that these transformers are larger, heavier and more expensive.

EREA currently carry two series of IRC transformers:

  • Our standard EC and ECT series currently include 3 single-phase low inrush current (EC) transformers and 3 three-phase (ECT) models. The capacity range of these transformers is primarily geared to the charging of electric vehicles.
  • In our standard PVT series we offer a range of 10 3-phase transformers. These range from 6kVA to 70kVA and are primarily intended for the connection of convertors for photovoltaic installations or to connect heat pumps.

Solution 3: reduce the inrush current with an IRC module

A second method of reducing the inrush current is to combine a standard transformer with an inrush current limiter.

These are available in 3 configurations: 8A – 16A – 25A

More information about safety devices used with transformers

Download our white paper 'EREA-Dimensioning-of-the-line-protection-of-a-transformer' here.

Download whitepaper

Or please contact us.

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