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Intermittent use of a transformer  

Transformers are designed for continuous nominal load. If a transformer is only loaded intermittently, its size can be reduced.

The intermittent use percentage can be determined with the following formula:

ED = [ton /(ton + toff)] x 100 %

  • ED = time of intermittent use in percentage
  • ton = transformer load time
  • toff = transformer idle time

Transformers that are continuously loaded using nominal power (Pn) can be intermittently loaded with power ( P2) as follows:

P2 = Pn x √ (100/ED)

  • P2 = allowed load in intermittent use (W)

The prerequisite of intermittent use is that the transformer's warm-up time constant is significantly larger than the sum of load and idle times.

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