Posts Tagged ‘secondary winding’

Current Transformers

August 2nd, 2013 | 1 Comment | Posted in Electrical distribution
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Hi there, here’s the last but one part of Nasir’s tutorial on transformers. The last one will be about “3 Phase Transformers”. Hope you’ll enjoy it and find it helpful.


Current transformers can be defined as the type of instrumental transformers which are used to convert very high currents which can burn or cause damage to measuring instruments like ammeters or other small devices like relays, into lower current values, which are in direct proportion to their higher, primary current values.

In this way, current can be easily measured through the device, and as it is directly proportional to the original high current, the true and precise values of current can also be found without damaging the instrument.

The secondary current differs in the phase angle from the primary current in a very small value which can almost be approximated to zero if the direction of the connections are appropriate.

On the basis of the output supply, the current transformers can be classified into two categories:

  1. Measuring Type Current Transformers
  2. Protection Type Current Transformers


Auto Transformer

July 19th, 2013 | 1 Comment | Posted in Electrical distribution
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Nasir, a member of the Electical Engineers Community sent us a 11 parts tutorial on transformers. Today here’s the 9th part focused on Auto transformers. As for the previous parts, you can find them in the blog and on the forum.

An auto transformer is the one which consists of a single winding, part of which acts as the primary winding of the transformer, and some part of which acts the secondary winding, which can be varied by switching between the contacts of the transformer. By varying the contact of the switch we can change the number of turns which are accommodated in the secondary winding.

Since the output voltage depends upon the number of turns of the secondary winding, so in this way the voltage output can also be varied. For this reason, an auto transformer is also known as a “Variac” because it is mostly used to vary (step up or step down ) the output voltage which has to be supplied to the circuit.

Construction and working of an Auto Transformer

In general transformers, there are two windings which are magnetically linked to each other, but re physically separated from each other. But in an auto transformer, both the primary and secondary windings are connected to each other, both physically and magnetically.

The internal construction of an auto transformer is shown in the figure below:

Auto transformer

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