Transformer Tap Voltage: What, Why, How To Find And Detailed Facts

This article elucidates on transformer tap voltage and its related phenomenon. Taps are connections provided on the windings to vary the secondary voltage levels. Most of the transformers use tap changers.

On load tap changers are generally found on the high voltage side. In transformers, the high voltage winding turns are more than the low voltage winding turns. Therefore if the tap changer is placed on the high voltage side, it gives better transformer tap voltage. On the contrary, off load tap changer is found on the low voltage winding.

What is transformer tap voltage?

Transformer tap voltage refers to the output voltage. Unlike the fine voltage regulation obtained from placing the tap changer on the high voltage side, tapping on the low voltage side may result in faulty voltage regulation.

To calculate transformer tap voltage, we need to follow the steps-

  1. Find the lost voltage and add that with the load voltage.
  2. Find the increase factor and from that find new Np( primary turns) using the Vs/Vp= Ns/Np relationship
  3. Subtract from the previous Np and find the percentage change
  4. Find the new voltage 
Transformer tap voltage
Transformer Taps on the high voltage side; Image Credits: Quora

Transformer center tap voltage?

Transformer center tap voltage is the output of a center tap transformer. Center taps are created using a wire exactly in the middle of the secondary winding of a transformer. Such a transformer is a center tap transformer.

Center tap divides the secondary winding of a transformer into two parts. Thus we can get two different transformer tap voltage outputs across two line ends. Suppose, the secondary voltage is 20 V. Then the voltage will be half i.e. the voltage of 10 V each will be received on both the lines.

Transformer Tap Voltage-FAQs

Center tapped transformer vs normal transformer

The key difference between a center tap transformer and a normal transformer is the variety of voltages. Any normal transformer can generate only one output voltage while a center tapped transformer can provide two.

The working principle of a center tap transformer is mostly the same as a normal transformer. Just at different loads, a center tap transformer is capable of providing two transformer tap voltages as the secondary winding of it is divided in two parts. This dual voltage generation is not possible in case of a normal transformer. 

What is tap changer in a transformer?

In large transmission and distribution systems, there can be a need for varied voltages. A tap changer provides tappings on the transformer coil and helps in changing the turn ratio and thus regulates the voltage. 

Tap changer can be on load and off load or de-energized. Off load tap changers are used when continuity of the load supply is not an issue and slight voltage regulation is required. In on load tap changers, the problem is solved and the load is connected for the entire time. They also have many taps on the windings.

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Why is tapping necessary?

Tapping on the winding of a transformer, can provide a certain number of windings in a transformer. We can change the turn ratio to obtain the voltage required by changing the connections from the different taps given.

According to the voltage requirement, the load keeps changing. At higher voltages, the losses are also significant. So, there is a need for voltage regulation to maintain almost the same voltage. Tap changers do that. Some on load tap changers follow the make before break method so that is supply remains unaffected.

Why tap changer is used in transformer?

Transformer tap changers can rise up or down the secondary voltage by changing the primary or secondary turn ratio. The tap changer is located at the high voltage section of the transformer as the current there is low.

Taps are placed on the winding that needs to be regulated. It is inside of the main transformer tank that is joined in series with the primary winding. Taps are provided to control the voltage. Taps are supplied to the high voltage side because the voltage variation range is high and the operating current is low.

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