Multi Tap Transformer: What, Why, Working, Applications, Detailed Facts

This article illustrates the all round information about multi tap transformers. Taps are some interconnected access points between the terminals of the transformer windings placed at some distance from each other. 

Depending on the turn ratio, any transformer has fixed rated voltages in its primary and secondary sides. But sometimes, there are requirements for different voltage levels. If we change the turn ratio, varying voltage is possible. Tapping is used for that purpose. A multi tap transformer has multiple such taps in its windings.

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What is multi tap transformer?

A multi tap transformer is known to be a generic step up or step down transformer with many taps present in the primary or the secondary side. These taps can adjust the turn ratio and voltage according to the need.

Multi tap transformers can be single phase or three phase. These transformers can provide voltage regulation and compensate for the line voltage drop. Each tap means different turns in the winding and different current transformation ratios. So, multi tap transformers are flexible for numerous applications.

What is a multi tap low voltage transformer?

Multi tap low voltage transformers are also known as lighting transformers as they are used for landscape lighting. Generally, these transformers have 300 watt power capacity with four taps ranging from 12- 15 volt. 

Multi tap low voltage transformers are usually made up of stainless steel with a toroidal core. For ease of use, the transformers come with a digital display and dusk to dawn sensor, making them ideal to use indoors. For the toroidal core, multi tap low voltage transformers are durable and provide calm and quiet operation. 

How does a multi tap transformer work?

We should first join the first 12 Volt tap with the transformer for tapping. The user should connect the other wire with the common white tap. Then, we have to measure the voltage of the first light with the help of a voltmeter.

In the next step, we shall calculate the voltage drop by subtracting the measured voltage from 12 Volt. Now, the equivalent voltage tap is ( voltage drop + 12 Volt). We can move the wire to the newly calculated voltage tap from the initial 12 Volt tap. We can leave the other wire unchanged, i.e., with the white tap.

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Uses of multi tap transformer

The primary reason to use a multi tap transformer is to cope with the varying supply voltage. Power and input voltage changes occur due to load conditions and other factors. Multi tap transformers help to balance that.

Heating appliances utilize multi tap transformers. Over time, the resistance of heating materials increases. Therefore, the current passing through them reduces. If we want to regain the amount of current in them, we must increase the applied voltage. The taps in the transformer do the job by recouping the voltage.

Multi tap transformer wiring

The wiring of three phase multi tap transformers can either be delta or wye configuration with three phase wires and one neutral. This kind of wiring can provide two to three different voltages for each tap. 

Delta connected multi tap transformer
Delta configuration; Image Credit:
Wye connected multi tap transformer
Wye configuration; Image Credit:

Multi tap transformer schematic

The diagram in image 3 represents a schematic of a general multi tap transformer.

Below is the schematic diagram of a multi tap transformer. We can see multiple taps on the secondary side. Similarly, there can be taps on the primary side as well. Both high voltage and low voltage sides are used for tapping. But in smaller ones, tapping is done on the low voltage side, and in bigger ones, tapping is done on the high voltage side.

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Schematic Of a Multi Tap Transformer

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Multi tap transformer connections

Let us understand the multi tap transformer connection with the help of an example. Suppose we want to connect the transformer in a delta configuration. We will first join the neutral to the transformer common or COMM. 

Then we will either connect phase A or C to the first tap (WHITE) on the transformer. We would join our neutral (GRAY) and any phase to the black and brown wires on the transformer for the wye configuration. Similarly, any two phases on the wye configuration should be connected to the gray and black wires on the transformer.

Multi tap control transformer

The control transformer is a multi tap step up or step down transformer with multiple taps in the primary or secondary winding. They can work continuously for a more extended period of time under small loads. 

Multi Tap control transformers are commonly used in machinery and equipment such as power control lights and indicator lights. Some multi tap control transformers have a single phase control converter with a high power rating, average AC supply voltage, and multiple secondary voltages operating in AC 50 Hz or 60 Hz circuits.

Multi tap current transformer

Multi tap current transformers are suitable for choosing the accurate, current transformation ratio required for any specific task. There can be up to ten ratios from which we can select according to the voltage needed.

Multi tap current transformers are suitable for relay testing. These transformers are integrated with primary apparatus such as bushing CTs on power transformers or gas insulated switchgears, circuit breakers. We can select the taps after testing, and details will be displayed on the screen. Taps can be manually changed.

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