Some Facts About Load Tap-changing Transformers

By Author: Cyrus Joseph
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Load Tap-Changing Transformers are the kind of device that is often being fitted on power transformers for the purpose of regulating the output voltage that is needed for certain levels. This is often achieved by modifying the ratio of the transformers on the system through altering a number of turns on one winding of a certain transformer. Supply authorities are often obliged to their customers to maintain enough voltage in between certain limits. These transformers provide variable control in keeping the supply voltage to stay within these limits. In fact, almost 96% of all Auto-Transformers these days that are above 10MVA are incorporated on the transformer as a way of regulating the voltage.

On Load or Off Load

You can choose between on load or off Load Tap-Changing Transformers. The on load tap changers often consist of a diverter switch as well as a selector switch that operates as a unit in order to effectively transfer current from one voltage tap to another. It was more than 60 years ago that the on Load Tap-Changing Transformers were introduced in order to provide power to transformers as a means of voltage ...
... control.

Two Fundamental Features

There are two fundamental features that you can find on tap changers. First is that some form of impedance is present which helps to prevent short circuiting of the tapped section. Another is that a duplicate circuit is being provided in order for the load current to be carried out by one circuit while switching is also being performed on the other.

The impedance stated above is either reactive or resistive. The Load Tap-Changing Transformers that has a resistive type of impedance often makes use of high speed switching while the reactive type makes use of slow moving switching. The high speed resistor switching is now considered to be the most popular method used worldwide.

Locations of the Tapped Portion

The tapped portion of the winding can be found on several different locations on the Auto-Transformers and this will usually depend on the type of winding. They can either be found on any of the following:

• at the bottom line of the winding

• in the middle of the winding

• at the star point

The most common types of arrangements are the last two, which is right in the middle of the winding as well as at the star point. This is due to the fact that they are able to give the least electrical stress in between the tap changer and the earth, along with subjecting the tapings into less physical as well as electrical stress due to the fault currents that get in to the terminals. At lower voltages, the Load Tap-Changing Transformers might be located on either the high voltage windings or the low voltage windings.

The Auto-Transformers are among the most expensive piece of equipment that is often used in a power system and the political consequences of failure might turn out damaging. This has been proven a lot of times in the past with the media and political attention surrounding blackouts on several locations all over the world.

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