Understanding The Grounding Transformer And Furnace Transformer

By Author: Carol England
Total Articles: 82
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The Grounding Transformer is also popularly known as “GT” in the transformer industry. It differs from the usual furnace transformer you have known since it is more commonly used as a means to establish a return path for certain ground fault currents on a system that is being isolated or un-grounded. The use of Grounding Transformer differentiates the construction in several different ways.

Basic Criteria Needed for the Design of GT

There are certain criteria that must be met when it comes to the design and construction of the Grounding Transformer and two of the most basic criteria are the following:
• They should be able to carry the fault current without the need for excessive heating which increases the tendency of the conductors and adjacent insulation to deteriorate.

• They must be created in a way that they could carry out the continuous phase and neutral currents without having to exceed on the temperature ratings.

It is on the second parameter that the separates the GT from other distribution transformers, including the furnace transformer. Some of these transformers ...
... are designed to carry out a fault current that is limited by their impedance, up to a maximum duration of 2 seconds for every standard set. On the other hand, the Grounding Transformer should be able to carry a fault current which is not limited by its impedance for durations that do not exceed the “two second” limitation. On most cases, it is often a “ten second” limitation and even more. The GT design should be done in a way that right at the end of the extended time period, the conductor temperature is lower than the critical thermal limit, known as the “standards”.

Main Concerns of Furnace Transformer

Among the main concerns of other distribution transformers, including the furnace transformer is the loading, especially when it comes to the heating process. Radiators will need to be added to the transformer in order to help control the insulating fluid at a steady state whenever the temperature would increase. Unfortunately, this will not help during fault conditions. The heat that is generated during a fault happens in only a short period of time, and in fact, in mere seconds only in some instances. Such calculation assumes that all heat is being stored on the conductor simply because the heat dissipation will not happen fast enough that it combats the rapidly heating conductors. The Grounding Transformer takes into this account and is designed in a way that the conductor will be able to easily handle fault heating without the need to rely on insulating oil for heat transfer in case of fault.

Grounding Transformer Specifications

Most of the GT specifications that met the criteria set for the design and implementation of the transformer allows the steady state cooling to be calculated with the help of some magnetizing current as well as HV 12R loss that results from the energizing core only. This often leads to the misconception that the Furnace Transformer is better cooled, although the opposite happens during faults.

For more information on Furnace Transformer, you can click here