Testing of power transformers and shunt reactors Intro 5 Testing of power transformers and shunt reactors Routine, type and special tests 2nd edition published May 2010 under participation of Ake Carlsson Franz Wegscheider Gottfried Schemel Jitka Fuhr ABB Ltd Transformers Affolternstrasse 44 P.O. Box 8131 CH-8050 Zurich Switzerland.
![]() Main Differences
Shunt Reactor and Transformer both appear similar in construction. Reactors are also often equipped with Fans for cooling similar to Power Transformers.
However, there are major differences between the two. While a Power Transformer is designed for efficient power transfer from one voltage system to another, a shunt reactor is intended only to consume reactive VArs (or in other words it can be stated as to produce lagging VArs).
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Thus, there are more than one winding on a Power Transformer with magnetic core which carry the mutual flux between the two. In reactor there is just one winding. The core is not therefore meant only to provide a low reluctance path for flux of that winding to increase the Inductance.
In case of a Power Transformer, primary Ampere-Turns (AT) is sum of exciting AT and secondary AT. AT loss (in winding resistance, eddy loss and hysteric loss) is kept to as minimum as possible. Exciting AT is small compared with the secondary AT. Rated current is based on the load transfer requirement.
Magnetizing current is small and is negligible value when compared with the secondary rated current. Further, since mutual flux is main flux which results in transformation, leakage flux is kept small and will be based on fault current limitation.
In case of a Shunt Reactor due to absence of other windings, all primary AT is equal to the exciting AT. Similar to a Power Transformer, loss in AT (in winding resistance, eddy current and hysteresis) are also kept to minimum by design. Magnetizing AT is major component of a Shunt Reactor. Reactor magnetizing current is its rated current.
Since a Shunt Reactor magnetizing current is large, if it is designed with Iron alone as a Power Transformer, there will be large hysteresis loss. Air gaps in Iron core are provided in a Shunt Reactor to reduce this loss and to minimize the remanent flux in the core.
Thus a Shunt Reactor may also be constructed without iron (air-core).
By construction, a Shunt Reactor can be oil immersed or dry type for both with and without iron core.
Dry type Reactors are constructed as single phase units and are thus arranged in a fashion to minimize stray magnetic field on surrounding (in the absence of metallic shielding). When such an arrangement is difficult, some form of magnetic shielding is required and designed with care to minimize eddy current loss and arcing at any joints within the metallic loops. One of the advantages of dry type reactor is absence of inrush current.
Oil immersed reactors can be core-less or with gapped iron core. These are either single phase or three phase design with or without fan cooling. These are installed within tanks which hold oil & act as metallic magnetic shields.
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