Understanding Potential Transformers
Introduction
A “PT” or “VT” (Potential Transformer or voltage transformer) is a precision instrument transformer connected in parallel across high-voltage lines in a wye-wye configuration for voltage monitoring and protection. PT’s are basically step down transformers with an extremely accurate turns ratio. They step down the high voltage to a level which can be measured by standard measuring instruments. PT’s have a large number of turns in the primary winding and a smaller number of turns in the secondary winding.
For example, a PT is typically rated in the form of a primary to secondary voltage ratio such as 2,400:120. This means the voltage across the secondary is 120VAC when the primary voltage is 2,400VAC. This is useful because as the primary voltage fluctuates between 0 and 2,400VAC, the secondary voltage will also fluctuate in a linear, directly proportional fashion between 0 and 120VAC. This PT secondary can be connected to the input of an instrument such as a power quality monitor, along with other devices such as CT’s (Current Transformers), in order to multiply the two input signals and produce a power reading in watts.
More About PT’s
PT’s are widely used in the Power and Utilities Industries in electrical substations and control rooms. They are also used in various control panel applications.
There are several manufacturers of PT’s (Potential Transformers), such as:
Flex-Core
Resa Power
PT distributors are located all around the continental US.
PT’s are available in single-phase, three-phase, indoor rated, outdoor rated, metering class, etc. Below are a few sample pictures of PT packages:
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