# You asked: What is a control voltage transformer?

Contents

## What is the purpose of a control transformer?

A control transformer is an isolation transformer designed to provide a high degree of secondary voltage stability (regulation) during a short period overload condition typically referred to as inrush.

## What is CPT power?

Medium Voltage Control Power Transformers (CPT) are single phase transformers used to supply control power in medium voltage switchgear and transformers. Nominal primary voltages range from 2.4kV to 15kV. The secondary voltage is typically configured for 120/240V (series parallel) operation.

## Where is the control transformer located?

Most Common Transformer Location

The vast majority of the time, the transformer for the control panel is located inside the air handler. It’s often near the bottom bolted to a back wall or, if the system includes a furnace, to a side wall. The transformer may also be mounted to an outside wall of the air handler.

## How do you test a transformer control circuit?

To test your transformer, simply touch the red and black pins of your ohmmeter to the opposite ends of the transformer’s wiring. Read the display and compare the resistance on your ohmmeter to the resistance stated on the transformer’s data sheet. This is sometimes listed on the transformer’s enclosure.

## Which transformer is used in home?

In distribution networks, the step-down transformer is commonly used to convert the high grid voltage to low voltage that can be used for home appliances.

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## How do you size a control transformer?

To determine the required transformer VA, multiply the secondary voltage by the required amperes: For example, VA=Volts x Amperes or 28V x 1.2 amperes = 33.6 VA. To determine the maximum transformer current, divide the transformer VA by transformer secondary voltage.

## How is inrush VA calculated?

This value is determined using the following formula: CPT INRUSH VA = (Total Inrush)2 + (Total Sealed)2 where ”Total Inrush” is the total sum of all the inrush power of the loads applied to the CPT, and ”Sealed Inrush” is the total sum of all the sealed power of the loads applied to the CPT.