Transformer Testing Knowledge

What is the difference between CT(Current Transformer) and PT (Potential Transformer)?

⚡ Current Transformer (CT) Facts

CT (Current Transformer)is used to measure high current by producing a proportionally smaller current.

It is connected in series with the load.
The primary winding carries actual current, while the secondary carries a scaled-down version.
CTs are used in relays, energy meters, and protective devices.
Standard output currents are typically 5A or 1A.
The secondary should never be left open—this can cause dangerously high voltage.
Accuracy is affected by burden, saturation, and magnetizing current.
Used in fault detection, overcurrent protection, and system monitoring.

CT and PT structure principle diagram

⚡ Potential Transformer (PT) Facts

PT (also called VT – Voltage Transformer) is used to measure high voltage.
It is connected in parallel to the circuit.
PT steps down high voltage to a standard value like 110V or 63.5V.
Provides voltage inputs to meters, relays, and control devices.
Accuracy class is defined (e.g., 0.1, 0.2, 0.5) for precision measurement.
Secondary should never be short-circuited.
Uses high dielectric insulation due to high voltage exposure.
Core is designed to work under low magnetic flux to avoid saturation.
Used in voltage protection, synchronizing, and metering applications.

this is the chart of difference between CT(Current Transformer) and PT (Potential Transformer)

Kingrun Transformer Instrument Co.,Ltd.

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