Difference between (CT) Current Transformer and (PT) Potential Transformer

For safety reasons, electrical instruments are not directly connected to high-voltage meters or control apparatus. When connecting electrical instruments to measuring instruments, instrument transformers such as voltage transformers and current transformers are used. These transformers convert high-voltage and high-current instruments to low-voltage and low-current instruments.

Current Transformer

This device converts higher-valued current to lower-valued current in terms of earth potential. It is used in conjunction with CT pt testing instruments to measure high current values.

The line current can be excessive, and measuring it directly is not easy. As a result, the current transformer reduces the high value of current to a fractional value that the instrument can easily measure.

Potential Transformer

Voltage transformers are a particular sort of instrument used to convert voltage between different levels. You can determine the line voltage by connecting the primary terminal of the voltage level to the line. A potential transformer converts a high voltage to a low voltage detected by a voltmeter or meter.

Key Differences 

• The current transformer converts the instrument’s high current to a low current. On the other hand, the potential transformer converts a high voltage to a low voltage.
• The primary winding of the current transformer has a connection series with the transmission line whose current is being measured. On the other hand, the potential transformer is connected in parallel with the line.
• The core of the current transformer contains stainless steel laminations. The body of the potential transformer is composed of a high-performance core capable of operating at low flux densities.
• The primary winding of the current transformer carries the measured current, whereas the primary of the potential transformer maintains the voltage.
• A current transformer’s primary winding has a few turns, whereas a potential transformer’s primary winding has many turns.
• The secondary windings of the current transformer are numerous, and they cannot be open-circuited while the transformer is in service. The secondary winding of the potential transformer is very small and maybe open during the services.
• The usual range of a current transformer for measuring current is 5 or 1 amp, whereas the standard voltage at the secondary winding of a potential transformer is up to 110 volts. The transformation ratio of a current transformer is always high, whereas the transformation ratio of a potential transformer is always low.
• Current transformers are primarily used to measure currents that are too large to be measured directly with a meter or instrument. On the other hand, the potential transformer is used to determine the high voltage of the current.

The current transformer is primarily used in the relay protective scheme because it ensuresṣ there is a reduced magnitude of primary current to a value suitable for relay operation. Additionally, the current transformer prevents the apparatus and personnel from high voltage by providing insulation against the high voltage generated by the CT pt testing power circuit.