Everything you ought to know about current transformers
Current transformer performs its function through electromagnetic fields. It raises or lowers the current
of an AC circuit in a predictable manner dependent on the ratio between the windings. For example, a
100: 1 ratio transformer, 100 amps flowing throw the primary transformer winding will result in a
current of 1 amp through the secondary winding.
This transformer has both primary and secondary coils with wire wrapped around a core, which is made
up of steel or a nickel alloy. Transformer windings are electrically insulated from each other and from
the core. The winding connected to the power supply is called the primary winding. The transformer
winding in which current is induced is called the secondary winding.
Advantages of current transformers
AC power supplies of appliances
Circuit interrupter circuit breaker
AC power supply grids
A current transformer is a meter of power to track energy use, monitors the current flow through a
circuit, relay of power through an energy grid, control of the state of a circuit in a ground fault circuit
interrupter and protection of instruments and appliances connected to AC power supplies.
Current across the secondary winding of a transformer is directly proportional to primary
winding. Direct measurement of current across the second winding allows an indirect
calculation of the current conducted across the primary winding.
Power grid transformers can be used to increase or decrease the current of the power supply.
Step-up transformers increase the current and decrease the voltage of power from an energy
plant generator before transmission over long distance power lines. This reduces the costs of
transmission by permitting use of smaller power lines with less energy loss. Step down
transformers lower current at the point of use.
Dimensions from the secondary winding of a current transformer may trigger switches in
controllers such as ground fault circuit interrupter circuit breakers when measurements exceed
Metering, monitoring and control equipment used with AC power supplies can be damaged by
high currents. For this reason, current transformers are also known as instrument transformers.
Long distance transmission cannot be used without current transformers as it is not cost
effective. Home use is not effective. Metering, monitoring, control and protection functions of
current transformers enable the essential role electricity plays in high technology societies.
Current transformers are used for various applications. Some devices are used to measure
current in electronics equipment or motors. Others are used in street lighting. Some
transformers are weatherproof or are related to outdoor use.
There are two types of current transformers – wound and toroidal. Wound transformers consist
of an integral primary winding that is inserted in series with the conductor that carries the
measured current. Toroidal transformers do not contain a primary winding.