50/60Hz Current Transformers and Current Sensors

A current transformer measures electrical currents. It creates a reduced current proportional to the circuit’s current (1/N x I) and isolates the circuit from the measuring equipment. Typically, to measure the current, you need a break in the circuit to connect the ammeter in series. You can place a current transformer at any location on a board without affecting the connectivity of the circuit. Unlike power transformers, current transformers don’t increase or decrease the voltage to power a piece of equipment. Instead, they simply measure the current running through a conductor and isolate the measurement from its source. Current transformers can use a toroidal or EI core. They use single turn and multi-turn windings. Typical turn ratios are 1 to 500 or 1 to 1000, indicating that the current through the winding can be reduced by 500 or 1000. This makes it possible to measure high currents safely and efficiently. Applications of a current transformer/current sensor include:

• Metering
• Coupling analog to digital circuits
• Sensing overload current
• Ground fault detection
• Load drop or shutdown