Voltage and Current Signals (Electrical Power Toolkit)

Voltage and current signals are common signal types for electrical power analysis.

Voltage Signals

Voltage is the energy per unit charge flowing through a conductor. The following equation describes the voltage associated with an alternating current.

You can obtain voltage signals through the analog input channel of a data acquisition device that contains an analog-to-digital converter (ADC). An ADC converts a continuous analog voltage signal into a discrete digital signal.

Current Signals

DC is the flow of electric charge with a constant polarity. Batteries, fuel cells, photovoltaic cells, dynamos, and thermocouples produce DC.

AC is the flow of electric charge that periodically reverses polarity. AC generators and alternators produce AC. AC typically takes the form of a sine wave that oscillates at a fundamental frequency of 50 Hz or 60 Hz, depending on geographic locations.

You can obtain current signals through the analog input channel of a data acquisition device that contains an analog-to-digital converter (ADC). An ADC converts a continuous analog current signal into a discrete digital current signal.

Transformers

A transformer transfers electrical energy between two circuits in an electrical power system or an electrical device. A transformer consists of two inductively coupled coils that wind around a ferromagnetic core. A time-varying current in the primary winding creates a varying magnetic flux in the core that, subsequently, induces a voltage in the secondary winding. The induced voltage in the secondary winding is proportional to the primary voltage. The following figure shows a transformer as a circuit element.

In an ideal transformer, the ratio of the secondary voltage to the primary voltage is equal to the ratio of the number of turns on the secondary coil to the primary coil.

You use transformers to step up the voltage at the source before transmission and step down the voltage at the destination.

Voltage transformers are useful in high-voltage circuits for measurement and protection of electrical components. Voltage transformers can transform a high voltage to a lower voltage that you can measure safely. You can use a low voltage to operate a protective relay.

Current transformers are useful for measurement and protection of electrical components. A current transformer induces a current in the secondary winding that is proportional to the current in the primary winding. You can use a current transformer to measure a high current in an electrical circuit by inducing a low current in the secondary winding that you can safely measure.