General Electrical Glossary
This glossary defines fundamental electrical terms including voltage, current, resistance, impedance, frequency, and power relationships used throughout industrial electrical systems, motors, and variable frequency drives.
Part of the VFDS.com glossary. View the full glossary index.
Related Glossaries:
- Electric Motor Glossary - motor types, torque, speed, thermal behavior, and construction terms
- Power Quality Glossary - electrical ratings, power factor, harmonics, and line-side effects
- Variable Frequency Drive Glossary - how VFDs interact with the electrical system
Term Index:
Definitions:
Amps
Amps, or amperes, are the unit of measurement for electrical current and represent the flow of electric charge through a conductor. Current levels determine heating, conductor sizing, and protection requirements in electrical systems.
Related terms: Current
Core Saturation
Core saturation occurs when the magnetic core of a transformer cannot support any additional magnetic flux. When saturation occurs, current increases rapidly, leading to overheating, distortion, and reduced efficiency.
Related terms: Inductance, Current, Transformer
Current
Current is the flow of electric charge through a conductor and represents how much electrical charge passes a point in a circuit over time. It is measured in amperes (amps), where one ampere equals one coulomb of charge flowing per second. In electrical systems, current is driven by voltage and limited by the impedance of the circuit.
In motors and variable frequency drive systems, current is closely related to torque production and load demand. As mechanical load increases, the motor typically draws more current to produce the required torque. Excessive current can lead to overheating, insulation damage, or protective trips, which is why current monitoring and protection are critical in electrical equipment.
Frequency
Frequency is the number of complete AC voltage or current cycles that occur each second, measured in Hertz (Hz). In power systems, standard supply frequency is typically 50 Hz or 60 Hz, depending on the region. In AC motors, frequency directly influences rotational speed because the speed of the stator’s rotating magnetic field is proportional to the supply frequency. Variable frequency drives control motor speed by adjusting the output frequency supplied to the motor.
Hertz
Hertz is the unit of frequency representing cycles per second in an alternating current waveform. Electrical power systems commonly operate at 50 Hz or 60 Hz.
Related terms: Frequency
Impedance
Impedance is the total opposition to current flow in an AC circuit, combining both resistance and reactance. Resistance opposes current directly, while reactance results from inductance and capacitance that oppose changes in current and voltage. Impedance influences current levels, voltage drop, fault behavior, and overall system stability in AC power systems. It is measured in ohms (Ω), the same unit used for electrical resistance.
Inductance
Inductance is the property of an electrical conductor or coil that resists changes in current by storing energy in a magnetic field. When current flowing through an inductive component changes, the magnetic field around the conductor expands or collapses, generating a voltage that opposes the change in current according to electromagnetic principles. Inductance is measured in Henries (H).
In AC power systems and motor drives, inductance influences current flow, voltage behavior, and harmonic performance. Inductive components such as reactors, transformers, and motor windings help smooth current, limit inrush current, reduce harmonic distortion, and affect power factor and transient response.
Ohms
Ohms (Ω) are the unit of electrical resistance, representing how strongly a material opposes current flow. Resistance influences heating, voltage drop, and power losses in circuits.
Related terms: Resistance
Phase
Phase describes the position of a voltage or current waveform relative to another waveform in an alternating current (AC) system. It indicates the timing relationship between waveforms and is typically measured in degrees of electrical angle. Two waveforms are said to be in phase when their peaks and zero crossings occur at the same time, and out of phase when one waveform leads or lags another.
In power systems, phase is especially important in three-phase electrical systems, where three AC waveforms are separated by 120 degrees. This arrangement allows power to be delivered more smoothly and efficiently than single-phase systems. Correct phase relationships are necessary for proper motor rotation, balanced loading, and reliable operation of electrical equipment.
Power Factor
Power factor is the ratio of real power, measured in watts or kilowatts, to apparent power, measured in volt-amperes or kilovolt-amperes, in an AC electrical system. It indicates how effectively electrical power is being converted into useful work.
A power factor of 1.0 represents ideal utilization, where all supplied power performs useful work. Lower power factor values indicate the presence of reactive power, harmonic distortion, or both, which increase current draw without increasing useful output.
In systems with inductive loads such as motors and transformers, power factor is reduced due to phase displacement between voltage and current. Power electronic equipment, including VFDs, can also reduce power factor through current distortion caused by rectification and switching.
Power factor is often described as either displacement power factor, which accounts only for phase shift, or true power factor, which includes both phase displacement and harmonic distortion. Utilities may impose penalties or limits based on true power factor because low power factor increases losses, reduces system capacity, and stresses electrical infrastructure.
Primary Winding
The primary winding is the coil of a transformer that is connected to the input power source. It receives electrical energy and creates a magnetic field in the core that enables energy transfer to the secondary winding.
Related terms: Transformer, Secondary Winding
Resistance
Resistance is the opposition to electrical current flow within a conductor and is measured in ohms. Electrical resistance converts energy into heat and contributes to power losses.
Secondary Winding
The secondary winding is the coil of a transformer that delivers electrical energy to the load. Voltage in the secondary winding is determined by the transformer turns ratio relative to the primary winding.
Related terms: Transformer, Primary Winding
Surge Protective Device
A surge protective device (SPD) protects electrical equipment from voltage spikes caused by lightning, switching events, or other transients.
Turns Ratio
Turns ratio is the ratio of the number of windings in the primary coil to the number of windings in the secondary coil of a transformer. It determines how voltage is increased or decreased between the input and output.
Related terms: Transformer, Voltage, Primary Winding, Secondary Winding
Voltage
Voltage is the electrical potential difference that drives current through a circuit. Proper voltage levels are essential for equipment performance and longevity.
Volts
Volts are the unit of electrical potential difference that drives current through a circuit. Voltage level determines insulation requirements, power capacity, and system design.
Related terms: Voltage
Watts
Watts (W) are the unit of real power and measure the rate at which electrical energy is converted into useful work or heat. In AC systems, watts represent the portion of power that actually performs work, unlike reactive power which does not produce usable output. Watts are commonly calculated as voltage times current times power factor in AC systems, and they are used to estimate energy consumption, heat load, and operating cost.