Glossary of Power Terms

Alternating Current: current that reverses its direction of flow periodically (Hz)

Ampere: a unit of measure for the rate of current flow

Apparent Power: applied voltage multiplied by current in an AC circuit

  • This value would not take the power factor into account
  • Unit is volt amperes (VA)
  • Is total power flowing

Balanced Load: AC power system using more than two wires, where the current and voltage are of equal value in each energized conductor

Bandwidth: the range of frequencies over which an instrument provides accurate measurement

Billing Consumption: total amount of energy consumed during a predetermined period (usually 28-33 days)

Consumption (active energy): actual electrical energy used measured in kilowatt hours (kWh) by the watt hour meter, regardless of the power factor

Current Transformer: an instrument accessory which detects current flow without breaking the circuit under test

  • An AC transformer, usually step-down
  • Typical ratio listing would be 1000:1
    • This would indicate 1000A on the primary and 1A on the secondary

Current Transformer Ratio: the ratio of primary amperes divided by secondary amperes

Delta Connection: a circuit formed by connecting three electrical devices in series to form a closed loop, most often used in three-phase connections

Demand (active, real, or true power): the power which is actually consumed by the load

  • This measurement takes the power factor into account

Derating Factor: a number defined as 1.414x average RMS phase current/peak phase current

  • When applied to the rated load of a transformer, this factor gives an indication as to the percent loading that is reasonable when that transformer must service nonlinear loads

Displacement Power Factor: the difference between apparent power and true power when only the phase relationship of voltage and current at the fundamental are taken into account

Distortion Factor (%DF): total harmonic distortion referenced the total RMS signal (THD-R)

Distortion Power Factor: the difference between apparent power and true power frequencies

Frequency: the number of complete cycles of AC voltage which occurs during one second (Hz)

Harmonics: current or voltages which have frequencies that are integer multiples of fundamental power frequency

  • Common and sometimes dangerous in nonlinear loads

Heating Effect: temperature increase in electrical distribution equipment caused by an increase in RMS current

Impedance: the total opposition to alternating current flow in an electrical circuit (Z)

Inductive Reactance: the force which acts as a resistance in an inductor to limit the flow of current

  • The force creates a leading power factor in AC circuits

Initiator Pulses: electrical impulses generated from utility revenue meters

  • Each pulse indicates a specific number of watts consumed
  • These pulses are used within energy analyzers to measure energy consumption and demand

K Factor: a number based on the harmonic content of load current that determines the maximum safe loading on a power source

K-Rated Transformers: a transformer that is rated or designed to serve as the source for a predefined capacity of harmonic current

Peak Demand (maximum RMS power): the highest average load during a specified time interval (kW)

Phase: time relationship between current and voltage in AC circuits

Potential Transformer: an instrument transformer used to step down high voltage potentials to lower levels acceptable for the input of electrical test instruments

Power Factor: the ratio of true power (watts) to apparent power (volt amperes)

  • Expressed in decimal form (ex: .98)

Ratchet Demand: determining the billing demand based upon a pre-established peak average demand

  • Usually at 75%, 80%, or 100% of the pre-established peak

Reactance: the opposition to current flow in an AC circuit introduced through inductance or capacitance

Reactive Compensation Power: the reactive power to be applied to an AC network for power factor correction

  • Also described as adding capacitance in order to bring the voltage and current waveform in phase

Reactive Power (kvar): power which is actually "borrowed" from the load and returned to the power source each cycle

  • Also known as unused power

Resolution: the smallest unit value that an instrument can measure

Resonance: when the inductance in the system and the natural capacitance of the system, or added capacitors, formed a tuned circuit resonant at one of more of the harmonic frequencies produced by nonlinear loads

RS-232: a computer interface connector used to connect serial devices such as instruments for information transfer

Sensitivity: the smallest input that will provide a specified output

Skin Effect: phenomenon in which high harmonic frequencies cause electrons to flow to the outer sides of a conductor, reducing its cross-sectional diameter, and hence its ampacity rating

Sliding Demand: calculating average demand by averaging the average demand over several successive time intervals, advancing one interval at a time

THD (%THD, Total Harmonic Distortion): the contribution of all harmonic frequency currents or voltages to the fundamental current or voltage, expressed as a percentage of the fundamental

THDF (Transformer Harmonic Derating Factor): method of calculating transformer derating established by CBEMA for phase-to-neutral loads

True RMS: capability to accurately measure the value of AC voltage and current having a non-sinusoidal waveform as well as sinusoidal wave forms

Unbalanced Load: an AC power system using more than two wires where the current is not equal in the current-carrying wires due to an uneven loading of the phases

Watt: the measure of real power

  • It is the power expended when one ampere of direct current flows through a resistance of one ohm

Wye Connection: a connection of three components made in such a manner that one end of each component is connected

  • Generally used to connect devices to a three-phase power system
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