# 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)

**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