go to TRANSCAT.com 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 voltamperes (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 to 33 days). Consumption (active energy) — actual electrical energy used measured in kilowatthours (kWh) by the watthour meter, regardless of the power factor. Crest factor — the ratio of the peak value of a waveform (voltage or current) to the RMS value. 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 secondar y. 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. Demand interval (integration period) — the period of time over which the energy is averaged. Typical demand intervals are 15, 30, or 60 minutes. Derating Factor — a number defined as 1.414 x average RMS phase current/ peak phase current. This factor, when applied to the rated load of a transformer, 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 to the total RMS signal (THD-R). Distortion power factor — the difference between apparent power and true power at all harmonic 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 the 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. This 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 (voltamperes). Expressed in decimal form, e.g., .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; 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; 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, form a tuned circuit resonant at one or more of the harmonic frequencies produced by nonlinear loads. RS232 — 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. Watt — the measure of real power. It is the power expended when one ampere of direct current flows through a resistance of one ohm. True RMS — capabiltity to accurately measure the value of AC voltage and current having a nonsinusoidal waveform as well as sinusoidal waveforms. 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. 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.
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