Glossary of Terms

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AC Power– Power delivered by a current that flows back and forth between the source and load. (see Alternating Current)

ALTERNATING CURRENT (AC) - A current that flows back and forth between the source and load. The amplitude of the current varies from zero, through a positive peak, back through zero, through a negative peak, and back to zero. This occurs a specified number of times per second. (see Frequency) and often the current appears to be sinusoidal. (see Sine Wave)

ADJUSTSTABLE SPEED DRIVE (ASD) – Also known as a “DC Drive”. A device to control the speed and efficiency of DC electric motors. The device operates by taking AC from the distribution system and rectifying it to power on a DC bus. The drive then controls the DC voltage level that powers the motor. Since the speed of a DC motor is proportional to the voltage level of the DC supply, the speed can be adjusted over a wide range. (see Inverter; Rectifier; AC Power; DC Power; Variable Frequency Drive)

AMBIENT TEMPERATURE - Temperature of the surroundings in which a piece of equipment is used or operated.

AMMETER - Meter for measuring the flow of current in an electrical circuit. Meters are available to measure AC or DC current. Low current measurements are often expressed in milliamperes (0.001 ampere) and higher currents are usually expressed in amperes. AC ammeters come in two main types: a “true rms ammeter” which measures rms current, and an “average responding, rms indicating ammeter” which only provides correct rms results when the current waveform is a sine wave. (see: Alternating Current; Direct Current, rms, fundamental.)

AMPERE - The unit of electrical current flow. Usually given the symbol “I.” Related to voltage and resistance by Ohm’s Law. Can be compared analogously to the flow of water in a pipe. The same unit is used for alternating current and for direct current, but they are measured differently. An ampere is often referred to as an “amp”, or the letter “A”; eg: 103 Amps or 103A (see: Voltage; Resistance; Ohm’s Law; Alternating Current; Direct Current; rms)  

AMPLITUDE – The height or value above or below the zero point reached by an AC waveform. (see: Alternating Current.)

APPARENT POWER – The total amount of power that must be delivered to a load to enable it to work. This includes the real power (useful power which does the work) and the reactive power (overhead, but necessary). Apparent Power = Real Power + Reactive power. Example: the Apparent Power necessary to turn a motor at a specific speed and torque consists of the Real Power (contributes to speed and torque) and the Reactive power (energizes the motor coil, but does not contribute to speed or torque). Apparent power is calculated by multiplying current times voltage. (Note that if the load is resistive, true power factor is unity and the apparent power equals the real power. If the true power factor is less than unity, apparent power will be greater than real power.) (see: Voltamp; Current; Watt; Power Factor; Real Power; Reactive Power.)

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CAPACITOR - A device that stores electrical charge.   Alternating current capacitors are used to provide reactive power which leads the real power. Direct current capacitors are used to store power by holding charge. Capacitors resist a change in voltage. The unit used to measure capacitors is “farad.” A farad, abbreviated “f” is a very large value, so the more common unit is “microfarad” (0.000001 f) or µf. The relationship between farads and voltage results in the reactive unit “VAR” or “kVAR” which is another unit capacitors are also measured in. (see: Alternating Current; Inductor; Real Power; Reactive Power; Leading; VoltAmp (Reactive); Lagging.)

Circuit - Any path through which an electric current can flow. A circuit can be made up of elements including such things as resistors, capacitors, wires, transformers, switchgear, motors, computers, etc.

CIRCUIT BREAKER – An over-current protective device, which consists of a mechanical switching device, that automatically switches off when the current exceeds a certain ampere value for a certain duration. Circuit breakers can be designed to have a long or short trip time depending on how critical small overloads are to a circuit. The trip time on a direct short circuit is almost instantaneous. Circuit breakers have an ampere trip rating for normal overload protection and a maximum magnetic ampere interrupting capacity (AIC) for short circuit protection. (see: Fuse)

Common Mode Voltage – Electrical “noise” voltage that is measured between the neutral conductor and the system ground. This “noise” is often generated when harmonic currents in power conductors couple into close, parallel, unshielded signal conductors, creating harmonic voltages and often results in loss of data which are being shared among computers on a network. (see: Isolated Ground, Conductor, Noise, Voltage,) .

CONDUCTOR - A wire, cable or bus bar designed to carry electrical current as part of a circuit. (see: Circuit.)

CONTACTOR - An electro-mechanical switch that is opened and closed by turning an electromagnetic coil on or off. The coil requires only a low current to operate, (and often operates at a low voltage) and the contactor is capable of switching large currents. A high-power circuit can be controlled with a small switch and small/thing wire from a remote location. (see: Contacts.)

CONTACTS – The part of an electrical switch that actually carries the current, contacts are found in all electrical switching devices including switches, circuit breakers, and contactors. (see: Circuit Breaker; Contactor; Switch, Disconnect.)

Crest Factor - The ratio of the peak value of an electrical waveform to the rms value of the waveform. The crest factor of a sinusoidal wave is the square root of two (1.414.) When a waveform is distorted the crest factor can be either higher or lower than the crest factor of a non-distorted sine wave. (see: rms Value, Distortion, Voltage Distortion, Current Distortion.)

Critical Load - Devices and equipment whose failure to operate satisfactorily jeopardizes the health or safety of personnel, and/or results in loss of function, financial loss, or damage to property deemed critical by the user. Sites that must operate critical loads with no failure or downtime permitted are often called “24 x 7 sites.”

CURRENT - see Ampere

Current Distortion Any current waveform deviation from the sinusoidal waveform. When a current waveform is distorted, current harmonics are present. (see: Harmonic, Distortion, Voltage Distortion, Sine Wave)

CYCLE – The repeat time for an alternating voltage or current wave. During one cycle, a single wave is completed. A cycle can also be measured in electrical degrees, with 360° equal to one cycle. The higher the frequency of an electrical wave, the shorter the cycle. For harmonic waves, the higher the harmonic number, the shorter the cycle, or the greater the number of complete harmonic cycles in one fundamental cycle. For a “60Hz” or “60 Cycle” distribution system, one cycle lasts 1/60 of a second (16ms). (see: Alternating Current; Fundamental; Hertz; Harmonic Number; Frequency.)

Cycling Loads - Loads that are not on constantly, but rather, go on and off frequently, either manually or automatically.

DC Power (Direct Current) – Power delivered by a current that flows in only one direction from source to load.

DIRECT CURRENT – Current that flows in only one direction from source to load.

DELTA CONNECTION - A method of connecting three phase transformer windings so that the three phase coils are connected end to end (eg: the end of one phase is connected to the beginning of the next phase). This configuration contains no neutral wire, and is intended for only phase-to-phase (aka line-to-line) loads. Schematically the three phase windings take the form of a triangle (or Greek letter delta) and the three phase wires are connected to the corners of the triangle. Some transformers are described as a “Delta-Delta” or “Delta-Wye” transformer, indicating that either the primary-and-secondary, or just the primary (respectively) has a Delta configuration. (see: Conductor; Neutral; Phase; Wye Connection; Transformer)

DipSee Sag.

DISCONNECTING MEANS (DISCONNECT) - A device or group of devices, or other means whereby all the ungrounded conductors of a circuit can be connected or disconnected simultaneously from their source of supply. (see Circuit Breaker; Switch.)

Displacement Power Factor – The ratio of real to apparent power for an inductive or capacitive linear load. (Displacement Power Factor= kilowatts60 Hz / kilovoltamps60 Hz, or FP (displacement) = kW60Hz / kVA60 Hz). For an inductive load the current lags the voltage and the power factor is called “lagging.” For a capacitive load the current leads the voltage and the power factor is called leading. In all cases if the current and voltage are in phase, the displacement power factor is unity (1). Displacement power factor ranges from unity to zero. The value of displacement power factor is also given by the cosine of the angle by which the current lags or leads the voltage. (see: Leading; Lagging; Linear Load; Power Factor.)

Distortion Any waveform deviation from the sinusoidal waveform. When a waveform is distorted, harmonics are present. (see: Harmonic, Current Distortion, Voltage Distortion, Sine Wave)

Distribution System - The wires, transformers, switchgear, meters and other equipment used to deliver electricity. A distribution system can be external to a facility, in which case the term usually refers to the utility, or internal to a facility, in which case the term refers to everything on the customer side of the utility. One can talk about the distribution system of a single floor of a facility or sometimes, of a single room. (see: Circuit; Conductor; Transformer.)

Electric Transmission System - The network of high-voltage lines over which the utility transports electricity, usually over long distances, from generating plants to substations.

ENCLOSURE - The cabinet or specially designed box in which electrical controls and apparatus are housed. It is required by the National Electrical Code (NEC) to protect persons from live electrical parts and limit access to only authorized personnel. It also provides mechanical and environmental protection. An enclosure should be designed to provide the required protection and sized to provide good, safe wire access and replacement of components. It can be manufactured of steel, galvanized or stainless steel, aluminum, or suitable non-metallic materials including fiberglass.

Equipment Grounding Conductor (EGC) A conductor used to connect the external surfaces of conduits, raceways, and equipment enclosures to ground. With all external surfaces connected together, there can be no voltage difference between different pieces of equipment and therefore no possibility of shock or electrocution of people working around the equipment. The EGC is connected to the ground rod at the main entrance (main panel) or secondary of a separately derived system, and nowhere else. In a Wye connected system it is also connected at the main entrance to the neutral conductor. (see: NFPA 70 (The National Electrical Code) 1999, Article 250 – Grounding; Wye Connection; Ground, Ground Rod; Grounded Neutral, Grounding Electrode Conductor, Main Entrance or Service)

Fault- Generally refers to a short circuit (an inadvertent connection between two phases or between a phase and ground) on the power system.

FlickerPerceived dimming (pulsing) of lights, usually due to rapid small changes in voltage on a distribution system. Flicker is also the term used for intermittent light dimming. EG: a large load goes on, the voltage sags for the duration of that load operation, and the lights dim, then brighten again when the load goes off. While not physically harmful to personnel, flicker can be very annoying. Due to the fact that the human eye can easily detect very small changes in light level, flicker is of great concern to the power quality industry.

FREQUENCY - The number of complete cycles of an alternating voltage or current per unit of time, expressed in cycles per second or Hertz (Hz). (see: Cycle; Hertz.)

Frequency Deviation - An increase or decrease in the frequency of a wave. In power systems any frequency deviation from the planned fundamental frequency is considered bad. The duration of a frequency deviation can be from several cycles to several hours. (see: Frequency; Cycle)

FOURIER ANALYSIS – A method of mathematically breaking a non-sinusoidal waveform into harmonic components so that the sum of these components represents the original waveform. This method was first published by John Baptiste Joseph Fourier in 1823. (see: Harmonic Number; Fundamental Component)

FULL LOAD CURRENT - The greatest current that a distribution system or part of such a system is designed to carry. For motors or other device the full load current is the current used by the device when it is operating at its maximum rating. Any current in excess of the full load current is considered an overload.

Fundamental (Component) – Voltage or current at the planned frequency for a distribution system. In the United States the fundamental is usually 60 Hz. In many European countries the fundamental is 50 Hz, and in some aircraft systems a fundamental of 400 Hz is used. When discussing harmonics the fundamental component is the 1st harmonic, or has a harmonic number equal to one (1.) (see: Frequency; Harmonic Number; Hertz)

FUSE - An over-current protective device, which consists of a conductor, that melts and opens the circuit when the current exceeds a certain ampere value for a certain duration. Fuses can be designed to have a long or short trip time depending on how critical small overloads are to a circuit. The trip time on a direct short circuit is almost instantaneous. Current limiting fuses are designed to trip very rapidly and to limit the energy in a short circuit to a small value, thus preventing a possible electrical explosion. (see: Circuit Breaker.)

Accordion Content

H1, H2, H3 – The names given to the three phase primary (input) terminals of a transformer. (see: Delta Connection; Wye Connection; X1, X2, X3.)

Harmonic (component) –An integral multiple of the fundamental frequency. A distorted waveform can be broken down into a series of harmonic components using equations developed by Fourier. The distorted waveform can be thought of as being composed of sinusoidal harmonic components, each component having a particular amplitude and phase relationship to the fundamental. (see: Amplitude; Distortion; Phase Relationship.)

Harmonic Distortion - Periodic distortion of the sine wave. See Distortion and Total Harmonic Distortion (THD).

Harmonic Filter A device for removing harmonic currents that are flowing in a power distribution system. Harmonic filters can be passive in operation, in which case they absorb harmonics using a tuned electrical circuit comprised of capacitors, resistors, and inductors, or they can be active in operation in which case they remove harmonics electronically. (see: Harmonic Suppression System.)

Harmonic Number - The integral number given by the ratio of the frequency of a harmonic to the fundamental frequency.   EG: for a frequency of 180 Hz, the harmonic number is “3” (180/60) or the “3rd harmonic”.

Harmonic Resonance - A condition in which a three-phase power distribution system becomes tuned to one of the harmonic frequencies. When such tuning occurs, huge amounts of harmonic current circulate within the system. If this condition persists for any length of time, the entire system can be destroyed by fire or explosion. This is a very dangerous situation that is usually found when an attempt is made to add capacitors to a 3-phase distribution system that is already carrying small amounts of harmonic currents.

HARMONIC SUPPRESSION SYSTEM – A device used to render a distribution system free of harmonic currents by preventing the formation of these currents. A harmonic suppression system differs from a harmonic filter in the way it deals with harmonic currents. Instead of removing harmonic currents after they are circulating in the distribution system (treatment) the suppression system keeps them from ever existing in the system (prevention.) Harmonic suppression systems are totally passive in their operation. (see: Harmonic Filter.)

HERTZ (Hz) - A unit used to express frequency. It is named in honor of Hertz who did pioneering work measuring the frequency of audio waves. This term is preferable to “cycles per second (and is easier to say.)   1 Hz = 1 cycle per second. (see: Cycle; Frequency.)

As budgets shrink and the demand for “green technology” expands, both the states and the federal government  have sought new ways of extending available funds and employing them in an environmentally favorable way. Harmonics Limited’s patented HSS® technology makes these objectives attainable! The following government organizations have already adopted this technology: Fort Polk (LA),  Dallas Police Department (TX), Vermont National Guard (VT), FDNY (NYC) and multiple facilities in the State of California.

Much of government’s non-human operating costs go to servicing the computers, largely in data centers, which enable government programs to run and be effective. These computers, which are non-linear loads, must run 24x7 for much of the year, and they create harmonic currents including the 3rd harmonic which can cause severe, long term damage: lost capacity, excess heat, increased energy requirements and more carbon emissions. The extra energy required also means it costs more to run each computer.

HL’s Harmonic Suppression System can be deployed in new projects with the use of a TransMax transformer, with the HSS already integrated, or, through the application of a SysteMax which can be added to any transformer already in operation. The HSS will restore system capacity, reduce the risk of excess heat, lower the energy demanded and save from 4% to 8% of energy costs annually for the life of the transformer. When one also realizes that a smaller carbon footprint ensues and that the initial cost of the technology is recovered quickly (a quick and compelling ROI result), the Harmonics Limited products become the preferred way to drive today’s power distribution units.

Impedance – The AC circuit equivalent of resistance in DC circuits. Impedance is the opposition to AC current flow made up of the available circuit elements of resistance, capacitive reactance, and inductive reactance. Each AC current frequency (harmonic) may be subject to a different impedance in the circuit.

Incoming Power - Electrical power being supplied either by a public utility or by self-generation.       

Inductive Load – A load that draws AC power through a magnetic coil. Examples include AC motors, lighting ballasts, and transformers. (see: Alternating Current; Capacitor; Inductor.)

INDUCTOR – Also called a reactor or line reactor. A device that stores electrical current as a magnetic field.   Inductors resist a change in current. Inductors are used to create system impedance by resisting a sudden change in current with the magnetic field. The unit used to measure inductors is “henry.” A henry, abbreviated “H”, is a very large value, so the more common unit is “milli” (0.001 H) or mH. (see: Capacitor; Inductive Load; Magnetic Field; Real Power; Reactive Power; Leading; Lagging.)

IN PHASE - A term used to describe the angular relationship between two or more waveforms. When the waveforms are in phase, the starting points of the various waveforms are at the same point in time and are not separated by any electrical degrees. (see: Out of Phase.)

IN-RUSH CURRENT - The maximum current drawn by a transformer when it is first energized or by a motor during the starting period. The inrush current on a transformer consists both of the current necessary to power connected loads and the current necessary to first magnetize the transformer windings. (see: Current; Transformer)

Interruption, Momentary - A type of short duration variation. The complete loss of voltage on one or more phase conductors for a time period between 30 cycles (0.5 seconds) and 3 seconds.   (see: Voltage; Cycle; Conductor)

Interruption, Sustained - Any interruption not classified as a momentary interruption. A type of long duration variation. The complete loss of voltage on one of more phase conductors for a time greater than 1 minute. (see: Interruption, Momentary)

Inverter - A device that converts DC power to AC power. Term “inverter” is sometimes used interchangeably with “Variable Frequency Drive” or “VFD”. (see: AC Power; DC Power; Adjustable Speed Drive; Rectifier; Variable Frequency Drive)

Isolated Ground - An extra insulated equipment grounding conductor run in the same conduit or raceway as the supply conductors and separate from the normal equipment grounding conductor. This conductor is insulated from the metallic raceway and all ground points from its origin at the grounding point in the main entrance to its termination at a special isolated ground-type receptacle. The theory is that by grounding sensitive electronic equipment with a separate isolated grounding wire, noise caused by currents flowing on the normal grounding system will not affect the sensitive equipment. There is no firm evidence that this extra isolated ground wire contributes substantially to better equipment operation. (see: Common Mode Voltage; Ground; Noise; Isolation; Main Entrance.)

Isolation - Separation of one section of a system from undesired influences of other sections. Isolated grounds, circuit breakers, and transformers are three very different examples of isolation.

Lagging – A term used to describe the relationship between voltage and current sine waves for a device being powered by an AC supply. When the current waveform starts later than the voltage waveform the current is said to be lagging. Induction motors have lagging currents. (see: Leading; Displacement Power Factor.)

Leading – A term used to describe the relationship between voltage and current sine waves for a device being powered by an AC supply. When the current waveform starts earlier than the voltage waveform the current is said to be leading. Capacitors have leading currents. (see: Lagging; Displacement Power Factor.)

Line – The name for the conductor between the utility and the distribution device (transformer, disconnect, drive). Usage: the “line side” of the transformer is also the “utility side” of the transformer, and is opposite the “load side” of the transformer. Also the name for one of the phases on a transformer. Usage:  the single-phase load is connected “line-to-neutral”. (see: Load; Transformer; Phase; Neutral; Distribution System.)

Line Loss - The power lost when a current passes through the resistance of the wires of an electrical distribution system from the source to the load.  This power is given in watts and is calculated using the formula: Line loss = I2R. To keep this loss at a minimum large wires are used to reduce the resistance. High harmonic currents increase line loss due to the large I2 factor, which is why it is important, in order to save power, to reduce harmonic current flow in a distribution system. (see: Ampere; Resistance)

Linear Load Electrical load which draws current continuously or whose current waveform is the same as the voltage waveform supplying the load. Systems with all linear loads do not have harmonic currents in the electrical distribution system. Linear loads typically draw sinusoidal current and voltage waveforms. Examples of linear loads include motors, incandescent lights, and heaters. (see: Nonlinear)

Load - Any piece of equipment that uses electricity to power it.  Examples are motors, computers, etc. Also the name for the conductor between a distribution device (transformer, disconnect, drive) and a piece of equipment. Usage: the “load side” of the transformer is also the side where the load is connected, and is opposite the “line side” of the transformer. (see: Line; Transformer; Distribution System)

Load Balance (or Load imbalance/Unbalance) – In a 3-phase Wye electrical distribution system powering loads connected phase-to-neutral, load balance refers to how closely the currents flowing in each of the phases are equal. To reduce neutral currents it is important to keep the phase loads as closely balanced as possible. (see: Wye; Current; Neutral; Voltage Imbalance)

Long Duration Variation - A variation of the rms value of the voltage from nominal voltage for a time greater than one minute. Usually further described using a modifier indicating the magnitude of a voltage variation (see: Undervoltage; Overvoltage; Voltage Interruption).

Magnetic Field (EMF) - The magnetic field formed any time current flows through a conductor.

Main Entrance or Service  - The place where the power enters the facility.  Sometimes referred to as the main panel, switchgear, service equipment, main entrance, main service, utility interface, or service entrance. (see: Switchgear)

MANUAL TRANSFER SWITCH – Main switchgear to transfer from one source of power to another source in case the first source is lost. A “manual” transfer switch is a transfer switch that is operated manually, by hand, intentionally. An “automatic” transfer switch is a transfer switch that is operated by some automation and/or alarm trigger event. (see: Disconnecting Means; UPS; Standby Power Supply; Incoming Power; Transfer Switch)

NEC - The National Electrical Code (NEC) is the safety standard of the National Board of Fire Underwriters for electric wiring and apparatus, as recommended by the National Fire Protection Association. Most civil jurisdictions in the United States have adopted the NEC as a standard for electrical safety and have given the document the authority of law.

NEMA - National Electrical Manufacturers Association, a non-profit trade association supported by the manufacturers of electrical apparatus and supplies. NEMA promulgates standards to facilitate understanding between the manufacturers and users of electrical products. Also, the term “Nema” has become the generic reference for enclosure ratings (indoor/outdoor/etc) and contactor types (NEMA vs. IEC).

NEUTRAL - The point common to all phases of a 3-phase Wye distribution circuit. A wire connected to this point is called the “neutral wire.”   This term is also used to denote the return conductor in a single-phase circuit. The neutral in most distribution systems is grounded at the service panel only. The neutral is also referred to as the “common”. (see: Grounded Neutral; Main Entrance or Service)

NEUtRALIZERtm Neutralizer is the trade marked name used by Harmonics Limited for technology that utilizes Blockade technology. Neutralizer products include: TransMax Series bundled products; SysteMax Series products; and the Pro series. (see: Blockade Technology)

Noise - Unwanted electrical signals occurring in an electrical distribution system, which can produce undesirable effects in the circuits of equipment powered by the system.

Nonlinear Load - Electrical load which draws current discontinuously or whose current waveform is different from the voltage waveform supplying the load. Systems with some or all nonlinear loads have harmonic currents in the electrical distribution system. Nonlinear loads typically draw distorted current and/or voltage waveforms. Examples of nonlinear loads include variable frequency drives, computers, fluorescent lighting. (see: Variable Frequency Drives; Distortion; Linear)

Normal Mode Noise - Electrical “noise” voltage that is measured between or among the phase conductors in a 3-phase Wye distribution system. (see: Noise; Common Mode Voltage; Phase; Voltage; Conductor; Wye)

Notch - A switching (or other) disturbance of the normal power voltage waveform that causes the voltage momentarily to go to zero. Notches often result when non-linear loads using SCR rectifiers are powered. Called “commutation notches,” these voltage variations are usually of very short duration, but their effect on sensitive electronic equipment can be quite serious. In severe cases a voltage notch can cross the zero amplitude point and disturb the operation of timing circuits. This symptom is often referred to as “multiple-zero-crossings”. (see: Voltage; Sinewave; SCR; Sag; Interruption; Rectifier)

OFF LINE – A term used to designate that a connected electrical load is not powered up and operating. In the case of a UPS, an off line device is ready to power the load from batteries but does not actually do so until the incoming power disappears. At that time the battery power is switched on in a very short time (usually 50 milliseconds) and the UPS now powers the load. (see: On Line; Incoming Power; Load, UPS)

OHM - Unit of electrical resistance. One volt will cause a current of one ampere to flow through a resistance of one ohm. Ohm is represented by the Greek letter for omega: “W.” (see: Resistance)

OHM’S LAW – The relationship between voltage, current and resistance in an electrical circuit. The law states that R = V / I. (The resistance equals voltage divided by current.) If any two of the parameters are known for a circuit, the third can be calculated using Ohm’s Law. (see: Voltage; Ampere; Ohm; Resistance)

OHMMETER - A meter for directly measuring electrical resistance expressed in ohms. (see: Ohm; Resistance)

On Line – A term used to designate that a connected electrical load is powered up and operating. In the case of a UPS, an on line device powers the load from batteries at all times, and the batteries are continuously charged by the line. When incoming power disappears there is no switching since the batteries are already powering the load. (see: Off Line; Incoming Power; Load; UPS.)

Out of phase – A term used to describe the angular relationship between two or more waveforms. When the waveforms are out of phase, the starting points of the various waveforms are at different points in time and are separated by some number of electrical degrees. (see: In Phase; Leading; Lagging)

Passive Filter A filter containing no active or electronic components. Usually constructed with inductors, capacitors, and resistors. (see: Harmonic Filter; Shunt Filter)

PHASE (THREE PHASE CIRCUIT) – One of the three line or load connection points on a transformer or the wire connected to that point. In a 3-phase transformer the sinusoidal voltage waves are out of phase with each other by exactly 120 electrical degrees.

Phase Shift - The displacement in time or in electrical degrees of one sinusoidal waveform relative to other sinusoidal waveform(s). (see: In Phase; Out Of Phase; Leading; Lagging)

Power Conditioner - Any device which helps to improve the quality of incoming power by carrying out one or more functions, such as reducing spikes and surges, lightening arrestor, removing harmonics, balancing loads, correcting power factor, etc. (see: Spike; Sag; Surge; Incoming Power; Harmonics; Load Balance; Power Factor)

Power Factor (True or Total Power Factor) - This is the ratio of real power to apparent power being supplied to any electrical load, linear or non-linear. Another way to describe power factor is: the ratio of the power that actually does useful work to the power that must be supplied to get the work done. If all the power supplied does useful work, the ratio is one (1) and the power factor is unity. (Power Factor (true) equals the real power, which is delivered at 60 Hz, divided by rms apparent power, or FPTrue = kW60 Hz / kVArms) Power factor ranges from zero (no useful work done) to unity. Resistive loads such as heaters have a unity power factor. When non-linear loads are being powered and harmonic currents are flowing in the system, true power factor is always lower than displacement power factor. (see: Linear Load; Nonlinear Load; Displacement Power Factor; rms)

ReactOR (LINE REACTOR) -- see: Inductor

Reactive Power – The power delivered that does no useful work, but must be present so that the work can be done. Example: the Apparent Power necessary to turn a motor at a specific speed and torque consists of the Real Power (contributes to speed and torque) and the Reactive power (energizes the motor coil, but does not contribute to speed or torque. The Reactive power is measured in volt amps-reactive, or kilo-volt amps-reactive; abbreviated “VAR” or “kVAR”. (see: Apparent Power; Real Power; Volt Amp Reactive)

Rectifier - A device that converts AC power to DC power. A rectifier may include SCRs, Diodes, or IGBTs for rectification. Only Diodes are passive non-controlled devices. (see: Inverter; SCR)

REAL POWER – The component of apparent power delivered that is useful and actually does the work. It flows from source to load and is totally used by the load. Example: the Apparent Power necessary to turn a motor at a specific speed and torque consists of the Real Power (contributes to speed and torque) and the Reactive power (energizes the motor coil, but does not contribute to speed or torque. Real power is calculated by multiplying current times voltage times true power factor. (Pwatts = I x V x FPtrue) Power losses in wires can be calculated by squaring the rms current and multiplying by the resistance. (Pwatts = I2rms x R). Real Power is measured in watts, or kilowatts; abbreviated “W” or “kW”. (see: Volt Amp; Current; Power Factor; Apparent Power; Ohm’s Law; Reactive Power; Watt)

RESISTANCE - The non-reactive opposition, which a device or material offers, to the flow of direct, or alternating current. Measured in ohms. Given the symbol R for resistance or, sometimes in AC circuits, Z for impedance. Can be compared analogously to the size of a pipe in a water system. (see: Current; Voltage; Ohm’s Law; Ohm; Reactive power)

Root Mean Square (rms) - A method of adding up AC sinusoidal waveforms so that the summed value equals the equivalent DC value. The rms value of current for a system containing numerous different harmonic currents is obtained by squaring the value of each harmonic current, summing the squares, and then taking the square root of the sum. This rms value of current if passed through a resistor, would produce the same amount of power as if a DC current of the same value were passed through the resistor.

Safety Ground - See: Equipment Grounding Conductor

SaG - A momentary decrease in voltage level lasting from a few milliseconds to a few hundred milliseconds. Sags are usually caused by the start-up power demands of many electrical devices (including motors, compressors, elevators, shop tools, etc.). Sags of longer than about 10 to 20 milliseconds may cause computer equipment to malfunction like have frozen keyboards and data errors. A sag may also be known as a dip or brownout. (see: Voltage)

SCR – A silicon controlled rectifier converts AC power to DC power.  It differs from a passive rectifier in that it has a control element that can be used to switch it on at any point in the electrical cycle. An scr is considered an active device. (see: Rectifier)

Shield - As normally applied to instrumentation cables, refers to a conductive sheath (usually metallic) applied, over the insulation of a conductor or conductors, for the purpose of reducing the induction of electrical noise from one wire to another. The shield is usually grounded so that unwanted currents are transferred to the grounding system, rather than to the wires in the circuit. (see: Conductor; Current; Ground)

shunt filter A passive filter consisting of inductors, capacitors, and resistors designed to eliminate one or more harmonics. The most common variety is an inductor in series with a shunt capacitor. When tuned to the proper harmonic frequency and connected phase-to-phase in a 3-phase distribution system, this shunt filter absorbs harmonic currents at the point where it is connected, keeping them from flowing back to the transformer. (see: Passive Filter; Inductor; Capacitor; Resistance; Harmonic; Harmonic Filter; Phase; Current)

Sine Wave - The normal waveform of an AC voltage or current. (see: Alternating Current)

Single Phase – A system for delivering electrical power that utilizes one phase conductor (often called the “hot” wire) with a neutral leg as a return line. 

Single Phase LOAD – A load connected between a phase wire and another return wire. In the case of single-phase loads connected in a 3-phase Wye distribution system, the loads are connected between a phase wire and the common neutral return wire. (see: Split Phase, Wye Connection)

 

SKIN EFFECT - Skin effect is the phenomenon where the apparent resistance of a wire increases as the frequency increases. At higher frequencies a thin surface layer of the wire carries all the current. Therefore the effective wire size is smaller. To avoid problems with increased resistance at high frequencies, large wires are often replaced with bundles of many small wires. Although the cross sections of the large and multiple-small wires are the same, the small wire bundle has a much larger surface area and therefore a greater current carrying capacity.

Spike - (slang for surge) A large momentary increase in the amount of voltage or current supplied to or carried by a circuit.

SPLIT Phase – A system for delivering electrical power which utilizes two phase conductors (often called the “hot” wires) with a neutral leg as a return line.  Most common in homes. The voltage is typically 120VAC from each phase to neutral. The voltage in one phase conductor wire will be 180° out of phase with the voltage in the other phase wire. The voltage is typically 240VAC from phase to phase. (see: Single Phase Load)

STANDBY POWER SUPPLY - The power supply that is available to furnish electric power when the incoming power supply is not available. (see: Manual Transfer Switch, Incoming Power, UPS)

STAR CONNECTION - Same as a “Y” or “Wye” connection. This three-phase connection is so called because, schematically, the joint of the “Y” points looks like a star. (see: Wye)

Surge – A Surge is an unwanted momentary transient over voltage that may be present on an AC power circuit. A Surge may be as brief as a few billionths of a second or as long as a few thousandths of a second (millisecond). For AC power circuits, surges are a few tens of volts constitute a surge. Electronic equipment connected to a circuit that experiences a surge may become damaged. (see: Swell)

SURGE ARRESTER - A protective device for limiting surge voltages on equipment by absorbing the surge voltage into MOVs. Also known as a surge suppressor and/or transient voltage surge suppressor (TVSS).

Swell - A temporary increase in the rms value of the voltage of more than 10% the nominal voltage, at the power frequency, for durations from 0.5 cycle to one minute. (see: Cycle; Voltage, Nominal)

SWITCH - A device for making, breaking, or changing connections in a circuit. (see: Contacts)

Switchgear - The panel containing circuit breakers, switches, meters, etc. that distributes power to an electrical distribution system. The term “switchgear” is often used to refer to the main service or entrance, but may also refer to a panel deep within a facility.   (see: Main Entrance or Service)

THREE PHASE CIRCUIT – See Phase (3-phase Circuit)

Three Phase Load– A load connected phase-to-phase so that it draws power equally from all three phases at the same time. Three phase loads can be powered either by a delta configured power distribution system or to a Wye connected system. When three phase loads are powered by a Wye system, the common or neutral wire is not used. (see: Delta; Wye; Phase; Distribution System; Neutral)

Total Harmonic Distortion (THD) - The ratio of the rms value of the harmonic currents or voltages to the value of the fundamental current or voltage. This is usually expressed as a percent of the fundamental current or voltage.

Transfer Switch - Any transfer switch is designed so that it will disconnect the load from one power source and reconnect it to another source while at no time allowing both sources to be connected to the load simultaneously. Also called a “Bypass Switch” (see: Disconnecting Means; UPS; Standby Power Supply, Incoming Power; Manual Transfer Switch)

TRANSFORMER - A passive electric device consisting of multiple coupled windings, used to transfer power by electromagnetic induction between circuits at the same frequency. A transformer can have the same input (primary) and output (secondary) voltage, in which case it is called an isolation transformer, or the output voltage can be higher than the input voltage (step-up transformer) or lower than the input voltage (step-down transformer.) Since the power supplied to the input must equal the power supplied at the output, current values will vary from primary to secondary in an inverse manner to the voltage. For instance, if a transformer is rated at 480 volts and 100 amps on the primary, at a 240 volt secondary the available current will be 200 amps. (see: Circuit; Frequency; Isolation; Volts; Amperes; Ohm’s Law; Current)

Triplen Harmonics - A term that refers to odd multiples of the third harmonic (i.e. 3rd, 9th, 15th, 21st, etc.) In a three-phase wye connected system triplen harmonics flowing in the phase wires are summed in the neutral so that the neutral carries more harmonic current than any of the phase wires.

Uninteruptabile Power Supply (UPS) - A device used to supply continuous power to critical loads in the event that power from the normal distribution system is lost. The device operates by taking AC from the distribution system and rectifying it to power on a DC bus. An inverter then re-converts the DC to AC that powers the loads. A UPS has a large DC battery supply that is available to be converted to AC power until the normal distribution system is restored or an emergency generator can take over. The more battery capacity a UPS has, the longer it can provide standby power. (see: Inverter; Standby Power Supply; DC Power; AC Power; Rectifier; Incoming Power; Transfer Switch; Distribution System; Generator)

Variable Frequency Drive (VFD) - A device to control the speed and efficiency of AC electric motors. The device operates by taking AC from the distribution system and rectifying it to power on a DC bus. An inverter with the capability to produce variable output frequencies then re-converts the DC to AC that powers the motor. Since the speed of an AC motor is proportional to the frequency of the AC supply, the speed can be adjusted over a wide range. (see: Adjustable Speed Drive; AC Power; DC Power; Rectifier; Inverter; SCR)

Volt Meter – Meter for measuring the potential difference (voltage) between two points. Meters are available to measure AC or DC voltage. The voltage is measured in volts. Typical measuring points are from phase-to-phase, phase-to-ground or phase-to-neutral. AC voltmeters come in two main types: a “true rms voltmeter” which measures rms voltage, and an “average responding rms indicating voltmeter” which only provides correct rms results when the voltage waveform is a sine wave. (see: Ammeter; Voltage; rms, Phase; Fundamental)

Voltage – The electrical force that causes current to flow in a circuit. (The proper name for voltage is “electromotive force” or “emf”) Given the symbol “V” for voltage or “E” for EMF. Voltage is analogous to pressure in a water system. (see: Current; Resistance; Ohm’s Law)

VOLTAGE (NOMINAL A) - A voltage value assigned to a circuit or system for the purpose of conveniently designating its voltage class. For a three-phase wye distribution system, voltage classes are specified as the nominal phase-to-phase voltage, then the nominal phase-to-neutral voltage. Examples: 600/340, 480/277, 380/220, 208/120, etc. The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment. (see: Voltage; Wye; Three-phase; Distribution System; Circuit)

Voltage Dip -(see: Dip)

Voltage Distortion - Any voltage waveform deviation from the sinusoidal waveform. When a voltage waveform is distorted, voltage harmonics are present. (see: Harmonic, Distortion, Current Distortion, Sine Wave)

Voltage Fluctuation - A series of voltage changes or a cyclical variation of the voltage. (see: Voltage)

Voltage Imbalance (Unbalance) In a 3-phase Delta or Wye electrical distribution system, voltage imbalance refers to a condition in which the three phase voltages differ in amplitude or are displaced from their normal 120-degree phase relationship or both. Three phase loads are very sensitive to voltage imbalance. Single-phase loads are typically not sensitive to voltage imbalance. (see: Wye; Delta; Voltage; Load Balance)

Voltage Interruption - Disappearance of the supply voltage on one or more phases. Usually qualified by an additional term indicating the duration of the interruption (e.g., Momentary, Temporary, or Sustained.) (see: Voltage; UPS, Transfer Switch; Incoming Power)

Voltage Regulation - The degree of control or stability of the rms voltage at the load. Often specified in relation to other parameters, such as input-voltage changes, load changes, or temperature changes.

Volt amp – The unit of measurement for apparent power (the total amount of power that must be delivered to a load to enable it to work.) Given the symbol VA or for large amounts, kVA.) (see: Watt; Apparent Power)

Volt amp (reactive) – The reactive component of power. Given the symbol VAR or for large amounts, kVAR. (see: Reactive power; Capacitor)

Watt - The unit of measurement for real power (the component of apparent power delivered that is useful and actually does the work.) Given the symbol W, or for large amounts, kW. (see: Volt amp; Current; Power Factor; Apparent Power; Reactive power; Real Power)

Waveform Distortion - A steady state deviation from an ideal sine wave of power frequency principally characterized by the spectral content of the deviation. See Harmonic Distortion.

WYE CONNECTION - A method of connecting three phase transformer windings so that one end of each of the three phase coils is connected together to a common point. The other ends of the three phase windings are connected to the phase conductors. The common point is connected to a fourth line or load wire, called the “neutral” wire. With this configuration, single-phase loads can be connected from each phase wire to the neutral wire (aka phase-to-neutral, line-to-neutral). The current in each phase wire returns to the transformer through the neutral wire. When only balanced fundamental currents are flowing in the phase wires, this configuration has the advantage that no current flows in the neutral, due to phase cancellation. If triplen harmonic currents are present in the phase wires, however, the triplen harmonic currents do not cancel in the neutral, but are additive. Thus the neutral can carry more harmonic or rms current than any of the phase wires. Schematically the three phase windings take the form of the letter “Y,” hence the name wye connection. Some transformers are described as a “Delta-Wye” transformer, indicating that the primary side of the transformer has a Delta and the secondary has a Wye configuration.   (see: Conductor; Delta Connection; Load Balance; Phase; Transformer; Neutral)

X1, X2, X3 – The names given to the three phase secondary (output) terminals of a transformer. (see: Wye Connection; Delta Connection; H1, H2, H3)

X0- The name given to the neutral secondary (output) terminal of a wye-connected transformer. (see: Wye Connection; X1, X2, X3; H1, H2, H3)

ZERO CROSSING – The point on an AC wave where the wave crosses the zero-amplitude line and changes sign from positive to negative or negative to positive. (see: Alternating Current)

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