Glossary for Surges, Sags, and Spikes: Protecting DAQ Systems, Personal Computer, and Related Electronics From Electrical Power

- A -

Actual Power—A term referring to the number of watts of power consumed by a load.

Alternating Current—Electrical cur rent which reverses direction periodically, expressed in hertz or cycles per second. Abbreviated AC.

Ampere—The quantitative unit measurement of electrical current. Abbreviated Amp or A.

Ampacity—A term used to describe the current-handling capacity of an electrical device.

Amperage—A term synonymous with current; used in describing electrical current.

Antimony—An element found in lead- acid batteries; used to harden the plate material.

Apparent Power—The load power as expressed in VA or kVA. This value is usually greater than real power or watts, due to circuit reactance. This reactance causes the timing between the voltage and current to vary. Device sizing must be in accordance with Volts times Amps rather than in Watts, since Volt-amperes is the apparent load seen by the power- handling device.

Arc—Sparking generated when cur rent flows between two points of different potential, due to leakage through the intervening insulator.

Arrester—A device placed from phase to ground whose nonlinear impedance characteristics provide a path for high-amplitude transients.

Autotransformer—A transformer that uses common turns for both the primary and secondary windings, thus providing no isolation for the input from the output.

- B -

Balance—A term used to describe the even distribution of loads on the legs of a three-phase system.

Battery—A group of cells connected in such a way that more current and ! or voltage is delivered than from one single cell.

Battery, Sealed—A battery containing a gelled or liquid electrolyte that has no opening for water replenishment.

Blackout—The total loss of commercial electrical power. Sometimes refers to the length of time that the power must be off to bring the computer down. Used synonymously with Outage.

Branch Circuit—A discrete division of a load that is protected by one fuse or breaker.

Breaker—Short for circuit breaker.

Brownout—A long-duration under- voltage condition, usually hours or days in length. Brownouts can be caused by heavy usage during peak hours, or they may be planned as an energy conservation strategy.

Building Service Entry—That point where commercial power enters the building.

Bus—A heavy, rigid conductor. Often equipped with screws or some other means by which a number of smaller conductors can be connected to it. Also called a bus bar.

Bypass Line—An alternate electrical path around a device, usually a UPS, that allows the flow of power to the load. This bypass may “make” before breaking power to the load or may drop power to the load in the switching process. Bypass lines are used for three purposes: to allow the performance of maintenance on equipment, to bypass damaged equipment, or to pass fault current to a circuit breaker upstream. Also called a bypass circuit.

- C -

Calcium—An element used in lead- acid batteries to harden the plate material.

Capacitance—A term referring to the electrical properties of a capacitor or to a circuit that displays capacitor-like behavior.

Capacitive Reactance—The behavior of alternating current as it interacts with capacitance encountered in a circuit.

Capacitor—A discrete electrical device which has two electrodes and an intervening insulator, which is called the dielectric.

Cell—A combination of two metal plates suspended in an electrolyte which, when connected to an external circuit, causes a current to flow.

Charge Voltage—The voltage that must be applied to storage batteries to maintain their maximum charge.

Choke—A form of inductor which is constructed to allow desirable frequency signals to pass while acting with high impedance to other signals at some undesirable frequency.

Circuit Breaker—A resettable device that responds to a preset level of excess current flow by opening the circuit, thereby preventing damage to circuit elements.

Coax—A cable constructed by using two concentric conductors separated by an insulator.

Common-Mode Noise—Abnormal signals that appear between a current- carrying line and its associated ground.

Compensating Winding—A winding on the primary of a ferroresonant transformer that is connected opposite to the output winding in order to improve regulation.

Converter—A device that changes alternating current to direct current, or a device that changes direct cur rent to alternating current, can be called by the general term of “converter.” In this sense, a rectifier! charger and an inverter might both be termed converters. The term converter is also applied to any of a family of devices that convert the frequency of the alternating current.

Core—The iron structure of a trans former around which the windings are wound. A choke also has a core but does not act as a transformer.

Core Saturation—That point at which the iron material, the core, of an inductor or transformer will no longer produce more lines of flux when current flow through the windings is increased.

CPU—An acronym used for the central processing unit of a computer.

Critical Load—That portion of electrical / electronic equipment for which power quality is a vital consideration. The term “load” applies to all current- carrying devices on a given circuit or feeder. The term “critical load” refines the language to include only those cur rent-using devices whose operation is considered essential.

CSA—An abbreviation for the Canadian Standards Association. This is a Canadian safety assurance agency similar to the Underwriter’s Laboratories.

Current—The flow of electricity in a circuit as expressed in amperes. Cur rent refers to the quantity or intensity of electrical flow. Voltage, on the other hand, refers to the pressure or force causing the electrical flow.

Current Balance—A term that describes the nearly equal flow of current on each leg of a three-phase power system. With this flow balanced, the theoretical flow of current in the neutral line, with respect to ground, will be zero.

Cycles Per Second—This term describes the frequency of alternating current. Frequency is more properly described using the term “hertz,” which is synonymous with cycles per second.

- D -

Delta—A term describing a kind of connection in a three-phase circuit; often the primary side of a trans former. A delta connection may or may not have a neutral conductor.

Delta/Wye Transformer—A three-phase transformer with a delta connection on one side and a wye connection on the other. Most often the delta connection is on the primary side.

Dip—Another term for Sag.

Direct Current—Electrical current which flows consistently in one direction. Abbreviated DC.

Disk—A memory device which uses a magnetic media for the storage of information. Disk, as a term, has expanded into other areas often used to describe the shape of the storage media, that is: floppy disk, compact disk, laser disk, or hard disk. It some times refers to the way in which the storage media mimics a disk media; that is, RAM disk or bubble memory.

Distortion—The waveshape of a signal that is not normal is distorted. Distortion is a term that describes abnormal waveshapes.

Distribution—The way in which power is routed to various current-using sites or devices. Outside the building, distribution refers to the process of routing power from the power plant to the users. Inside the building, distribution is the process of using feeders and circuits to provide power to devices.

Dropout—A total loss of voltage for a short period of time.

- E -

Electrolyte—The acid or alkaline solution in which the plates of a battery cell are immersed.

Electromagnetic Interference—A term that describes electrically induced noise or transients. Abbreviated EMI.

Engine Generator—A combination of an internal combustion engine and a generator; often referred to as a diesel generator.

- F -

Feedback—Energy that is fed from the output of a circuit back to its input.

Ferroresonance—When an iron-core inductor is part of an LC circuit and it's driven into saturation, causing its inductive reactance to increase to equal the capacitive reactance of the circuit, this action is called ferroresonance.

Ferroresonant Transformer—A

transformer that uses the principle of ferroresonance to regulate the out put voltage.

Filter—An electronic device which opposes the passage of a certain frequency band while allowing other frequencies to pass. Filters are designed to produce four different results. A high-pass filter allows all signals above a given frequency to pass. A low-pass filter allows only frequencies below a given frequency to pass. A bandpass filter allows a given band of frequencies to pass while attenuating all others. A trap filter allows all frequencies to pass but acts as a high-impedance device to the tuned frequency of the filter.

Flashover—Arcing that is caused by the breakdown of insulation between two conductors where a high current flow exists, with a high potential difference between the conductors.

Flywheel—A heavy, wheel-like piece of metal or steel which acts as a governor to provide an inertial force generally found in motor generators.

Fuse—A device that automatically self- destructs when the current passing through it exceeds the rated value of the fuse.

- G -

Gassing—The process by which hydro gen gas is produced from the break down of the water in an electrolyte solution during battery charging.

Ground—A general term that refers to the point at which other portions of a circuit are referenced when making measurements. Power-systems grounding is that point to which the neutral conductor, safety ground, and building ground are connected. This grounding electrode may be a water pipe, driven ground rod, or the steel frame of the building.

Ground Fault—An undesired path that allows current to flow from a line to ground.

Ground Loop—The condition of having two or more ground references in a common system. When two or more grounds have a potential difference between them, current can flow. This flow of current is a new circuit or loop which can interfere with the normal operation of the system.

- H -

Harmonic—A frequency that is a multiple of the fundamental frequency. e.g., 120 Hz is the second harmonic of 60 Hz, 180 Hz is the third harmonic, and so forth.

Harmonic Distortion—Excessive harmonic content that distorts the nor mal sinusoidal waveform is harmonic distortion. This can cause overheating of circuit elements and might appear to a device as data-corrupting noise.

Hertz—A term describing the frequency of alternating current. The term, hertz, is synonymous with cycles per second. Abbreviated Hz.

- I -

Impedance—Measured in ohms, impedance is the total opposition to current flow in a circuit where alternating current is flowing. This includes inductive reactance, capacitive reactance, and resistance. Symbol is Z.

Impulse—A disturbance of the voltage waveform that is less than about one millisecond. Voltages can rise to hundreds or even thousands of volts in a very short period of time. An impulse may be additive or subtractive. (Sometimes called a notch.)

Inductance—This term describes the electrical properties of a coil of wire and its resultant magnetic field when an alternating current is passed through it. This interaction offers an impedance to current flow, thereby causing the current waveform to lag behind the voltage waveform. This results in what’s known as a lagging power factor.

Inductive Reactance—A term used to describe the impedance to alternating current offered by an inductive circuit. Reactance is expressed in a unit called the “henry.”

Inductor—A discrete circuit element which has the property of inductance. It should be noted that at very high radio frequencies, a straight wire or a path on a printed-circuit board can act as an inductor.

Inrush—A term used to describe the high-current demand of a device when it's initially turned on, due to a low load impedance before the device has reached its normal operating value.

Inverter—The subassembly of a UPS that converts DC power into AC power.

Isolation—The degree to which a device can separate the electrical environment of its input from its out put, while allowing the desired trans mission to pass across the separation.

- J -

Junction Box—A metal box inside which electrical connections are made. Also called a f-Box.

- K -

Kilohertz—A term meaning 1000 cycles per second. Abbreviated kHz.

Kilovoltamperes—Abbreviated kVA. Voltage times amperage is expressed in kVA. Kilovoltamperes is the “Apparent Power,” and can be found by dividing kilowatts by the power factor.

Kilowatts—Term for “Real Power,” or the power actually used by the load.

- L -

LC—An abbreviation for the inductance and capacitance that is used in the same circuit.

Light-Emitting Diode—A semiconductor that emits light when a cur rent is applied to it. Abbreviated

LED.

Lightning Arrester—A device used to pass large impulses to ground. it's vital that this device be placed upstream from the computer ground.

Line—A term used generally to describe a current-carrying conductor.

Line to Line—A term used to describe a given condition between conductors of a multiphase feeder.

Line to Neutral—A term used to describe a given condition between a phase conductor and a neutral conductor.

Load—Any electrical device connected to a power source may be called by the general term of “load.”

- M -

Magnetic Field—The lines of force that exist around an energized electrical conductor, magnet, or inductor.

Magnetic Synthesizer—A marketing term for a certain variety of ferroresonant regulator.

Maintenance Bypass—A line that allows power to be routed around a power device so maintenance or repair can be performed on the unit.

Mean Time Between Failure—A statistical estimate of the time a component, subassembly, or operating unit will operate before failure will occur. Abbreviated MTBF.

Mean Time to Repair—A statistical estimate of the repair time for a failed item. Abbreviated MTTR.

Megahertz—A term for one million hertz (cycles per second). Abbreviated MHz.

Motor Alternator—A device that consists of an AC generator mechanically linked to an electric motor, which is driven by utility power or by batteries. An alternator is an AC generator.

Motor Generator—A term used synonymously for “motor alternator.”

- N -

National Electrical Code—A set of rules and regulations, plus recommended electrical practices, that are put out by the National Fire Protection Association. Abbreviated N.E.C.

Neutral—One of the conductors of a three-phase wye system is the neutral conductor. Sometimes called the return conductor, it carries the entire current of a single-phase circuit and the resultant current in a three-phase system that is unbalanced. The neutral is bonded to ground on the out put of a three-phase delta-wye trans former.

Noise—An undesirable signal, which is irregular yet oscillatory, that is superimposed on the desired signal. See Common-Mode Noise and Nor mal-Mode Noise.

Normal-Mode Noise—A noise signal which appears between a set of phase conductors, irrespective of their associated ground conductor.

Notch—Slang for a negative or subtractive impulse.

- O -

Ohm—The unit of measurement for resistance (symbol R), impedance (symbol Z), and reactance (symbol X).

Ohm’s Law—The mathematical relationship between Volts, Amperes, and Ohms: Volts = Amperes times Ohms.

Orderly Shutdown—The turning off of power to computer devices in such a way that data is not lost or corrupted.

Oscillation—Generally used to mean an electrical phenomenon that produces a number of occurrences above or below a given instantaneous voltage level.

Outage—A long-term loss of voltage resulting from a localized utility failure.

Overvoltage—Similar to a surge but for a longer period of time, over 2.5 seconds.

- P -

Peak—The maximum instantaneous measurement of an electrical event.

Phase—A term used to describe the timing between two or more events tied to the same frequency.

Phase Balancing—The practice of placing equal electrical loads on each leg of a three-phase system. See also Neutral, Balance.

Phase Rotation—The sequence in which a comparable voltage appears in all three phases (A, B, and C) of a three-phase system.

Planté Plate—A kind of lead-antimony grid used in the construction of battery plates.

Power—A general term which means the capacity for doing work. In the electrical environment, this is usually measured in watts.

Power Distribution Unit—A portable electrical distribution device that provides an easily expandable and flexible electrical environment for a computer and its associated peripherals. Abbreviated PDU.

Power Factor— Watts divided by volt- amperes, or the ratio of actual power to apparent power.

Power-Line Monitor—A measuring device which reports information on the changing conditions of electrical power.

Primary—The input winding of a transformer.

Pulsating DC—A voltage that periodically rises and falls but does not change polarity.

Pulse-Width Modulation—Process for varying the width of a train of pulses by tying it to the characteristics of another signal. Abbreviated PWM.

- R -

Radio-Frequency Interference— Electromagnetic signals of a frequency associated with electromagnetic radiation, which are coupled to a conductor either directly or as with an antenna. Abbreviated RFI.

Reactance—The opposition to the flow of alternating current in a circuit, usually described as either capacitive or inductive reactance.

Rectifier/Charger—A subassembly of a UPS that performs the function of converting the incoming AC into DC for driving the inverter and charging the batteries.

Redundancy—The practice of providing backup modules to support a function, in case other modules should fail.

Reflection—The wave that is generated when a traveling wave reaches the point at which line impedance changes.

Regulation—A term used to describe the action of holding a constant electrical value in the face of fluctuations.

Remote Emergency Power Off—A device that permits the total shut down of electrical power devices from an exit, in the event of an emergency. Abbreviated REPO.

Resistance—A term describing the opposition of elements of a circuit to alternating or direct current. Symbol is R.

Resistor—A discrete electronic component designed to produce a DC voltage drop when current passes through it.

Root Mean Square—The square root of the arithmetic mean of the squares of a set of electrical amplitudes. Abbreviated RMS.

Rotary—A term used in describing certain electrical power equipment which functions through rotational mechanics.

- S -

Safety Ground—A conductive path that bonds all cabinets and conductor shields to the power-source ground.

Sag—A short-term RMS voltage decrease which exceeds an established upper limit for less than 2.5 seconds.

Secondary—The output winding of a transformer.

Shield—A conductive enclosure or barrier that prevents electrical interference from external sources.

Shunt Trip—A type of circuit breaker that can also be activated by a circuit other than the one it's protecting.

Sine Wave—A fundamental waveform produced by periodic oscillation that expresses the sine or cosine of a linear function of time or space, or both.

Single Phase—That portion of a power source which represents only a single phase of the three phases that are available.

Single-Point Ground—The practice of tying the power neutral ground and safety ground together at the same point, thus avoiding a differential ground potential between points in a system.

Surge—A short-term voltage increase that exceeds established upper limits for less than 2.5 seconds.

Synchronization—In the context used here, the term relates to maintaining a constant phase relationship between AC signals.

- T -

Tap—A terminal on a transformer winding.

Tap Switching—The action of changing from one terminal on a trans former winding to another, thereby changing the turns ratio of the device to maintain a desire voltage relationship.

Three Phase—An electrical system with three different voltage lines or legs, which carry sine-wave wave forms that are 1200 out of phase from one another.

Total Harmonic Distortion—A term that refers to the alteration of a wave- shape by the presence of multiples of the fundamental frequency of the signal. Abbreviated THD.

Transfer Switch—A device used to transfer the load of a power unit from itself to a bypass line.

Transformer—A device used for changing the voltage of an AC circuit and /or isolating a circuit from its power source.

Transient—An electrical event of a non-repetitive nature. The term is used interchangeably with the term “impulse”; however, the term relates more to the intermittent occurrence of “surges” and “sags.”

Transverse-Mode Noise—Often used as a synonym for normal-mode noise, it more clearly relates to noise that is the result of the conversion of common-mode noise to normal- mode noise after it passes through a transformer.

- U -

UL—The abbreviation for Underwriter’s Laboratories, Inc., an independent United States product-safety assurance agency.

Undervoltage—Like a sag, but for a longer period of time; over 2.5 seconds.

Uninterruptible Power System—A power-conditioning and supply sys tem that provides power during out ages. Abbreviated UPS.

- V -

Volt—The quantitative measurement of electrical force or potential; also called electromotive force.

Voltage Regulator—A circuit that has a constant output voltage when input voltage fluctuates.

Voltampere—The unit of measurement of apparent power.

- W -

Watt—The unit of measurement of actual power.

Waveform—The graphic form of an electrical parameter.

Wye—A three-phase connection with a single common neutral conductor and three phase conductors.

- Z -

Zero Signal Reference—The result of a properly installed ground structure is a constant potential over a broad band of frequencies between the devices that are part of the structure. This highly desirable state is called the zero signal reference, meaning the potential between points on the ground reference is equal to zero over a broad range of frequencies.

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