PEC电气工程专业英语证书考试-电气工程专有名词3.doc

PEC电气工程专业英语证书考试-Glossary of Electrical Engineering Terms3o AmpereThe measurement of intensity of rate of flow of electrons in an electriccircuit. An ampere is the amount of current that will flow througha resistance of one ohm under a pressure of one volto Ampere RatingThe current-carrying capacity of a fuse. When a fuse is subjected toa current above its ampere rating, it will open the circuit after a predeterminedperiod of timeo Ampere Squared Seconds, l2tThe measure of heat energy developed within a circuit during thefuses clearing. It can be expressed as “Melting l2t”, “Arcing l2t” orthe sum of them as “Clearing l2t”. “l” stands for effective let-throughcurrent (RMS), which is squared, and “t” stands for time of opening,in seconds.o Arcing TimeThe amount of time from the instant the fuse link has melted until theovercurrent is interrupted, or clearedo Cartridge FuseA fuse consisting of a current responsive element inside a fuse tubewith terminals on both endso Class CCFuses600V, 200,000 ampere interrupting rating, branch circuit fuses withoverall dimensions .Their design incorporates a rejectionfeature that allows them to be inserted into rejection fuse holdersand fuse blocks that reject all lower voltage, lower interruptingrating fuses.o Class G Fuses20A600VAC, 25-604480VAC, 100,000 ampere interruptingrating branch circuit fuses that are size rejecting to eliminate over fusing.These are available in ratings from 1 amp through 60 amps.Class H Fuses250V and 600V, 10,000 ampere interrupting rating branch circuitfuses that may be renewable or non-renewable. These are availablein ampere ratings of 1 amp through 600 amps.o Class J FusesThese fuses are rated to interrupt a minimum of 200,000 amperesAC. They are labelled as “Current-Limiting”, are rated for 600 voltsAC, and are not interchangeable with other classes.o Class K FusesThese are fuses listed as K-1, K-5, or K-9 fuses. Each subclass hasdesignated I2t and lp maximums. These are dimensionally the sameas Class H fuses, and they can have interrupting ratings of 50,000,100,000, or 200,000 amps. These fuses are current-limiting.However, they are not marked “current-limiting” on their label sincethey do not have a rejection feature.o Class L FusesThese fuses are rated for 601 through 6000 amperes, and are ratedto interrupt a minimum of 200,000 amperes AC. They are labeled“current-limiting” and are rated for 600 volts AC. They are intended tobe bolted into their mountings and are not normally used in clips. SomeClass L fuses have designed in time-delay features for all purpose use.o Class R FusesThese are high performance fuses rated 1/10 600 amps in 250 voltand 600 volt ratings. All are marked “current-limiting” on their labeland all have a minimum of 200,000 amp interrupting rating. Theyhave identical outline dimensions with the Class H fuses but have arejection feature which prevents the user from mounting a fuse oflesser capabilities (lower interrupting capacity) when used withspecial Class R Clips. Class R fuses will fit into either rejection ornon-rejection clips.o Class T FusesAn industry class of fuses in 300 volt and 600 volt ratings from 1amp through 1200 amps. They are physically very small and can beapplied where space is at a premium. They are fast-acting andtime-lag fuses, with an interrupting rating of 200,000 amps RMS.o Classes of FusesThe industry has developed basic physical specifications and electricalperformance requirements for fuses with voltage ratings of600 volts or less. These are known as standards. If a type of fusemeets the requirements of a standard, it can fall into that class.Typical classes are K, RK1, RK5, G, L, H, T, CC, and Jo Clearing TimeThe total time between the beginning of the overcurrent and thefinal opening of the circuit at rated voltage by an overcurrent protectivedevice. Clearing time is the total of the melting time and thearcing timeo Current-LimitationA fuse operation relating to short-circuits only. When a fuse operatesin its current-limiting range, it will clear a short-circuit in less than 1/2cycle. Also, it will limit the instantaneous peak let-through current toa value substantially less than that obtainable in the same circuit ifthat fuse were replaced with a solid conductor of equal impedance.o OhmThe unit of measure for electric resistance. An ohm is the amount ofresistance that will allow one ampere to flow under a pressure ofone volt.o Dual-Element FuseFuse with a special design that utilizes two individual elements inseries inside the fuse tube. One element, the spring actuated triggerassembly, operates on overloads up to 5-6 times the fuse currentrating. The other element, the short-circuit section, operates onshort-circuits up to its interrupting rating.o Electrical LoadThat part of the electrical system which actually uses the energy ordoes the work required.o Fast Acting FuseA fuse which opens on overload and short circuits very quickly. Thistype of fuse is not designed to withstand temporary overloadcurrents associated with some electrical loads, when sized near thefull load current of the circuit.o FuseAn overcurrent protective device with a fusible link that operatesand opens the circuit on an overcurrent condition.o High Speed FusesFuses with no intentional time-delay in the overload range anddesigned to open as quickly as possible in the short-circuit range.These fuses are often used to protect solid-state deviceso Inductive LoadAn electrical load which pulls a large amount of current an inrushcurrent when first energized. After a few cycles or seconds thecurrent “settles down” to the full-load running currento Interrupting CapacityActual test current an overcurrent device sees during theshort circuittest.o Interrupting RatingThe rating which defines a fuses ability to safely interrupt and clearshort-circuits. This rating is much greater than the ampere rating ofa fuse. The NEC defines Interrupting Rating as “The highest currentat rated voltage that an overcurrent protective device is intendedto interrupt under standard test conditionso Melting TimeThe amount of time required to melt the fuse link during a specifiedovercurrent. (See Arcing Time and Clearing Time.)o “NEC” DimensionsThese are dimensions once referenced in the National ElectricalCode. They are common to Class H and K fuses and provide interchangeabilitybetween manufacturers for fuses and fusible equipmentof given ampere and voltage ratingso Ohms LawThe relationship between voltage, current, and resistance,expressed by the equation E = IR, where E is the voltage in volts, Iis the current in amperes, and R is the resistance in ohmso One Time FusesGeneric term used to describe a Class H nonrenewable cartridgefuse, with a single elemento OvercurrentA condition which exists on an electrical circuit when the normalload current is exceeded. Overcurrents take on two separate characteristics overloads and short-circuitso OverloadCan be classified as an overcurrent which exceeds the normal fullload current of a circuit. Also characteristic of this type of overcurrentis that it does not leave the normal current carrying path of thecircuit that is, it flows from the source, through the conductors,through the load, back through the conductors, to thesource againo Peak Let-Through Current, lpThe instantaneous value of peak current let-through by a currentlimitingfuse, when it operates in its current-limiting rangeo Renewable Fuse (600V & below)A fuse in which the element, typically a zinc link, may be replacedafter the fuse has opened, and then reused. Renewable fuses aremade to Class H standards.o Resistive LoadAn electrical load which is characteristic of not having any significantinrush current. When a resistive load is energized, the currentrises instantly to its steady-state value, without first rising to a highervalue.o RMS CurrentThe RMS (root-mean-square) value of any periodic current is equalto the value of the direct current which, flowing through a resistance,produces the same heating effect in the resistance as theperiodic current does.o Semiconductor FusesFuses used to protect solid-state deviceso Short-CircuitCan be classified as an overcurrent which exceeds the normal fullload current of a circuit by a factor many times (tens, hundreds orthousands greater). Also characteristic of this type of overcurrent isthat it leaves the normal current carrying path of the circuit it takesa “short cut” around the load and back to the source.o Short-Circuit Current RatingThe maximum short-circuit current an electrical component cansustain without the occurrence of excessive damage when protectedwith an overcurrent protective device.o Single-PhasingThat condition which occurs when one phase of a three-phase systemopens, either in a low voltage (secondary) orhigh voltage(primary)distribution system. Primary or secondary single-phasing canbe caused by any number of events. This condition results in unbalancedcurrents in poly phase motors and unless protective measuresare taken, causes overheating and failure.o Threshold CurrentThe symmetrical RMS available current at the threshold of thecurrent-limiting range, where the fuse becomes current-limitingwhen tested to the industry standard. This value can be read off ofa peak let-through chart where the fuse curve intersects the A-Bline. A threshold ratio is the relationship of the threshold current tothe fuses continuous current rating.o Time-Delay FuseA fuse with a built-in delay that allows temporary and harmlessinrush currents to pass without opening, but is so designed to openon sustained overloads and short-circuits.o Voltage RatingThe maximum open circuit voltage in which a fuse can be used, yetsafely interrupt an overcurrent. Exceeding the voltage rating of afuse impairs its ability to clear an overload or short-circuit safely.o Withstand RatingThe maximum current that an unprotected electrical componentcan sustain for a specified period of time without the occurrence ofextensive damage.