熔断器和断路器的比较
施耐德断路器和熔断器的比较
Data Bulletin0600DB06012/2007 Cedar Rapids, IA, USAA Comparison of Circuit Breakers and Fuses forLow-Voltage ApplicationsTony Parsons, PhD, P.E.,Square D / Schneider Electric Power Systems EngineeringI. Introduction Recent claims by fuse manufacturers regarding the arc-flash and simplified-coordination benefits of fuses do not tell the entire story regarding whichtype of device is “best” for a given power system. In reality, not only doesthe wide range of available circuit breaker types allow them to besuccessfully used on nearly any kind of power system, they can be appliedso as to provide selective coordination, arc-flash protection, advancedmonitoring and control features, all in a renewable device. This paper givesa feature-by-feature comparison of the merits of circuit breakers vs. fuses,discussing the relative merits of fuses and circuit breakers in each section.While both circuit breakers and fuses are available for application insystems that operate at higher voltage levels, the focus of this guide is onlow-voltage systems operating at 600 V or below.II. Basic Definitions and Requirements Article 240 of the National Electrical Code® (NEC) [1] provides the basic requirements for overcurrent (i.e., overload, short-circuit, and/or ground fault) protection in a power system. Special requirements for overcurrent protection of certain types of equipment are also contained in other articles—for example, details on protection requirements for motors and motor circuits are given in Article 430, while transformer protection requirements are given in Article 450.The NEC defines the two basic types of Overcurrent Protective Devices (OCPDs):fuse—An overcurrent protective device with a circuit-opening fusible part that is heated and severed by the passage of overcurrent through it.circuit breaker—A device designed to open and close a circuit bynonautomatic means and to open the circuit automatically on apredetermined overcurrent without damage to itself when properlyapplied within its rating.The NEC also requires that circuits be provided with a disconnecting means, defined as “a device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply.” Since fuses are designed to open only when subjected to an overcurrent, they generally are applied in conjunction with a separate disconnecting means (NEC 240.40 requires this in many situations), typically some form of a disconnect switch. Since circuit breakers are designed to open and close under manual operation as well as in response to an overcurrent, a separate disconnecting means is not required.Both fuses and circuit breakers are available in a variety of sizes, ratings, and with differing features and characteristics that allow the designer of an electrical system to choose a device that is appropriate for the system under consideration.Data Bulletin2/2007Low-voltage fuses are available in sizes from fractions of an amp tothousands of amps, at voltage ratings up to 600 V, and with short-circuitinterrupting ratings of 200 kA or more. Fuses are inherently single-poledevices (i.e., an individual fuse can only operate to open one phase of amulti-phase circuit), but two or three individual fuses can be applied togetherin a disconnect to protect a multi-phase system. Low-voltage fuses aretested and rated according to the UL 248 series of standards. Several typescan be classified as current-limiting, which per the NEC definition meansthat they “...reduce the current flowing in the faulted circuit to a magnitudesubstantially less than that obtainable in the same circuit if the device werereplaced with a solid conductor having comparable impedance.” In otherwords, the current-limiting fuses open very quickly (within 1/2 cycle) in thepresence of a high-level fault, allowing them to provide excellent protectionfor distribution system components or load equipment. Fuses can beapplied in equipment such as panelboards, switchboards, motor controlcenters (MCCs), disconnect switches/safety switches, equipment controlpanels, etc.Circuit breakers are also available with a wide range of ratings—10 A tothousands of amps, also with short-circuit interrupting ratings to 200 kA—and are available as 1, 2, 3, or 4-pole devices. The three basic types of LVcircuit breakers are the molded-case circuit breaker (MCCB), low-voltagepower circuit breaker (LVPCB), and insulated-case circuit breaker (ICCB).MCCBs are rated per UL 489, have all internal parts completely enclosed ina molded case of insulating material that is not designed to be opened(which means that the circuit breaker is not field maintainable), and can beapplied in panelboards, switchboards, MCCs, equipment control panels,and as stand-alone disconnects inside a separate enclosure. LVPCBs,which are rated per ANSI standards and are applied in low-voltage drawoutswitchgear, are larger, more rugged devices that may be designed to befully field maintainable. ICCBs can be thought of as a “cross” betweenMCCBs and LVPCBs—they are tested per UL 489 but may share somecharacteristics with LVPCBs, including two-step stored energy mechanismavailability in drawout construction and partial field maintainability [2].Both types of OCPDs can meet the basic requirements of the NEC, but arecircuit breakers or fuses best suited for a particular application?Unfortunately, there is no simple answer to this question—several otherfactors must be taken into account, such as the level of protection providedby the OCPD, selective coordination requirements, reliability, renewability,and flexibility. The remainder of this guide will provide a discussion of eachof these topics.III. System Protection As discussed above, both circuit breakers and fuses meet the basic NECrequirements for overcurrent protection of electric power distributionsystems and equipment. Any type of OCPD must be sized and installedcorrectly after taking all derating factors and other considerations intoaccount. Particularly for overloads and phase faults, both circuit breakersand fuses provide excellent protection and either is suitable for mostapplications. A bit more consideration is warranted for some other aspectsof system protection, as discussed in the remainder of this section.A. Ground-Fault Protection Conventional wisdom states that the most common type of fault in a powersystem (by far) is a single-phase-to-ground fault. On solidly-grounded powersystems, the available ground-fault current level can be significant. In somesituations, ground fault current levels that are even higher than themaximum three-phase fault current level are theoretically possible.However, many ground faults produce only relatively low levels of faultcurrent due to impedance in the fault path (due to arcing or to some other2/2007Data Bulletinsource of impedance from phase to ground). While such faults can causesignificant equipment and facility damage if not cleared from the systemquickly, phase overcurrent protective devices may not respond quickly tothe lower fault levels—if they detect the fault at all. For example, an 800 Aground fault might simply appear as an unbalanced load to a 4000 A fuse orcircuit breaker not equipped with ground-fault protection. Because of this,NEC 230.95 requires supplementary ground-fault protection on servicedisconnects rated 1000 A or more on solidly-grounded, wye systemsoperating at more than 150 V to ground but not more than 600 V phase-to-phase (e.g., 277/480 V systems). The NEC also defines special ground-faultprotection requirements for health care facilities and emergency systems.See the appropriate NEC articles for more details.Circuit breakers can be equipped with integral ground-fault protectionthrough addition of either electronic trip units that act as protective relayingto detect the ground fault and initiate a trip, or through addition of add-onground-fault protection modules. Ground-fault trip units typically use thecurrent sensors internal to the circuit breaker to detect the ground faultcondition, though an external neutral sensor is normally required to monitorcurrent flowing on the neutral conductor in a 4-wire system. If desired,external relaying and current transformers (CTs) can also be used forground-fault detection provided that the circuit breaker is equipped with ashunt trip accessory that can be actuated by the external relay.By themselves, fuses cannot provide ground-fault protection except forrelatively high-level ground faults. When ground-fault protection is requiredin a fusible system, the disconnecting means (usually a switch, sometimes acontactor) must be capable of tripping automatically, and external relayingand a zero-sequence CT or set of residually-connected phase CTs must beinstalled to detect the ground faults and send the trip signal to thedisconnecting means.While either system can function well if installed properly, extra care mustbe taken with a fusible system (or circuit breaker-based system withexternal ground relaying) to ensure that all external sensors are orientedcorrectly and that all sensor and relay wiring is installed correctly.Performance testing of the ground-fault system, as required in NEC230.95(C) when the system is installed, should allow for identification of anyinstallation issues.B. Device Interrupting Ratings NEC 110.9 states that “equipment intended to interrupt current at faultlevels shall have an interrupting rating sufficient for the nominal circuitvoltage and the current that is available at the line terminals of theequipment.” Protective devices that are inadequately rated for either thesystem voltage or available fault current levels present a safety hazard, asthere is no guarantee that they will be able to interrupt faults withoutdamage either to themselves or to other equipment in the system. Thiscould result in extended downtime and present a significant fire hazard.Several types of low-voltage fuses (class R, class J, etc.) carry interruptingratings of 200 kA or more at up to 600 V. This is typically high enough tointerrupt even the most severe fault in the “stiffest” system. In addition, sincefuses are single-pole devices, their single-pole interrupting capability equalsthe full rating of the fuse. Note that the withstand rating of the equipment(e.g., panelboards, switchboards) in which fuses are applied may notalways be equal to the ratings of the fuses themselves—equipmentmanufacturers should be consulted, particularly when system fault currentsexceed 100 kA. Note also that some LV fuses have interrupting ratings aslow as 10 kA, so care should always be taken to ensure that fuses selectedare appropriate for the installation.Data Bulletin2/2007Circuit breakers of all types are also available with interrupting ratings up to200 kA. In the not-too-distant past, fused circuit breakers were required toachieve the 200 kA interrupting ratings, but modern circuit breakers canachieve this rating without fuses. Circuit breakers with lower ratings are alsoavailable, typically at a lower cost. Circuit breakers have single-poleinterrupting ratings that are adequate for installation on the majority of powersystems, though special consideration may be required in some cases. See[3] for additional information.C. Motor Protection Overcurrent Protective Devices (OCPDs) in motor circuits have a relativelydifficult job to perform. They must not trip on motor inrush current, but shouldbe sensitive enough to provide both overload protection and short-circuitprotection to the motor and its associated branch circuit. In many cases, thefuse/circuit breaker (or motor circuit protector—MCP which is essentially amolded-case circuit breaker with no overload element), is oversized toaccommodate motor inrush current and a separate overload relay is addedthat will open the motor contactor during overload conditions. These twodevices then combine to provide overload and short-circuit protection for themotor circuit.Motors can also be damaged by conditions other than short-circuits andoverloads. On three-phase systems, one of the most problematic abnormalconditions is system voltage unbalance, which can cause an increase inphase currents and create high negative-sequence currents that flow in themotor windings. Both of these cause increased heating in the motorwindings, which can cause insulation degradation or breakdown that canultimately result in failure of the motor. Unbalance from system sources suchas unbalanced load in a facility or voltage unbalance on the utility system ispotentially problematic whether circuit breakers or fuses are used as motorOCPDs. However, the use of fuses has the potential to produce a severeunbalance condition commonly referred to as single-phasing.Single-phasing occurs when one phase in a three-phase motor circuit opensbut the other two phases remain in service. If the single-phasing occursupstream of the motor but at the same voltage level, then zero current flowson the phase with the open fuse and elevated current levels flow in one orboth of the remaining phases, depending on whether the motor is wye ordelta-connected. Single-phasing on the primary side of a transformer feedingthe motor can produce elevated currents in all three phases, with two beingslightly elevated and the third current roughly double that of the other two.To help guard against motor damage or failure due to single-phasing:•Use a circuit breaker-based protection system. If properly maintained, allthree phases of a circuit breaker will open in response to a fault or overload,so single-phasing in the facility will be far less likely to occur. However, notethat if the utility supply is protected by fuses, this possibility still exists.•Apply phase-failure or current unbalance relaying, either at the facility main(in smaller installations) or at high-value loads (e.g., larger motors that aremore expensive to replace, critical loads where the downtime associatedwith a motor failure cannot be tolerated, etc.)•Size motor circuit fuses closer to the full-load current rating of the motor.One fuse manufacturer recommends sizing dual-element, time-delay fusesat 100–125% of the motor's actual load level (not the nameplate rating) toprovide better levels of protection against damage resulting from single-phasing [4]. Note that this does not eliminate the possibility of single-phasingoccurring, and could increase the possibility of nuisance fuse operation onsustained overloads. In applications where loading on a particular motorvaries widely, or in new facilities where actual current draw of a motor maynot be known, sizing the fuses properly could be a challenge. Application ofexternal relaying at high-value loads may still be warranted.2/2007Data Bulletin D. Component Protection One of the great advantages of a current-limiting overcurrent protectivedevice is that it can literally limit the peak magnitude of fault current thatflows through it by opening within the first half-cycle after fault initiation,before the fault current has a chance to reach its peak value. This helpsprovide a degree of protection for downstream equipment that couldotherwise be damaged by the magnetic or thermal effects produced by thehigh-level faults. Several types of low-voltage fuses are current-limiting toone degree or another. Highly current-limiting fuses for special applications,such as semiconductor fuses that are designed to protect power electronicequipment, are also available. Same is true of breakers, only that fuses areoften more current-limiting.Current-limiting molded-case circuit breakers are also available in a rangeof sizes and with interrupting ratings of 200 kA. As with current-limitingfuses, these circuit breakers are tested to determine the peak-let-throughcurrent (i p) and let-through energy (i2t). While these circuit breakers are notas current-limiting as the faster-acting current-limiting fuses (e.g., class J orclass RK-1), they do provide a degree of protection beyond that of a non-current-limiting circuit breaker or fuse, and may be appropriate for manyapplications.Proper protection, whether of conductors, motors, or other equipment,depends on OCPDs being applied appropriately. This includes ensuring thatdevices are sized properly and that they are installed on systems wherenone of the equipment ratings are violated.To help prevent misapplication of fuses, NEC 240.60(B) requires thatfuseholders are designed to make it difficult to insert fuses intended forapplication on higher amperage or lower voltage circuits. Additionally,fuseholders intended for current-limiting fuses should reject insertion of anon-current-limiting fuse.Switchboards and panelboards where circuit breakers are applied do nottypically have rejection features that prevent installation of a circuit breakerthat is of a compatible frame type but that has a lower interrupting rating.Realistically, any device can be improperly applied—and improper use ofprotective devices is an application issue, not an equipment issue. In the“real world”, inadequately-rated circuit breakers can be installed, fuses of agiven cartridge size but of a higher ampere rating can be installed into arejection fuseholder, fuses can be replaced with “slugs” (produced by themanufacturer or of the “homemade” variety), or fuseholders or circuitbreakers can be jumpered out altogether by a “creative” electrician with arelatively short length of wire. Proper selection, installation, andmaintenance of all OCPDs are all key requirements in providing goodsystem protection.Data Bulletin2/2007 E. Arc-Flash Protection With the increased interest in arc-flash hazards in recent years, the ability ofOCPDs to provide protection against arcing faults has received muchinterest. The potential severity of an arc-flash event at a given location in apower system depends primarily on the available fault current, the distanceof the worker away from the source of the arc, and the time that it takes theupstream OCPD to clear the arcing fault from the system. In many cases,little can be done about the first two factors—the available fault currentlevels depend on utility system contribution, transformer impedance values,etc.; while the working distance is limited by the fact that a worker workingon a piece of equipment must, in most cases, be physically close to theequipment.Proper selection and application of OCPDs can have a great deal of impacton the fault clearing time. Clearing the fault more quickly can provide a greatdeal of protection for workers, as the available incident energy is directlyproportional to the duration of the arcing fault—i.e., the incident energy canbe cut in half if the fault can be cleared twice as quickly. Equationsappearing in IEEE Standard 1584-2002 [5] provide the present “state-of-the-art” methods for determining the arc-flash hazard levels in a system andfor evaluating the impact of potential arc-flash mitigation options.For low-voltage systems, which OCPDs provide the best protection againstarc flash?•Circuit breakers, with adjustable trip units that can be set to strike abalance between providing selective coordination and arc-flashprotection?•Current-limiting fuses, which can clear high-level faults very quickly andminimize damage to both equipment and personnel?Unfortunately, there is no simple answer to this question, despite claimsmade by manufacturers of both types of OCPDs. In some cases, both circuitbreakers and fuses provide excellent protection. There are situations whencircuit breakers can perform better than fuses, and there are situationswhere fuses can perform better than circuit breakers. And there aresituations where neither circuit breakers nor fuses provide much arc-flashprotection at all, requiring either use of other means of protection(alternative system designs, installing systems that allow for remoteoperation of equipment, etc.) or a total prohibition of work on or nearenergized parts.When evaluating OCPDs in terms of the arc-flash protection that they mayprovide, three general principles are important to consider:•Evaluate specific devices when possible•Evaluate devices at the actual system fault current levels•Evaluate adjustable-trip circuit breakers at their chosen settings Evaluate Specific Devices The IEEE 1584 standard contains three basic calculation models that canbe used to determine arc-flash hazard levels—an empirically-derived,general model; simplified equations based on testing of current-limiting(class RK-1 and class L) low-voltage fuses; and simplified equations basedon calculations performed on “typical” low-voltage circuit breakers. Thegeneral equations require information on available fault current levels in thesystem as well as knowledge of the trip characteristics of OCPDs in thecircuit, but can provide accurate results for any type of OCPD and for a widerange of system conditions. The simplified circuit breaker and fuseequations require little to no knowledge of actual device trip characteristics,but differences in the way these equations were developed mean that theyshould not be used to conduct a direct “apples-to-apples” comparison ofspecific protective devices.2/2007Data BulletinAs discussed above, the simplified fuse equations are based on field testingof specific types of fuses, the simplified circuit breaker equations are basedon classes of circuit breakers and on the assumption that the relevant tripsettings are maximized, and not on specific devices or actual trip settings.The circuit breaker equations are meant to allow calculation of the “worst-case” arc-flash levels allowed by any example of a circuit breaker within agiven class—e.g., 100–400 A MCCBs. If the IEEE 1584 empirical equationsare used to calculate arc-flash levels downstream of such a circuit breaker,the values should never be higher than (and in many cases will be wellbelow) those shown by the simplified circuit breaker equations. This isparticularly true when using the equations to analyze larger LVPCBs—thesimplified IEEE 1584 equations assume that the circuit breaker'sinstantaneous and/or short-time pickup and delay settings are set to themaximum levels, which can result in the calculation of very conservativearc-flash levels if the circuit breakers are actually set differently. Forexample, Figure1 shows the incident energy levels vs. bolted fault currentvalues for 2000 A circuit breakers in a 480 V, solidly-grounded system.Figure1:Incident Energy vs. Bolted Fault Current for 2000 A CircuitBreaker’s Simplified Equations vs. Actual DataThe “LVPCB w/ST” and “LVPCB w/INST” curves are based on the IEEE1584 simplified equations for low-voltage power circuit breakers with short-time and instantaneous pickup, respectively. The “NW-L” and “NW-LF”curves show arc-flash values based on actual devices (2000 A Masterpact®NW-L and NW-LF circuit breakers set to trip instantaneously for an arcingfault, respectively).As shown in the plot, the simplified equations (particularly for the “LVPCBw/ST” curve) are well above the results calculated based on the actualdevice characteristics. When possible, a comparison of the level of arc-flashprotection a given device can provide, should be based on actual devicecharacteristics, not generic equations.Data Bulletin2/2007 What is the system fault current range?Current-limiting fuses can provide excellent protection and reduce theavailable incident energy downstream to minimal levels . . . as long as theyare operating within their current-limiting range. For lower fault currentlevels, the arc-flash levels can elevate.Thermal-magnetic MCCBs can provide excellent protection as long as theytrip instantaneously, but arc-flash levels can escalate for low-level faults thatrequire operation of the thermal element to clear the arc. For higher levels offault current, RK-1 and L fuses tend to allow a lower level of incident energythan a similarly-sized circuit breaker, but both devices provide an excellentlevel of protection—allowing for the use of Category 0 PPE in many cases.For example, see Figure2, which shows incident energy levels vs. boltedfault current for a 400 A Square D® LH circuit breaker, a 400 A Square D LCcircuit breaker, and a 400 A class RK-1 low-voltage fuse. The circuitbreakers are assumed to trip instantaneously.Figure2:Incident Energy vs. Bolted Fault Current for 400 A CircuitBreakers and 400 A Class RK-1 Fuses.As shown in Figure2, the relative performance of the circuit breakers isbetter for low-level faults, while the incident energy allowed by the fuses islower for higher fault current levels. However, the incident energy levels foreach device over the entire range of fault currents considered is less than2.0 cal/cm2 —the maximum level allowed for Category 0 PPE [6], indicatingthat both circuit breakers and fuses provide excellent protection.For larger devices, the relative performance of circuit breakers and fusesfollows these same guidelines, though the impact can be quite a bit larger.See Figure3, which shows the incident energy levels allowed by 1600 AClass L current-limiting fuses, as well as two varieties of 1600 AMasterpact® NW circuit breakers. Again, the circuit breakers are assumed totrip instantaneously for an arcing fault so circuit breaker settings must beconsidered, (see “Consider Circuit Breaker Settings” below), but this doesshow that 1600 A circuit breakers can perform significantly better than fusesfor systems with relatively low available fault current levels.2/2007Data BulletinFigure3:Incident Energy Comparison for 1600 A Protective DevicesConsider Circuit Breaker Settings For circuit breakers with adjustable trip settings, proper selection of settinglevels is important for both arc-flash protection and for system coordination.The best protection will be provided when the circuit breakers can be set totrip instantaneously. Little to no protection may be provided by a circuitbreaker when the settings are blindly set to maximum, as is sometimesdone after a “nuisance trip” of the device. Arc-flash studies can beperformed to determine optimum settings for circuit breakers and otherdevices in a system, but even then, it may not be possible to reduce circuitbreaker settings below a certain level to provide additional arc-flashprotection if system coordination is to be maintained.However, an adjustable circuit breaker still gives the flexibility to provide arc-flash protection in such situations, if only on a temporary basis. Forexample, the instantaneous pickup level of a circuit breaker feeding an MCCcan be turned down to the minimum setting when workers are present at theMCC, then turned back up when work is complete. This could allow thecircuit breaker to trip instantaneously and provide the best possible level ofprotection at the MCC when workers are present and exposed to thehazard, while the normal setting allows for proper coordination duringnormal operation. While this can provide an obvious benefit, it also has itsdrawbacks, including:•Requirement for analysis to determine to what level the circuit breakersettings should be reduced to provide additional protection, as well as whatlevel of protection is actually provided.•Uncertainty over how to provide arc-flash warning labels for such alocation—should labels show the available incident energy and requiredPPE with the “normal” circuit breaker settings, the reduced settings, orboth?•Temporary loss of selectivity can become semi-permanent if the circuitbreaker settings are not restored to normal when work is complete.While a full discussion of issues surrounding arc-flash hazards and theirmitigation is beyond the scope of this paper, many other references areavailable which discuss the subject in more depth, including [7] and [8].。
熔断器和断路器在低压电容器柜中的应用比较
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断路器,隔离开关,负荷开关,熔断器的区别
断路器、隔离开关、负荷开关、熔断器的区别在电气领域中，断路器、隔离开关、负荷开关和熔断器是常见的设备，用于保护电路和电气设备。
尽管它们的主要目标是保护电路免受过载和短路等故障的影响，但它们在操作原理和应用范围上存在一些差异。
本文将介绍这些设备的区别。
断路器断路器是一种自动的电气保护设备，用于保护电气回路免受过电流和过热的影响。
它能在电路中检测到故障发生时迅速切断电源，以防止过电流引起火灾或其它损坏。
断路器通常由一个电磁铁和一些释放机构组成，使其能够自动打开电路并切断电源。
断路器有不同的额定电流和断路容量，以适应不同电路的需求。
当电流超过断路器的额定电流时，电磁铁会触发释放机构，将断路器打开切断电源。
断路器还可以进行手动操作，以实现对电路的控制。
隔离开关隔离开关，又称为刀开关，是一种用于隔离电路的电气开关。
与断路器不同，隔离开关只负责将电路与电源隔离，无法在故障发生时自动切断电源。
它常用于维修或检修电气设备前，将设备与电源隔离，以确保工作人员的安全。
隔离开关通常采用带有可拆卸手柄的单刀、双刀结构。
手柄的拔出使接线柱与电源断开，从而隔离电路。
隔离开关的额定电压和额定电流必须与电路相匹配。
负荷开关负荷开关是一种主要用于手动控制电路的开关。
它具有开和闭的功能，可以手动操作以打开或关闭电路。
负荷开关适用于低压电力系统，用于分配和控制电流。
负荷开关通常由一个可手动操作的开关机构和一个电流传感器组成。
通过手动操作开关机构，可以打开或关闭电路。
负荷开关的电流传感器可以实时监测电流情况，并在超过额定电流时触发保护装置进行切断。
熔断器熔断器是一种过电流保护设备，广泛应用于电气回路中。
它可以根据电路中的电流大小进行自动断开。
熔断器的主要部分是一个熔断体，当电流超过额定值时，熔断体会因过热而熔断，切断电路。
熔断器有不同的额定电流和断路容量，以适应不同电路的需求。
当电流超过熔断器的额定电流时，熔断体会迅速熔断，并打开电路。
熔断器能否用断路器代替
熔断器能否用断路器代替想要知道断路器是不是能够代替熔断器工作，主要得了解以下几下面。
熔断器与断路器有何区别？熔断器里面装有熔丝而断路器是属于闸刀开关，虽然熔断路与断路器都属于一种保护器，但是熔断路是一次性，在起保护作用后必须得更换里面的保险丝再能二次使用，而断路器不一样，它可以多次的重复使用，在起保护作用之后可以直接复位再断续工作。
熔断路与断路器的作用？断路器的界线划分的比较模糊，使用范围一般分为高压断路器与低压断路器，一般我们通常将3kv以上的电压称之为高压电器，而低压断路器又称之为自动开关，它是一种既具有手动开关的作用，还具有自动进行失压、欠压、过载和短路保护装置的电器。
而断路器又分为万能式断路器与塑壳式断路器。
断路器还可用来分配电能，不频繁地启动异步电动机，对电源的线路及电动机等实行保护作用，当它们发生严重的过载或者短路及欠压等故障情况下能够自动切断电路，其功能相当于熔断器式开关与过欠热继电器等的组合。
而且在分断故障电流后一般不需要变更零部件，一获得了广泛的应用。
断路器也可以实现线路的短路和过载保护，不过原理不一样，它是通过电流底磁效应（电磁脱扣器）实现断路保护，通过电流的热效应实现过载保护（不是熔断，多不用更换器件）。
而熔断器是通过电流保护电器熔断器是根据电流超过规定值一定时间后，以熔断器自身产生的热量促使熔体熔化，从而使电路断开的原理制成的一种电流保护器,熔断器一般广泛应用于低压配电系统和控制系统及用电设备中，作为短路和过电流保护，是应用最普遍的保护器件之一。
所以，断路器是能够代替熔断器工作的，只要能够保证熔断路与断路器二者之间的额定工作电流与额定分断电流一样便可。
但是倘若要把断路器当作熔断器作用的话，是不是有些大材小用的感觉？。
高压断路器,低压断路器,熔断器之间的区别
熔断器断路器都是一种电路保护器熔断器主要由熔体和熔管以及外加填料等部分组成。
使用时，将熔断器串联于被保护电路中，当被保护电路的电流超过规定值，并经过一定时间后，由熔体自身产生的热量熔断熔体，使电路断开，从而起到保护的作用。
熔断器以金属导体作为熔体而分断电路的电器，串联于电路中，当过载或短路电流通过熔体时，熔体自身将发热而熔断，从而对电力系统、各种电工设备以及家用电器都起到了一定的保护作用。
具有反时延特性，当过载电流小时，熔断时间长；过载电流大时，熔断时间短。
因此，在一定过载电流范围内至电流恢复正常，熔断器不会熔断，可以继续使用。
熔断器主要由熔体、外壳和支座3 部分组成，其中熔体是控制熔断特性的关键元件。
断路器按其使用范围分为高压断路器和低压断路器，高低压界线划分比较模糊，一般将3kV以上的称为高压电器。
低压断路器又称自动开关，俗称"空气开关"也是指低压断路器，它是一种既有手动开关作用，又能自动进行失压、欠压、过载、和短路保护的电器。
它可用来分配电能，不频繁地启动异步电动机，对电源线路及电动机等实行保护，当它们发生严重的过载或者短路及欠压等故障时能自动切断电路，其功能相当于熔断器式开关与过欠热继电器等的组合。
而且在分断故障电流后一般不需要变更零部件，已获得了广泛的应用。
1 熔断器(1) 熔断器的主要优点和特点①选择性好。
上下级熔断器的熔断体额定电流只要符合国标和IEC标准规定的过电流选择比为1.6：1 的要求，即上级熔断体额定电流不小于下级的该值的1.6 倍，就视为上下级能有选择性切断故障电流;②限流特性好，分断能力高;③相对尺寸较小;④价格较便宜。
(2) 熔断器的主要缺点和弱点①故障熔断后必须更换熔断体;②保护功能单一，只有一段过电流反时限特性，过载、短路和接地故障都用此防护;③发生一相熔断时，对三相电动机将导致两相运转的不良后果，当然可用带发报警信号的熔断器予以弥补，一相熔断可断开三相;④不能实现遥控，需要与电动刀开关、开关组合才有可能。
低压熔断器和断路器的比较和应用
低压熔断器和断路器的比较和应用低压熔断器和断路器是电力系统中常见的两种电气保护设备。
它们的作用是在电路中出现过载、短路等故障时，自动切断电路，保护电器设备及人身安全。
在实际应用中，熔断器和断路器都有其各自的优点和特点，需要根据具体的电力系统结构、负载特点、设备要求等多方面因素选择使用。
首先，简单介绍一下低压熔断器和断路器的基本原理和特点：1. 低压熔断器：低压熔断器是一种保护电路的装置，它采用金属导体引线作为熔丝，当电路中过载或短路时，熔丝被加热，熔断丝的熔断量可以根据负载电流和断路时间来选择。
低压熔断器有以下特点：简单、可靠、价格低廉。
它适用于额定电压低于1000V、额定电流小于1000A的电路保护。
2. 断路器：断路器是一种主动式保护器件，它不同于熔断器的是，它可以在保护电路后主动恢复电路。
当电路中发生过载或短路时，断路器会及时切断电流，避免设备及线路的损坏。
并且，断路器除了过载及短路保护外，还具有欠电压、过电压、地故障等多种保护功能。
断路器有以下特点：能够及时切断电路，对电气设备的保护更加完全。
断路器适用于电流高、电压大、频繁开关、需要多重保护等场合。
接下来，对低压熔断器和断路器进行比较：1. 保护功能：低压熔断器只具有过载、短路保护功能，而断路器不仅具有过载和短路保护，还可实现过电流、过电压、欠电压、地故障等多项保护功能。
2. 切断能力：断路器的切断能力比熔断器强，可以实现大电流切断和频繁开关，可以满足高电压大电流、高频次开关的电路保护要求。
3. 使用寿命：熔断器的使用寿命比断路器要短。
由于熔丝在保护电路后需要更换，所以使用寿命受到熔丝的耐久程度的限制，而断路器则不需要更换内部零件，使用寿命较长。
4. 安全系数：熔断器相对于断路器来说，具有较低的安全系数。
在熔断器保护电路的过程中，如果熔丝被损坏或热量不均匀，可能导致保护失败，而断路器则在保护电路的过程中具有更高的可靠性和安全性。
最后，对低压熔断器和断路器在实际应用中的使用进行简述：低压熔断器适用于电气负载电流小、额定电压低的场合，如办公楼、商场等室内配电系统。
低压断路器与熔断器如何选择
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的 的 电器 。熔 断 器 是 一 次性 设 备 ， 熔 断 后 就需 要 进 行 更换和处理 ， 是 一 种价 格 便 宜 而且 应 用 较 多 的保 护 控 制 元件 。 ２ 低 压 断 路 器 和 熔 断 器 的选 择 在 实 际应 用 中 ， 是 选 断路器 还 是熔 断器 ， 应根 据 低 压 配 电线路 故 障特 点 、 工 作 需要 和两 种 低 压保 护 电器 的 优 势 劣 势 综 合 分 析 来 进 行 因 地 制 宜 的 选 择 。 依 照 “ 技术 先进 ， 经 济合 理 ” 的原 则 ， 两 种 保 护 电 器 的选 型 大 致有 ４ 个 方案 。
低压断路器和低压熔断器的选用及比较
低压断路器和低压熔断器的选用及比较低压配电系统通常采用低压断路器和熔断器作短路保护，尽管两者在作短路保护的功能是相同的，但它们在使用上也有很大区别和不同，电气工程技术人员应该了解并掌握它们的选择和使用上的差异。
一、低压断路器低压断路器（LowV oltageCircuitBreakers）又称之为自动空气开关或空气断路器，是一种不仅可以接通和分断正常负荷电流和过负荷电流，还可以接通和分断短路电流的低压开关电器。
低压断路器在电路中除起控制作用外，还具有一定的保护功能，如过负荷、短路、欠压等保护功能。
它可用来分配电能、不频繁地启动电动机，对电源线路及电动机等实行保护，当供电回路发生严重的过载、短路及欠压等故障时能自动切断电路，其功能相当于熔断器式开关与过欠热继电器等组合。
低压断路器在分断故障电流后一般不需要更换其内部零部件，使用方便，已广泛应用于交直流低压配电系统各级馈出线，各种机械设备的电源控制和用电终端的控制和保护，包括用于不频繁地起动电动机及操作转换电路中。
1.低压断路器的分类低压断路器的分类方式较多，通常分为以下几种：（1）按交直流系统的不同，分为低压交流断路器和低压直流断路器。
（2）按灭弧介质分，有空气式和真空式，但目前使用的多为空气式低压断路器。
（3）按使用类别分，无选择型（保护装置参数不可调）和有选择型（保护装置参数可调）两类：A类：在短路情况下，断路器无明确指明用作串联在负载侧的另一短路保护装置的选择性保护，即在短路情况下，无选择性保护所需要的人为短延时，因而无短时耐受电流要求。
B类：在短路情况下，断路器明确指明用作串联在负载侧的另一短路保护装置的选择性保护，即在短路情况下，可实现选择性保护，有人为短延时（可调节），因而有短时耐受电流要求。
（4）按结构型式分框架断路器（ACB：AirCircuitBreakers）：也称万能式断路器，将所有的零部件都安装在一个绝缘的或金属的框架上，有较多的结构变化、较多种的脱扣器、较多数量的辅助触头，一般选择性断路器，特别是大容量断路器，多设计成框架断路器。
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义责任，而且是财政和法律责任。
己的专业人员是解决问题的唯一途径。
为高级安全保护推荐最好的解决方案是 HSE（健康和安全委员会）出版物：电气开关
您和我们的责任。
安全保障
上图是用高速数码录像机在测试时拍 下的镜头，它显示了操作失误或使用 不当可能会造成的爆炸形势。
为了工作安全，必须进行风险评估和维修保养 只有通过风险评估才能制定各项预防措施以保 证工作安全。 为防止危险事故发生，所有的电气设施，器件 都应由专业人员定期进行保养, 检查 和 测试。 这些设备应自始至终在安全的条件下运行。
熔断器提供最好的短路保护 电动机绕组绝缘功能的劣化会导致短 路。在维修过程中的错误连接可能会 造成这种劣化。 熔断器和断路器都可起到短路保护的 作用。但短路限流作用强的器件保护 电动机起动器的效果更好。
热继电器监测 过载和断相
所有的现代化热继电器都有监测断相的功能 断相会造成电动机过热。以下设备有断相保护功能： - 断路器 - 带接触器的热继电器。所有现代化热继电器都
电气设施保护
溯高美电气公司
工业开关与保护系统
电气设施保护:
这是您的责任
这本册子的目的在于帮助行业顾问和最终用户选择最合适的电气保护器件，并了解在选择，使用和维修 保养低压设备中所承担的责任。
电是致命的
每年仅在英国 就有数百起工作事故 是由电击或电灼烧造成的，其中大 约三十例是致命的。
除了丧失生命，还要损失财产
熔断器的选择性与其品牌无关 熔断器的熔断和限流特性曲线是根据 IEC 60269 国际标准制定的，也就是 说熔断器的品牌对它的选择性没有直 接意义。比如拿一个其它牌子的熔断 器来替代溯高美的熔断器，其选择性 不会改变。 但断路器则不同，只有同一厂家而且 是同一批的产品的选择性才一致。
上游断路器 D1 保护下游断路器 D2。 D2的分断 能力低于短路电 流强度。
给线路重新通电是一个重大危险源 给一个被电路保护器切断的电路重新通电 是一个重大的危险源，在没有确认可以对 设备及电路进行安全通电之前，不要轻易 将断路器合闸或更换熔断器。 无论是使用熔断器还是断路器，操作都应 由接受过严格而正规训练的人员进行。
两种选择: 熔断器或断路器
习惯和偏爱 :
熔断器和断路器，哪个是线路保护的最佳方案？这一直是个争论的话题。 两种器件性能都很好，在许 多应用上两者各有其优势。 在这些情况下，选择经常出于习惯或个人偏好。
发生过载后，过载保护器的启动时间与电 流有关，电流越大，过载部分断开得越快。 保护功能由以下设备提供： - 带接触器或断路器的热过载继电器 - 电子继电器 - 集成热保护装置用来保护驱动器或电动 机起动器等电子设备。
电流
电动机供电线路拥有多个开关 装置或控制设备, 对这些元件的 参数必须进行合理匹配才能保 证电动机的正常运行。
小型断路器适用于负载保护 断路器可在故障后再合闸，其操作简 便，适于家用或类似家用保护。在配 电终端，电气故障会由过载（锅炉或 其他加热器过多）或其他产品的连接 方式不当而引起。因此选用小型断路 器作为这一侧的保护比较合适。
在配电保护上，熔断器更有优势 配电盘上的保护器会在故障（电缆损 坏，维修后的短路）或系统缺乏选择 性时启动。 之后设备必须被检修。在 系统的这一阶段短路电流强度很大， 故障后再合闸会对系统造成严重损害。 熔断器具有很强的分断能力和无比的 可可靠性，更适于这一侧的保护。
能源利用率
一个需求, 一个方案
能源利用率的高低对企业的竞争力有越来越重要的影响。因为供电故障会降低产量，并造成某些 功能的停滞如照明，取暖，电梯等，所以对电气设施的设计必须达到把故障损失和不良影响降到 最低的目的。
分断能力, Icu 和 Ics (IEC 947-2)
Icu (极限短路分断能力) lcu (kA 有效值)是断路器可切断的最 大短路电流。它是经一定的标准试 验程序来验证的。 它的试验程序是 分断—合闸—立即再分断。 通过这一试验程序, 断路器不得有危 险性。这个特性还要由一个特定额 定电压Ue来决定 Ics (额定运行短路分断能力) lcs (kA 有效值) 由生产厂家给定， 表达形式为Icu的百分数。 这一性能 非常重要，它指出了断路器在连续 切断三次短路电流以后的正常工作 能力。
保护器还能 100% 保证安全吗? 给断路器再合闸不等于排除故障 如果配电系统的一个保护器启动了， 在故障部分未被查明并切除之前，不 能重新启动设备。但在此期间，可更 换熔断器或检修断路器并重合闸。
能源利用率
怎样将故障损失降到最小: 选择性和级联保护
配电系统应具有选择性，其目的在于只将故障部分从配电网络切除，尽可能缩小停电范围。 如果配电系统元件的参数匹配不合理，一个故障会启动多个电路保护器, 造成网络中大部分无故障区域 停电。
电动机起动器的保护
时间
所有的电动机起动器都具备过载，
短路，带载切断和隔离的保护装置。
这些设备可以是独立的部件，比如
一组熔断器或一个塑壳断路器，一
个接触器和一个热过载继电器。
过载是故障的首要原因 过载的原因有以下几种: - 电气故障 (断相，电压超限等) - 机械故障，扭矩过大或电动机受损, 起 动时间过长. 95%的故障都是由过载引起的。 热继电器监测过载
目录:
能源利用率
- 一个产品, 一个方案 ............................ 4 -怎样将故障损失降到最小: 选择性和级联保护................................ 5 - 电动机保护和二型协调........................ 6
安全性和可靠性
时间
熔断器
达到完全选择性
的条件是上下游
熔断器之比为1.6
X 1.6
使用熔断器就不需要采用级联保护 级联保护的目是通过采用一个短路分断 能力低的廉价断路器来节约成本。 当电流强度介在两个断路器之间时，上 游断路器对下游有保护功能，因此可选 用廉价的短路切断能力低的断路器作下 游保护。 而熔断器不需要级联，因为即使最小的 熔断器也具有很高的分断能力： NFC 和 DIN 熔断器的分断能力可达100kA (有效值)，BS可达80 kA, UL熔断器 可 达200 kA 。
更换熔断器，确保100%安全有效 与断路器动作后可再合闸的性能不 同，熔断器在熔断后必须进行更换。 新换上的熔断器保持原有性能，保 护系统依然100%安全有效。
断路器可被合闸多少次 根据断路器的特性而定, 也要考虑 到以下因素：每次故障发生后的检 修是否必要，在没有进行维修的情 况下故障断路发生的频率。 合闸还是更换?
熔断器保护通常允许使用较小的 接触器
接触器和热继电器的短路耐受性 与机体的大小有关。 与断路器相
比，熔断保护器件的允通电流小， 通常允许使用较小的接触器
熔断器的启动快 (几个毫 秒)，这使它具用很强的短 路限流功能
可提供差动保护 - 带熔断监测的熔断器 (电弧或电子监测)
能源利用率
电动机保护和配合类型2
为了避免故障必须对各部件的参数进行合理匹配。需要考虑的因素有：电缆和设备过热会引起火 灾，开关设备的触头熔焊会造成开关失灵，对以后的使用带来危险。 配合的主要目的是保证电动机起动器安全地承受所有级别的故障电流，配合类型是根据 IEC 947-4 国际标准而制定的。
时间 (秒)
时间与选择性
上下游断路器之间的 保护和配合类型2
当今的高科技商业基地和工业制造厂家都具有昂贵的电动机和启动器，为此必须具备合适的保 护装置。高效，高产量和工作安全是首要考虑的问题。为了把计划外的停机降到最低，就必须 具备最优秀的保护产品。
OSHA §1910.334 : 在电路保护系统 动作后，重新接通电路 “当线路被电路 保护器切断后, 在没有确认可以对设备 和电路进行安全通电之前，不可以重 新为该线路 进行人工通电。 禁止对断路器进行反复人工合闸或通 过更换熔断器而重新接通线路”
OSHA 职业安全健康管理局 是美国一家主要的联邦政府机关， 其任务是以法律手段来加强对职工 健康和安全的保障
只有熔断器具有完全选择性，且不受短 路电流的限制。
一个保护器件，如果只有当短路电流达 到某一值时，它才发挥选择性，我们称 它为部分选择性。对断路器来说，如果 想判断它们对每个线路是否有选择性， 就必须要对短路电流强度进行研究。
而熔断器就不受短路电流的制约，它们 具有完全选择性。只要电路中上下游的 熔断器之比为1.6，它们就能发挥选择 性。熔断器在电流达到一定强度时会切 断电路。为此，额定电流低的熔断器所 需的能量少于额定电流高的熔断器，这 一原理保证了它门的完全选择性。
开关设备必须由受过训练的专业人员来操作
除了职工伤亡，企业还会遭受由更换设 开关设备须由专业人员来操作, 他们也被称为
备，停机等造成的经济损失。
“ 授权人” 。但有的用户不具备这样的专业员
这就意味着，采用安全可靠的电气设施, 工，他们就把开关的操作和维修保养工作全
并进行充分的风险评估，不仅是一项道 部承包出去。这种做法是不妥当的，拥有自
Isc
电流
时间 (秒)
断路器
选择性或级联保 护只能由生产厂 家通过实验数据 来决定。