Kurtalanê Pîvanan Motorê an MPCB
Motor protection circuit breakers ji tiyên elektrikî yên pêşvegerandina xas û taybetmendin dike ku ji bo motoran elektrikî piştgirî dike. Motoran elektrikî hûn çend vêna bikar anîn û ji bo dirêj bikeya her tîpa cihazên mekanîkî bikar anîn, bistanîn da ku bi serfirazî bi MPCBs pêşvegirî bide. Ji dê hatine werger çend misalên cihazên ku ji bo motoran elektrikî di binên endustriyî û komersiyî de bikar anîn:
Kondîsyonerên çepî, çiller, kompresor, pompa çewit û kuleyan çewit.
Fanên derketina û ketina havî, û birîkarên keşanîya hav.
Sisteman pambeyan.
Asansör û yekîtiyên din dikane.
Bandên conveyer û yekîtiyên din bikar anîn di procesên endustriyî de.
Di hemî wan vêna endustriyî û komersiyî de ku motoran elektrikî bikar anîn, MPCB rola serkeftî ya pêşvegirîya elektrikî da.
Motor Protection Circuit Breaker çi ye û funksyonan wê çendin?
Motor protection circuit breaker, an jî MPCB, ji tiyên electromekanîkî taybetmend e ku ji bo cihazên motor 60 Hz û 50 Hz bikar anîn. Li gorî funksyonan weha wê çendin ku motoran elektrikî pêşvegirî bide:
Pêşvegirî ji çend şertên elektrikî, wê ji sêmeya short circuits, line-to-ground faults û line-to-line faults. MPCB dikare her çend şertê elektrikî ku ji qeydê breaking capacity ya we ya li ber be veqetin.
Pêşvegirî ji overload motor, gava motor ê ampera elektrikî ji nîşankirina nameplate value ya we ya li ber be veqetin. Pêşvegirîya overload normalda di MPCBs de adjustable e.
Pêşvegirî ji unbalance phase û phase loss. Her du şertê ji bo three-phase motor zêde danûst û MPCB motor ra ji re disconect bikat gavê ku şertê were detekt kirin.
Thermal delay bikat gavê ku motor ji re start bike bidexa overload, motorê demê bikat gavê ku cool down bike. Motorê ji re start bike gava overheat bike dikare damage permanent bikat.
Switching Motor Circuit – MPCBs normalda bi buttons û dials equip kerdin.
Fault Signaling – Most models of motor protection circuit breakers have a LED display that is turned on whenever the MPCB has tripped. This is a visual indication for nearby personnel that a fault has occurred and the electric motor must not be connected again until the fault is addressed.
Automatic Reconnection – Some MPCB models allow a cool down time to be input in case there is an overload, after which the motor will restart automatically.
Electric motors are expensive equipment, so the role of the motor protection circuit breaker is very important. If a motor is not protected correctly, it may be necessary to carry out costly repair works or even replace the equipment completely. An electric motor that is adequately protected with an MPCB will have a much longer service life.
Motor Protection Circuit Breaker Working Principle
Motor protection circuit breaker dikare were şînîn ji subtypes of a thermal magnetic circuit breaker, lê bi funksyonên ekstra ku ji bo pêşvegirîya motoran elektrikî dizayn kirin. The basic working principle is similar to all other circuit breakers.
Thermal protection bikar anîn ji bo pêşvegirîya motoran elektrikî ji overload. Wê li gorî expanding and contracting contact ê ku motor disconect bikat gava ampera excessive current detekt bikat. It is very important to know that thermal protection has a delayed response, to allow the high inrush currents when a motor starts. However, if the motor is unable to start for some reason, thermal protection will trip in response to the extended inrush current.
Magnetic protection bikar anîn ji bo şertên short circuit, line fault, û other high current electric fault. Unlike thermal protection, magnetic protection is instantaneous; to immediately disconnect the dangerous fault currents.
The main difference between the MPCB and other circuit breakers is that the MPCB can provide protection against phase unbalance and phase loss. Three-phase circuit motors require three live conductors with balanced voltages in order to operate effectively. An unbalance of more than 2% will be detrimental to the motor’s service life. If one of the phase voltages is suddenly lost, the effect is even more damaging because the motor will keep on running with only two phases. The motor protection circuit breaker is capable of detecting these conditions by measuring the differences among phase voltages, and disconnects the motor immediately when they occur. It is important to note that phase current unbalance is normal in three-phase systems that power separate single-phase loads, but is unacceptable when the three-phase circuit powers an electric motor.
MPCBs are also equipped with a manual interruption mechanism, allowing disconnection of electric motors for replacement or maintenance.
Motor protection circuit breakers are available in a wide variety of current ratings, and one of their best features is that many models allow the current rating to be adjusted. This means that the same MCPB can be configured to protect motors of different capacities.
Asynchronous Motor Protection
Most motors used in the industry are asynchronous motors, also known as squirrel-cage induction motors. These motors use three-phase power to create a rotating magnetic field, which in turn magnetizes the rotor and creates rotational movement. When designing the electrical protection for an asynchronous motor and selecting motor protection circuit breakers, there are some very important factors to consider that aren’t present when protecting other types of electrical circuits.
Asynchronous motors draw a very high inrush current during startup, because they must establish a rotating magnetic field. This current can reach values of 500% to 800% of the rated value for a few fractions of a second. For this reason, the MPCB magnetic protection trips at values greater than 10 times the rated current, unlike some types of miniature circuit breakers which trip at values as low as 3 times rated current. In these cases, using a circuit breaker other than an MPCB will not even allow starting the motor before the magnetic protection trips. In order to reduce the inrush current, a very common practice is to complement the motor protection circuit breaker with a reduced voltage motor starter.
Asynchronous motors require the three phase conductors to have a balanced voltage in order to operate properly. If the phase conductors have an unbalance greater than 2%, the motor will suffer damage over time and will have a reduced service life. The electric motor will also tend to overheat, causing additional energy expenses as waste heat. For this reason, a motor circuit breaker must be able to detect phase imbalance and disconnect the motor accordingly.
If one of the phases is disconnected completely, the motor will keep operating but the current in the remaining two phases will rise above the rated value due to the electrical unbalance, and will probably burn the motor’s windings. For this reason, motor protectors must trip immediately as soon as phase unbalance or phase loss is detected. This is normally achieved by measuring the differences in current among the phase conductors. If one of the phase currents rises or drops considerably compared with the other two, it is indicative of unbalance. Likewise, if one of the phase currents drops to zero while the other two remain, a phase loss has occurred.
Then, what kinds of breakers can be used for the protection of asynchronous motors? Manufacturers generally offer three different motor protection circuit breakers, available for a wide range of voltages and currents, in order to meet most asynchronous motor protection needs.
It is very common to complement motor protection circuit breakers with a contactor to allow automatic control of motor startup and disconnection. The system might also include and under-voltage protection device, which disconnects the motor in case the system voltage drops considerably below the rated value.
Motor Protection Circuit Breaker Sizing (Selection Guide)
The two main factors that determine the adequate motor protection circuit breaker size are the nameplate voltage and nameplate current, of the motor itself.
The MPCB voltage rating must match the nameplate voltage of the motor. Normally, motor protection circuit breakers can be used in a wide variety of voltage ratings such as 230 V, 380 V, 415 V, 440 V, 500 V, and 660 V AC.
Once the voltage is known, it is necessary to check the nameplate current of the electric motor. It is important to note that the actual operating current may be lower than nameplate current, especially if the motor isn’t fully loaded. However, the MPCB must always be selected according to nameplate current value in order to allow the inrush current when a motor starts. For example, a motor with a nameplate current of 20 amperes might draw a much lower current during part-load operation, but the MPCB must be selected according to the rated value of 20 amperes, or it might trip if the motor is used at full load.
Motor protection circuit breakers can then be calibrated to the exact current value that is adequate for the electric motor being protected. They typically have an adjustment range. For example, a MPCB rated at 32 amperes might be usable for motors with rated currents as low as 22 amperes. This is very useful if an electric motor is replaced with a more efficient model that requires a lower current, since it will not be necessary to replace the motor breaker.
Even if a motor protection circuit breaker is sized correctly according to the electric motor being protected, it is also important to use adequate wiring. In order to provide adequate protection, the wire must be able to conduct the rated current safely. An undersized wire will overheat, the insulation will melt, and electric faults may occur even with a breaker installed.
Motor Protection Circuit Breaker Specification Chart
MPCB manufacturers typically provide charts where the technical specifications of the circuit breaker are presented, in order to simplify the selection process. The following chart, provided as an example, is for the motor circuit breaker SGV2-ME model manufactured by CGSL.
The current values at which the thermal and magnetic protections operate are displayed in the thermal release and magnetic release columns. Before installing a MPCB, it is very important to verify that voltage and current ratings are compatible with the motor being protected.
Conclusions of Motor Protection Circuit Breaker
Motor protection circuit breakers have a very important role in electrical safety, since the motors they protect have a wide variety of applications in commercial buildings and industry.
Asynchronous motors, the most common type of electric motor in industrial and commercial settings, has special protection requirements that can only be met by a motor protection circuit breaker. It is also possible to complement MPCB with other protection or automation devices such as under-voltage protection, timers, and reduced voltage motor starters.
Adequate selection of the MPCB is key in order to provide reliable motor protection. An undersized MPCB will not even allow the motor to start, while an oversized MPCB might be unable to detect over-current conditions for the electric motor being protected.
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