Kamfutukar Maimaita ko MPCB
MPCB (Motor Protection Circuit Breakers) shine wata irin alamomin kawar da aka fadada da yake daɗe don kawar motoci. Motoci suna da muhimmanci sosai a cikin abubuwa daban-daban, saboda haka ya kamata a kunne ta da MPCB. Wadannan sun fi siffar wasu abubuwan da suke fito da motoci a wurare na masana'antu da tattalin arzikin:
Motoci da suke fito da rooftop air conditioners, chillers, compressors, heat pumps da cooling towers.
Extraction da injection fans, kamar hasen air handling units.
Sistemai da suke pumpa ruwa.
Elevators da wasu abubuwan da suke nemi waɗanda ba su.
Industrial conveyor belts da wasu abubuwan da ake amfani da su a cikin tattalin arzikin.
A cikin duk wadannan abubuwan da motoci ke fito a wurare na masana'antu da tattalin arzikin, MPCB yana da muhimmanci sosai wajen kawar da kawar motoci.
Wani shine MPCB (Motor Protection Circuit Breaker) da kuma abubuwan da yake iya yi?
MPCB (Motor Protection Circuit Breaker) shine wata irin alamomin kawar da aka fadada da yake daɗe don kawar motoci. Yana da muhimmanci wajen kawar da kawar motoci a kan 60 Hz da 50 Hz. Yana da abubuwan da yake iya yi wajen kawar da kawar motoci:
Kawar da kawar motoci a kan electrical faults kamar short circuits, line-to-ground faults da line-to-line faults. MPCB yana iya kawar da duk electrical fault da ya zama ta hanyar breaking capacity.
Kawar da kawar motoci a kan overload, idan motoci ya ƙara electric current da ya ƙarin da nameplate value. Overload protection yana iya ƙunshi da adjustment a cikin MPCB.
Kawar da kawar motoci a kan phase unbalances da phase loss. Duk wadannan shugaban yana iya ƙasa motoci, saboda haka MPCB yana iya kawar da motoci a lokacin da faɗinsu ya ƙasa.
Thermal delay don kawar da motoci bai ƙara ba a kan bayan an ƙara overload, domin motoci ya ci gaba. Idan motoci ya ƙara biyu a lokacin da ya ƙasa, zai iya ƙasa daɗi.
Switching of Motor Circuit – MPCB suna da buttons ko dials don hakan.
Fault Signaling – A baya da models of MPCB suna da LED display wanda ya faru a lokacin da MPCB ya ƙara. Wannan shine alama visual don maɓallace da ya ƙara fault, kuma motoci ba za a ƙara ba har zuwa a lokacin da faɗinsu ya ƙasa.
Automatic Reconnection – Wasu models of MPCB suna da cool down time input a lokacin da ya ƙara overload, bayan haka motoci zai ƙara automatically. Motoci suna da maiyawa, saboda haka muhimmancin MPCB yana da muhimmanci sosai. Idan motoci ba a kunne ta da MPCB, zai iya ƙara repair works ko replacement. Motoci da a kunne ta da MPCB zai ƙara mafi tsawon shekaru.
Muhimmancin MPCB (Motor Protection Circuit Breaker)
MPCB (Motor Protection Circuit Breaker) yana da muhimmancin thermal magnetic circuit breaker, amma da abubuwan da suka ƙunshi da yake iya kawar da motoci. Muhimmancinsu yana da muhimmanci sama da all other circuit breakers.
Thermal protection yana da muhimmanci wajen kawar da motoci a kan overload. Yana da expanding and contracting contact wanda yake kawar da motoci idan ya ƙara excessive current. Thermal protection yana da delayed response, don inrush currents a lokacin da motoci ya ƙara. Amma idan motoci ba a ƙara ba, thermal protection yana ƙara a lokacin da inrush current.
Magnetic protection yana da muhimmanci a lokacin da short circuit, line fault, ko high current. Magnetic protection yana ƙara immediately, don kawar da fault currents.
Tashin MPCB da all other circuit breakers shine cewa MPCB yana iya kawar da phase unbalance da phase loss. Three-phase circuit motors suna bukatar three live conductors da balanced voltages. Unbalance of more than 2% yana ƙasa motoci. Idan 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.
MPCB suna da 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.
Kawar da Asynchronous Motor
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.
Sizing of Motor Protection Circuit Breaker (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.
Chart of Motor Protection Circuit Breaker Specifications
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.
Conclusion 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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