Three-phase motor open phase protection and current changes

One, foreword As is known to all, three-phase asynchronous motor for power fault phase operation and the number of fire alarming, its mostly because of the low voltage circuit breaker or disconnecting switch contact undesirable: ac contactor singeing, cannot be connected to reliable contact; Too long could fuse and fuse oxidation corrosion, is impacted by the starting current burn out, etc. General motor open phase running occurs: vibration increases, have abnormal sound, temperature, speed drops, electricalmotor1.blogspot.com current increase, lack of phase start have a strong "buzzing" sound, cannot be started. In order to protect the motor, according to the phase of possible fault point, add open phase protection set to three-phase motor circuit. In this paper, the author introduces three phase motor open phase protection circuit. 

Second, the motor phase specific situation analysis 1. Motor phase operation deficiency. Motor open phase running, the stator's rotating magnetic field serious imbalance, the rotor current rights, can cause the rotor severe fever, lacks when the motor load capacity fell sharply, since there is a serious inhomogeneous magnetic field, can make the machine shake seriously increase, thus bearing damage and stand, can still operate after the motor is running short of phase, only the distortion of magnetic field, the harmful composition of current increases sharply, eventually lead to the winding burn. Motor phase break specific provision can't run, because the motor stator coil after disconnection will not produce a rotating magnetic field, only pulse magnetic field is produced, not motor rotates, but due to the operation of the inertia, so will rotate, but due to the load ambassador motor rotating gradually slow magnet generator down. 2. Start motor phase. If the motor stop short of a phase, when the power switch, normally only happens "buzzing" sound and cannot start, this is because the motor ventilation with symmetrical three-phase alternating current will produce a rotating magnetic field in the stator core, but when the lack of a phase after the power supply, single-phase pulsating magnetic field is generated in the stator core, it can't make the start torque motor. Therefore, the power supply lacks when the motor can't start. 3. The motor is short of two phase. When lack of two-phase motor can't start at all, no running motor response, because the phase thread inside the motor winding cannot produce current loop, cannot produce magnetic field winding, no damage to the motor. 4. Lack of phase change of motor current. Normal starting or running, for balanced load three-phase motor, three phase current are equal in size, less than or equal to the rated value. Break after a phase, three phase current imbalance or too big. When starting phase: motor can't start, the winding current for 4 to 7 times the rated current. Calorific value for the normal temperature of 16 and 49 times, because of its exceed the permitted temperature rise quickly and makes the motor burn down. When full load running lack of phase, the motor is in a state of flow, the current more than rated current, electric opportunity from weakness to blocked, not more the phase line current is added, cause rapid burning motor. three phase induction motor When light load running lack of phase, not open phase winding current increase rapidly, make this phase winding burned due to temperature rise too high.

The inverter from what respect to protection on the motor

The inverter from what respect to protection on the motor Abstract: the frequency converter is widely used in various industries, mainly due to its energy saving and the function of the frequency control of motor speed in the working condition of equipment and system application, the frequency converter from what respect to the protection of motor? Tags: frequency control, frequency converter, motor, energy-saving frequency converter is widely applied in industry control engineering net all rights reserved, mainly due to its energy saving and the function of the frequency control of motor speed in the working condition of equipment and system application, so the inverter is from what respect to the protection of motor? Below we will analyze this problem solve. Frequency converter for motor protection mainly has the following several aspects: over voltage protection, low voltage protection, over current protection, open phase protection, reverse phase protection, overload protection, earthing protection, short circuit protection, overclocking protection and protection of the stall. Here are the several types of the frequency converter for motor protection method were introduced simply. 1. The over voltage protection: the inverter output voltage detection function, frequency converter can automatically adjust the output voltage, the motor is not withstand overvoltage. Even if the output voltage and output voltage adjustment by more than 110% of the normal voltage, frequency converter can also through the outage protection for motor. 2. The under voltage protection: when the voltage is less than 90% of the normal voltage of the motor, frequency converter to ac synchronous motor protect downtime. 

3. The over current protection: when the motor current by more than 150% of the rating / 3 seconds, or 200% of the rated current / 10 microseconds, frequency converter through the magnet generator downtime to protect the motor. 4. Open phase protection: monitoring the output voltage, when the output phase, frequency converter alarm, after a period of time frequency converter through the downtime to protect the motor. 5. Reverse protection: frequency converter motor can only rotate along one direction, unable to set the direction of rotation, unless the user changes motor wiring A, B, C phase sequence, there is no reverse phase. 6. Overload protection: monitoring frequency converter motor current, when the motor current is more than 120% of the rated current / 1 minute, the frequency converter via down to protect the motor. 7. Grounding protection: frequency converter is equipped with special grounding protection circuit, generally made up of earthing protection of the transformer and relay, when a phase or two phase ground, inverter alarm. If the user requirements, of course, we can also design for the grounding protection immediately after downtime. 8. Short circuit protection: after the inverter output short circuit, inevitably cause over-current, within 10 microseconds inverter through down to protect the motor. 9. Overclocking protection: frequency converter has a maximum and minimum frequency limit function, make the output frequency can only be within the prescribed scope, thus realizing the overclocking protection function. 10. Stalling protection: general for synchronous motor stalling protection. For asynchronous motor CONTROL ENGINEERING China all rights reserved, accelerate the process of stall will be performance for current, frequency converter by over current and overload protection to realize the protection function. Reduction in the process of stall can www.facebook.com/dongfeng.motor be set in the process of debugging to avoid safety deceleration time.