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12 watt dc fan baldor reliance industrial motor manual

12 watt dc fan baldor reliance industrial motor manual

28. what causes single-phase operation of three-phase asynchronous motor? What is the phenomenon of single-phase operation?

Answer: cause: during the operation of three-phase asynchronous motor, if one phase fuse is burnt out or has poor contact, one phase contact of disconnector, circuit breaker, cable head and conductor is loose, and one phase of stator winding is disconnected, the motor will operate in single phase.

Phenomenon: when the motor is in single-phase operation, the ammeter indication rises or becomes zero (for example, when one phase of the ammeter is disconnected, the current indication becomes zero), the speed drops, the sound is abnormal, the vibration increases, the motor temperature rises, and the motor may be burned out after a long time.

29. what are the functions of comprehensive protection for HV auxiliary motor?

Answer: the motor (transformer) plant integrated protection adopts the single-chip microcomputer protection technology developed by advanced software and hardware technology. Generally, it adopts the two-phase three element mode. Phase B is generated by software and generally has the following functions: (1) quick break protection; (2) Overcurrent protection; (3) Overload protection; (4) Negative sequence current protection; (5) Zero sequence current protection; (6) Thermal overload protection.

30. what protections are generally installed for HV auxiliary motors? How is protection configured?

Answer: station motors of 1000V and above shall be equipped with interphase short-circuit protection device composed of relays, which usually adopts non time limited quick break protection, and generally adopts two-phase type, which acts on tripping. When the sensitivity coefficient of current quick break protection is not enough for motors with capacity of 2000kW or above or motors with phase separation outgoing line at neutral point below 2000kW, differential protection shall be installed.

Overcurrent protection: when the motor is equipped with differential protection or quick break protection, overcurrent protection should be installed as the backup protection of differential protection or quick break protection.

Overload protection shall be installed for motors prone to overload during operation or motors with poor starting and self starting conditions and long starting and self starting time.

Low voltage protection is mainly to ensure the self starting of main motors in the recovery process after short-term reduction or interruption of power supply voltage. Generally, some unimportant motors shall be cut off by using low voltage protection devices. In addition, low voltage protection is also used to cut off some motors that are not allowed to start automatically according to the requirements of production process and technical safety.

 

 

12 watt dc fan baldor reliance industrial motor manual

31. what protections are generally installed for low-voltage auxiliary motors?

Answer: for low-voltage auxiliary motors below 1000V and less than 75kW, fuses or releases of low-voltage circuit breakers are widely used as phase to phase short-circuit protection.

When the neutral point of low-voltage auxiliary power system is directly grounded, when the phase to phase short-circuit protection can meet the sensitivity coefficient of single-phase grounding short-circuit, the phase to phase short-circuit protection can also be used as grounding short-circuit protection. When it cannot be met, additional grounding protection shall be installed. The protection device is generally composed of a current relay connected to the zero sequence current transformer, which acts instantaneously to trip the circuit breaker.

Overload protection shall be installed for motors prone to overload. The protection device can act on the signal or trip according to the characteristics of the load. The motor operating apparatus is the power supply circuit of magnetic starter or contactor, and its overload protection is composed of thermal relay. For the circuit composed of automatic switch, when a separate relay protection is installed, the inverse time limit current relay can be used as overload protection. However, the motor type automatic switch can also use its own thermal release as overload protection.

The operating appliance is the power supply circuit of the magnetic starter or contactor. Since the holding coil of the magnetic starter or contactor can be automatically released at low voltage, it is not necessary to set another low voltage protection.

32. what are the common motor faults and abnormal working conditions?

Answer: among the auxiliary motors in the power plant, the phase to phase short circuit of the stator winding is the most serious fault of the motor. The short-circuit current generated by this fault will cause serious damage to the insulation of the motor, significantly reduce the voltage of the power supply network and damage the normal operation of other electrical equipment. Therefore, phase to phase short circuit protection must be installed to cut off the faulty motor without time limit.

Motor faults include single-phase grounding fault and turn to turn short circuit of one phase winding. The harm degree of single-phase grounding to motor depends on the grounding mode of neutral point of power supply network. In the 3~6kv high voltage auxiliary power grid, the neutral point is not grounded. Whether to install grounding protection should depend on the capacitance current. For the auxiliary motor in the 380V direct grounding system, if the grounding fault occurs, the coil and iron core will be burned, so the grounding protection is installed to cut off the fault motor without time limit.

The abnormal working state of the motor is mainly over-current. Long-term over-current operation will make the temperature rise of the motor exceed the allowable value, accelerate the aging of coil insulation, and even burn out the motor.

33. what are the common causes of motor failure?

(1) Short circuit and other faults of the motor and its electric circuit make the protection act on the fuse fuse fusing or act on the circuit breaker tripping.

(2) The mechanical part of the motor has a serious fault, and the motor load increases sharply and is overloaded, which makes the overcurrent protection act and trip the circuit breaker.

(3) Motor protection maloperation, if it is purely due to this error, the system has no impact.

(4) The equipment carried by the motor is controlled by the interlocking conditions and interlocked.

 

12 watt dc fan baldor reliance industrial motor manual

34. what causes the non full phase operation of three-phase asynchronous motor? What is the phenomenon during incomplete phase operation?

Answer: cause: during the operation of three-phase asynchronous motor, if one phase fuse is burnt out or poorly contacted, one phase contact of disconnector, circuit breaker, cable head and conductor is loose, and one phase of stator winding is disconnected, the motor will operate in single phase.

Phenomenon: when the motor is in single-phase operation, the ammeter indication rises or becomes zero (for example, when one phase of the ammeter is disconnected, the current indication becomes zero), the speed drops, the sound is abnormal, the vibration increases, the motor temperature rises, and the motor may be burned out after a long time.

35. can fuse be used as overload protection for asynchronous motor?

Answer: the fuse can not be used as overload protection for asynchronous motor.

In order not to blow the fuse when the motor is started, the rated current of the selected fuse shall be 1.5~2.5 times greater than the rated current of the motor, so that the fuse will not blow even if the motor is overloaded by 50%, but the motor will not burn out within 1 hour. Therefore, the fuse can only be used as the short-circuit protection of motor, conductor and switchgear, but can not play the role of overload protection. Only adding thermal relay and other equipment can be used as overload protection of motor.

36. what are the requirements for the allowable starting times of the motor?

Answer: when the motor is started, the starting current is large and there is much heating. The allowable starting times are determined based on the principle that the heating will not affect the insulation life and service life of the motor. Continuous multiple closing and starting will often overheat the motor, or even burn the motor. It must be prohibited. The general requirements for starting times are as follows:

(1) Under normal conditions, the motor is allowed to be started twice in cold state with an interval of 5min, and it is allowed to be started once in hot state.

(2) In case of accident (or emergency) and if the starting time does not exceed 2 ~ 3S, the motor can be started once more than normal.

(3) The balance test shall be carried out mechanically, and the starting interval of the motor is:

Motors below 200kW shall not be less than 0.5h;

200 ~ 500kW motor shall not be less than 1 hour;

For motors above 500kW, it shall not be less than 2 hours.

12 watt dc fan baldor reliance industrial motor manual

37. how to handle the tripping of circuit breaker when the motor is started?

Answer: (1) check whether the protection operates and whether the setting value is correct.

(2) Check the electrical circuit. If no obvious fault point or equipment abnormality is found, cut off the power and measure the insulation resistance.

(3) Check whether the mechanical part is stuck or started with load.

(4) Check whether the accident button is manually connected (stuck for a long time)

(5) Whether the power supply voltage is too low.

After the cause is found out through inspection, power on and start up after the fault is eliminated.

38. how to deal with fuse fusing when the motor is started?

Answer: (1) check the electrical circuit. If no obvious fault point or equipment abnormality is found, cut off the power and measure the insulation resistance.

(2) Check whether the mechanical part is stuck or started with load.

(3) Check whether the power supply voltage is too low.

(4) Check the fusing condition of the fuse to determine whether there is any fault or whether the capacity of the capacitor meets the requirements.

39. how to deal with tripping during motor operation?

Answer: when the motor trips during operation, either the equipment or the power supply has problems, and the protection and personnel maloperation are not excluded, the following treatment should be carried out:

(1) Immediately start the standby equipment and put it into operation. Important motors without standby equipment can be forced to send once. Minimize the loss and impact on production caused by motor tripping.

(2) Measure the insulation resistance of the motor and its circuit.

(3) Check whether the motor protection operates. For low-voltage motors, check whether the circuit breaker, fuse and thermal relay are normal.

(4) Check the motor and its circuit for signs of fireworks, short circuit and damage.

(5) Check whether the power supply is normal.

(6) Check whether the mechanical part is normal and whether the motor bearing is damaged to hold the main shaft.

(7) Whether there is any maloperation of protection or accident button.

40. what items should be checked before the motor is powered on?

Answer: (1) the motor and its surroundings shall be clean and free of any objects that may hinder the operation.

(2) The oil quantity of oil ring is sufficient, the oil color is transparent, and the oil level and oil circulation are normal.

(3) The foundation and screws of each part shall be firm, and the grounding wire shall be in good contact.

(4) The cooling device is in good condition and operates normally.

(5) For wound motor, it shall be checked that the commutator, slip ring and brush are in good contact, the starting device is in the starting position, and the adjustment resistance is not jammed. For wound motor started with frequency sensitive resistance, it shall be checked that the frequency sensitive resistance and short-circuit switch are normal, and the short-circuit switch is in the off position.

(6) Try to turn the rotor as much as possible, check whether there is friction between the stator and rotor, and whether the mechanical part is blocked.

(7) Check that the interlock switch position is correct, and the electrical and thermal instruments are complete and correct.   

 

12 watt dc fan baldor reliance industrial motor manual

41. when the motor is started, after the switch is closed, the motor cannot rotate and makes a sound, or it cannot reach the normal speed. What may be the reason?

Answer: (1) one phase of stator circuit is disconnected.

(2) Broken line or poor contact of rotor circuit.

(3) Broken line or poor contact of rotor circuit.

(4) The motor or the driven machinery is stuck.

(5) Stator winding wiring error.

42. what are the possible reasons for sparks or smoke from the motor during startup or operation?

Answer: the center is not correct or the bearing bush is worn, causing the rotor and stator to collide; The copper (aluminum) strip of the squirrel cage rotor is broken or in poor contact.

43. what are the possible reasons for the periodic oscillation of stator current of the running motor?

Answer: (1) the copper (aluminum) strip of the squirrel cage rotor is damaged.

(2) The wound rotor winding is damaged.

(3) The slip ring short circuit device or rheostat of wound motor has poor contact and other faults.

(4) The mechanical load changes unevenly.

44. what are the possible reasons for the violent vibration of the motor?

Answer: (1) the center between the motor and its machinery is not correct.

(2) The unit is out of balance.

(3) The rotating part rubs against the stationary part.

(4) The coupling and its connecting device are damaged.

(5) Mechanical damage caused by.

45. what are the possible reasons for the high motor bearing temperature?

Answer: (1) insufficient oil supply, insufficient or too much grease in rolling bearings.

(2) The oil is not clean, the oil is too thick, there is water in the oil, and the oil model is used incorrectly.

(3) The drive belt is too tight, the bearing cover is too tight, the bearing bush surface is not scratched well, and the bearing clearance is too small.

(4) The bearing and shaft of the motor are inclined.

(5) The center is not aligned or the convex teeth of the elastic coupling work unevenly.

(6) Internal wear of rolling bearing.

(7) There is current flowing through the bearing, the journal is not well worn, the bearing bush alloy is dissolved, etc.

(8) The rotor is not in the center of the magnetic field, causing axial movement, bearing knocking or bearing extrusion.

46. inspection items before startup of boiler water circulating pump?

Answer: (1) confirm that the air in the motor has been exhausted.

(2) The water for the motor shall be slowly fed from the bottom and the flow shall be kept at 1.607m3 / H ~ 1.118m3 / h.

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