1 rpm motor geared motor manufacturers in india
47. inspection items during startup and operation of boiler water circulating pump?
Answer: Inspection during operation:
(1) The flushing water flow of the motor shall be kept at 0.671m3/h ~ 1.118m3/h during hot or cold operation until the air bag pressure reaches 1.6Mpa and the ferric chloride content is lower than -0.3ppm.
(2) The cleanliness of motor cooling water shall be sampled and analyzed every 12 hours in cold operation, and once a week in normal operation.
Startup precautions:
(1) The standby pump shall be operated once a month for 10-15 minutes.
(2) The standby pump still needs to monitor that the motor cooling water temperature is not lower than 40 ℃, and pay attention to anti freezing.
(3) The starting time interval of the motor shall not be less than 15 minutes.
48. under what circumstances must the motor of boiler water circulating pump be shut down?
Answer: (1) the motor temperature is higher than 60 ℃.
(2) The current increases suddenly or returns to zero after current impact.
(3) The low-pressure cooling water of the high-pressure cooler is interrupted and an alarm is given.
(4) The vibration value exceeds 12.5 ~ 15 wires (5 ~ 6mil) (0.127mm ~ 0.152mm).
(5) If the motor fails to start within 5 seconds, it shall be stopped quickly to find out the cause.
49. what causes the vibration and noise of induction motor?
Answer: the sound of the normal operation of the motor is caused by two aspects: the vibration of the iron core silicon steel sheet due to the action of electromagnetic force after passing through the alternating magnetic flux, and the blowing effect of the rotor. These sounds are uniform. In case of abnormal noise and vibration, it may be caused by the following reasons:
(1) Causes of electromagnetic emission:
a) Wiring error. For example, one phase winding is connected reversely, and the windings of each parallel circuit have different turns.
b) The winding is short circuited.
c) Individual branches in multi-channel winding are open circuit.
d) Broken rotor bar.
e) The iron core silicon steel sheet is loose.
f) The supply voltage is asymmetric.
g) The magnetic circuit is asymmetrical
(2) Mechanical reasons:
a) The foundation is not fixed firmly.
b) The motor and the towed machinery are not aligned.
c) Rotor eccentricity or protruding stator slot wedge causes friction between stator and rotor (motor sweeping).
d) The bearing is short of oil, the steel ball of rolling bearing is damaged, the bearing and bearing sleeve are rubbed, and the bearing bush seat is moved.
e) The rotor fan is damaged or the balance is damaged.
f) The abnormal vibration of the carried machinery causes the motor vibration.
1 rpm motor geared motor manufacturers in india
50. what is the function of DC motor excitation circuit connected in parallel with resistance?
Answer: when the excitation circuit of the DC motor is disconnected, a high potential will be induced at both ends of the field winding due to self induction, which may be dangerous to the turn to turn insulation of the winding. In order to eliminate this danger, a resistance is connected at both ends of the field winding, which is called discharge resistance. The discharge resistance can form a circuit of the magnetic field winding. Once a dangerous potential occurs, a current is formed in the circuit, so that the magnetic field energy is consumed in the resistance.
51. what is asynchronous?
Answer: the speed of the rotor of the asynchronous motor must be less than the speed of the stator rotating magnetic field. The two speeds cannot be synchronized, so it is called "asynchronous".
52. what is the slip of asynchronous motor?
Answer: the difference between synchronous speed and rotor speed of asynchronous motor is called slip, and the percentage value of the ratio of slip to synchronous speed is called slip of asynchronous motor.
53. what factors are related to the no-load current of asynchronous motor?
Answer: it is mainly related to the power supply voltage. Because the power supply voltage is high, the magnetic flux in the iron core increases, and the magnetic resistance will increase. When the power supply voltage reaches a certain value, the magnetic resistance in the iron core increases sharply and the inductive reactance of the winding decreases sharply. At this time, a slight increase in the power supply voltage will lead to a large increase in the no-load current.
54. what causes excessive no-load current of asynchronous motor?
Answer: (1) the power supply voltage is too high: This is because the saturation of the motor iron core makes the no-load current too large.
(2) Improper assembly or excessive air gap.
(3) The number of turns of stator winding is not enough or the star connection is wrongly connected into triangle connection.
(4) The silicon steel sheet is corroded or aged, which weakens the magnetic field strength or damages the insulation between sheets.
55. what will happen if the motor is overloaded?
Answer: the overload operation of the motor will destroy the electromagnetic balance relationship, reduce the motor speed and increase the temperature. If the short-term overload can maintain the operation, if the long-term overload exceeds the rated current of the motor, the insulation will overheat and accelerate the aging, and even burn the motor.
56. what factors are related to the maximum torque of asynchronous motor?
Answer: (1) the maximum torque is proportional to the square of the voltage. (2) The maximum torque is proportional to the leakage reactance.
57. what is electric corrosion?
Answer: there is often a kind of corrosion phenomenon on some insulated surfaces in the stator bar slot of high-voltage motor, including the inner and outer surfaces of the anti halo layer. It is light that the anti halo layer changes color, heavy that the anti halo layer becomes crisp, and there are pits in the main insulation. This phenomenon is called "electric corrosion".
58. is low speed allowed for DC motor?
Answer: the low-speed operation of DC motor will increase the temperature rise and have many adverse effects on the motor. However, if effective measures are taken to improve the heat dissipation capacity of the motor, it can run for a long time under the premise of not exceeding the rated temperature rise.
1 rpm motor geared motor manufacturers in india
59. what should be paid attention to when starting the motor?
Answer: (1) if the power switch is turned on and the motor rotor does not move, the switch shall be pulled off immediately, and the restart is allowed only after the cause is found out and the fault is eliminated.
(2) After the power switch is turned on, if the motor makes abnormal noise, it shall be immediately switched off and the driving device and fuse of the motor shall be checked.
(3) After the power switch is turned on, the starting time of the motor and the change of the ammeter shall be monitored. If the starting time is too long or the ammeter does not return for a long time, the switch shall be opened immediately for inspection.
(4) During startup, if the motor is found to be on fire or vibrated excessively after startup, it shall be shut down immediately for inspection.
(5) Under normal conditions, the auxiliary motor is allowed to be started twice in cold state, and the interval between each time shall not be less than 5 minutes; Start once in hot state. Only when dealing with accidents and the starting time is not more than 2 ~ 3 seconds, the motor can be started once more.
(6) If it is found that the motor is reversed after starting, it shall be switched off and powered off immediately, and any two-phase wiring of the three-phase power supply shall be replaced before restarting.
60. what are the reasons why the DC motor cannot be started normally?
Answer: (1) the brush is not on the neutral line. (2) The supply voltage is too low. (3) The excitation circuit is disconnected. (4) The reversing pole coil is connected reversely. (5) Poor brush contact. (6) The motor is seriously overloaded.
61. why does the asynchronous motor generate overvoltage when it is switched off?
Answer: because the current in the inductance coil (winding) is cut off at the moment of switching, the magnetic flux generated by the current changes sharply, resulting in overvoltage. This overvoltage may occur at the ends of stator and rotor windings of wound motor.
62. what is the cause of motor single-phase grounding?
Answer: (1) the winding is damp.
(2) The winding is overloaded for a long time or local high temperature makes the insulation brittle and fall off.
(3) The silicon steel sheet of iron core is loose or has sharp thorns, cutting the insulation.
(4) The winding lead insulation is damaged or collides with the casing.
(5) Hidden dangers are left during manufacturing, such as abrasion of the lower line, displacement of slot insulation, falling into metal objects, etc.
1 rpm motor geared motor manufacturers in india
63. what items should be checked before starting the newly installed or overhauled asynchronous motor?
Answer: focus on the following phases:
(1) Measure whether the insulation resistance of motor stator circuit is qualified.
(2) Check whether the motor grounding wire is in good condition.
(3) Check whether the screws of each part of the motor are fastened.
(4) According to the motor nameplate, check whether the power supply voltage of the motor is consistent and whether the winding wiring mode is correct.
(5) Use a hand to move the motor rotor, which shall rotate flexibly without jamming and friction.
(6) Check whether the transmission device, cooling system, coupling, housing and starting device are in good condition.
(7) Check whether the capacity, protection and fuse setting of control elements, light indication signals and instruments meet the requirements.
(8) Whether the motor body and its surroundings are clean and free of sundries that may affect startup and inspection.
Single phase AC motor has only one winding and the rotor is squirrel cage type. When the single-phase sinusoidal current passes through the stator winding, the motor will produce an alternating magnetic field. The strength and direction of the magnetic field will change sinusoidally with time, but it is fixed in the spatial direction. Therefore, it is also called an alternating pulsating magnetic field. This alternating pulsating magnetic field can be decomposed into two rotating magnetic fields which are opposite to each other at the same speed and direction of rotation. When the rotor is stationary, the two rotating magnetic fields generate two torques of equal size and opposite direction in the rotor, making the synthetic torque zero, so the motor cannot rotate. When we use an external force to make the motor rotate in a certain direction (such as clockwise rotation), the motion of the cutting magnetic line of force between the rotor and the rotating magnetic field in the clockwise rotation direction becomes smaller; The cutting magnetic line of force motion between the rotor and the rotating magnetic field in the counterclockwise rotation direction becomes larger. In this way, the balance is broken, the total electromagnetic torque generated by the rotor will no longer be zero, and the rotor will rotate along the driving direction.
To make the single-phase motor rotate automatically, we can add a starting winding in the stator. The space difference between the starting winding and the main winding is 90 degrees. The starting winding should be connected with a suitable capacitor in series, so that the phase difference between the current and the main winding is approximately 90 degrees, that is, the so-called phase separation principle. In this way, two currents with a time difference of 90 degrees are connected to two windings with a space difference of 90 degrees, which will generate a (two-phase) rotating magnetic field in space, as shown in Figure 2. Under the action of this rotating magnetic field, the rotor can start automatically. After starting, when the speed rises to a certain level, the starting winding is disconnected with the help of a centrifugal switch or other automatic control devices installed on the rotor. Only the main winding works during normal operation. Therefore, the starting winding can be made into a short-time working mode. However, in many cases, the starting winding does not open continuously. We call this motor a capacitive single-phase motor. To change the direction of this motor, we can change the position of the series connection of capacitors.
1 rpm motor geared motor manufacturers in india
In single-phase motor, another method to generate rotating magnetic field is called shaded pole method, also known as single-phase shaded pole motor. The stator of this kind of motor is made of salient pole type, which has two poles and four poles. Each magnetic pole is provided with a small slot at the 1/3--1/4 full pole surface, as shown in Figure 3. The magnetic pole is divided into two parts, and a short-circuit copper ring is sleeved on the small part, as if this part of the magnetic pole is covered, so it is called covered pole motor. The single-phase winding is sheathed on the whole magnetic pole, and the coils of each pole are connected in series. When connecting, the polarity generated must be arranged in N, s, N and s in turn. When the stator winding is energized, the main magnetic flux is generated in the magnetic pole. According to Lenz's law, the main magnetic flux passing through the short-circuit copper ring generates an induced current in the copper ring that lags behind 90 degrees in phase. The magnetic flux generated by this current also lags behind the main magnetic flux in phase. Its function is equivalent to that of the starting winding of a capacitive motor, thus generating a rotating magnetic field to make the motor rotate.
To make single-phase AC motor forward and reverse, it depends on the form of motor, which is generally divided into four types
1 is a split phase motor There are two groups of coils, one is the running coil and the other is the starting coil. Reversing the two wire ends of any one of the two groups of coils can turn the motor over
2 is a push-pull motor. Usually, we can change the rotation direction of the motor by moving the brush at the position of the inverter
3. Shaded pole motor, in which the motor can be reversed only by taking out the stator core of the motor in two directions
4. The power cord head of ordinary series excited motor with changeable electric or magnetic field is OK
