13 questions about electric motors

When we use the electric motor, we will always encounter some small problems, today let's learn about the motor of 13 small knowledge about the working principle

Why do the electric motors generate shaft currents?

The current in the shaft - bearing housing - base circuit of the electric motor is called shaft current.

Causes of shaft currents.
Asymmetry of the magnetic field.
Harmonics in the supply current.
Poor manufacturing and installation, uneven air gap due to rotor eccentricity.
Gaps between two semicircles of the detachable stator core.
There is a fan-shaped stacked stator core of the number of pieces of collocation is not selected appropriately.

Hazards: the electric motor bearing surface or ball erosion, shape course point microporous, so that the bearing running performance deterioration, friction loss and heat increase, and eventually cause bearing burn for the electric motor.

Why can't the general electric motors be used in highland areas?

Altitude has a negative impact on electric motor temperature rise, electric motor corona (high voltage motors) and DC motor commutation, electric generator .

The following three aspects should be noted:

The higher the altitude, the greater the temperature rise of the electric motor and the smaller the output power. But when the temperature decreases with the rise in altitude enough to compensate for the effect of altitude on temperature rise, the rated output power of the electric motor can be unchanged.
Anti-corona measures should be taken when high voltage motors are used in the plateau.
Altitude is not good for DC motor commutation, pay attention to the choice of carbon brush material.

Why should not electric motor run at light load?

Electric Motor operation at light load results in;

Low electric motor power factor, electrical energy
Low electric motor efficiency,mechanical energy
It will cause equipment waste and uneconomical operation.

What are the causes of electric motor overheating?

Excessive load.
Lack of phase for electric motors.
Blockage of air ducts.
Excessive low speed running time, rotor speed .
Excessive power supply harmonics, converts electrical energy.

What do I need to do before putting the electric motor into use for a long time?

Measure the insulation resistance of stator and motor winding between each phase and motor winding to ground.

Insulation resistance R should meet the following formula.

R＞Un/(1000+P/1000)(MΩ)

Un: rated voltage of electric motors winding (V)

P: motor power (KW)

For the motor with Un = 380V, R＞0.38MΩ.

If the insulation resistance is low, it can be.

a: no-load operation of the electric motors for 2 to 3h drying.

b: using 10% of the rated voltage of low-voltage alternating current into the winding or three-phase winding in series with DC baking, keeping the current at 50% of the rated current.

c: use the fan to send in hot air or heating elements to heat.

Clean the electric motor by electric fans .
Replace bearing grease.

Why can't I arbitrarily start the electric motor in a cold environment?

A motor left in a cold environment for too long will.

Cracking of motor insulation.
Freezing of bearing grease.
Solder pulverization of conductor joints.

Therefore, the motor should be heated and preserved in the cold environment, and the windings and bearings should be checked before running.

What are the causes of electric motor three-phase current unbalance?

Unbalanced three-phase voltage for ac motor, check the voltage level .
Poor welding or poor contact of a phase branch within the electric motor.
Short circuit between turns of electric motor winding or short electric circuit to ground or phase to phase for electric motors .
Wiring error of electrical motors.

Why 60Hz electric motor can not be connected to 50Hz power supply?

The electric motor is generally designed to make the silicon steel sheet work in the magnetization curve of the satiation area.

When the supply voltage is certain, reduce the frequency will increase the flux, excitation current, resulting in increased motor current, copper consumption, and eventually lead to higher motor temperature for the ac motor, and in serious cases, may also burn the electric motor due to coil overheating.

What are the causes of electric motor phase loss?

Power supply:

Poor switch contact.
Transformer or line disconnection.
Fused insurance.

Electrical Motor side:

Loose motor junction box screws poor contact.
Poor welding of internal wiring for electric circuit .
electric Motor winding disconnection.

What are the causes of abnormal vibration and sound of the motor?

Mechanical aspects.

Poor bearing lubrication and bearing wear.
Loose fastening screws.
There are debris in the electrial motor.

Electromagnetic aspects.

induction Motor overload operation.
Three-phase current imbalance.
Lack of phase of ac motor .
Stator, rotor winding short-circuit fault for the induction motors .
Broken bars caused by open welding of the cage rotor part.

What do I need to do before starting the electric motor?

Measure insulation resistance (should not be less than 0.5MΩ for low voltage ac motor).
Measure the power supply voltage. Checking whether the motor wiring is correct and whether the power supply voltage meets the requirements.
Checking whether the starting equipment is good.
Check whether the fuse is suitable.
Check whether the electric motor grounding, zeroing is good.
Checking whether the transmission device is defective.
Check whether the electrical motor environment is suitable, remove flammable materials and other debris.

What are the causes of electric motor bearing overheating?

induction Motor itself.

Bearing inner and outer ring fit too tight.
Problems with the tolerance of the shape of parts, such as the seat, end cover, shaft and other parts coaxiality is not good.
Improper bearing selection.
Poor bearing lubrication or poor bearing cleaning and debris in the grease.
Shaft current of the induction motors .

Use the electrical motor aspects;

Improper installation of the unit, such as the shaft coaxiality of the electrical motors shaft and the shaft of the device being dragged a requirement.
Belt pulley pulling too tight.
Poor bearing maintenance, insufficient grease or over the use period, dry and deteriorated.