Why is the motor phase-to-phase insulation resistance measured with a megometric zero?

Introduction Why is the motor phase-to-phase insulation resistance measured with a megometric zero? The motor stator winding is an inductor coil. The output voltage of the megometer is a direct voltage. The inductive reactance of the inductor coil is proportional to f

Why is the motor phase-to-phase insulation resistance measured with a megometric zero?

The motor stator winding is an inductance coil. The output voltage of the megger is a DC voltage. The inductance of the choke coil is therefore proportional to the frequency. while the resistance of the motor stator winding (forward resistance) is very small, so the phase interval is 0.

The oscillator consists of a manual generator, one vote and three terminals (i.e. L: line end, E: ground end, G: shield end). It is widely used in the installation and maintenance of coal mines. and suitable for checking the insulation of motors, electrical appliances and circuits and measuring high value resistance.

Detailed information

When the power supply voltage is too low, if the electromagnetic torque of the motor remains unchanged, the magnetic flux will decrease, the rotor current will increase accordingly, and the load power component of theStator current will increase accordingly, causing winding problems. Copper losses will increase, causing the stator and rotor windings to overheat.

When the measured resistance is low or zero, the current flowing through the current coil is large and the coil has been deflected to a place where the magnetic flux density is low and the deflection angle caused by it will not be very big. In this way, a non-linear correction is obtained. Typically, the resistance display on the Megger head should span several orders of magnitude.

Baidu Encyclopedia-Electric Motor

Baidu Encyclopedia-Megometer

When using a megometer to measure insulation resistance, why should do you read the value out loud by shaking it?

The insulation resistance of the generator should not be less than 0.5MΩ.

Insulation resistance is the indicator ofThe most basic insulation for electrical equipment and electrical circuits. For transfer testing of low-voltage electrical equipment, the insulation resistance of motors, distribution equipment and distribution lines at normal temperature should not be less than 0.5MΩ (for equipment and lines in operation , the insulation resistance should not be less than 1 MΩ/kV).

As long as the insulation resistance of the generator rotor winding is not less than 0.5MΩ, it can be considered qualified.

The insulation resistance of the generator stator is not less than 1MΩ per kV and can be considered qualified.

Detailed information:

< p>The insulation resistance of the generator stator winding is greatly affected by dirt, humidity, temperature, etc., so the adjustmentsCurrent relevant publications do not establish rigid regulations, but can only be compared with the results of previous measurements to judge the insulation quality of the stator winding.

Since insulation resistance is greatly affected by temperature, insulation resistance will decrease by half for every 10°C increase in temperature. Therefore, for ease of comparison, the insulation resistance at different temperatures is usually converted into a value. insulation at 75°C.

Factors affecting insulation resistance

1. Ambient temperature and humidity:

The insulation resistance value of general materials decreases with increasing ambient temperature and humidity. Relatively speaking, surface resistance (rate) is more sensitive to ambient humidity, while volume resistance (rate) is more sensitive to temperature. Therefore, when measuringure of insulation resistance, it is necessary to specify the temperature and humidity at which the sample and the environment are in equilibrium.

2. Cable-specific factors: When the cable is heated and damp, it will definitely age. The edge material will age. Its insulation resistance is reduced.

Baidu Encyclopedia - Generator Test

Baidu Encyclopedia - Insulation Resistance

Since the megger is a generator, there are 500 V and 1000 V and 2500 V. 5000 V meggers should not be less than 120 rpm per minute. Only when the rotation speed is sufficient can they reach the voltage level to be accurate, so the value read during stirring is accurate. This statement “so that the value read by shaking is precise” is not accurate. The insulation resistance curve of the high voltage measurement should first fall, then increase, and last for 2 minutes. LThe low voltage measurement insulation resistance curve is relatively stable and lasts 2 minutes.

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