The megohmmeter detects whether the three phase asynchronous motor housing is short circuited for sp

Generally, a 500V megohmmeter is used to measure the resistance between U V W and the motor housing, shake it a few times, and the reading pointed by the pointer is regarded as low insulation to the ground, and it may be damp, and it is almost 0 as a short circuit.

It can only be regarded as low insulation to the ground, which does not meet the requirements of use, may be damp, and cannot be simply regarded as a short circuit to the ground. The resistance measured by the megohmmeter is very small, almost 0 before the short circuit can be judged.

Confirm the voltage level of the megohmmeter (in addition to measuring high-voltage motors, generally use a 500V megohmmeter), and then short the two wires of the megohmmeter, and gently shake the crank handle one or two times to confirm that the watch hand can return to zero. Then any one of the two wires of the megohmmeter is in reliable contact with the motor housing, and the other is connected to any phase of the motor winding, and the hand crank handle at a constant speed (120 revolutions), after the pointer swings to stop, the reading pointed by the pointer is regarded as a short circuit or grounding.

Confirm the voltage level of the megohmmeter first (in addition to measuring high-voltage motors, a 500V megohmmeter is generally used), and then short the two wires of the megohmmeter, and gently shake the crank handle one or two times to confirm that the watch hand can return to zero. Then any one of the two wires of the megohmmeter is in reliable contact with the motor housing, and the other is connected to any phase of the motor winding, and the hand crank handle at a constant speed (120 revolutions), after the pointer swings to stop, the reading pointed by the pointer is regarded as a short circuit or grounding.

Measure the resistance of a, b, c, and ground to each other.

The multimeter can measure the short circuit of the three-phase asynchronous motor with the resistance gear to measure the resistance value of each phase winding, generally with the minimum gear, if the short circuit then it is basically zero, if there is more than 2 ohms is basically good. If there is a lack of phase, you can directly measure the resistance, and if there is resistance, it is good, and if there is no resistance, it means that there is a lack of phase. The resistance value of the winding to the ground is generally measured with a shake meter, and the multimeter measurement is inaccurate, more than 3 trillion ohms is good, and less than 3 trillion ohms indicates that the insulation is not enough.

Strictly speaking. An analog multimeter cannot completely determine the quality of the motor. But it can still be roughly judged:

1. First hit the multimeter to 1 gear. School schedule. Then measure the resistance between any two of the three wires drawn out of the motor, and the resistance value of the large motor is generally smaller.

Only a few ohms to a dozen ohms. Small motors, such as fan motors, may have two or three hundred ohms. In this way, the multimeter is to shift the measurement.

If any two wires are measured to be of the same magnitude. It shows that there is basically no problem with the motor coil.

2. Roughly measure the insulation resistance: open the multimeter to 10k gears, calibrate the meter, and connect any one of the lead wires with a meter pen. First, the pen should contact the metal part of the shell of the motor, and if the multimeter has a reading.

Indicates poor insulation. Under normal circumstances, it is not a table.

Friends - 1, the use of a multimeter to judge the three-phase asynchronous motor short circuit, strictly unscientific is also inaccurate, a slight turn short circuit, the same slot in the winding coil short circuit can not be judged at all, must use the bridge (resistance tester).

2. Lack of phase: star wiring - connect the neutral point with a multimeter pen, and connect the three-phase winding coil A, B and C with another meter pen respectively, observe the resistance value, the value becomes large for the contact is not good, and the value is infinite for the open circuit that is the lack of phase.

3. How much is the ground resistance of the winding to be qualified? The insulation resistance check of the motor must be measured by using a shake meter (insulation tester), and the low-voltage motor is not less than 1m kv, and the high-voltage motor is not less than 1m kv.

When there is a short circuit in the winding of the three-phase asynchronous motor, it can be checked according to the following methods:

External observation method: observe whether the junction box and winding end of the three-phase motor are burned, and the winding is overheated to leave dark brown and odor.

Temperature detection method: run for 20 minutes without load (stop immediately when abnormality is found), and touch each part of the winding with the back of your hand to see if it exceeds the normal temperature.

Energizing test method: measured with an ammeter, if the current of a certain phase is too large, it means that there is a short circuit in the phase.

Bridge inspection: measure the DC resistance of each winding, generally the difference should not exceed 5%, if exceeded, the resistance of the small phase has a short circuit fault.

Short-circuit reconnaissance method: If there is a short circuit in the winding to be measured, the steel sheet will vibrate.

Multimeter or megohmmeter method: measure the insulation resistance between any two phase windings, if the reading is very small or zero, it means that there is a short circuit between the two phase windings.

Voltage drop method: After connecting the three windings in series, a low-voltage safe alternating current is passed, and the group with a small measured reading has a short-circuit fault.

Current method: 220V AC three-phase motor no-load operation, first measure the three-phase current, in the exchange of two-phase measurement and comparison, if not with the power supply and change, the larger current of the one-phase winding has a short circuit.

A short circuit, in the case of a motor, is a short circuit between the winding coils, and the current becomes larger as the resistance decreases. Open circuit, in the motor refers to the winding coil turns are not open, and the current cannot pass through, then there is no current.

1.Interphase short circuit, each phase winding of the three-phase motor has a good interphase insulating paper for isolation, generally when there is a phase short circuit, you can clearly see the current breakdown to the copper wire melting, and the burned parts are the phase separation paper, when it is not obvious, the motor terminal at the piece is removed, and the resistance between the phases is measured with a multimeter. For example, the resistance value of phase A and phase B is 10, phase A and phase C is 8, and phase B and phase C are 5 ohms.

Then consider whether it is a short circuit between B and C, and the bridge line should be disconnected for further judgment. It is normal for the resistance of each phase coil to be equal.

2.Inter-turn short circuit, is the same phase winding in a coil turn between the short circuit, generally not easy to directly see the problem, the same motor terminal at the piece removal, measure the in-phase winding resistance and the rest of the two comparisons, such as AB two phase resistance value of 10, C phase is 8 or smaller, indicating that C phase may have a short circuit, should be C phase winding in the bridge wire disconnection, one by one measurement. The resistance of each coil is equal to normal.

Use a multimeter or megohmmeter to measure the insulation resistance between any two phase windings, if the reading is very small or zero, it means that there is a short circuit between the two phase windings.