Three-phase asynchronous motors are widely used in various industries, including the automotive industry. The principle of operation of such a motor is based on the conversion of alternating current electrical energy into mechanical energy through the use of a rotating magnetic field. In some cases, it becomes necessary to check the correct connection of the motor windings.
It is necessary
- - accumulator battery;
- - megohmmeter;
- - millivoltmeter.
Instructions
Step 1
To check the correctness of the connections of the three-phase windings, it is necessary to determine the beginning and end of each of the phases. Prepare a millivoltmeter and a megohmmeter for this.
Step 2
First, using a test lamp, determine the belonging of one or another winding terminal to a separate phase. After that, connect a direct current source to one of the phases through a circuit breaker. The power source must be such that a small current flows through the winding of the electric motor (a battery designed for a voltage of 2V is suitable). Also include a rheostat in the circuit to reduce the current.
Step 3
Turn on the breaker. At the moment of the beginning of the electrical connection, as well as when the circuit is opened, an electromotive force will be induced in the windings of the two remaining phases. The direction of the electromotive force is determined by the polarity of the ends of the winding of the tested phase, in which the storage battery is connected.
Step 4
Pay attention to the direction in which the millivoltmeter needle deflects when the switch is turned on and off, which must be alternately connected to the output ends of the other two phases. If the “plus” of the battery is connected to the “beginning”, and “minus” is connected to the “end”, then when the breaker is disconnected on the other phases, there will be “plus” on the initial outputs and “minus” on the final ones. When the circuit is closed, the polarity on the remaining phases will be reversed as indicated above.
Step 5
If the motor has three leads when the winding is delta or star connected, check that the connection is correct by connecting undervoltage across the two leads. In this case, measure the voltage between the third terminal and other terminals connected to the network with a voltmeter. If the connection is correct, these voltages will be equal to half the voltage applied across the two terminals.
Step 6
Perform the described measurements at least three times, each time supplying current to a different pair of terminals. If the phase is connected incorrectly, then with two attempts out of three, the voltage values between the third terminal and the rest will be different.
