Method for determining the start and end points of a three-phase asynchronous motor winding using a multimeter
One of the methods
Step 1: First, set the multimeter to the R×100 range. Measure the six leads from the motor junction box two at a time to determine the three-phase winding. Specifically, connect the red (or black) probe to one lead; then connect the black (or red) probe to the other five leads in sequence. The two leads with the best flow (greater deflection and lower resistance) constitute one phase. Mark these phases (using knots or coloring is recommended) to distinguish them from the following two phases. Continue this process to divide the six leads into three groups.
Step Two: Set the multimeter to the microamplitude range and connect the wires as shown in the diagram to determine the start and end points of the two-phase windings. The specific method is as follows:
(1) Set the multimeter to the microamplitude range;
(2) Connect the red and black probes of the multimeter to the two terminals of one of the windings of the motor;
(3) Then, the two terminals of the other phase of the motor are successively connected to the negative and positive terminals of the dry cell battery (or the battery in the multimeter is taken out for testing) (9V or 1.5V battery);
(4) If the multimeter pointer deflects in the positive direction, the terminal connected to the positive terminal of the battery and the terminal connected to the negative terminal (black probe) of the multimeter are the same type of terminal; conversely, the terminal connected to the negative terminal of the battery and the terminal connected to the negative terminal (black probe) of the multimeter are the same type of terminal; as shown in the figure, the black dots mark the first (or last) terminal, i.e., the same type of terminal. Use the same method to determine the first and last terminals of the other phase.
Method 2: Star Connection Determination
Step 1: Determine the three-phase windings (the method is the same as above, but note that each phase should be simply and clearly marked after it is detected in order to distinguish the three-phase stator windings).
Step 2: Determine the start and end points of the three-phase windings in a star connection.
Specific method: (1) Set the multimeter to the microampere range;
(2) Short-circuit one end of each of the three windings of the three-phase asynchronous motor together and connect it to the red probe. Connect the other three ends together and then connect them to the black probe.
(3) Rotate the motor at a constant speed and observe the pointer deflection.
(4) If the pointer deflects almost nothing, the three wires connected together in each winding are the same-name terminals (as shown in Figure 3). Otherwise, wire swapping should be performed.
Step 3: Line-Changing Pattern
(1) Mark the beginning and end of the three windings respectively, and predetermine the end numbers.
(2) One set of windings (assumed to be terminals ⑤-⑥) is kept fixed as a reference.
(3) After swapping the beginning and end of any one of the other two groups, judge according to specific methods (1)-(4). If there is still a deviation, swap the beginning and end of the other group and judge according to specific methods (1)-(4) again. You will definitely be able to judge the correct same-name end.
