Three-phase motors need to simulate three-phase electricity through
Three-phase motors (usually with a rated voltage of 380V three-phase alternating current) need to simulate three-phase electricity through **phase shifting or frequency conversion** when connected to a 220V single-phase power supply. The specific method depends on the motor power and usage scenario. Here are two common solutions and precautions:
**I. Small - power motors (≤1.5kW): Capacitor phase - shifting method**
Principle: Use the capacitive reactance characteristic of capacitors to "split" the single - phase 220V electricity into two - phase electricity with a phase difference of about 90°, simulate the rotating magnetic field of three - phase electricity, and drive the motor to run.
**Steps:**
1. **Confirm the motor winding type**
Three - phase motors usually have two connection methods: "star (Y)" or "delta (△)". You need to first check the motor nameplate or the wiring diagram in the junction box to identify the 6 lead terminals of the windings (usually marked as U1, U2, V1, V2, W1, W2).
2. **Reconnect the windings to "star" or "single - phase compatible connection"**
- If it was originally a star connection (the ends of the 3 windings are connected together): keep the star connection (U2, V2, W2 are short - circuited).
- If it was originally a delta connection (the head and tail of the windings are connected): it needs to be changed to a star connection (short - circuit the ends of the three windings) to reduce the voltage of each phase winding (to avoid burning due to overvoltage).
3. **Select the phase - shifting capacitor**
The capacitance capacity needs to be estimated according to the motor power. The formula is: **C (μF) ≈ 10 × power (kW)** (for example, a 1kW motor is about 10μF). For actual reference:
- 0.5kW: 4 - 6μF
- 1kW: 8 - 12μF
- 1.5kW: 12 - 16μF
The withstand voltage of the capacitor should be ≥400V (it is recommended to use CBB60 type start/run dual - purpose capacitor, or configure a start capacitor and a run capacitor separately. The capacity of the start capacitor is 2 - 3 times that of the run capacitor, and it is connected in series with a centrifugal switch).
4. **Wiring method**
- Connect the live wire (L) of the 220V power supply to the U1 terminal of the motor;
- Connect the neutral wire (N) of the power supply to the V1 terminal of the motor;
- Connect one end of the capacitor to U1 and the other end to the W1 terminal;
- If the motor reverses, the other end of the capacitor can be reconnected to V1 (or swap the connection of any two winding wires).
**II. Medium and high - power motors (>1.5kW): Frequency converter method**
Principle: Use a frequency converter with "single - phase 220V input and three - phase 220V output" to convert single - phase electricity into three - phase electricity to directly drive the motor (the motor must support 220V three - phase voltage. If it is originally a 380V motor, the winding needs to be changed to a star connection so that each phase voltage is adapted to 220V).
**Steps:**
1. **Select a suitable frequency converter**
The rated power of the frequency converter should be ≥ the motor power (for example, a 2.2kW motor should choose a frequency converter with ≥2.2kW), with an input voltage of 220V single - phase and an output of 220V three - phase.
2. **Reconnection of motor windings**
For a motor originally with a 380V delta connection, it needs to be changed to a star connection (short - circuit the ends of the three windings and connect the head ends to the output of the frequency converter) so that each phase winding can bear 220V voltage (380V/√3≈220V).
3. **Wiring and settings**
- Connect the input terminals (L, N) of the frequency converter to the 220V single - phase power supply (note that the grounding terminal PE must be reliably grounded);
- Connect the output terminals (U, V, W) of the frequency converter to the head ends of the three windings of the motor (U1, V1, W1);
- After power - on, set the frequency converter parameters: input voltage 220V, output voltage 220V, motor power/rated current/speed (set according to the motor nameplate), and select "panel start" or "external control" for the start mode.
**III. Precautions**
1. **Power limit**
The capacitor phase - shifting method is only applicable to small - power motors (≤1.5kW). Otherwise, it will cause difficulty in starting, insufficient torque, and overheating of the motor (the efficiency is only 60% - 70% of the original three - phase power supply); high - power motors must use frequency converters, otherwise the motor may be burned.
2. **Capacitor selection**
An excessively large capacitor capacity will cause excessive current to burn the windings, and an excessively small one will result in weak starting. It is necessary to strictly match according to the power (priority is given to special motor phase - shifting capacitors, and ordinary electrolytic capacitors should be avoided).
3. **Safe operation**
Be sure to cut off the power before wiring, confirm the head and tail ends of the windings (the resistance of the same phase winding can be measured with a multimeter, which is small and consistent) to avoid short circuits caused by wrong connection; the motor shell must be grounded to prevent electric leakage.
4. **Performance difference**
After reconnection, the motor speed is slightly lower than the rated value (about 5% - 10% lower), and the torque decreases. It is not suitable for heavy - load starting scenarios (such as compressors, crushers, etc.), but can be used for light - load equipment (such as fans, water pumps).
If the motor power is large or the performance requirement is high, it is recommended to choose the frequency converter scheme first; for small - power and light - load scenarios, capacitor phase shifting can be tried, but parameter matching and heat dissipation measures must be done well.
