Collegamenti stella e triangolo dei motori

The star connection (Y connection) and delta connection (△ connection) of motors are two core wiring methods for the stator windings of three-phase asynchronous motors. They directly affect the operating voltage, attuale, power and starting characteristics of the motor, and the two should be reasonably selected according to power supply specifications and load requirements in industrial applications.

1. Definition and Wiring Methods
2. Star Connection (Y Connection)

Wiring Principle: Connect the three terminals (tail ends: U2, V2, W2) of the motor stator three-phase windings together to form a common neutral point (N point); connect the three head ends (U1, V1, W1) to the three-phase AC power supply respectively.

Structural Characteristics: The windings bear phase voltage at both ends. The neutral point can lead out a neutral wire (forming a three-phase four-wire system) or be left floating (three-phase three-wire system).

Typical Marking: Marked as `Y` type in the motor junction box. The terminal connection method is that `U2-V2-W2` are short-circuited, and `U1-V1-W1` are connected to the power supply.

2. Delta Connection (△ Connection)

Wiring Principle: Connect the head and tail ends of the motor stator three-phase windings in sequence, i.e., connect `U1` to `V2`, `V1` to `W2`, `W1` to `U2`, to form a closed delta loop; connect the three junctions to the three-phase AC power supply respectively.

Structural Characteristics: The windings bear line voltage at both ends. There is no neutral point, and it belongs to three-phase three-wire system wiring.

Typical Marking: Marked as `△` type in the motor junction box. The terminal connection method is that `U1-V2`, `V1-W2` and `W1-U2` are short-circuited in pairs and then connected to the power supply.

1. Comparison of Core Electrical Characteristics

III. Scenari applicativi

1. Application of Star Connection (Y Connection)

Step-down Starting: When starting high-power motors (≥7.5kW), star-delta step-down starting is adopted. First, start with Y connection (reduce winding voltage and starting current to avoid impacting the power grid), and switch to △ connection for rated operation after the speed stabilizes.

Low-voltage Adaptation: When the power supply line voltage is 380V and the motor winding rated phase voltage is 220V, Y connection must be adopted (380V/√3≈220V), otherwise the windings will burn out due to overvoltage.

Light-load Operation: Suitable for light-load starting equipment such as fans and water pumps, which can reduce the impact of starting current on the power grid.

2. Application of Delta Connection (△ Connection)

Rated Power Operation: When the power supply line voltage is 380V and the motor winding rated phase voltage is 380V, △ connection is adopted, and the motor outputs rated power to meet the demand of heavy-load operation.

Direct Starting: Small-power motors (≤7.5kW) can be directly started with △ connection without step-down, and the control circuit is simple.

Frequency Converter Drive: When used with frequency converters such as Schneider ATV303, if the motor needs to output full power, △ connection is preferred (the output voltage of the frequency converter can adapt to the rated voltage of the windings).

1. Key Precautions
2. Wiring Matching Principle: The connection method must be selected according to the rated voltage and connection method marked on the motor nameplate and cannot be changed at will. Per esempio, for a motor marked “380V △/660V Y” on the nameplate, use △ connection when the power supply is 380V, and Y connection when the power supply is 660V.
3. Star-delta Starting Conditions: Only applicable to motors that operate in △ connection under normal conditions, and the load is light-load or no-load starting. It is not suitable for heavy-load starting scenarios (insufficient starting torque).
4. Connection Selection for Frequency Converter Drive: The output voltage of the frequency converter can be flexibly adjusted. If the motor runs below the rated speed for a long time, Y connection can also be used, but attention should be paid to winding heat dissipation (the heat dissipation effect of the fan decreases at low speed).
5. Fault Risks: If a motor designed for △ connection is mistakenly connected in Y connection, the motor output power will be insufficient, resulting in problems such as “unable to drive the load” E “current overload”; if a motor designed for Y connection is mistakenly connected in △ connection, the windings will generate heat due to overvoltage and eventually burn out.
6. Working Principle of Star-delta (Y-△) Step-down Starting

This is the most commonly used step-down starting method in industry, with the core logic of “step-down starting first, then full-voltage operation”:

1. Starting Phase: The contactor controls the motor windings to be in Y connection. The winding voltage is 1/√3 of the power supply voltage, and the starting current is reduced to 1/3 of direct starting, reducing the impact on the power grid and equipment.
2. Switching Phase: When the motor speed rises to 80%~90% of the rated speed, the contactor is switched through the time relay, the windings are changed to △ connection, and the motor enters the rated power operation state.