The Three Phase Motor Connection in star and delta depending on the supply voltage. In a Three Phase Motor Connection, there are six individual windings, two for each phase. The internal construction and connections of the coil within the motor are determined during motor manufacturing.
Three-phase motor connections can be done in two ways: star and delta.
In the high-voltage configuration, the two windings of each phase are connected in series. The highest value of the supply voltage is shared equally between the windings, and the nominal current passes through each winding.
In the low-voltage configuration, the two windings of each phase are connected parallel. Thus, the lower supply voltage is equally shared between the windings, and the nominal current passes through each winding.
Note that the low-voltage connection will draw twice the amount of current from the source compared to the high-voltage connection. Most motors display two values for voltage and current on their nameplates.
Three-phase motor Connections have three independent windings. The stator holds all three windings in the stator slots. These windings are displaced 120 degrees electrically from each other. It is powered by a three-phase alternating current (AC) system.
There are two types of 3-phase asynchronous or induction motors.
- Those with wound rotors belong to the class first. These are also called slip-ring motors.
- Class second is one with the rotor in a short circuit, also known as the squirrel cage rotor. This is due to its shape, which is similar to a cage.
Motor Connection 3 Phase (3Ø) motors
In a 3-phase motor connection, three motor windings can be connected in a star or delta configuration. In the star connection, three ends of the motor’s coils are connected to a common point, and the other three ends of the coils are connected to a 3-phase supply source.
On the other hand, the delta connection connects each end of the motor’s coil to the beginning of the next phase, allowing the system to be fed through the connection points.
In the star connection, the current flowing through each phase equals the line current, while the voltage across each phase is (1/√3) of the line voltage.
On the other hand, in the delta connection, the current in each phase is 1/√3 times of the line current, while the voltage across each phase is the same as the line voltage.
We will discuss the configuration of Star and Delta and how to connect a 3-phase motor in Star and Delta.
The Star-Delta 3 Phase Induction Motor Connection
The stator of a 3 Phase Induction Motor Connection has three windings, each with two ends. The first winding has ends called U and X or U1 and U2. The second winding, V and Y, is also called V1 and V2. The third winding W and Z, is also called W1 and W2.
1. Star Motor Connection
Connecting a motor in a star (Y) configuration involves connecting each of the motor windings to a common point (neutral) and the other ends to the power supply phases.
The motor star connection is shown in the diagram below.
Here’s a step-by-step procedure for Star Motor Connection.
- Identify the Motor Terminals: Three-phase motors have six terminals, typically labeled U1, U2, V1, V2, W1, and W2.
- Determine the Winding Pairs: The terminals are usually paired as U1-U2, V1-V2, and W1-W2. Each pair represents one of the motor windings.
- Create a Neutral Point: Connect the ends of each winding (U2, V2, and W2) to form a common neutral point, the “star” point.
- Connect the Phases: Connect the remaining terminals (U1, V1, and W1) to the three-phase power supply. Each phase line (L1, L2, L3) is connected to one of these terminals.
The diagram below shows how the motor windings are connected in the star connection.
2. Delta connection
Connecting a motor in a delta (Δ) configuration involves connecting the ends of each winding to form a closed loop, with each junction connected to a power supply phase.
The motor star connection is shown in the diagram below.
Here’s a step-by-step procedure for Star Motor Connection.
- Identify the Motor Terminals: Three-phase motors have six terminals, typically labeled U1, U2, V1, V2, W1, and W2.
- Determine the Winding Pairs: The terminals are usually paired as U1-U2, V1-V2, and W1-W2. Each pair represents one of the motor windings.
- Create the Delta Connections: Connect U1 to W2, V1 to U2, and W1 to V2. This creates a closed loop where the end point of each winding is connected to the start point of another winding, forming a triangle (delta (Δ)) shape.
- Connect the Phases: Connect the three-phase power supply lines (L1, L2, L3) to the three junctions created in the previous step—for example, L1 to U1-W2 junction, L2 to V1-U2 junction, and L3 to W1-V2 junction.
The diagram below shows how the motor windings are connected in the delta connection.
Depending on the motor-rated voltage and the input supply voltage, you can connect the electric motors in either a star or delta configuration. You can also start the motor in a star-delta setup using a star-delta starter. To do this, the motor’s voltage rating in a delta connection should be equal to its rated supply voltage.
Precaution for Dual-rated voltage motors
When dealing with dual-rated voltage motors (motors that can operate at two different voltage levels), specific precautions must be taken to ensure safe and efficient operation. It is crucial to confirm the motor’s voltage ratings and corresponding connection diagrams (star and delta configurations) on the nameplate.
If an electric motor has a nameplate indicating 690/400 (Y-Δ) volts, it can be connected in either a star or delta connection. When connected in a star connection, the motor’s optimum performance requires a supply voltage of 690 volts. However, it can also function with a lower voltage of 400 volts in the star connection, but its torque delivery will be reduced. On the other hand, when connected in a delta connection, the motor should be supplied with 400 volts. If 690 volts is supplied in the delta connection, the motor will burn out.
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