In this article, we will discuss the operation of a three-phase induction motor. The motor consists of three separate sets of coils in the stator. Each set of coils is connected to terminals within the electrical terminal box. Below, we will explore how these connections are made.
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When the motor is connected to an electrical supply, the stator generates a rotating electromagnetic field. This field is responsible for the motor's operation. By understanding the working of variable frequency drives, you can gain a deeper insight into the motor's functionality. If you want to learn more about this topic, feel free to check out our previous article on variable frequency drives.
The stator contains all the coils or windings needed to create the rotating electromagnetic field. When electricity flows through these coils, it powers the motor. To facilitate this, there is an electrical terminal box on top or sometimes on the side of the motor. Inside this box, there are six electrical terminals labeled as u1, v1, w1, w2, u2, and v2. These terminals are crucial for connecting the coils and completing the circuit.
The coils
are connected to the terminals as follows: phase 1 coil is connected to
terminals u1 and u2, phase 2 coils are connected to terminals v1 and v2, and
phase 3 coil is connected to terminals w1 and w2. It's important to note that
the terminal arrangement is different on each side of the box, which we will
explain shortly.
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Now, let's bring in the three-phase power supply and connect it to the respective terminals.
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To ensure the motor runs smoothly, we need to complete the circuit. There are two ways to achieve this: the delta configuration and the star or wire configuration.
Delta configuration
In the
delta configuration, we connect terminals u1 to w2, v1 to u2, and w1 to v2.
This forms a delta configuration, allowing AC current to flow between phases.
As the direction of AC power reverses in each phase at different times, the
terminals' different arrangements in the terminal box facilitate this flow of
electricity.
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Star (Wye) configuration
Alternatively, we can use the star or wire configuration by connecting terminals w2, u2, and v2 on only one side. This forms a star or Y equivalent connection. In this configuration, electrons are shared between the terminals of different phases due to their design differences.
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Star (Wye) Delta Calculations
Let's examine the difference between these two configurations using an example.
Delta
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Let's say we have a motor connected in delta configuration with a supply voltage of 240 volts. If we use a multimeter to measure the voltage between any two phases, we will get a reading of 240 volts, which is called our line-to-line voltage.
If we measure across the two ends of a coil, we again see a line-to-line voltage of 240 volts. Let's assume each coil has a resistance or impedance of 20 ohms. This means we will get a current reading on the coil of 12 amps, which can be calculated by dividing 240 volts by 20 ohms.
However, the current in the line will be different. It will be 20.7 amps, calculated by multiplying 12 amps by the square root of 3 (approximately 1.732). This difference occurs because each phase is connected to two coils.
Star
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Now let's consider the star or wire configuration. Again, we have a line-to-line voltage of 240 volts when measuring between any two phases. However, in this configuration, all our coils are connected together and meet at a common start or neutral point.
When we measure the voltage across the ends of any coil in this configuration, we get a lower voltage of 138 volts. This is because one end of the coil is directly connected to a phase, while the other end is connected to a shared point. As a result, the voltage is shared among the coils, and each phase is always in reverse.
We can calculate this by dividing 240 volts by the square root of 3 (approximately 1.732), which gives us 138 volts. If this coil also has an impedance of 20 ohms, then dividing 138 volts by 20 ohms equals a current of 6.9 amps on the coil.
The line current will also be 6.9 amps in this configuration. Therefore, we can see that in the delta configuration, the coil is exposed to the full 240 volts between two phases. On the other hand, in the star configuration, it is only exposed to 138 volts between the phase and the neutral point.
As a result, the star configuration uses less voltage and less current compared to the delta version.
That wraps up this article on three-phase induction motors. If you want to continue learning about electrical topics, feel free to check out one of our other articles."Remember to stay connected with us on Instagram and TikTok for even more informative content! Don't hesitate to leave a comment 💬💬💬 below as well – we love hearing from our valued readers!"👍👍👍
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