To operate an electrical device, motor, or transformer in a three-phase network, it is necessary to connect the windings according to a certain circuit. The most common connection patterns are delta and star, although other connection methods may be used.
What is a star connection?
A three-phase motor or transformer has 3 workers, windings independent from each other. Each winding has two terminals - the beginning and the end. A star connection means that all ends of the three windings are connected into one node, often called the neutral point. This is where the concept of zero point comes from. 
The beginning of each winding is connected directly to the phases of the supply network. Accordingly, the beginning of each winding is connected to one of the phases A, B, C. Between any two beginnings of the windings, the phase voltage of the supply network is adjusted, often 380 or 660 V.
What is a delta winding connection?
Connecting windings in a triangle consists of connecting the end of each winding to the beginning of the next. The end of the first winding is connected to the beginning of the second. The end of the second is from the beginning of the third. The end of the third winding creates an electrical loop because it completes the electrical circuit. 
With this connection, a linear voltage is adjusted to each winding, usually equal to 220 or 380 V. Such a connection is physically implemented using metal jumpers, which must be provided with the factory equipment of the electrical equipment.
Difference between delta and star connection
The main difference is that, using one power supply network, it is possible to achieve different parameters of electrical voltage and current in a device or device. Of course, these connection methods differ in implementation, but it is the physical component of the difference that is important.
The most commonly used connection of windings is a star connection, which is explained by the gentle mode for an electric drive or transformer. When the windings are connected in a star, the current flowing through the windings is less than when connected in a triangle. At that moment, the voltage is greater by the root of 1.4.
The use of the triangle connection method is often used in cases of powerful mechanisms and large starting loads. Having greater current flowing through the winding, the motor receives greater self-induction EMF, which in turn guarantees greater torque. Having large starting loads and at the same time using a star connection can cause damage to the engine. This is due to the fact that the motor has a lower current value, which leads to lower torque values.
The moment of starting such a motor and its reaching the rated parameters can be prolonged, which can lead to thermal effects of the current, which during switching may exceed the current ratings in 7-10 times.
Advantages of star connection of windings
The main advantages of connecting windings in a star are as follows:
- Reducing equipment power in order to increase reliability.
- Stable operating mode.
- For an electric drive, this connection allows for a smooth start.
Some electrical equipment, which is not designed to operate on other connection methods, has internal winding ends connected. Only three pins are output to the terminal block, which represent the beginning of the windings. Such equipment is easier to connect and can be installed in the absence of competent specialists.
Advantages of connecting windings in a triangle
The main advantages of connecting the windings in a triangle are:
- Increasing the power of equipment.
- Lower starting currents.
- High torque.
- Increased traction properties.
Equipment with the ability to switch the connection type from star to delta
Often electrical equipment has the ability to operate in both star and delta modes. Each user must independently determine the need to connect the windings in a star or delta.
In particularly powerful and complex mechanisms, an electrical circuit with combining a triangle and a star. In this case, at the moment of start-up, the windings of the electric motor are connected in a triangle. After the engine reaches its nominal values, the triangle switches to star using a relay-contactor circuit. In this way, maximum reliability and productivity of the electrical machine is achieved, without the risk of causing damage to it or rendering it inoperable.
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