Electric motor connection diagram with triangle. Star and triangle connection principle. Star and delta connection of electric motor windings. Motor with magnetic starter

Asynchronous motors have a whole range of undoubted advantages. Among the advantages of asynchronous motors, first of all, I would like to mention the high performance and reliability of their operation, the very low cost and unpretentiousness of motor repair and maintenance, as well as the ability to withstand fairly high mechanical overloads. All these advantages that asynchronous motors have are due to the fact that this type of motor has a very simple design. But, despite the large number of advantages, asynchronous motors also have certain negative aspects.

In practical work, it is customary to use two main methods of connecting three-phase electric motors to the electrical network. These connection methods are called: “star connection” and “delta connection”.

When a three-phase electric motor is connected using the star connection type, then the ends of the stator windings of the electric motor are connected at one point. In this case, three-phase voltage is supplied to the beginning of the windings. Below, in Figure 1, the connection diagram for a star asynchronous motor is clearly illustrated.

When a three-phase electric motor is connected using the “delta” connection type, then the stator windings of the electric motor are connected in series one after another. In this case, the beginning of the subsequent winding is connected to the end of the previous winding, and so on. Below, in Figure 2, the connection diagram of a delta asynchronous motor is clearly illustrated.

If you do not go into the theoretical and technical foundations of electrical engineering, then you can take for granted the fact that the operation of those electric motors whose windings are connected in a star configuration is softer and smoother than that of electric motors whose windings are connected in a delta configuration ". But here it is worth paying attention to the fact that electric motors, the windings of which are connected in a star configuration, are not capable of developing the full power declared in the passport characteristics. In the event that the windings are connected according to a delta circuit, the electric motor operates at the maximum power stated in the technical data sheet, but at the same time there are very high starting currents. If we make a comparison in terms of power, then electric motors whose windings are connected in a delta configuration are capable of delivering power one and a half times higher than those electric motors whose windings are connected in a star configuration.

Based on all of the above, in order to reduce currents during startup, it is advisable to use a combined delta-star connection of the windings. This type of connection is especially relevant for electric motors with greater power. Thus, due to the delta-star connection, the starting is initially carried out in the star configuration, and after the electric motor has gained momentum, switching is carried out in automatic delta mode.

The electric motor control circuit is shown in Figure 3.

Rice. 3 Control circuit

Another version of the electric motor control circuit is as follows (Fig. 4).

Rice. 4 Engine control circuit

The NC (normally closed) contact of time relay K1, as well as the NC contact of relay K2, in the circuit of the short-circuit starter coil, is supplied with supply voltage.

After the short-circuit starter is turned on, the normally closed short-circuit contacts disengage the circuits of the K2 starter coil (prohibition of accidental activation). The short circuit contact in the power supply circuit of the starter coil K1 closes.

When the magnetic starter K1 starts, the K1 contacts close in the power circuit of its coil. The time relay turns on at the same time, the contact of this relay K1 in the short circuit starter coil circuit opens. And in the starter coil circuit K2 it closes.

When the short circuit starter winding is disconnected, the short circuit contact in the starter coil circuit K2 will close. After the K2 starter turns on, it opens the power circuit of the short-circuit starter coil with its K2 contacts.

Three-phase supply voltage is supplied to the beginning of each of the windings W1, U1 and V1 using the power contacts of the starter K1. When the short-circuit magnetic starter is triggered, then with the help of its short-circuit contacts a short circuit is made, through which the ends of each of the electric motor windings W2, V2 and U2 are connected to each other. Thus, the motor windings are connected using a star connection.

A time relay combined with a magnetic starter K1 will operate after a certain time. In this case, the short-circuit magnetic starter is turned off and the magnetic starter K2 is simultaneously turned on. Thus, the power contacts of the starter K2 will be closed and the supply voltage will be supplied to the ends of each of the windings U2, W2 and V2 of the electric motor. In other words, the electric motor is switched on according to the “delta” connection diagram.

In order to start the electric motor using a delta-star connection, various manufacturers produce special starting relays. These relays can have various names, for example, “start-delta” relay or “start time relay”, as well as some others. But the purpose of all these relays is the same.

A typical circuit made with a time relay designed for starting, that is, a delta-star relay, to control the starting of a three-phase asynchronous type electric motor is shown in Figure 5.

Fig. 5 Typical circuit with a starting time relay (star/delta relay) for controlling the start of a three-phase asynchronous motor.

So, let's summarize all of the above. In order to reduce starting currents, starting the electric motor is required in a certain sequence, namely:

1. first, the electric motor is started at low speeds connected in a star configuration;
2. then the electric motor is connected in a delta pattern.

The initial start according to the "triangle" circuit will create the maximum torque, and the subsequent connection according to the "star" circuit (for which the starting torque is 2 times less) with continued operation in the nominal mode, when the engine has "picked up speed", there will be a switch to the "delta" connection circuit "in automatic mode. But do not forget about the load that is created on the shaft before starting, since the torque is weakened when connecting in a star configuration. For this reason, it is unlikely that this starting method will be suitable for electric motors with high loads, since they may then lose their functionality.

The current-carrying windings of the electric motor are led out into the distribution box. The terminals of the windings form two parallel rows, each marked with the letter C and numbers from 1 to 6. This is done in order to mark the beginning and end of all three windings.
The connections are quite complicated. This can be found out using a simple tester. Calling the terminals of the windings, we will find that only two of them are connected along a large diagonal. The rest are connected along small diagonals.
Ringing the windings is necessary when using an old electric motor; in a new one, such work is unlikely to be required. After checking, the motor can be connected either in a star or delta configuration.
Note: a combined star-delta circuit is also used to connect electric motors with a power of more than 5 kW.

Turning on the windings with a star

The "star" circuit involves connecting the ends of the windings at one point, which is called the neutral, and applying supply voltage to the beginning of each of the windings. The "triangle" circuit provides for a series connection of windings.

For a star connection, two jumpers (three jumpers are included with the electric motor) are installed on the terminals in the same row. Then the jumpers are fixed with nuts. Wires from a three-phase network are connected to the three terminals of the second row.

Switching on the motor windings with a triangle

The “triangle” circuit is used to connect the electric motor to a single-phase 220 V network. Three jumpers connect the terminals located opposite each other. On one side, the jumpers are fixed with nuts, on the opposite side we connect wires from the network to two terminals, and to the third - a wire from the working capacitor (the capacitance must be calculated correctly).

Tip: when purchasing an electric motor, it is advisable to check the number of wires in the junction box. The presence of 6 wires to the contacts indicates the possibility of connecting the motor according to any scheme. Three wires mean that the winding contacts are already connected in a star configuration and connection to a single-phase network in a delta configuration is impossible. In this case, you will have to open the engine and remove the missing ends. This will be quite difficult to do.
Each connection scheme has its own characteristics. The electric motor, when connected in a star configuration, operates smoothly, but cannot develop the power that is indicated in the product data sheet.
The "triangle" circuit allows the electric motor to achieve maximum power, but to reduce the value of the resulting starting currents, it is necessary to use a starting rheostat.

By reducing the starting torque and limiting the starting current, the star-delta switching method of starting an asynchronous motor is used. At the first moment of start-up, the voltage is connected to the stator windings in a star (Y) circuit. As soon as the engine accelerates, its power is switched on in a delta (∆) pattern.

Advantages

Some three-phase low voltage motors above 5 kW are rated at 400 V in delta (∆) or 690 V in star (Y). This connection scheme makes it possible to start the engine at a lower voltage. When starting the engine according to the star-delta circuit, it is possible to reduce the starting current to 1/3 of the direct starting current from the network. Star-delta starting is especially suitable for mechanisms with large flywheel masses, when the load is applied after the engine has accelerated to rated speed.

Disadvantages of starting an asynchronous motor using star-delta switching

When starting the engine by switching “star-delta”, the starting torque also decreases by approximately 33%. This method can only be used for three-phase asynchronous motors that can be connected in a delta configuration. With this option, there is a danger of switching to delta at too low a speed, which will cause the current to rise to the same level as the current for a direct start DOL.

When switching from star to delta, an induction motor can quickly reduce its rotational speed, which also requires a sharp increase in current to increase. The figure shows a diagram of starting an engine using starters KM1, KM2, KM3. The starter KM1, KM2 turns on the electric motor according to the “star” circuit. After the time allotted for starting and exiting the engine at 50% of the rated speed, the KM2 starter is turned off and KM3 is turned on, switching the engine to delta.

The starting torque and current when starting with star-delta switching are significantly lower than with direct starting.

Comparison of direct starting method DOL and starting with star-delta switching

These diagrams show the starting currents for a pump with a 7.5 kW three-phase induction motor using direct on line (DOL) and star-delta starting, respectively. The figure shows that the DOL direct starting method is characterized by large inrush currents, but which after some time decreases and becomes constant.

The star-delta starting method is characterized by lower, low starting currents. However, at the moment of startup, during the transition from “star” to “triangle”, current surges occur. During star starting, after (t = 0.3 s), the current decreases. However, during switching from star to delta, after a time t = 1.7 s, the current reaches the level of the inrush current for direct starting. Moreover, the current surge can become even larger because no voltage is supplied to the motor during switching and the motor slows down before full voltage is applied.

In three-phase circuits, two types of connection of the windings of transformers, electrical receivers and generators are usually used. One of these connections is called a star, the other is called a triangle. Let's take a closer look at what these compounds are and how they differ from each other.

Definition

Star connection means a connection in which all the working ends of the phase windings are combined into one node, called the zero or neutral point and denoted by the letter O.

Triangle connection is a circuit in which the phase windings of a generator are connected in such a way that the beginning of one of them is connected to the end of the other.

Comparison

The difference in these schemes is the connection of the ends of the windings of the electric motor generator. IN star pattern, all ends of the windings are connected together, whereas in triangle pattern the end of one phase winding is mounted with the beginning of the next.

In addition to the basic assembly diagram, electric motors with star-connected phase windings operate much smoother than motors with delta-connected phase windings. But when connected by a star, the electric motor is not able to develop its full rated power. Whereas, when the phase windings are connected in a triangle, the engine always operates at its full declared power, which is almost one and a half times higher than when connected in a star. The big disadvantage of delta connection is the very large inrush currents.

Conclusions website

1. In a star connection scheme, the ends of the windings are mounted in one unit.
2. In a delta connection diagram, the end of one winding is mounted with the beginning of the next winding.
3. An electric motor with star-connected windings runs smoother than a delta-connected motor.
4. When connected by a star, the engine power is always lower than the rated value.
5. When connected in a triangle, the engine power is almost one and a half times higher than when connected in a star.

Today, asynchronous electric motors are popular due to their reliability, excellent performance and relatively low cost. Motors of this type are designed to withstand strong mechanical loads. In order for the unit to start up successfully, it must be connected correctly. For this purpose, star and delta connections are used, as well as a combination of them.

Types of connections

The design of the electric motor is quite simple and consists of two main elements - a stationary stator and an internal rotating rotor. Each of these parts has its own windings that conduct current. The stator one is placed in special grooves with a mandatory distance of 120 degrees.

The principle of operation of the engine is simple - after turning on the starter and applying voltage to the stator, a magnetic field appears, causing the rotor to rotate. Both ends of the windings are brought out into the distribution box and are arranged in two rows. Their conclusions are marked with the letter “C” and receive a numerical designation ranging from 1 to 6.

To connect them, you can use one of three methods:

• "Star";
• "Triangle";
• "Star-triangle".

If all ends of the stator winding are connected at one point, then this type of connection is called “star”. If all ends of the winding are connected in series, then it is a “triangle”. In this case, the contacts are arranged so that their rows are shifted relative to each other. As a result, opposite terminal C6 is pin C1, etc. This is one of the answers to the question of what is the difference between star and delta connections.

In addition, in the first case, smoother operation of the motor is ensured, but maximum power is not achieved. If a delta circuit is used, then large inrush currents arise in the windings, which negatively affect the service life of the unit. To reduce them, you have to use special rheostats that make the start as smooth as possible.

If a 3-phase motor is connected to a 220 volt network, then the torque is not enough to start. To increase this indicator, additional elements are used. In domestic conditions, the optimal solution would be a phase-shifting capacitor. It should be noted that the power of three-phase networks is higher in comparison with single-phase ones. This suggests that connecting a 3-phase motor to a single-phase electrical network will certainly lead to a loss of power. It is impossible to say for sure which of these methods is better, since each has not only advantages, but also disadvantages.

Pros and cons of "star"

The common point at which all ends of the winding are connected is called neutral. If there is a neutral conductor in the electrical circuit, then it will be called four-wire. The beginning of the contacts is connected to the corresponding phases of the power supply network. The connection diagram of the electric motor windings “star” has a number of advantages:

• Ensures long-term non-stop operation of the electric motor.
• Due to the reduction in power, the service life of the unit increases.
• A smooth start is achieved.
• During operation, there is no significant overheating of the engine.

There is equipment that has an internal connection of the ends of the winding and only three contacts are brought into the box. In such a situation, using a connection scheme other than “star” is not possible.

Advantages and disadvantages of the “triangle”

Using this type of connection allows you to create an unbroken circuit in the electrical circuit. The circuit received this name because of its ergonomic shape, although it can also be called a circle. Among the advantages of the “triangle” it is worth noting:

• The maximum power of the unit is achieved during operation.
• A rheostat is used to start the motor.
• Significantly increases torque.
• A powerful traction force is created.

Among the disadvantages, one can note only high values ​​of starting currents, as well as active heat generation during operation. This type of connection is widely used in powerful mechanisms that contain large load currents. It is due to this that the EMF increases, affecting the power of the torque. It should also be said that there is another connection diagram called “open delta”. It is used in rectifier installations designed to produce triple-frequency currents.

Combining circuits

In highly complex mechanisms, a combined star and delta connection of a three-phase motor is often used. This allows you not only to increase the power of the unit, but also to extend its service life if it is not designed to work using the “triangle” method. Since the starting currents in high-power motors are high, when the equipment starts, fuses often fail or circuit breakers turn off.

To reduce the linear voltage in the stator winding, various additional devices are actively used, for example, autotransformers, rheostats, etc. As a result, a voltage reduction of more than 1.7 times is achieved. After the motor has been successfully started, the frequency begins to gradually increase and the current decreases. The use of a relay contact circuit in such a situation makes it possible to switch the star-delta connection of the electric motor. In this situation, the smoothest possible start of the power unit is ensured.