To designate conductors, the Latin letters A, B, C, L and numbers 1, 2, 3 are used. This results in a longer service life.
The delta connection consists of a series connection of windings.
In order to reduce starting currents, starting the electric motor is required in a certain sequence, namely: first, the electric motor is started at low speeds connected in a star configuration; then the electric motor is connected in a delta pattern. Star and triangle connection. The difference between them
The delta connection consists of a series connection of windings. Due to this, the starting current decreases.
You can switch from star to delta only those electric motors that are designed to operate when connected in a delta, that is, having windings designed for linear mains voltage. That is, an increase in voltage by 1.73 times reduces the current by exactly the same amount.
By the way, the frequency converter also changes not only the frequency of the current, but also the voltage, however, it does this wisely. Therefore, we get one more additional zero output.
The time relay turns on at the same time, the contact of this relay K1 in the short circuit starter coil circuit opens.
The drawings very well clearly show how and what should be.
Determination of the beginning and end of the phase windings of an asynchronous electric motor
Connecting a 380V electric motor. Star-delta starting circuit
So, let's summarize all of the above. Now to the wires that connect them. But what is the purpose of these types of connections, why are star-delta connections used in different electrical installations, what is the effectiveness of both. Classic mode switching scheme with current and time relays After turning on the three-phase automatic switch AB, the starter is ready for operation.
In this case, the star or delta connection is made inside the engine at the frontal end part. After the K2 starter turns on, it opens the power circuit of the short-circuit starter coil with its K2 contacts.
Accordingly, in these two cases, only the currents in the conductors leading to the motor differ; they are indicated on the nameplate, while the current in the winding will be the same, as can be seen in the figure above.
In most cases, gaining speed takes up to a second.
There are also certain differences in ergonomics.
So, K of the first phase is connected to H of the second. how to connect the wires of a three-phase motor in a triangle
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Differences between "star" and "triangle"
The engine will simply burn out, since when the windings are connected in a triangle, it will be powered by an increased voltage: its operating phase voltage is V, and its linear voltage is V. In fact, it turns out that the generator voltage at star, equal to volts, is converted into volts if you switch from one option to another. This is what the terminal block of a standard configuration engine looks like. In a three-phase system it is equal to degrees.
For ease of reading, it is divided into two circuits: control and power parts. Electric motors can be connected in other ways when a double or triple star is used.
When control voltage is applied, the magnetic starter K3 is triggered - the power circuit of its coil is closed by the normally closed contacts of the time relay K1 and contactor K2. Accordingly, if you need to use such a motor in a country with a lower line voltage, for example, in the USA where the linear voltage is V and the phase voltage is V at a current frequency of 60 Hz, then it will not be possible to normally connect such a motor to their single-phase network through a capacitor.
With such a decrease in voltage, the incandescence of the lamps decreases, the torque of other electric motors decreases, and the contactors spontaneously turn off. If you confuse the end and the beginning, the connected machine will not work. Technical plate on the side of the engine housing. This is achieved due to the possibility of creating a simpler and at the same time effective design, which, in turn, follows from the efficiency indicators.
Switching engine modes: star-delta
Star and delta connection of windings All three-phase electric motors have windings connected in a star or delta configuration. Such an incident happened here.
Why is this necessary? Simultaneously with the launch of KM2, with the help of its additional normally open contact BKM2, a time relay is started, the contacts of which are switched, but KM1 does not operate, since BKM2 is open in the circuit of the KM1 coil. The time relay combined with the K1 starter in this circuit operates in a control circuit with small currents, therefore, it can be replaced by a conventional time relay with three pairs of block contacts. Otherwise it will be three-wire.
Therefore, for Russia, linear voltage B for such a motor must be used in a star connection scheme. Therefore, different methods are used to reduce the inrush current. Connecting a 220V electric motor with a triangle and a star. Demonstration of work. Which type is better?
Connection to a single-phase network
To connect a three-phase 380V electric motor to a single-phase 220V network, a circuit with phase-shifting capacitors (starting and running) is most often used. Without capacitors, the engine may start, but only without a load, and you will have to turn its shaft by hand when starting.
The problem is that for the IM to operate, it requires a rotating magnetic field, which cannot be obtained from a single-phase network without additional elements. But by connecting one of the windings through a choke, you can shift the voltage phase to -90˚ and using a capacitor by +90˚ relative to the phase in the network. We discussed the issue of phase shift in more detail in the article: https://samelectrik.ru/chto-takoe-aktivnaya-reaktivnaya-i-polnaya-moshhnost.html.
Most often, capacitors are used for phase shifting, rather than chokes. In this way, not a rotating one is obtained, but an elliptical one. As a result, you lose about half of the nominal power. Single-phase IMs work better with this connection, due to the fact that their windings are initially designed and located on the stator for such a connection.
You can see typical motor connection diagrams without reverse for star or delta circuits below.
The resistor in the diagram below is needed to discharge the capacitors, since after turning off the power, voltage will remain at its terminals and you may get an electric shock.
You can select the capacitor capacity for connecting a three-phase motor to a single-phase network based on the table below. If you experience a difficult and lengthy startup, you often need to increase the starting (and sometimes working) capacity.
Or calculate using the formulas:
If the engine is powerful or starts under load (for example, in a compressor), you also need to connect a starting capacitor.
To simplify switching on, instead of the “ACceleration” button, use “PNVS”. This is a button for starting motors with a starting capacitor. It has three contacts, phase and zero are connected to two of them, and a starting capacitor is connected through the third. There are two keys on the front panel - “START” and “STOP” (as on AP-50 machines).
When you turn on the engine and press the first key all the way, three contacts close, after the engine has spun up and you release “START”, the middle contact opens, and the two outer ones remain closed, and the starting capacitor is removed from the circuit. When you press the “STOP” button, all contacts open. The connection diagram is almost the same.
You can watch the following video for details about what it is and how to properly connect the NVDS:
The connection diagram for a 380V electric motor to a single-phase 220V network with reverse is shown below. Switch SA1 is responsible for reverse.
The windings of a 380/220 motor are connected in a triangle, and for motors 220/127 – in a star, so that the supply voltage (220 volts) corresponds to the rated voltage of the windings. If there are only three outputs, and not six, then you will not be able to change the winding connection diagrams without opening them. There are two options here:
- Rated voltage 3x220V - you're in luck and use the circuits above.
- Rated voltage 3x380V - you are less lucky, since the engine may start poorly or not start at all if you connect it to a 220V network, but it’s worth a try, it might work!
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But when connecting a 380V electric motor to 1 phase 220V through capacitors, there is one big problem - power loss. They can reach 40-50%.
The main and effective way to connect without losing power is to use a frequency converter. Single-phase frequency converters output 3 phases with a linear voltage of 220V without zero. In this way you can connect motors up to 5 kW; for higher power, it is simply very rare to find converters that can work with single-phase input. In this case, you will not only receive full engine power, but will also be able to fully regulate its speed and reverse it.
Now you know how to connect a three-phase motor for 220 and 380 Volts, as well as what is needed for this. We hope the information provided helped you understand the issue!
The asynchronous electric motor is powered from a three-phase AC network. Such a motor, with a simple connection diagram, is equipped with three windings located on the stator. Each winding is shifted relative to each other by an angle of 120 degrees. A shift at such an angle is intended to create rotation of the magnetic field.
The ends of the phase windings of the electric motor are brought out to a special “block”. This was done for ease of connection. In electrical engineering, two main methods are used for connecting asynchronous electric motors: the “delta” connection method and the “star” method. When connecting the ends, jumpers specially designed for this purpose are used.
Star and delta connection of windings
In this case, if the current relay is excluded from the circuit, and mode switching is carried out according to the timer setting, then at the moment of transition to the triangle, the same current surges will be observed of almost the same duration as when starting from a stationary rotor state.
The beginning of the terminals is connected to the corresponding phases of the supply network. For these purposes, when operating an asynchronous electric motor, special manual control electrical devices are used, which include reversing switches and batch switches or more modernized remote control devices - reversing electromagnetic starters and switches. To compensate for the losses, you have to find a high-capacity μF capacitor with an operating voltage of at least V.
If it is a low-power unit, then the protection can withstand such a current, but if it is a high-power electric motor, then no protective blocks will withstand it.
There is no neutral wire in it, there is simply nowhere to connect it. With such wiring, you should be guided solely by the information indicated on the technical plate. It is not possible to configure such engines in any other way, in everyday conditions. However, simplicity requires sacrifice.
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Star connection and its advantages
When three-phase voltage appears in the windings, magnetic fluxes are formed at their poles. In general, he connected it incorrectly, which is why the engine burned out. It is also worth paying attention to the fact that the starting-protective equipment is selected for the rated power of the electric motor, but if the star connection is incorrect, it simply physically cannot perform its functions.
Soft start of the engine. For alternating current networks of 50 Hz, the linear voltage is higher than the phase voltage by the square root of three times, that is, approximately 1. When quoting site materials, there is an active hyperlink to l With such a decrease in voltage, the incandescence of the lamps decreases, the torque of other electric motors decreases, and the contactors spontaneously turn off. Star and triangle connection principle.
Catalog of relays and equipment
Star-delta switching can only be used for electric motors that have a freely rotating load on the shaft - fans, centrifugal pumps, shafts of machine tools, centrifuges and other similar equipment. True, sometimes there are specimens of a slightly different configuration.
After the electric unit accelerates, that is, its rotation speed corresponds to the passport data, a transition to a triangle from a star will occur. In addition, it cannot be denied that when the contactor of one connection Y is turned off, and the engine has not yet reached the required speed, the self-induction factor is triggered, and increased voltage enters the network, which can disable other nearby equipment and devices. In other words, the electric motor is switched on according to the “delta” connection diagram. A typical circuit made with a time relay intended for starting, that is, a delta-star relay, to control the starting of a three-phase asynchronous electric motor is shown in Figure 5. To avoid troubles, the motor should always be operated at the rated voltage, and if required, reduce shaft rotation speed, then you need to use gearboxes or AC frequency converters, and not try to solve the issue in the cheapest way. What are star and delta in a transformer?
Blitz tips
- At the moment of starting the electric motor , its starting current is 7 times greater than the operating current.
- The power is 1.5 times greater when connecting the windings using the delta method.
- To create a smooth start and protect against motor overloads , frequency wires are often used.
- When using the star connection method , special attention is paid to the absence of “phase imbalance”, otherwise the equipment may fail.
- Linear and phase voltages in a delta connection are equal to each other, as are line and phase currents in a star connection.
- To connect the motor to a household network, a phase-shifting capacitor is often used.
