In life, there are situations when you need to start a 3-phase asynchronous electric motor from a household network. The problem is that you have only one phase and "zero" at your disposal.
What to do in such a situation? Is it possible to connect a three-phase motor to a single-phase network?
If you approach the work with the mind, everything is real. The main thing is to know the basic schemes and their features.
Design features
Before starting work, understand the design of AD (asynchronous motor).
The device consists of two elements - a rotor (moving part) and a stator (fixed assembly).
The stator has special grooves (recesses) in which the winding is placed, distributed in such a way that the angular distance is 120 degrees.
The windings of the device create one or more pairs of poles, the number of which determines the frequency with which the rotor can rotate, as well as other parameters of the electric motor - efficiency, power and other parameters.
When an asynchronous motor is connected to a network with three phases, current flows through the windings at different time intervals.
A magnetic field is created that interacts with the rotor winding and causes it to rotate.
In other words, there is a force that rotates the rotor at different time intervals.
If you connect HELL to a network with one phase (without preparatory work), the current will appear in only one winding.
The torque generated will not be enough to displace the rotor and keep it spinning.
That is why, in most cases, the use of starting and running capacitors is required to ensure the operation of a three-phase motor. But there are other options.
How to connect an electric motor from 380 to 220V without a capacitor?
As noted above, a capacitor is most often used to start an ED with a squirrel-cage rotor from a single-phase network.
It is he who provides the start-up of the device at the first moment of time after the supply of a single-phase current. In this case, the capacity of the starting device should be three times higher than the same parameter for the working capacity.
For blood pressure motors with a power of up to 3 kilowatts and used at home, the price of starting capacitors is high and sometimes commensurate with the cost of the motor itself.
Consequently, many are increasingly avoiding containers that are used only at the time of start-up.
The situation is different with working capacitors, the use of which allows you to load the motor by 80-85 percent of its power. In the absence of them, the power indicator can drop up to 50 percent.
However, a capacitorless start of a 3-phase motor from a single-phase network is possible due to the use of bidirectional switches that operate for short periods of time.
The required torque is provided by the displacement of the phase currents in the windings of the IM.
Two schemes are popular today, suitable for motors with power up to 2.2 kW.
Interestingly, the start-up time of HELL from a single-phase network is slightly lower than in the usual mode.
The main elements of the circuit are triacs and symmetrical dinisters. The former are controlled by bipolar pulses, and the latter by signals coming from a half-cycle of the supply voltage.
Scheme No. 1.
Suitable for 380 volt motors up to 1500 rpm with delta windings.
An RC circuit acts as a phase shifter. By changing the resistance R2, it is possible to achieve a voltage on the capacitance shifted by a certain angle (relative to the voltage of the household network).
The main task is taken over by the VS2 symmetrical dynistor, which in certain moment time connects the charged capacity to the triac and activates this key.
Scheme No. 2.
Suitable for electric motors with a speed of up to 3000 rpm and for blood pressure, characterized by increased resistance at the time of start.
Such motors require more starting current, so the open star circuit is more relevant.
Feature - the use of two electronic keys, replacing the phase-shifting capacitors. During the adjustment process, it is important to ensure the required shift angle in the phase windings.
This is done as follows:
- Voltage is supplied to the electric motor through a manual starter (it must be connected in advance).
- After pressing the button, it is required to select the starting moment using the resistor R
When implementing the considered schemes, it is worth considering a number of features:
- For the experiment, non-radiator triacs (types TS-2-25 and TS-2-10) were used, which proved to be excellent. If you use triacs on a plastic case (imported), you cannot do without radiators.
- Symmetrical dinistor type DB3 can be replaced by KP Despite the fact that KP1125 is made in Russia, it is reliable and has a lower switching voltage. Main disadvantage- the scarcity of this dinistor.
How to connect through capacitors
First, decide which circuit is assembled on the ED. To do this, open the bar cover, where the blood pressure terminals are output, and see how many wires come out of the device (most often there are six of them).
The designations are as follows: C1-C3 - the beginning of the winding, and C4-C6 - its ends. If the beginnings or ends of the windings are combined with each other, this is a "star".
The most difficult thing is if six wires just come out of the case. In this case, you need to look for the appropriate designations on them (C1-C6).
To implement the scheme for connecting a three-phase ED to a single-phase network, two types of capacitors are required - starting and working.
The former are used to start the motor at the first moment. As soon as the rotor spins up to the desired number of revolutions, the starting capacitance is excluded from the circuit.
If this does not happen, possible serious consequences up to damage to the motor.
The main function is taken by the working capacitors. Here it is worth considering the following points:
- Run capacitors are connected in parallel;
- The rated voltage must be at least 300 volts;
- The capacity of the working capacities is selected taking into account 7 microfarads per 100 W;
- It is desirable that the type of the working and starting capacitors be identical. Popular options are MBGP, MPGO, KBP and others.
If you take into account these rules, you can extend the life of the capacitors and the motor as a whole.
The capacitance calculation should be made taking into account the rated power of the electric motor. If the motor is underloaded, overheating is inevitable, and then the capacitance of the working capacitor will have to be reduced.
If you choose a capacitor with a capacitance less than the allowable one, then the efficiency of the electric motor will be low.
Remember that even after the circuit is turned off, voltage remains on the capacitors, so it is worth discharging the device before starting work.
Also note that connecting an electric motor with a power of 3 kW or more to ordinary wiring is prohibited, because this can lead to shutdown or burnout of plugs. In addition, the risk of melting the insulation is high.
To connect ED 380 to 220V using capacitors, proceed as follows:
- Connect the containers together (as mentioned above, the connection must be in parallel).
- Connect the parts with two wires to the ED and a single-phase alternating voltage source.
- Turn on the engine. This is done in order to check the direction of rotation of the device. If the rotor moves in the right direction, no additional manipulations are necessary. Otherwise, the wires connected to the winding should be swapped.
With a capacitor, an additional simplified one is a star for the circuit.
With a capacitor, an additional simplified one is for a triangle circuit.
How to connect with reverse
In life, there are situations when you need to change the direction of rotation of the motor. This is also possible for three-phase electric motors used in a household network with one phase and zero.
To solve the problem, it is required to connect one output of the capacitor to a separate winding without the possibility of a break, and the second - with the possibility of transferring from the "zero" to the "phase" winding.
To implement the circuit, you can use a switch with two positions.
Wires from “zero” and “phase” are soldered to the extreme conclusions, and a wire from the capacitor is connected to the central one.
How to connect according to the "star-delta" scheme (with three wires)
For the most part, a star circuit has already been assembled in the ED of domestic production. All that is required is to reassemble the triangle.
The main advantage of the star/delta connection is the fact that the engine produces maximum power.
Despite this, such a scheme is rarely used in production due to the complexity of implementation.
To connect the motor and make the circuit workable, three starters are required.
The current is connected to the first (K1), and the stator winding is connected to the other. The remaining ends are connected to starters K3 and K2.
When the K3 starter is connected to the phase, the remaining ends are shortened, and the circuit is converted into a "star".
Please note that the simultaneous activation of K2 and K3 is prohibited due to the risk short circuit or knocking out the AB supplying the ED.
To avoid problems, a special interlock is provided, which means that one starter is turned off when another is turned on.
The principle of operation of the circuit is simple:
- When the first starter is connected to the network, the time relay starts and supplies voltage to the third starter.
- The engine starts to work in a star pattern and starts to work with more power.
- After some time, the relay opens contacts K3 and connects K2. In this case, the electric motor operates according to the “triangle” scheme with reduced power. When it is required to turn off the power, K1 turns on.
Results
As can be seen from the article, it is realistic to connect a three-phase current electric motor to a single-phase network without power loss. At the same time, for home conditions, the simplest and most affordable option is to use a starting capacitor.
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The connection of the electric motor 380V to 220V is carried out through a capacitor. For this connection, you need to use paper (or starting) capacitors, wherein IMPORTANT to capacitor rated voltage was greater than or equal to the mains voltage(in this case, it is recommended that the capacitor voltage be 2 times the mains voltage). Capacitors of the following brands (types) can be used:
MBGO, MBGCH, MBGP, MBGT, MBGV, KBG, BGT, OMBG, K42-4, K42-19, etc.
Capacitor capacitance can be determined by the formulas below, or using .
The first thing to do is to correctly connect the terminals of the motor windings. As already known from the article: the windings of the electric motor can be connected along (indicated by - Y) or by (indicated - Δ), while, as a rule, to connect the electric motor to 220V, the "triangle" scheme is used, in order to determine the connection diagram of the windings, you need to look at nameplate attached to it:
Record: "Δ / Y 220/380V" means that to connect this electric motor to 220V it is necessary to connect its windings according to the scheme, and to connect to 380V - according to the scheme how to do it.
The second thing to decide is how the electric motor will be started, under load (when a load is applied to its shaft at the time of starting the electric motor and it cannot rotate freely) or without load (when the motor shaft rotates freely at the time of starting, for example, emery , fan, circular saw, etc.).
When starting the engine without load, 1 capacitor is used which is called the working one, and if it is necessary to start the engine under load in the circuit, in addition to the working one, the 2nd capacitor is additionally used which is called the starting one, it turns on only at the moment of start.
Let's analyze the connection diagrams of the electric motor 380 to 220 for both cases:
Schemes for connecting an electric motor through a capacitor.
1) Connecting the electric motor through a capacitor according to the "triangle" scheme, starting - without load:
The capacity of the working capacitor for connecting the electric motor with a “triangle” winding connection scheme is calculated by the formula:
CR=4800 * In/ UWith; microf
where: In- rated current of the electric motor in Amperes (accepted in accordance with); UWith— mains voltage in Volts.
In the circuit, a single-pole circuit breaker is used to turn on the electric motor, but its use is not necessary; you can turn on the electric motor directly to the network through a socket using a regular plug or, for example, turn it on through a regular light switch.
2) Connecting the electric motor through a capacitor according to the "star" scheme, starting - without load:
The capacity of the working capacitor for connecting the electric motor with the “star” winding connection scheme is calculated by the formula:
CR=2800 * In/ UWith; microf
where: In- rated current of the electric motor in Amperes (accepted in accordance with the passport data of the electric motor); UWith— mains voltage in Volts.
If a 380 to 220 Volt engine is started under load, a starting capacitor must additionally be used in the circuit, otherwise the torque on the motor shaft will not be enough to spin it up and the engine will not be able to start.
The starting capacitor is connected in parallel with the working one and should be turned on only at the moment the engine is started, after the engine picks up speed it must be turned off.
Start Capacitor should be 2.5 - 3 times larger than the working one.
CP= (2,5…3) * CR; microf
With this scheme, to start the electric motor, you must press and hold the SB button, then apply voltage by turning on the circuit breaker, as soon as the engine starts, the SB button must be released. As a button, you can also use a regular switch.
However the best option to connect an electric motor 380 to 220 is to use PNVS-10 (pressure starter with starting contact):
The “start” buttons in these starters have 2 contacts, one of them opens when the “start” button is released, turning off the starting capacitor, and the second remains closed and voltage is supplied to the electric motor through it through the working capacitor, the shutdown is performed by the “stop” button.
Reverse motor connected to 220 volts through a capacitor.
So, from the diagrams above, it follows that with any method of connecting the windings (star or delta), three points remain in the motor terminal box for connecting it to the network, conditionally: zero is connected to the first output, phase is connected to the second, and phase is supplied to the third through a capacitor, but what if the engine started to rotate in the wrong direction at startup? To change the direction of rotation of a motor connected through a capacitor, you simply need to switch the phase wire from one output of the electric motor to another, while leaving the neutral wire on the same output, i.e. conditionally: leave zero on the first output, apply the phase to the third, and apply the phase to the second through the capacitor.
Content:The design of a three-phase electric motor is an electric machine, for the normal operation of which three-phase networks are required alternating current. The main parts of such a device are the stator and rotor. The stator is equipped with three windings shifted by 120 degrees. When a three-phase voltage appears in the windings, magnetic fluxes are formed at their poles. Due to these flows, the motor rotor begins to rotate.
In industrial production and in everyday life, the widespread use of three-phase induction motors. They can be single-speed, when a star and delta connection of the motor windings is made, or multi-speed, with the ability to switch from one circuit to another.
Connection of windings with a star and a delta
For all three-phase electric motors, the windings are connected in a star or delta pattern.
When connecting the windings according to the star scheme, their ends are connected at one point at the zero node. Therefore, one more additional zero output is obtained. The other ends of the windings are connected to the phases of the 380 V network.
The triangle connection is serial connection windings. The end of the first winding is connected to the start end of the second winding, and so on. Ultimately, the end of the third winding will connect to the beginning of the first winding. Three-phase voltage is supplied to each connection node. The triangle connection is distinguished by the absence of a neutral wire.
Both types of compounds have received approximately the same distribution and do not have significant distinguishing features among themselves.
There is also a combined connection, when both options are used. This method is used quite often, its purpose is a smooth start of the electric motor, which cannot always be achieved with conventional connections. At the moment of direct start, the windings are in the star position. Next, a relay is used that provides switching to the delta position. Due to this, the starting current is reduced. The combined circuit is most often used during the start-up of electric motors with high power. For such motors, a significantly higher starting current is also required, exceeding the nominal value by about seven times.
Electric motors can be connected in other ways when a double or triple star is used. These connections are used for motors with two or more variable speeds.
Starting a three-phase electric motor with switching from star to delta
This method is used in order to reduce the starting current, which can be about 5-7 times the rated current of the motor. Units with too much power have such a starting current at which fuses easily blow out, circuit breakers turn off and, in general, the voltage drops significantly. With such a decrease in voltage, the incandescence of the lamps decreases, the torque of other electric motors decreases, and the contactors also spontaneously turn off. Therefore, apply different ways, in order to reduce the starting current.
Common to all methods is the need to reduce the voltage in the stator windings at the time of direct start. To reduce the starting current, the stator circuit can be supplemented with a choke, rheostat or automatic transformer during the start.
The most widespread is the switching of the winding from a star to a triangle position. In the star position, the voltage becomes 1.73 times less than the nominal voltage, so the current will also be less than at full voltage. During start-up, the motor speed increases, the current decreases and the windings switch to the delta position.
Such switching is allowed in electric motors with an easy start mode, since the starting torque decreases by about half. In this way, those engines are switched that can be structurally connected in a triangle. They must have windings capable of operating at.
When to switch from delta to star
When it is necessary to make a star-delta connection of the motor windings, it should be remembered that it is possible to switch from one type to another. The main option is the star-delta switching circuit. However, if necessary, the reverse is also possible.
Everyone knows that motors that are not fully loaded experience a decrease in power factor. Therefore, it is desirable to replace such motors with devices with lower power. However, if replacement is not possible and there is a large power reserve, delta-star switching is performed. The current in the stator circuit must not exceed the nominal value, otherwise the motor will overheat.
Widespread use of asynchronous electric motors connected in a "star" and "triangle" is known. These connections are available at each production site, three-phase motors, generators, transformers are connected with a “star”. "Triangle" is used mainly in engines with a long start and run cycle. It is also used in transformer connection diagrams, mainly where there is a symmetrical load.
Used joint inclusion in the work of both connections "star" and "triangle" when starting powerful electric motors. The start starts from the "star" with the subsequent switching by the relay circuit to the "triangle" circuit upon reaching the revolutions. The engine continues to run long time on the triangle.
Connection of circuits according to the "triangle" scheme
This connection is called a delta only when both ends of the windings are connected to each other. It is necessary to connect in a delta when the mains voltage is suitable for such a consumer. The start of electric motors according to the “triangle” scheme is expressed by large values of starting currents and does not have a very good effect on the durability of the windings. But when working on this connection, the power is equal to that stated in the passport of the electric consumer, which is sometimes necessary.
The Triangle scheme is divided into "open" and "open". The difference between the two types lies in the fact that an open triangle is a connection by a triangle with one point, torn to the consumer. And the open one is different in that one winding is replaced by the consumer.
Connection of three-phase circuits according to the "star" scheme
For example: let's take a network of 380 to 220, a star connection, the voltage at the consumer is 220V. If you connect according to the triangle scheme, the voltage on the windings will be 380, based on the voltage, the power P = UI will become greater. (In practice, a normal motor will burn out because the voltage will become 380V. However, 220/127 for this motor, delta is normal, star operation with power loss).
In the case of consumers operating in a "star", it is very important that there is no "phase imbalance". If the neutral has, for example: poor contact, then a difference will occur - load asymmetry, at which one consumer will be under some voltage. This potential difference depends on the distribution of the load at the moment when the neutral wire burns out. From this potential difference, consumers in the apartments turned out to be energized, which could cause an old TV set to burn out or a refrigerator to fail. I think many people know such stories in the past.
Special cases of application of the described connection schemes
Application of star connection schemes:
Implementation of triangle switching schemes:
Many questions arise on the difference between the connection of a star and a triangle. The difference, in my opinion, is in the constructive organization of the supply network. For the engine, the first method is preferable in those circuits and mechanisms where there is frequent operation. FROM Please note that with this connection, the supply voltage, usually 380V, must be taken into account. In the second case, the supply voltage is taken into account in the presence of 220V. With this connection, the motor has high starting currents, which wears it out much faster.
Rarely found in the industry is a triangle connection. More often, low-power motors operate precisely in a star. Powerful engines are mostly equipped with frequency converters and then the probability of failure of an expensive, custom-made engine is reduced to almost zero.
Powerful hydraulic and pneumatic engines use the "star" scheme at the metallurgical enterprise. Presumably to prevent engine wear. Engines are used in aggressive environments, so three degrees of protection are used: the first - fuses for each phase, the fuse must be semiconductor (burns out more quickly and does not allow the windings to heat up); the second is a circuit breaker, which, as a rule, works in extremely rare cases, if the fuse has not blown; the third protection - on temperature. The temperature sensor is connected through a low voltage relay, which, when the sensor is triggered, breaks the relay in the power circuit of the windings.
The asynchronous motor is powered by a three-phase AC network. Delta and star connection can be used for operation. In order for everything to work stably, it is necessary to use special jumpers created for this, whether it is a star or delta connection. These are the most convenient options for connection and, accordingly, having a high degree of reliability.
Connection differences
First you need to find out what is the difference between a star and a triangle. If we approach this issue from the point of view of electrical engineering, then the first option allows the engine to run more smoothly and softly. But there is one moment: the engine will not be able to reach full power, which is presented in the characteristics of the technical plan.
The delta connection allows the engine to quickly reach maximum power. Therefore, the efficiency of the device is applied at full power. However, there is a serious drawback, which is high starting currents.
The fight against such phenomena as high inrush currents is to connect a start-up rheostat to the circuit. This makes it possible to carry out a much smoother start of the engine and improve its performance.
Star connection
The star connection is that the ends of all 3 windings are reunited at a common point called neutral. If there is a neutral wire, then such a circuit is considered four-wire, if it is absent, it is three-wire.
The beginning at the conclusions is fixed to certain phases of the power supply network. The voltage that is applied to these phases is 380 volts or 660 volts. . The main advantages of such a scheme include:
- Non-stop operation of the engine for a long time and with stability.
- By reducing the power of the equipment, the reliability and operating time for the star circuit are increased.
- The start of the electric type drive due to this connection has increased smoothness.
- It is possible to influence the parameters by short-term overload.
- During operation, the case of the equipment will not become available for overheating.
There is equipment with a connection of the windings inside. Since only three terminals are placed on the block of such equipment, other connection methods cannot be applied. Such an implementation does not require the presence of qualified specialists.
Triangle scheme
Instead of a star circuit, you can use a triangle connection, the essence of which is to connect the ends and the beginnings of the windings in a sequential manner. The end at the winding of phase C closes the circuit and creates a whole circuit. Due to this form, the resulting circuit will be more ergonomic.
On each of the windings there is a linear voltage of 220 or 380 volts. Among the main advantages of the scheme are:
- Power electric motors reaches its highest value.
- The use of an appropriate rheostat for a smoother start.
- Significantly increased torque.
- High tractive effort.
The triangle is used in such mechanisms where significant starting loads and energy are required for powerful mechanisms. A significant moment of rotation is achieved by increasing the self-induction EMF indicators. This phenomenon is caused high currents leaks.
Star and triangle combination
If the design is of a complex type, then a combined star and triangle method is used. The use of this method leads to the fact that the power increases greatly. But in the case where the engine cannot fit the technical specifications everything will overheat and burn out.
To reduce the line voltage in the stator windings, a star circuit should be used. After the current flow decreases, the frequency will increase. The relay-contact type circuit helps to switch the delta to the star.
It is this combination that gives the greatest reliability and significant productivity of the equipment used without fear of failure. This scheme is effective for engines where a lightweight starting scheme is involved. But with a decrease in the starting current and a constant moment, it should not be used. An alternative is a phase rotor with a rheostat for starting.
The current during engine start is 7 times the operating current. One and a half times more power when connected in a triangle, starting with high smoothness is obtained using frequency-type wires.
The star reconnection method requires taking into account the fact that phase imbalances must be corrected, otherwise there is a risk of equipment failure.
Linear and phase voltages with a triangle are equal to each other. If you want to turn on the engine in a household network, then you need a phase-shifting type of capacitor. In this way, use of delta or wye circuit depends on motor design and home network requirements. Therefore, you should carefully look at the engine performance and the necessary parameters that need to be increased for more effective work designs.
