It is better to connect the motor with a star or triangle. Special cases of application of the described connection diagrams. How the transition circuit works

Three-phase asynchronous motors, which are often used due to their widespread use, consist of a stationary stator and a moving rotor. Winding conductors are laid in the stator slots with an angular distance of 120 electrical degrees, the beginnings and ends of which (C1, C2, C3, C4, C5 and C6) are brought out into the junction box. The windings can be connected according to a “star” (the ends of the windings are connected to each other, the supply voltage is supplied to their beginnings) or a “triangle” (the ends of one winding are connected to the beginning of another).

In the distribution box, the contacts are usually shifted - opposite C1 is not C4, but C6, opposite C2 - C4.

When connecting a three-phase motor to a three-phase network through its windings in different moment Over time, a current begins to flow in turn, creating a rotating magnetic field that interacts with the rotor, causing it to rotate. When the motor is turned on in a single-phase network, no torque is created that can move the rotor.

Among different ways connecting three-phase electric motors to a single-phase network is the simplest - connecting the third contact through a phase-shifting capacitor.

Rotation speed of a three-phase motor powered by single-phase network, remains almost the same as when it was included in three-phase network. Unfortunately, this cannot be said about power, the losses of which reach significant values. Exact values power losses depend on the connection diagram, engine operating conditions, and the capacitance value of the phase-shifting capacitor. Approximately, a three-phase motor in a single-phase network loses about 30-50% of its power.

Not all three-phase electric motors are capable of working well in single-phase networks, but most of them cope with this task quite satisfactorily - except for the loss of power. Basically, for operation in single-phase networks, asynchronous motors with a squirrel-cage rotor (A, AO2, AOL, APN, etc.) are used.

Asynchronous three-phase motors are designed for two rated mains voltages - 220/127, 380/220, etc. The most common electric motors with an operating voltage of the windings are 380/220V (380V for star, 220 for delta). Higher voltage for star, lower for delta. In the passport and on the motor plate, among other parameters, the operating voltage is indicated winding voltage, their connection diagram and the possibility of changing it.

Designation on the plate A indicates that the motor windings can be connected either as a “triangle” (at 220V) or a “star” (at 380V). When connecting a three-phase motor to a single-phase network, it is advisable to use a delta circuit, since in this case the motor will lose less power than when connected to a star.

Tablet B informs that the motor windings are connected in a star configuration, and the distribution box does not provide the ability to switch them to delta (there are only three terminals). In this case, you can either accept a large loss of power by connecting the motor in a star configuration, or, by penetrating the electric motor winding, try to bring out the missing ends in order to connect the windings in a delta configuration.

If the operating voltage of the engine is 220/127V, then the engine can only be connected to a single-phase 220V network using a star circuit. If you connect 220V in a delta circuit, the engine will burn out.

Beginnings and ends of windings (various options)

Perhaps the main difficulty in connecting a three-phase motor to a single-phase network is to understand the wires going into the junction box or, in the absence of one, simply leading out of the motor.

The simplest case is when the windings in an existing 380/220V motor are already connected in a delta circuit. In this case, you just need to connect the current supply wires and the working and starting capacitors to the motor terminals according to the connection diagram.

If the windings in the motor are connected by a “star”, and it is possible to change it to a “triangle”, then this case also cannot be classified as complex. You just need to change the connection diagram of the windings to a “triangle”, using jumpers for this.

Determination of the beginnings and ends of windings. The situation is more complicated if 6 wires are brought out into the junction box without indicating their belonging to a specific winding and marking the beginnings and ends. In this case, it comes down to solving two problems (But before doing this, you need to try to find some documentation for the electric motor on the Internet. It may describe what wires of different colors belong to.):

identifying pairs of wires belonging to one winding;
finding the beginning and end of the windings.

The first task is solved by “ringing” all the wires with a tester (measuring resistance). If you don’t have a device, you can solve the problem using a flashlight light bulb and batteries, connecting the existing wires in a circuit in series with the light bulb. If the latter lights up, it means that the two ends being tested belong to the same winding. In this way, three pairs of wires (A, B and C in the figure below) belonging to three windings are determined.

The second task (determining the beginning and end of the windings) is somewhat more complicated and requires a battery and a pointer voltmeter. Digital is not suitable due to inertia. The procedure for determining the ends and beginnings of the windings is shown in diagrams 1 and 2.

To the ends of one winding (for example, A) a battery is connected to the ends of the other (for example, B) - pointer voltmeter. Now, if you break the contact of the wires A with a battery, the voltmeter needle will swing in one direction or another. Then you need to connect a voltmeter to the winding WITH and do the same operation with breaking the battery contacts. If necessary, change the polarity of the winding WITH(switching ends C1 and C2) you need to ensure that the voltmeter needle swings in the same direction, as in the case of the winding IN. The winding is checked in the same way. A- with a battery connected to the winding C or B.

As a result of all manipulations, the following should happen: when the battery contacts break from any of the windings, an electric potential of the same polarity should appear on the other 2 (the device needle swings in one direction). Now all that remains is to mark the terminals of one bundle as the beginning (A1, B1, C1), and the terminals of the other as the ends (A2, B2, C2) and connect them according to the required circuit - “triangle” or “star” (if the motor voltage is 220/127V ).

Retrieving missing ends. Perhaps the most difficult case is when the engine has a star connection of the windings, and there is no way to switch it to a delta (only three wires are brought into the distribution box - the beginning of the windings C1, C2, C3) (see figure below) . In this case, to connect the motor according to the "triangle" diagram, it is necessary to bring the missing ends of the windings C4, C5, C6 into the box.

To do this, gain access to the motor winding by removing the cover and possibly removing the rotor. The place of adhesion is found and released from insulation. The ends are separated and flexible stranded insulated wires are soldered to them. All connections are reliably insulated, the wires are secured with a strong thread to the winding and the ends are brought out to the terminal board of the electric motor. They determine whether the ends belong to the beginnings of the windings and connect them according to the “triangle” pattern, connecting the beginnings of some windings to the ends of others (C1 to C6, C2 to C4, C3 to C5). The job of bringing out missing ends requires some skill. The motor windings may contain not one, but several solders, which are not so easy to understand. Therefore, if you do not have the proper qualifications, you may have no choice but to connect a three-phase motor in a star configuration, accepting a significant loss of power.

Schemes for connecting a three-phase motor to a single-phase network

Delta connection. In the case of a household network, from the point of view of obtaining greater output power, the most appropriate is single-phase connection three-phase motors in a delta configuration. Moreover, their power can reach 70% of the nominal. Two contacts in the distribution box are connected directly to the wires of a single-phase network (220V), and the third is connected through a working capacitor Cp to any of the first two contacts or network wires.

Start-up support. A three-phase motor without a load can also be started from a working capacitor (more details below), but if the electric motor has some kind of load, it either will not start or will pick up speed very slowly. Then for quick start an additional starting capacitor Sp is required (calculation of the capacitor capacity is described below). The starting capacitors are turned on only while the engine is starting (2-3 seconds, until the speed reaches approximately 70% of the nominal), then the starting capacitor must be disconnected and discharged.

Connection three-phase electric motor into a single-phase network according to the "triangle" circuit with a starting capacitor Sp

It is convenient to start a three-phase motor using a special switch, one pair of contacts of which closes when the button is pressed. When it is released, some contacts open, while others remain on - until the "stop" button is pressed.

Reverse. The direction of rotation of the motor depends on which contact ("phase") the third phase winding is connected to.

The direction of rotation can be controlled by connecting the latter, through a capacitor, to a two-position toggle switch connected by its two contacts to the first and second windings. Depending on the position of the toggle switch, the engine will rotate in one direction or the other.

The figure below shows a circuit with a starting and running capacitor and a reverse button, allowing convenient control three-phase motor.

Star connection. A similar scheme for connecting a three-phase motor to a network with a voltage of 220V is used for electric motors whose windings are designed for a voltage of 220/127V.

The required capacity of working capacitors for operating a three-phase motor in a single-phase network depends on the connection diagram of the motor windings and other parameters. For a star connection, the capacitance is calculated using the formula:

For a triangle connection:

Where Cp is the capacitance of the working capacitor in microfarads, I is the current in A, U is the network voltage in V. The current is calculated by the formula:

I = P/(1.73 U n cosph)

Where P is the electric motor power kW; n - engine efficiency; cosф - power factor, 1.73 - coefficient characterizing the relationship between linear and phase currents. The efficiency and power factor are indicated in the data sheet and on the engine plate. Typically their value is in the range of 0.8-0.9.

In practice, the capacitance value of the working capacitor when connected in a triangle can be calculated using the simplified formula C = 70 Pn, where Pn - rated power electric motor in kW. According to this formula, for every 100 W of electric motor power, about 7 μF of working capacitor capacity is required.

The correct selection of capacitor capacity is checked by the results of engine operation. If its value is greater than required under given operating conditions, the engine will overheat. If the capacity is less than required, output power motor will be too low. It makes sense to select a capacitor for a three-phase motor, starting with a small capacitance and gradually increasing its value to the optimal one. If possible, it is better to select the capacitance by measuring the current in the wires connected to the network and to the working capacitor, for example, with a current clamp. The current value should be as close as possible. Measurements should be made in the mode in which the engine will operate.

When determining the starting capacity, we proceed, first of all, from the requirements for creating the necessary starting torque. Don't be confused starting capacity with capacity starting capacitor. In the above diagrams, the starting capacitance is equal to the sum of the capacitances of the working (Cp) and starting (Sp) capacitors.

If, due to operating conditions, the electric motor starts without load, then the starting capacitance is usually taken to be equal to the working capacitance, that is, a starting capacitor is not needed. In this case, the switching circuit is simplified and cheaper. To simplify this and, most importantly, reduce the cost of the circuit, it is possible to organize the possibility of disconnecting the load, for example, by making it possible to quickly and conveniently change the position of the engine to loosen the belt drive, or by making a pressure roller for the belt drive, for example, like the belt clutch of walk-behind tractors.

Starting under load requires the presence of additional capacity (Cn) connected while the engine is starting. An increase in the switchable capacitance leads to an increase in the starting torque, and at a certain value, the torque reaches its highest value. A further increase in capacitance leads to the opposite result: the starting torque begins to decrease.

Based on the condition of starting the engine under a load close to the rated load, the starting capacitance should be 2-3 times greater than the working capacitance, that is, if the capacity of the working capacitor is 80 µF, then the capacitance of the starting capacitor should be 80-160 µF, which will give the starting capacitance (the sum capacity of the working and starting capacitors) 160-240 µF. But if the engine has a small load when starting, the capacity of the starting capacitor may be less or, as stated above, it may not exist at all.

Starting capacitors operate for a short time (only a few seconds during the entire switching period). This allows you to use when starting the engine the cheapest launchers electrolytic capacitors, specifically designed for this purpose (http://www.platan.ru/cgi-bin/qweryv.pl/0w10609.html).

Note that for a motor connected to a single-phase network through a capacitor, operating without load, the winding fed through the capacitor carries a current 20-30% higher than the rated one. Therefore, if the engine is used in an underloaded mode, the capacity of the working capacitor should be reduced. But then, if the engine was started without a starting capacitor, the latter may be required.

It is better to use not one large capacitor, but several smaller ones, partly due to the possibility of selecting the optimal capacitance by connecting additional ones or disconnecting unnecessary ones; the latter can be used as starting ones. Required amount microfarads are collected by parallel connection of several capacitors, based on the fact that the total capacitance at parallel connection calculated using the formula: Ctot = C 1 + C 1 + ... + C n.

Metallized paper or film capacitors are usually used as workers (MBGO, MBG4, K75-12, K78-17 MBGP, KGB, MBGCh, BGT, SVV-60). The permissible voltage must be at least 1.5 times the mains voltage.

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Today, asynchronous electric motors are popular due to their reliability, excellent performance and comparatively 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".

However combined scheme cannot be used if it is necessary to reduce the starting current, but at the same time a large torque is required. In this case, you should use an electric motor with a wound rotor equipped with a rheostat.

If we talk about the advantages of combining two connection methods, then we can note two:

Thanks to the smooth start, the service life is increased.
You can create two power levels for the unit.

Today, the most widely used electric motors are those designed to operate in 220 and 380 volt networks. The choice of connection diagram depends on this. Thus, it is recommended to use “delta” at a voltage of 220 V, and “star” at 380 V.

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 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".

However, a combined circuit cannot be used if it is necessary to reduce the starting current, but at the same time a large torque is required. In this case, you should use an electric motor with a wound rotor equipped with a rheostat.

If we talk about the advantages of combining two connection methods, then we can note two:

Thanks to the smooth start, the service life is increased.
You can create two power levels for the unit.

The widespread use of asynchronous electric motors connected in star and delta is known. These connections are available in every production; three-phase motors, generators, and transformers are connected as a star. "Triangle" is used mainly in engines with a long starting and operating cycle. It is also used in transformer connection diagrams, mainly where there is a symmetrical load.

The joint inclusion of both “star” and “delta” connections is used. when starting powerful electric motors. The start begins with a “star”, followed by switching by the relay circuit to a “triangle” circuit when the speed is reached. The engine continues to operate for a long time on the “triangle”.

Connecting circuits according to the "triangle" scheme

This connection is called a delta connection only when both ends of the windings are connected to each other. It is necessary to connect in a triangle when the mains voltage is suitable for such a consumer. Starting electric motors according to the “triangle” scheme is expressed large values inrush 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 declared in the power consumer passport, which is sometimes necessary.

The "Triangle" scheme is divided into "open" and "open". The difference between the two types is that an open triangle is a connection by a triangle with one point broken to the consumer. And the open one differs in that one winding is replaced by the consumer.

Connection of three-phase circuits according to the "star" scheme

The next connection is called a “star” if the ends of the windings are connected into one node, which has the name “neutral point”, the second name is “neutral”. Connecting an engine using this type will reduce the engine power. Connecting these two types determines at what voltage your windings will operate. Typically, the voltage on the motor is marked for a specific connection method, as well as appropriate speed and power.

For example: let’s take a 380 by 220 network, star connection, consumer voltage 220V. If you connect it according to a triangle circuit, the voltage on the windings will be 380, based on the voltage, the power P=UI will become greater. (In practice, a regular engine will burn out because the voltage will become 380V. However, 220/127 for of this engine triangle normal mode, star operation with power loss).

In the case of “star” operation of consumers, it is very important that there is no “phase imbalance”. If the neutral has, for example: bad contact, then a difference will arise - load asymmetry, in which one consumer will be under some voltage. This potential difference depends on the load distribution at the moment when the neutral wire burns out. Because of this potential difference, consumers in apartments found themselves under voltage, which could cause them to burn out. old TV or the refrigerator fails. I think many people know such stories in the past.

Special cases of application of the described connection diagrams

Application of star switching circuits:

Implementation of triangle connection schemes:

Many questions arise about the difference between a star and a triangle connection. The difference, in my opinion, lies in the constructive organization of the supply network. For an engine, the first method is preferable in those circuits and mechanisms where there is frequent operation. WITH It should be remembered that with such a connection it is necessary to take into account the supply voltage, usually 380V. In the second case, taking into account the supply voltage is the presence of 220V. With this connection, the motor has high starting currents, which wears it out much faster.

The triangle connection is rarely found in industry. More often, low-power engines operate in a star pattern. 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 motors are used in a metallurgical plant in a “star” configuration. Presumably, to prevent engine wear and tear. Motors are used in aggressive environment, That's why three degrees of protection are used: first - fuses for each phase, the fuse must be semiconductor (it burns out more quickly and does not allow the windings to heat up); the second is a circuit breaker, which, as a rule, trips in extremely rare cases unless the fuse is blown; The third protection is based on temperature. The temperature sensor is connected via a relay low voltage, which, when the sensor is triggered, breaks the relay in the power supply circuit of the windings.

When you move to a new home, you start life with clean slate. Gradually you inspect and master everything, turn on the electrical equipment, and don’t even think about what danger may lie in wait for you, because the sockets may not be grounded.

This is a common problem in secondary homes, especially in older homes with two-wire wiring. Soviet sockets were not grounded, and many continue to use them.

But times change, as do security requirements. Now that large quantity electrical equipment creates more high load on the network, outdated sockets have become dangerous.

03.07.2018

Absolute called total pressure created by the environment; barometric- the pressure produced by the weight of the air column of the atmosphere. Overpressure represents the difference between absolute and barometric pressure: P=P a -P b

Underpressure(P p) is the difference between barometric and absolute pressure: P p = P b - P a. Deep rarefaction is called vacuum.

Since January 1, 1980, the basic unit of pressure has been used - pascal (Pa = 1 N/m2); multiple units are kilopascal (1 kPa = 1000 Pa) and megapascal (1 MPa = 1000 Pa).

29.05.2018

Type KS consist of separate easily removable modules, included in the circuit using plug connectors. If the device malfunctions, you need to replace the modules one by one, detect the faulty one, establish the cause and eliminate it. Possible faults and ways to eliminate them are indicated in table. 1.

IN Maintenance automatic measuring instruments includes changing the chart tape, filling the ink bottle writing device, cleaning or changing the pen and capillary, lubricating and cleaning parts of the mechanism, replacing the spring with the contacts of the slider, cable, motors, amplifier and stabilized power source.

The chart tape is changed as follows. Filming tape mechanism, install a roll of clean tape between the axle shafts and put it on the spring-loaded axle shaft, then, pressing it against the wall of the bracket, put the roll on the second axle shaft. In this case, the flat spring should be pressed against the roll. Then the tape is thrown over the drive drum, putting the perforations on the lugs, and passed between the ruler and the bracket of the tape drive mechanism. Wind up the return spring by turning the sleeve clockwise 15-20 turns and holding it with your hand so that the spring does not unwind. Secure the end of the tape to the sleeve by winding two layers of paper. The sleeve is released, and the wound spring, unwinding, provides tension to the tape. After loading the paper, the tape drive mechanism is installed in place.