First, consider the difference between 380 and 220 volt devices. So obvious, how incomprehensible to the uninitiated. They got used to it, each home appliance is connected with two wires, one is the phase, the second is the circuit earth. Most of the equipment is grounded. If it concerns single-phase motors, it is done in case of breakdown of the winding-housing. Phase appears on the casing - good enough. Consider ways to connect electric motors according to type, let's start with the number of phases - one or three.
Three-phase and single-phase motors
Motor connection schemes star, triangle
Anticipating the discussion of the connection of the motor star / triangle, let's recite a theory. Three-phase and single-phase motors are sometimes supplied with three wires of connection. Throw to go far. Take the following two cases:
- The three-phase motor has an internal switching of the windings by the star circuit. The poles are equipped with one common point. Three phases are connected to opposite ends of the windings. Coils are absolutely identical, identical. Inside a rotating field is created, due to which the shaft moves. The rotor is represented by a silumin drum with copper streaks. The current is not supplied, the magnetic poles form by induced currents. Captured by the rotating field of the rotor, the movement begins. A feature of the design is the impossibility( without special measures) of connecting the 230-volt network. It would be necessary to connect the windings with a triangle pattern, it is impossible to make. Of course, the stator can be opened, find a common point, make three taps, breaking the contacts between the coils. The second feature of the engine is the absence of a neutral wire. It confuses many things - where does the current go? The charges move through the wires between the phases. The law of electrical engineering says: to connect the three phases to the load it is not necessary to have a common wire, if the consumption of the three branches is the same. Otherwise, you will need to provide a neutral. Life example: let's say you need to connect a 380 volt electric kettle. Marasmus? Each phase with an amplitude of 230 volts, the workers want boiling water - it is impossible to refuse. We take one of the phases, the other output of the plug is hung on the neutral. Consider that the phases within the same consumer must be shared equally( roughly speaking, give the teapot of each line), otherwise the negative consequences will affect the supply transformer of the substation.
Electrical switching of the motor
- A single-phase motor can have three leads. Grounding with nothing, is separate eye on the body. As for the three conclusions, feed the start( or capacitor), the working winding. One wire is common, there will be a circuit earth. Without this, the engine will refuse to work. True, a three-phase motor is easier? Because use production. As for the connection of a single-phase motor, one coil usually has more resistance. The difference is significant, double shows the starting winding. Resistance of a higher nominal. It is necessary to hang a capacitor in parallel( the capacitance is determined, for example, by the minimum current consumed), when the shaft unwinds, the circuit terminates. Otherwise, after a period of time, the starting winding will fail due to excessive overheating. If the engine is capacitor( bifilar), the circuit with the capacitor runs continuously. The normal mode, due to the phase shift created by the reactive element, forms the rotating field of the stator of the desired shape.
So, there are two engines, similar in appearance, you need to connect in a different way. An important part of the body is the wiring diagram of the electric motor. Located on the nameplate, stamped on the casing. It becomes clear how many phases the motor is designed for, how to cut it into a chain. Information is missing - try to modify the defect with their own hands. You will need a Chinese tester.
In a three-phase motor, three contacts in pairs will give the same resistance equal to twice the value of the winding rating. Motor 230 volt measurement results will be unequal:
- The largest tester indicator between phase ends. The voltage of 220 volts is fed directly to one, to the other through a capacitor. Capacity is highly dependent on power, speed of rotation of the shaft. The parameter defines the average shaft load in the operating mode.
- The smallest value is formed between the ends of the working winding.
- The third denomination occupies an intermediate position. The sum with the resistance of the working winding is equal to the first item in the list.
We connect the neutral between the windings, diverts the current unbalance. The thickness of the wiring is half that of the phases. The method of disconnecting at the right time starting winding uses start-protective relays. Manually not controlled.
The issue of site acquisition is closely related to the use of special directories. Alien start-up relay with this type of electric motor is absolutely impossible to use. Chances of incorrect operation, the device failure. Almost craftsmen manually break the chain. The way is wrong, has the right to exist.
Add that the loss of one phase can adversely affect some types of engines. Experimenting with the unit, realizing the connection of the star-delta engine, try to avoid situations. It is customary to carry out start-up with special protective automats, which cut the power supply in the event of danger.
Synchronous, asynchronous, collector motors
In addition to the number of phases, we see a constructive feature. From the point of view of the consumer, the moment is paramount. Collector motors are used primarily by home appliances. Replace asynchronous with the same parameters, unprofitable. The collector engine turns out much smaller( but overheats more strongly).It is important to determine the type. Although by and large three-phase electric motors of asynchronous type are the dominant link in agricultural, garage and other applications. The issue of nutrition is discussed separately.
Let's discuss three types of engines:
. Electric motor.
- . The manifolds are equipped with two to four leads. The latter makes it possible to reverse. Change the polarity of the stator, rotor. Collector motors differ in the ability to work from AC and DC.In the latter case, the characteristics are optimal. It becomes possible due to constantly switching working windings of the rotor( collector section).The stator field is constant. The main thing is to present the desired polarity. The wiring diagram of a DC motor resembles an alternating one. The speed of rotation of the shaft is regulated by the amplitude of the supply voltage. Either the divider formed by the power key is taken, or part of the sinewave cycle is cut off. The effect is similar: the effective value of the voltage drops.
- Asynchronous motors in fact dominant in the industry. The reverse is formed by a change in the polarity of switching on the starting winding of single-phase motors, by switching the three-phase phase sequence. The change in speed is implemented in a similar way. The variation of the amplitude of the supply voltage. Asynchronous motors have poor adaptability to change speeds. Another reason for the rare use in household appliances. It is time to say: the collector motors are usually designed for one phase, asynchronous feed voltage of 380 volts. The alignment of forces is formed due to the corresponding switching of the windings. In practice, it is realized by connecting the electric motor with a triangle, a star. Can reproduce the rotating field inside the stator. Why the connection scheme of the asynchronous star motor is unsuitable for 230 volts. It is necessary to create phase shifts, it becomes possible for a triangle pattern. A voltage of 230 volts is applied to one winding, the second is shifted by a capacitor by 90 degrees, and the third produces a difference, which is changed according to the necessary law. Far from ideal: star and triangle motor connections are unequal.
Synchronous motor
- Synchronous motors are called for the rotation of the shaft according to the law of change of the supply voltage. In household appliances, industry is rarely used, excluding the area of servo drives. Asynchronous motors are named for the speed of rotation of the shaft, which differs from the frequency of the supply voltage. The shaft slips, the effect is used to regulate the momentum. Synchronous motors stand out, use is limited. What is so special about. Good efficiency. The rotor is performed according to the circuit with a current collector, devoid of brushes, there is no need for separation of the surface by segments( the current flows continuously).It seems to make it possible to use where the collector motors succumb. Some problems are noticed. Three-phase synchronous motor cannot be started by rotating the stator phases. The shaft due to the inertia can not be field. It is necessary to apply the delights of promotion. Subject interesting. The rotor of the synchronous motor is powered by direct current, the winding - one or three phases, determined by the type of motor.
Let's understand the difference between synchronous motors and asynchronous motors. The literature question is carefully circumvented. The answer lies on the surface: the stator field of a synchronous motor is much stronger, the rotor is magnetized( or phase), so the rotation does not slip. The synchronism of rotation of the shaft to the supply voltage. The frequency is determined by the number of poles. To solve problems with the start( see above), such techniques are used, for example:
- A shaft of a synchronous motor with a drum equipped with a squirrel cage is cut when it starts through a rheostat. Formed field, as in an asynchronous motor, exciting the shaft, serves as a starting lever. Turns are recruited - the chain is broken. A rheostat needs to repay induction currents. Choose a resistance of 7-8 more than the nominal "squirrel cage".
- Sometimes you notice on the rotor of a synchronous motor - do not believe it - the collector. The start is performed by the brushes, then they are switched off from work.
And if the connection of the asynchronous star-delta motor is eroded in full, synchronous motors are little discussed. Meet infrequently.
