Industrial synchronous motors are electromagnetically excited from an independent DC source. As such sources are used: DC generators (exciters), which can be located on the same shaft with a synchronous motor (Fig. 7.6.6) or driven by a separate motor (Fig. 7.6, i); thyristor controlled rectifiers that can be powered from an industrial network (Fig.7.6, v), or from a special alternator located on the same shaft with a synchronous motor. In the latter case (Fig. 7.6, d), semiconductor rectifiers are located on the rotor of a synchronous machine (a system with rotating rectifiers), therefore, no brushes and rings are required to supply current to the field winding, i.e. synchronous machine becomes contactless.

During acceleration, when the motor is in asynchronous mode, the exciter can be connected to the rotor winding when the exciter voltage is removed. (circuit with a deafly connected exciter), and can be disconnected from the excitation winding by the KM contactor (see diagrams in Fig. 7.1 and 7.6). In the latter case, the field winding is shorted to resistance or short-circuited. It is impossible to leave the ends of the excitation winding open during acceleration, since a significant slip EMF is induced in the winding with large slips.

When using a thyristor converter or rotating rectifiers as an exciter, the excitation winding is short-circuited through the shunt thyristors during start-up.

Rice.a- from a separate motor-generator; 6 - from a generator located on the shaft of a synchronous motor; v- from a thyristor exciter; g - from the built-in generator

Consider the circuit in Figure 7.6, c. When starting the motor in asynchronous mode, the voltage of the thyristor converter UD is equal to zero. In the excitation winding, a variable slip EMF is induced, under the action of which through zener diodes VD auxiliary thyristors open VS, and the excitation winding closes to the discharge resistance R. When the motor reaches the subsynchronous speed, the slip EMF becomes small, the zener diodes turn off, and the thyristors VS the discharge resistance is turned off, after which a direct current is supplied to the excitation winding from the converter UD.

In recent years, pathogens built into the design of a synchronous machine have become widespread (see Fig. 7.6, d). The exciter consists of a synchronous generator G, the rotor of which is located on the shaft of a synchronous motor D, an uncontrolled rectifier, auxiliary thyristors VS and discharge resistances R2 and R3, also located on the shaft of a synchronous motor. The excitation current is controlled by changing the excitation current of the generator G. When the subsynchronous speed is reached, the circuits shunting the excitation winding open, and a direct current is supplied to the winding, after which the motor is pulled into synchronism, its speed reaches synchronous, and then it operates in a synchronous mode.

The regulation of the excitation current of the motor during operation in the synchronous mode is carried out, as a rule, by the excitation ACS. It has two main functions. The first is to ensure stable synchronous operation. With load surges or with a decrease in the supply voltage, the excitation ACS boosts (increases) the excitation current, thereby increasing the maximum motor torque in the synchronous mode (see Fig. 7.4). The second is the implementation of automatic control of reactive power circulating in the stator circuit of the engine.

The block diagram of the excitation current is usually built in two-circuit (Fig. 7.7). The internal field current loop serves to stabilize the specified field current. The field current regulator p () is taken proportional or proportional-integral. Ensuring that the given φ is maintained constant is achieved by generating a signal for setting the excitation current with positive feedback according to the value of the actual φ of the stator circuits:

If the excitation current corresponding to U B is insufficient to obtain a given power factor at a given load, then the compounding feedback increases the excitation current. An increase in the coefficient increases the accuracy of maintaining a given φ, but causes fluctuations in the stator current when a load is applied. To reduce the oscillation of the stator current, the circuit provides flexible feedback on the effective value of the stator current. Flexible feedback form as a differentiating link with a filter.

On the rotor of the synchronous generator there is an MDS source (inductor), which creates a magnetic field in the generator. With the help of a drive motor (PD), the rotor of the generator is driven into rotation with a synchronous frequency n 1 . In this case, the magnetic field of the rotor also rotates and, interlocking with the stator winding, induces an EMF in it.

The main way to excite synchronous machines is electromagnetic excitation, the essence of which is that an excitation winding is located at the rotor poles. When a direct current passes through this winding, an excitation MDS arises, which induces a magnetic field in the magnetic system of the machine.

Until recently, special independent excitation direct current generators, called exciters B (Fig. 82, a), the excitation winding of which (OB) received direct current power from another generator (parallel excitation), called the exciter (PV). The rotor of the synchronous machine and the armatures of the exciter and the exciter are located on a common shaft and rotate simultaneously. In this case, the current enters the excitation winding of the synchronous machine through slip rings and brushes. To regulate the excitation current, adjusting rheostats are used, which are included in the excitation circuit of the exciter ( r 1) and the exciter ( r 2).

In synchronous generators of medium and high power, the process of controlling the excitation current is automated.

In synchronous generators of high power - turbogenerators - sometimes inductor-type alternators are used as the exciter. At the output of such a generator, a semiconductor rectifier is turned on. In this case, the excitation current of the synchronous generator is adjusted by changing the excitation of the inductor generator.

Applied in synchronous generators contactless electromagnetic excitation system, in which the synchronous generator does not have slip rings on the rotor.

In this case, an alternating current generator is also used as an exciter (Fig. 82, b), in which the winding 2, in which the EMF (armature winding) is induced, is located on the rotor, and the excitation winding 1 located on the stator. As a result, the exciter armature winding and the excitation winding of the synchronous machine turn out to be rotating, and their electrical connection is carried out directly, without slip rings and brushes. But since the exciter is an alternating current generator, and the excitation winding must be supplied with direct current, a semiconductor converter is turned on at the output of the exciter armature winding 3, fixed on the shaft of a synchronous machine and rotating together with the excitation winding of the synchronous machine and the armature winding of the exciter. DC power supply to the field winding 1 the exciter is carried out from the exciter (PV) - a direct current generator.

Rice. 82. Contact (a) and contactless (b) systems of electromagnetic

excitation of synchronous generators

The absence of sliding contacts in the excitation circuit of a synchronous machine makes it possible to increase its operational reliability and increase efficiency.

In synchronous generators, including hydrogenerators, the principle of self-excitation(Fig. 83, a), when the AC energy required for excitation is taken from the stator winding of the synchronous generator and is converted into DC energy through a step-down transformer and a rectifier semiconductor converter (PC). The principle of self-excitation is based on the fact that the initial excitation of the generator occurs due to the residual magnetism of the machine's magnetic circuit.

Rice. 83. The principle of self-excitation of synchronous generators

In fig. 19.2, b presents a structural circuit of an automatic self-excitation system a synchronous generator (SG) with a rectifier transformer (VT) and a thyristor converter (TP), through which AC electricity from the SG stator circuit, after being converted into direct current, is supplied to the excitation winding. The thyristor converter is controlled by an automatic excitation regulator ARV, the input of which receives voltage signals at the SG output (through the VT voltage transformer) and the SG load current (from the CT current transformer). The circuit contains a protection block BZ, which protects the excitation winding and thyristor converter TP from overvoltage and current overload.

In modern synchronous motors for excitation, they use thyristor exciters, connected to the AC network and carrying out automatic control excitation current in all kinds of engine operating modes, including transient ones. This method of excitation is the most reliable and economical, since the efficiency of thyristor exciters is higher than that of DC generators. The industry produces thyristor exciters for various excitation voltages with a permissible constant current of 320 A.

The most widespread in modern series of synchronous motors are excitatory thyristor devices of the types TE8-320 / 48 (excitation voltage 48 V) and TE8-320 / 75 (excitation voltage 75 V).

The excitation power is typically 0.2 to 5% of the machine's net power (the lower value applies to high power machines).

In synchronous machines of low power, the principle excitation by permanent magnets, when there are permanent magnets on the rotor of the machine. This method of excitation makes it possible to rid the machine of the excitation winding. As a result, the design of the machine is simplified, more economical and more reliable. However, due to the scarcity of materials for the manufacture of permanent magnets with a large supply of magnetic energy and the complexity of their processing, the use of permanent magnet excitation is limited only to machines with a capacity of no more than a few kilowatts.

Control questions

1. What are the ways to excite synchronous machines?

2. Explain the purpose of the thyristor converter in the self-excitation system of the synchronous generator?

3. Explain the design of salient-pole and implicit-pole rotors?

4. Explain the structure of the SDN2 series synchronous motor?

5. What methods of pole fixing are used in synchronous salient-pole machines?

6. What is the reason for the uneven air gap in the synchronous machine?

Structural diagram of the machine. Synchronous machines are made with a fixed or rotating armature. High-power machines for the convenience of removing electrical energy from the stator or supplying it are performed with a fixed armature (Fig. 1.2, a)

Since the excitation power is low compared with the power removed from the armature (0.3-3%), the supply of direct current to the excitation winding using two rings does not cause any particular difficulties. Synchronous machines of low power are performed with both a fixed and a rotating armature.

Rice. 1.2 - Structural diagram of a synchronous machine

with a fixed and rotating anchor:

1 - armature, 2 - armature winding, 3 - inductor poles,

4 - excitation winding, 5 - rings and brushes

Synchronous, machine with a rotating armature and a fixed inductor (Fig. 1.2, b) are called reversed.

Rice. 1.3 - Rotors synchronous salient(a) and implicit(6) machines:

1 - rotor core, 2 - excitation winding

Rotor design

Rotor design. In a machine with a fixed armature, two rotor designs are used: salient pole - with pronounced poles (Fig. 1.3, a) and implicit pole - with implicitly expressed poles (Fig. 1.3, b). The salient pole rotor is usually used in machines with four and a large number poles. In this case, the excitation winding is made in the form of rectangular cylindrical coils, which are placed on the pole cores and reinforced with pole pieces. The rotor, pole cores and pole pieces are made of steel. Two- and four-pole machines of high power, operating at a rotor speed of 1500 and 3000 rpm, are made, as a rule, with an implicit-pole rotor. The use of a salient-pole rotor in them is impossible due to the conditions of ensuring the necessary mechanical strength of the fastening of the poles and the field winding. The excitation winding in such a machine is placed in the slots of the rotor core, made of massive steel forging, and reinforced with non-magnetic wedges. The frontal parts of the winding, which are subject to significant centrifugal forces, are fastened using massive steel bands. To obtain a distribution of magnetic induction close to sinusoidal, the excitation winding is placed in slots that occupy 2/3 of each pole division.

Rice. 1.4 - Design of a salient pole machine:

1 - housing, 2 - stator core, 3 - stator winding, 4 - rotor,

5 - fan, 6 - stator winding leads, 7 - slip rings,

8 - brushes, 9 - pathogen

In fig. 1-4 shows the structure of a salient-pole synchronous machine. The stator core is assembled from insulated sheets of electrical steel and a three-phase armature winding is located on it. The excitation winding is located on the rotor.

Pole shoes in salient pole machines are usually shaped so that the air gap between the pole piece and the stator is minimum under the pole center and maximum at its edges, so that the distribution curve of the induction in the air gap approaches a sinusoid.

In synchronous motors with a salient pole rotor, rods are placed in the pole pieces starting winding(Fig. 1-5), made of a material with increased resistivity (brass, etc.). The same winding (of the "squirrel cage" type), consisting of copper rods, is used in synchronous generators; they call her sedative or damper winding, since it provides fast damping of rotor oscillations arising during transient modes of operation of a synchronous machine. If a synchronous machine is made with massive poles, then eddy currents arise in these poles during start-up and transient modes, the action of which is equivalent to the action of the current in short-circuited windings. The damping of rotor oscillations during transient processes is provided in this case by eddy currents, which are closed in a massive rotor.

Synchronous machine excitation

Excitation of a synchronous machine. Depending on the method of supplying the excitation winding, a distinction is made between systems of independent excitation and self-excitation. With independent excitation, a direct current generator (exciter) installed on the rotor shaft of a synchronous machine serves as a source for powering the excitation winding (Fig. 1.6, a), or a separate auxiliary generator driven by a synchronous or asynchronous motor.

With self-excitation, the excitation winding is powered from the armature winding through a controlled or uncontrolled rectifier - semiconductor or ionic (Fig. 1.6, b). The power required for excitation is small and amounts to 0.3-3% of the power of the synchronous machine.

In powerful generators, sometimes, in addition to the pathogen, an exciter is used - small generator direct current, serving to excite the main pathogen. In this case, a synchronous generator together with a semiconductor rectifier can be used as the main exciter. At present, the power supply of the excitation winding through a semiconductor rectifier assembled on diodes or thyristors is increasingly used both in engines and generators of small and medium power, and in powerful turbo- and hydrogenerators (thyristor excitation system). Excitation current regulation I in is carried out automatically by special excitation regulators, although in low-power machines, regulation is also used manually by a rheostat included in the excitation winding circuit.

V recent times in powerful synchronous generators, the so-called brushless excitation system began to be used (Fig. 8-6, v). With this system, a synchronous generator is used as an exciter, in which the armature winding is located on the rotor, and the rectifier is mounted directly on the shaft.

Rice. 1.5 - Placement of the starting winding in synchronous motors:

1-rotor poles, 2-short-circuiting rings, 3 - squirrel cage rods,

4 - pole lugs

The exciter field winding is powered from the exciter via a voltage regulator. With this method of excitation, there are no sliding contacts in the power supply circuit of the excitation winding of the generator, which significantly increases the reliability of the excitation system. If it is necessary to force the excitation of the generator, the exciter voltage is increased and the output voltage of the rectifier is increased.

Synchronous machines- these are machines in which the rotor speed coincides with the rotational speed magnetic field stator. The main parts of the synchronous machines are armature and inductor. The most common design is that the armature is located on the stator, and an inductor is located on the rotor separated from it by an air gap. The anchor is one or more alternating current windings. In motors, the currents supplied to the armature create a rotating magnetic field, which is coupled with the inductor's field, and thus energy is converted. In generators, the armature reaction field is created by alternating currents induced in the armature winding from the inductor. The inductor consists of poles- DC electromagnets or permanent magnets. Inductors of synchronous machines have two different designs: salient pole or implicit pole. An explicit pole machine differs in that the poles are pronounced and have a structure similar to the poles of a DC machine. With an implicit-pole design, the excitation winding fits into the grooves of the inductor core, it is very similar to the winding of the rotors of induction machines with a phase rotor, with the only difference that a place is left between the poles that is not filled with conductors (the so-called large tooth). Non-salient pole designs are used in high-speed machines to reduce mechanical stress on the poles. To reduce magnetic resistance I use ferromagnetic rotor and stator cores. Basically, they are a laminated structure made of electrical steel. Any synchronous machine needs an excitation process- guidance of a magnetic field in it. The main method of excitation of synchronous machines is electromagnetic excitation, the essence of which is that an excitation winding is located at the rotor poles. When a direct current passes through this winding, an excitation MDS arises, which induces a magnetic field in the magnetic system of the machine. To power the field winding, special DC generators of independent excitation are used, called exciters B , the excitation winding of which (OB) received direct current power from another generator (parallel excitation), called the exciter (PV). The rotor of the synchronous machine and the armatures of the exciter and the exciter are located on a common shaft and rotate simultaneously. In this case, the current enters the excitation winding of the synchronous machine through slip rings and brushes. To regulate the excitation current, adjusting rheostats are used, which are included in the excitation circuit of the exciter (r 1) and the exciter (r 2).

A non-contact electromagnetic excitation system has been used in synchronous generators, in which the synchronous generator does not have slip rings on the rotor.

As an exciter, in this case, an alternating current generator is used, in which the winding in which the EMF is induced (armature winding) is located on the rotor, and the excitation winding is located on the stator. As a result, the armature winding of the exciter and the excitation winding of the synchronous machine turn out to be rotating, and their electrical connection is carried out directly, without slip rings and brushes. But since the exciter is an alternating current generator, and the excitation winding must be supplied with direct current, a semiconductor converter is turned on at the output of the exciter armature winding, fixed on the shaft of the synchronous machine and rotating together with the excitation winding of the synchronous machine and the exciter armature winding. DC power supply to the exciter field winding is carried out from the exciter (PF) - a direct current generator. In synchronous generators, including the number of hydrogenerators, the principle of self-excitation has become widespread, when the alternating current energy required for excitation is taken from the stator winding of the synchronous generator and is converted into direct current energy through a step-down transformer and a rectifier semiconductor converter (PP). The principle of self-excitation is based on the fact that the initial excitation of the generator occurs due to the residual magnetism of the machine's magnetic circuit.

Question 58. Characteristics of a synchronous generator: no-load, short-circuit, external characteristic, regulation, load, angular characteristics. Their appearance and analysis. No-load characteristic of a synchronous generator... It has straight and curved sections, which is associated with the saturation of the steel of the magnetic system. Short-circuit characteristic: This is the dependence of the stator current on the excitation current with closed terminals of the stator winding and a constant speed. The machine will work in a straight line load characteristic, and the characteristics of the short-circuit. will be straightforward. External characteristic... It is the dependence of the voltage at the terminals of the stator winding on the load current: U 1 = f(I 1) at I in = const; cos φ 1, = const; n 1 = n nom = const. Adjustment characteristic... It shows how to change the excitation current of the generator with changes in the load so that the voltage at the terminals of the generator remains invariably equal to the nominal: I in = f(I 1) at U 1 = U 1nom = const; n 1 = n nom = const and cos φ 1 = const. ++++ Figures

Question 57. Magnetic field and the reaction of the armature of a synchronous machine. Equation of voltages of a synchronous generator. Vector diagrams of a synchronous generator for various types of loads. The impact of the MDS of the stator (armature) winding on the MDS of the field winding is called the armature response. The armature reaction affects the working properties of a synchronous machine, since a change in the magnetic field in the machine is accompanied by a change in the EMF induced in the stator winding, and therefore, a change in other quantities associated with this EMF. The influence of the armature reaction on the operation of a synchronous machine depends on the value and nature of the load. Synchronous generators, as a rule, operate on a mixed load (active-inductive or active-capacitive). But in order to clarify the question of the influence of the armature response on the operation of a synchronous machine, it is advisable to consider the cases of generator operation with loads of a limiting nature, namely: active, inductive and capacitive. With active load current in the stator winding is in phase with its EMF... This means that the maximum will correspond to the maximum current. Having shown the direction of the magnetic fluxes of the excitation and stator windings according to the "gimbal" rule, we see that the stator flux Ф is directed perpendicular to the excitation flux Фо, that is, there is a transverse armature reaction. In a synchronous machine, the lateral reaction of the armature leads to the same consequences as in a DC machine, the resulting field of the machine is distorted. The magnetic field is weakened under the running edge of the pole and amplified under the running down edge of the pole. Since the field gain is limited by the saturation of the steel and the attenuation is not limited, the resulting magnetic flux of the machine is reduced. This leads to a decrease in the EMF of the machine. With inductive load the stator current lags behind the EMF in phase by 90 °. Therefore, when the stator current reaches its maximum, the rotor will have time to turn 90 ° and the stator flux Ф г is directed along the axis of the rotor pole opposite to the main flux Ф - Thus, the stator flux with an inductive load weakens the machine field, and the armature reaction has a longitudinal demagnetizing effect. With capacitive load That is, the stator current is ahead of the EMF by 90 °, and the current will be maximum when the rotor has not yet turned to the vertical position by 90 °, and the fluxes of the stator and the field winding will coincide. In this case, the magnetic field of the machine increases, the reaction of the armature is longitudinally magnetized.

Question 60. Parallel operation of synchronous generators. Necessity and conditions for parallel operation of synchronous generators. Methods for connecting synchronous generators for parallel operation. The use of several parallel-connected synchronous generators instead of one generator of total power is necessary to ensure uninterrupted power supply in the event of an accident in any generator or disconnecting it for repair. To turn on a synchronous generator for parallel operation, the following conditions must be met: 1. The voltage of the connected machine must be equal to the voltage of the mains or the running machine. 2. The frequency of the connected generator must be equal to the mains frequency. 3. The voltages of all phases of the connected machine must be opposite in phase to the voltages of the corresponding phases of the mains or running machine. 4. To connect a three-phase synchronous generator for parallel operation, it is also necessary to ensure the same phase sequence of the connected machine and the network. Bringing the generator to a state that satisfies all the specified conditions is called synchronization. Failure to comply with any of the synchronization conditions leads to the appearance of large equalizing currents in the stator winding, an excessive value of which can cause an accident. Connect the generator to the network with parallel operating generators can be either accurate synchronization method, or self-synchronization method Precise synchronization method... The essence of this method is that, before connecting the generator to the network, it is brought into a state that satisfies all of the above conditions. The moment these conditions are met, that is, the moment of synchronization, is determined by a device called a synchroscope. Self-Synchronization Method... The rotor of the unexcited generator is driven into rotation by the prime mover to a rotation frequency that differs from the synchronous one by no more than 2-5%, then the generator is connected to the network. In order to avoid overvoltages in the rotor winding at the moment the generator is connected to the network, it is closed to some active resistance. Since at the moment the generator is connected to the network, its EMF is zero (the generator is not excited), then under the action of the network voltage in the stator winding, a sharp current rush is observed that exceeds the rated value of the generator current. After switching on the stator winding, the excitation winding is connected to the network to a direct current source and the synchronous generator, under the influence of an electromagnetic moment acting on its rotor, is drawn into synchronism, i.e., the rotor speed becomes synchronous. In this case, the stator current decreases rapidly.

Question 62. Synchronous machines for special purposes. Reactive synchronous, hysteresis, stepper motors. Purpose, device and principle of operation. The jet engine is salient pole synchronous machine without excitation winding. The flow of the engine and its torque is created by p.m. from. armature reactions, hence the name - jet engine. The motor torque M d arises due to the additional power R d, which occurs due to the unequal conductivity of the rotor along the axes d and q. The most favorable ratio x q / x d can be considered a value close to 0.5. Jet engines do not have an initial starting torque. Therefore, their rotors are equipped with a squirrel-cage starting winding. With synchronous rotation, the short-circuited winding is a damping winding that dampens rotor vibrations. Lack of jet engines- low maximum torque, power factor (cosφ = 0.5) and efficiency. For motors with a power of several tens of watts η = 35 ÷ 40%, and for motors with a power of several watts η<25%. К достоинству реактивных синхронных двигателей следует отнести отсутствие колебаний ротора и высокую надежность работы.Stepper motors.To convert control pulses to a given angle of rotation, synchronous motors are used, in which the field does not rotate uniformly, but when a signal is applied, it rotates abruptly. These motors are called stepping motors. On the stator, the stepper motors have two(sometimes three) spatially shifted windings, which can be lumped or distributed. The rotor of motors always has an explicit design. Stepper motors are divided into active rotor motors (with field winding or permanent magnets) and reluctance motors (without excitation). The stepper motor works as follows. The stator winding (or stator combination) is supplied with direct current. In this case, the rotor poles are installed against the excited stator poles, through the windings of which the current flows. When direct current is applied to the other stator windings, the rotor rotates one step to a position in which its poles are set against the next energized stator poles. Each time the DC current is switched in the control windings, the rotor of the motor rotates one step. Stepper motors have the following requirements: reliability in operation, speed, small step, inadmissibility of accumulation of errors with an increase in the number of steps, absence of free oscillations when working out a step, the minimum number of control windings. A hysteresis motor is a synchronous motor, the torque of which is created due to the phenomenon of hysteresis during magnetization reversal of the ferromagnetic material of the rotor. The stator of a hysteresis motor is made similar to the stator of an induction motor: it has a winding that creates a rotating magnetic field (three-phase, two-phase with a permanently switched on capacitor, concentrated with a shaded pole, etc.). The rotor of the engine is made made of magnetically hard material and has no winding. The torque of the hysteresis motor arises due to the strongly pronounced hysteresis of the rotor material. The essence of hysteresis is that when the magnetic field external to the rotor changes (rotates), elementary magnets are set (rotated) in the direction of the field with some lag due to molecular friction forces. turning the stator winding into an alternating current network, a rotating magnetic field is formed in the machine; the induced rotor poles rotate at the same frequency as the stator poles. In the absence of hysteresis, the rotor poles are located exactly under the stator poles:

Question 61. Synchronous motors. Basic information and principle of operation. Synchronous motors start. Working and U-shaped characteristics of synchronous motors. Synchronous compensator. Purpose and device. A synchronous machine consists of two main parts: a stationary one - a stator and a rotating one - a rotor, and has two main windings. One winding is connected to a DC power source. The current flowing through this winding creates the main magnetic field of the machine. This winding is located at the poles and is called the field winding. Sometimes machines of low power have no excitation winding, and the magnetic field is created by permanent magnets. The other winding is the armature winding. The main EMF of the machine is induced in it. It fits into the slots of the armature and consists of one, two or three phase windings. If a direct current flows through the excitation winding, then it creates a magnetic field constant in time with alternating polarity. When the poles rotate and, therefore, the magnetic field relative to the conductors of the armature winding, variable EMF is induced in them, which, summing up, determine the resulting EMF of the phases. If three identical windings are laid on the armature, the magnetic axes of which are shifted in space by an electrical angle equal to 120 °, then EMF is induced in these windings, forming a three-phase system. The frequency of the EMF inducted in the windings depends on the number of pole pairs p and the rotor speed n: f1 = pn / 60.

It is not possible to start a synchronous motor by direct connection to the network. , since the rotor, due to its significant inertia, cannot be immediately carried away by the rotating field of the stator, the speed of which is set instantly. As a result, there is no permanent magnetic coupling between the stator and the rotor. To start a synchronous motor, it is necessary to use special methods, the essence of which is to preliminarily bring the rotor into rotation to a synchronous or close to it frequency, at which a stable magnetic connection is established between the stator and the rotor.

One of the main disadvantages of sync engines is the complexity of their start-up. Synchronous motors can be started using an auxiliary starting motor or asynchronous starting. Starting a synchronous motor with an auxiliary motor ... If the rotor of a synchronous motor with excited poles is deployed with another, auxiliary motor to the speed of rotation of the stator field, then the magnetic poles of the stator, interacting with the rotor poles, will force the rotor to rotate further independently without assistance, in time with the stator field, i.e. synchronously. To start, it is necessary that the number of pole pairs of the induction motor is less than the number of pole pairs of the synchronous motor, because under these conditions, the auxiliary induction motor can turn the rotor of the synchronous motor to synchronous speed. The complexity of starting and the need for an auxiliary motor are significant disadvantages of this method of starting synchronous motors. Therefore, it is rarely used at present. Asynchronous start of a synchronous motor. To implement this starting method, an additional short-circuited winding is placed in the pole pieces of the rotor poles. Since during start-up, a large e is induced in the excitation winding of the motor. with, then for security reasons it closes with a switch for resistance. When the voltage of a three-phase network is switched on in the stator winding of a synchronous motor, a rotating magnetic field arises, which, crossing the short-circuited (starting) winding embedded in the pole pieces of the rotor, induces currents in it. These currents, interacting with the rotating field of the stator, will cause the rotor to rotate. When the rotor reaches the highest number of revolutions (95-97% of the synchronous speed), the switch is switched so that the rotor winding is connected to the DC voltage network ... The disadvantage of asynchronous starting is a large starting current. The dependence of the armature current on the excitation current is called U -O brave characteristic of a synchronous machine. Analyzing these characteristics, we see that the minimum value of the armature current occurs at a certain specific value of the excitation current, corresponding to work with cosφ = 1. For any change (increase or decrease) in the excitation current, the armature current I a increases due to an increase in the reactive component. Synchronous motor performance

Synchronous compensators are used to regulate the modes of operation of power systems, to maintain an optimal voltage level, reduce power losses in networks, increase throughput and ensure the stability of power systems.

Synchronous compensators are synchronous machines that operate in motor mode without active load and generate reactive leading (capacitive) or lagging (inductive) current into the network.

EXCITATION SYSTEMS OF SYNCHRONOUS MOTORS SERIES WTE, VTP

Thyristor exciters of the VTE, VTP series are designed to power the excitation windings of synchronous motors with a power of up to 12,500 kW, automatically controlled by direct current, with their direct and reactor start-up, synchronous operation and in emergency modes.

The exciters meet the requirements of GOST 24688-81, GOST 18142.1-82 and can be used instead of rectifiers of the TV-320, TV-400, TV-600, TVU, VTE-320, TE8-320, V-TPE8, V-TPP8, KTES series ...

Exciters are produced for rated currents of 200, 320, 400, 630, 800 and 1000 A, rated voltages from 24 to 300 V. Exciters for currents of 200, 320 and 400 A, have natural air cooling, and for currents of 630, 800 and 1000 A - forced air from built-in fans.

ADVANTAGES OF USE

easily reprogrammed when setting up the structure of automatic control systems;

stabilization of the excitation current in manual mode;

stator voltage regulation;

regulation of cos? at the load node;

regulation of stator reactive current;

two-wire interfaces for external automation and diagnostics;

automatic testing mode before switching on;

checking overvoltage protection circuits;

checking the serviceability of power circuits.

branched protection system;

built-in system of diagnostics and recording of "emergency trace";

any object orientation at the request of the Customer.

DEVICE

Power supply VTE, ECP (hereinafter referred to as "exciter") can be carried out from one input with a voltage of ~ 380 V, 50 Hz. It is also possible to power the controls from a separate input. To control the on and off circuits with oil switches, a voltage input of 220 (110) V is provided. The circuit and composition of the relay-switching part of the exciter is determined by the requirements of a specific application object.

The exciter rectifier is made according to a three-phase bridge circuit with one thyristor in the arm. Parallel to the load (excitation winding of a synchronous motor) through a contactless switch on thyristors, a starting resistance is connected, intended for asynchronous start and reduction to the permissible value of overvoltages arising in the rotor winding during asynchronous modes of motor operation. Moreover, the switching on of the thyristors of the key is carried out both from the microprocessor control system in the starting mode, and directly from the overvoltages arising on the excitation winding.

The microprocessor control system controls the entire complex of the exciter equipment, starting from receiving external and internal discrete and analog signals and ending with the issuance of control potential and pulse signals, as well as indication of all operating modes of the exciter using the built-in control terminal (PT).

Before switching on the exciter to the operating mode, a testing mode is performed, in which it is checked:

serviceability of the rotor overvoltage protection circuits by supplying voltage pulses of a real value and fixing the operation of the key thyristors in both directions;

serviceability of the converter and external power circuits.

The exciters have operating modes for automatic and manual control of the excitation current. Switching from mode to mode is carried out without switching off the exciter by a switch installed on the converter door. There are also installed measuring instruments (stator current, excitation current, excitation voltage, cos?) And a control terminal, with which you can select the structure of the automatic control system, change the parameters of regulators and settings of the control and protection system. The same procedures can be carried out with the help of a PC, for which a complex of service software has been developed, which greatly facilitates and accelerates the setup process.

In manual control mode, the exciter provides:

automatic supply of excitation in the rotor slip function in the range of 1-5% with the choice of the optimal half-wave of the rotor current during direct or reactor start of a synchronous motor;

regulation of the excitation voltage in the range from 0.1 to 2.0 nominal;

limiting the excitation voltage to a minimum from 0 to 0.5 rated, excitation current to a maximum of 1.75 nominal;

forcing excitation in voltage by a factor of not less than 2.0 nominal at the nominal voltage of the supply network and "boost" current by a factor of 1.75 nominal;

limiting the rotor current during overload in time - current characteristic;

protection against internal short circuits in the converter, against external short circuits on the DC side;

extinguishing the field during normal and emergency shutdowns of the motor by transferring the converter to the inverter mode;

protection of a synchronous motor from loss of excitation and from prolonged start-up with a response time of up to 30 s. In the automatic control mode, the exciter, in addition to the above, provides automatic regulation of the excitation current according to the stator voltage, cos? at the load node or stator reactive current.

SYMBOL STRUCTURE

GENERAL DESIGN INFORMATION

Structurally, the exciter is made in the form of a cabinet with two-way service. Controls, measuring instruments and alarm lamps are located on the cabinet door. Cooling of thyristors is natural or forced (VTE, ECP) ​​air. The cables for external connections are supplied through the openings in the bottom of the cabinet, sealed with pressure seals. Brackets are provided for fixing the cables. The power converter transformer is installed separately.

Dimensions of the WTE (VTP) cabinet (WxHxD) mm. - 800 (1000) x 2000 (2150) x 600.

BASIC TECHNICAL DATA

Table 1. Main technical data of synchronous motor excitation systems

ENVIRONMENTAL CONDITIONS

Table 2. Environmental conditions