What elements does the stator of a synchronous generator consist of and the principle of operation?
- Package of stator windings;
- Stator core or package;
- Wires for connection output.
The stator itself is made of three windings, three different current values are formed in them, this circuit is a three-phase output. The ends of each winding extend from the generator body (they are connected to it), the second end is connected to the rectifier. To concentrate and enhance the magnetic field in the generator, a core made of metal plates is used.
The stator winding of a synchronous generator is located in special slots, usually there are 36 such slots. In each slot, the winding is held by a wedge. This wedge is made of insulating materials.
Air cooled generator
There are two air cooling systems - flow and closed.
A flow cooling system is rarely used and only in turbogenerators with a capacity of up to 2 MBA, as well as in hydrogenerators up to 4 MBA. At the same time, air from the machine room is forced through the generator, which quickly contaminates the insulation of the stator and rotor windings, which ultimately reduces the service life of the generator.
With a closed cooling system, the same volume of air circulates in a closed loop. The air circulation with such cooling for a turbogenerator is shown schematically in Fig. 1. To cool the air, an air cooler 1 is used, through the tubes of which water continuously circulates. The air heated in the car exits through pipe 2 into the hot air chamber 3, passes through the air cooler and returns to the car through the cold air chamber 4. Cold air is pumped into the machine by built-in fans 5. In generators with a long active part, cold air is supplied from both ends of the machine, as shown in Fig. 1.
Fig.1. Closed air cooling system for turbogenerator
In order to increase the cooling efficiency of turbogenerators, the length of the active part of which is particularly long and the air gap is small, a multi-jet radial ventilation system is used. To do this, vertical planes 6 divide the cooling system of turbogenerators into a number of sections. Air enters each section from the air gap (Sections I and III) or from a special axial channel 7 (Section II).
To increase the surface of contact of heated parts with cooling air in the active steel of the machine, a system of ventilation ducts is installed. Having passed through the radial ventilation channels in the steel, the heated air goes into exhaust chambers 8. Multi-jet ventilation ensures uniform cooling of the turbogenerator along its entire length. To compensate for losses due to leaks, additional air intake is provided through double oil filters 9 installed in the cold air chamber.
Domestic factories produce turbogenerators with a closed air cooling system with a capacity of up to 12 MW inclusive.
The closed system of indirect air cooling in hydrogenerators is used much more widely. The largest indirect air-cooled generator of the SV series with a capacity of 264.7 MBA was produced by Elektrosila for the Bratsk Hydroelectric Power Plant. The hydrogen generator ventilation diagram is shown in Fig. 2.
Fig.2. Closed-loop ventilation system of the hydrogenerator 1 - rotor; 2 - stator; 3 — air cooler; 4 — fan blades
In hydrogenerators, cooling of salient-pole rotors is facilitated due to the presence of interpolar gaps and a larger cooling surface of the rotor.
Cooling a smooth rotor of a turbogenerator is less efficient, since in the case under consideration it is cooled only from the air gap side. The latter circumstance largely determines the limited possibilities of air cooling for turbogenerators. Air-cooled generators are equipped with a device for extinguishing fires with water.
Reasons for disruption of stable operation of the generator stator
Before checking, you need to find out exactly which generator is installed on your car. This can be found out from the manual, but the best way to find out the model and parameters of the generator is to look under the hood to find the manufacturer's tag. On it you will find all the necessary values. If differences in generator models are not taken into account, the test result will be inaccurate. Knowing the basics of electrics, it is not difficult to identify various problems in the operation of the generator, and other systems of the electrical system.
All stator failures can be divided into two groups:
- Broken winding wires;
- Wire short to ground.
If the vehicle is operated in conditions of high humidity or with sudden changes in temperature, the insulation may crack and delaminate. This can provoke an interturn short circuit and even failure of the entire generator, which will cause a sudden discharge of the battery, since the generator will not be able to fully charge it.
Possible malfunctions: signs and causes
Two types of failures can occur in the operation of the stator mechanism: a break in the windings or a short circuit to ground. As a result of prolonged exposure to humidity and temperature changes, the insulation on the end surface of the core may delaminate and crack. This, in turn, can cause a short circuit and accelerated failure of the unit as a whole. Regardless of the cause, there is only one sign of a malfunction - the generator unit stops functioning normally, problems appear in its operation, and the unit cannot generate current.
Checking the generator stator using a multimeter, how to check with a test light
The generator stator is checked for either an open circuit or a short circuit. To check the resistance, use a multimeter; in extreme cases, you can use a test light.
The multimeter should be switched to ohmmeter mode, after which its probes are connected to the terminals of the windings. If there is no break, the tester will show a resistance of 10 ohms. If there is a break, the resistance will show a value tending to infinity. With this result, three conclusions are checked. To obtain more accurate verification results, it is better to check the received data with your passport data. You should know that inexpensive Chinese multimeters are not able to accurately show the resistance being measured (accuracy is sometimes required to tenths of an ohm), so you should get a good branded device.
If it is not possible to get any multimeter, but you need to check, you can use a test light (control). It won't show the exact resistance, but it will help you find the gap. Using an insulated wire, a negative charge is supplied from the battery to the winding contact. A positive charge should be applied through the light bulb to another contact. If the light is on, then the gap has not been found and the device is functioning properly. This procedure is repeated for all outputs.
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Diagnostics for short circuits is also carried out using a multimeter or a test light. The positive probe must be connected to any winding contact, and the negative probe to the stator. This should be repeated with each output. The turn-to-turn short circuit is determined using a test lamp in a similar way. Call all findings.
Possible malfunctions: signs and causes
Two types of failures can occur in the operation of the stator mechanism: a break in the windings or a short circuit to ground. As a result of prolonged exposure to humidity and temperature changes, the insulation on the end surface of the core may delaminate and crack. This, in turn, can cause a short circuit and accelerated failure of the unit as a whole. Regardless of the cause, there is only one sign of a malfunction - the generator unit stops functioning normally, problems appear in its operation, and the unit cannot generate current.
DIY generator repair
Stator repair usually means rewinding the generator stator. For this procedure you will need an impressive set of tools:
- Winding machine;
- Copper wire (about 8 coils may be required);
- Tamping;
- Drilling machine;
- Device for drying a varnished stator;
- Hammer, set of screwdrivers and keys.
Winding the stator of a car generator is the repair of the stator. First you need to remove the stator itself from the generator. The old winding is scorched, but before this, a diagram of the generator stator winding must be drawn up, identical to the old three-phase or single-phase winding. When scorched, the magnetic properties of the metal stator package do not deteriorate, so there is no need to worry. When the winding is completely burnt, the seat should be completely cleaned. Syntoflex insulating gaskets are cut and installed in the grooves.
The winding should be rewinded according to a pre-drawn pattern. The linear principle is used in a single-phase generator, and the three-phase stator winding involves a star or delta connection. When rewinding, the wire from the first groove should go directly to the fourth. First, half the turns are wound in one direction, then the second half in the opposite direction. The grooves are sealed with the protruding parts of the gaskets, after which the coils need to be tapped with a hammer. To avoid damaging the winding, you need to use a spacer.
Before checking the performance of the stator with currents, you should make sure that there is no short circuit. If there is a short circuit, it means the insulation was installed poorly. You should find the problem area and, using a gasket, eliminate the breakdown.
Before impregnation with varnish, you need to check the dimensions of the rewound unit; it should not protrude beyond the edges when assembling the generator. The contacts are connected with a thread that will not melt when dried and placed in a container with varnish. After impregnation of the stator, it is placed in an oven for drying, after allowing the element to flow around. If there is no suitable furnace, the stator can simply be suspended by installing a heating element underneath. When the varnish stops sticking, drying is complete. When using heating, drying usually takes about 2-3 hours.
When the generator operates unstable, for many the solution to the problem is to replace the entire unit. But if you know how to check all the elements of the generator, then even the stator winding procedure will be within your grasp.
Features of repairing an asynchronous machine
Engine problems of any type can be mechanical or electrical in nature. In the first case, strong vibration and characteristic noise may indicate a malfunction; as a rule, this indicates problems with the bearing (usually in the end cover). If the malfunction is not corrected in time, the shaft may jam, which will inevitably lead to failure of the stator windings. In this case, the thermal protection of the circuit breaker may not have time to operate.
“Burnt” wires of the stator winding
Based on practice, in 90% of failures of asynchronous machines, problems arise with the stator winding (break, interturn short circuit, short circuit to the frame). In this case, the short-circuited armature, as a rule, remains in working condition. Therefore, even if the damage is mechanical, it is necessary to check the electrical part.
Tractor generator design
The differences between the unit are mainly in geometric parameters and characteristics. For this reason, the device is similar to standard devices in passenger cars. The generators include the following elements:
- rotor and stator;
- slip rings;
- diode bridge;
- regulator and its relay;
- bearing and shaft;
- front and back cover.
These are the main elements that are also divided into component parts.
In the event of a breakdown, repair of MTZ tractor generators is usually carried out by replacing the faulty unit. However, our craftsmen are ready to restore parts if possible. We will rewind the stator, restore the shaft geometry and other types of work if they help restore the operating parameters of the device. Sign up for repairs
We will call you back on the specified phone number and confirm your appointment.
