(1) The generator does not operate according to the specified technical conditions. If the stator voltage is too high, the iron loss will increase; When the load current is too large, the copper loss of stator winding increases; The frequency is too low, which slows down the speed of the cooling fan and affects the heat dissipation of the generator; The power factor is too low, which increases the excitation current of the rotor and leads to the rotor heating. Check whether the indication of monitoring instrument is normal. If there is any abnormality, necessary adjustment and treatment should be made to make the generator run according to the specified technical conditions.
(2) The three-phase load current of the generator is unbalanced, and the overloaded one-phase winding will overheat; If the difference between the three-phase currents exceeds 10% of the rated current, it is a serious phase current imbalance, which will produce a negative sequence magnetic field, increase the loss, and cause the components such as pole windings and ferrules to heat up. The three-phase load should be adjusted to keep the phase current as balanced as possible.
(3) The air duct is blocked by dust, which leads to poor ventilation and makes it difficult for the generator to dissipate heat. Dust and grease in the air duct should be removed to make the air duct unobstructed.
(4) The inlet air temperature is too high or the inlet water temperature is too high, and the cooler is blocked. The temperature of inlet air or water should be lowered to clear the blockage in the cooler. Before the fault is eliminated, the generator load should be limited to reduce the generator temperature.
(5) If the bearing is oiled too much or too little, it should be oiled according to regulations, which is generally 1/2~ 1/3 of the bearing cavity (the upper limit is low speed and the lower limit is high speed), and it is advisable to not exceed 70% of the bearing cavity.
(6) Bearing wear. If the wear is not serious, the bearing will overheat locally; If the wear is serious, the stator and rotor may rub, resulting in overheating of the stator and rotor. Check the bearing for noise. If there is friction between stator and rotor, immediately stop the machine for maintenance or replace the bearing.
(7) The insulation of stator core is damaged, which leads to short circuit between pieces, which will increase the eddy current loss of the core and generate heat, which will damage the stator winding in severe cases. Stop the machine immediately for maintenance.
(8) The parallel wires of the stator winding are broken, which increases the current of other wires and generates heat. Stop the machine immediately for maintenance.
2. Abnormal neutral voltage of generator to ground.
(1) In general, due to the influence of higher harmonics or manufacturing process, the air gap is uneven, and the extremely low voltage generated by the unequal magnetic potential under each magnetic pole is not dangerous if the voltage is between one volt and several volts, so it is not necessary to deal with it.
(2) The generator winding is short-circuited or the insulation to the ground is poor, which leads to the deterioration of the performance of electrical equipment and the generator and is easy to generate heat. It should be repaired in time to avoid the accident from expanding.
(3) There is no voltage between neutral line and ground when there is no load, but there is voltage when there is load, which is caused by three-phase imbalance, so the three-phase load should be adjusted to make it basically balanced.
3. The generator current is too large.
(1) The load is too large, so the load should be lightened.
(2) In case of phase-to-phase short circuit or grounding fault of the transmission line, the line shall be overhauled, and it can return to normal after troubleshooting.
4. The terminal voltage of the generator is too high.
(1) The grid voltage of the parallel generator is too high, so the voltage of the parallel generator should be reduced.
(2) The excitation device is over-excited due to its failure, so the excitation device should be overhauled in time.
5. Lack of motivation
Because the voltage source compensation of the excitation device with compound excitation is insufficient, it can't provide the excitation current needed for armature reaction, which makes the generator terminal voltage lower than the grid voltage and can't deliver the rated reactive power. The following measures should be taken:
(1) Connect a three-phase voltage regulator between the generator and the excitation reactor to increase the terminal voltage of the generator and gradually increase the magnetic potential of the excitation device.
(2) By changing the phase between the voltage magnetic flux potential of the excitation device and the terminal voltage of the generator, the synthesized total magnetic flux potential is increased, and the resistors of several thousand ohms and 10W can be connected in parallel at both ends of each phase winding of the reactor.
(3) Reduce the resistance of rheostat to increase the excitation current of generator.
6, stator winding insulation breakdown, short circuit
(1) The stator winding is damp. For generators that have been stopped or overhauled for a long time, the insulation resistance should be measured before they are put into operation, and those who fail are not allowed to be put into operation. The generator affected with damp should be dry.
(2) Winding insulation breakdown or mechanical damage caused by winding defects or improper maintenance process. Insulation materials should be selected according to the specified insulation grade, and winding embedding and paint dipping and drying should be carried out in strict accordance with the process requirements.
(3) The winding is overheated. Overheating of insulation will reduce insulation performance, and sometimes it will cause rapid breakdown of insulation at high temperature. Daily patrol inspection should be strengthened to prevent overheating of various parts of the generator and damage to winding insulation.
(4) Insulation aging. General generator operation 15~20 years, winding insulation aging, electrical performance changes, and even insulation breakdown. Do a good job in generator maintenance and preventive test. If unqualified insulation is found, defective winding insulation should be replaced or windings should be replaced in time to prolong the service life of the generator.
(5) Metal foreign matter enters the generator. Never leave metal objects, parts or tools in the stator hole after the generator is overhauled; Fasten the binding line of the rotor and fasten the end to avoid loosening due to centrifugal force.
(6) Overvoltage breakdown: 1) The line is struck by lightning, and the lightning protection is not perfect. Lightning protection facilities should be improved. 2) Misoperation, such as raising the generator voltage too high when there is no load. The booster of the generator should be carried out in strict accordance with the operating procedures to prevent misoperation. 3) generator internal overvoltage, including operating overvoltage, arc grounding overvoltage and resonance overvoltage, should strengthen the preventive test of winding insulation, timely find and eliminate the defects of stator winding insulation.
7, stator core relaxation
Due to improper manufacture and assembly, the iron core is not fastened properly. If the whole iron core is loose, for a small generator, two iron plates smaller than the inner diameter of the stator winding end can be padded on the stud to fasten the iron core. After restoring the original state, tighten the original clamping bolt of the iron core. If the local iron core is loose, silicon steel sheet paint can be coated between the loose sheets first, and then hard insulating materials can be pumped into the loose parts.
8. Short circuit between iron sheets
(1) The core lamination is slack, and the core vibrates when the generator is running, which damages the insulation; If the insulation part of iron filings is damaged or the iron core is overheated, the insulation will age, and the treatment will be carried out according to the method in the original scheme.
(2) There is burr on the edge of iron filings or mechanical damage during maintenance. Remove burrs with a fine file, trim the damaged area, clean the surface, and then apply a layer of silicon steel sheet paint.
(3) If the iron core is short-circuited by solder or copper particles, the metal solder joint shall be scraped or chiseled, and the surface treatment shall be done well.
(4) The short circuit of winding arc may also cause the short circuit of iron core, so the burnt part should be chiseled away with a chisel and the surface treatment should be done well.
9. The generator loses remanence and cannot generate electricity when it is started.
(1) After shutdown, the remanence is often lost, because the material used in the exciter pole is close to low carbon steel, and the remanence is less. When there is no current in the excitation winding after shutdown, the magnetic field disappears, and the battery should be magnetized before power generation.
(2) If the magnetic pole of the generator loses magnetism, DC current greater than the rated current should be introduced into the winding to magnetize it (for a short time), which can restore sufficient remanence.
10, the excitation reactor temperature of automatic excitation device is too high.
(1) The reactor coil is partially short-circuited, so the reactor should be overhauled.
(2) The air gap of the reactor magnetic circuit is too large, so the air gap of the magnetic circuit should be adjusted.
1 1. After the generator is started, the voltage will not rise.
(1) The excitation circuit is disconnected and the voltage cannot rise. Check whether the excitation circuit is disconnected and in good contact.
(2) The remanence disappears. If the exciter voltmeter does not indicate the disappearance of remanence, the exciter should be magnetized.
(3) The polarity of the exciter magnetic field coil is reversed, and its positive and negative connecting wires should be reversed.
(4) When doing some tests in generator maintenance, the magnetic field coil is mistakenly connected to the DC, resulting in the disappearance or reversal of remanence, which should be re-magnetized.