First, the generator is overheated?
1, the generator does not operate according to the specified technical conditions, such as the stator voltage is too high, the iron loss increases; 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 overload 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 and has poor ventilation, which 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 lubricated too much or too little, it should be lubricated 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, stator core insulation damage, resulting in short circuit between pieces, resulting in increased local eddy current loss of the core and heating, which will seriously damage the stator winding. 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. ?
Second, the generator neutral voltage to ground is abnormal?
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 one to several volts, so it is unnecessary to deal with it.
2. The generator winding is short-circuited or the insulation to the ground is poor, and the performance of electrical equipment and generator is deteriorated, which 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 will be voltage when there is load, which is caused by three-phase imbalance. The three-phase load should be adjusted to make it basically balanced.
Third, the generator overcurrent
1, the load is too large, so the load should be reduced. ?
2. In case of phase-to-phase short circuit or grounding fault of the transmission line, the line shall be overhauled, and it can be restored to normal after troubleshooting.
Fourth, the generator terminal voltage is too high.
1. If the grid voltage of the generator connected in parallel with the grid is too high, reduce the voltage of the generator connected in parallel.
2. Over-excitation caused by fault of excitation device shall be timely overhauled.
5. Insufficient reactive power?
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. Changing the phase between the voltage magnetic flux potential of the excitation device and the terminal voltage of the generator increases the synthesized total magnetic flux potential, and several thousand ohms and 10W resistors can be connected in parallel at both ends of each phase winding of the reactor.
3. Reduce the resistance of rheostat and increase the excitation current of generator. ?
Six, stator winding insulation breakdown and 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 itself defects or improper maintenance process, leading to winding insulation breakdown or mechanical damage.
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. Foreign metal objects enter the generator. Never leave metal objects, parts or tools in the stator hole after repairing the generator; Fasten the binding line of the rotor and fasten the end to avoid loosening due to centrifugal force.
6, overvoltage breakdown
(1) The line was struck by lightning, but the lightning protection was 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) Internal overvoltage of generator, including operating overvoltage, arc grounding overvoltage and resonance overvoltage. Preventive test of winding insulation should be strengthened to find and eliminate the defects of stator winding insulation in time.
Seven, 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.
Eight, short circuit between iron pieces
1, the core lamination is slack, and the core vibration damages the insulation when the generator is running; 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 there is solder or copper short-circuit iron core, the metal solder joint should be scraped or chiseled, and the surface treatment should be done well.
4, winding arc short circuit, may also cause iron core short circuit, the burning part should be cleared with a chisel, surface treatment.