1. The generator is overheating
(1) The generator did not operate in accordance with the prescribed technical conditions, such as the stator voltage being too high and the iron loss increasing; When the load current is too large, the copper loss of the 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 rotor excitation current and causes the rotor to heat up. It is necessary to check whether the indications of the monitoring instruments are normal. If it is abnormal, necessary adjustments and treatments should be made to ensure that the generator operates in accordance with the prescribed technical conditions.
(2) If the three-phase load current of the generator is unbalanced, the overloaded phase winding will overheat. If the difference between the three-phase currents exceeds 10% of the rated current, it is considered a severe three-phase current imbalance. Three-phase current imbalance will generate a negative sequence magnetic field, thereby increasing losses and causing the magnetic pole windings, clamps and other components to heat up. The three-phase load should be adjusted to keep the currents of each phase as balanced as possible.
(3) The air ducts were blocked by accumulated dust, resulting in poor ventilation and making it difficult for the generator to dissipate heat. Dust and grease accumulated in the air ducts should be removed to ensure their unobstructed flow.
(4) The inlet air temperature is too high or the inlet water temperature is too high, and there is a blockage in the cooler. The intake air or water temperature should be reduced and the blockages in the cooler should be cleared. Before the fault is eliminated, the generator load should be restricted to lower the generator temperature.
(5) If too much or too little grease is added to the bearing, it should be added as per the regulations, usually 1/2 to 1/3 of the bearing housing (take the upper limit for low speed and the lower limit for high speed), and it is advisable not to exceed 70% of the bearing housing.
(6) Bearing wear. If the wear is not severe and causes local overheating of the bearing; If the wear is severe, it may cause the stator and rotor to rub against each other, resulting in overheating of the stator and rotor. It is necessary to check whether the bearings are noisy. If friction between the stator and rotor is found, the machine should be stopped immediately for maintenance or bearing replacement.
(7) The insulation of the stator core is damaged, causing short circuits between the plates, which increases the local eddy current loss of the core and leads to heating. In severe cases, it may damage the stator winding. The machine should be stopped immediately for maintenance.
(8) The parallel wires of the stator winding break, increasing the current in the other wires and causing them to heat up. The machine should be stopped immediately for maintenance.
2. There is an abnormal voltage between the neutral line of the generator and ground
Under normal circumstances, if very low voltages occur due to uneven air gaps and unequal magnetic potentials under each magnetic pole caused by high-order harmonics or manufacturing processes, and the voltage is within one to several volts, there is no danger and no need for treatment.
(2) If there is a short circuit in the generator winding or poor insulation to ground, it will cause the performance of the electrical equipment and the generator to deteriorate, making it prone to overheating. Timely maintenance should be carried out to prevent the accident from escalating.
(3) When there is no load, the neutral line has no voltage to ground, but voltage appears when there is a load. This is caused by three-phase imbalance. The three-phase load should be adjusted to make it basically balanced.
3. The generator current is too large
(1) If the load is too heavy, it should be reduced.
(2) In the event of an interphase short circuit or ground fault in a transmission line, the line should be inspected and repaired. Once the fault is eliminated, it can return to normal.
4. The terminal voltage of the generator is too high
(1) If the grid voltage of a generator connected in parallel with the power grid is too high, the voltage of the generator connected in parallel should be reduced.
(2) If the excitation device malfunctions and causes over-excitation, it should be repaired in a timely manner.
5. Insufficient power
Due to insufficient compound excitation compensation of the excitation device voltage source, the excitation current required for the armature reaction cannot be provided, resulting in the generator terminal voltage being lower than the grid voltage and unable to deliver the rated reactive power. The following measures should be taken:
A three-phase voltage regulator is connected between the generator and the excitation reactor to increase the terminal voltage of the generator, gradually increasing the magnetic potential of the excitation device.
(2) By changing the phase of the voltage flux potential of the excitation device and the terminal voltage of the generator to increase the combined total flux potential, a resistor of several thousand ohms and 10W can be connected in parallel across each phase winding of the reactor.
(3) Reduce the resistance value of the rheostat to increase the excitation current of the generator.
6. Insulation breakdown and short circuit of the stator winding
(1) The stator winding is damp. For generators that have been out of service for a long time or have undergone prolonged maintenance, the insulation resistance should be measured before they are put into operation. Those that fail to meet the standards are not allowed to be put into operation. Damp generators need to be dried.
(2) Defects in the winding itself or improper maintenance techniques can cause insulation breakdown or mechanical damage to the winding. Insulating materials should be selected in accordance with the specified insulation grade. The embedding of windings and the drying of impregnation varnish must be carried out strictly in accordance with the process requirements.
(3) Winding overheating. Overheating of insulation will reduce its insulation performance. Sometimes, it can cause insulation breakdown very quickly at high temperatures. Regular inspection and patrol should be strengthened to prevent overheating of various parts of the generator and damage to the winding insulation.
(4) Insulation aging. Generally, after 15 to 20 years of operation, the winding insulation of a generator ages, its electrical performance changes, and even insulation breakdown occurs. It is necessary to do a good job in the maintenance and preventive tests of the generator. If the insulation is found to be substandard, the defective winding insulation should be replaced in time or the winding should be replaced to extend the service life of the generator.
(5) Metal foreign objects may enter the generator. After the generator is repaired, do not leave any metal objects, parts or tools in the stator chamber. Tighten the binding wires of the rotor and secure the end parts to prevent them from loosening due to centrifugal force.
(6) Excessive voltage breakdown: 1) The line is struck by lightning, but the lightning protection is not perfect. Lightning protection facilities should be improved. 2) Misoperation, such as raising the generator voltage too high when it is no-load. The generator should be pressurized strictly in accordance with the operating procedures to prevent misoperation. 3) Internal overvoltage of the generator, including operating overvoltage, arc grounding overvoltage and resonant overvoltage, etc., should strengthen the preventive test of winding insulation to promptly detect and eliminate defects existing in the stator winding insulation.
7. The stator core is loose
Due to improper manufacturing and assembly, the core was not tightened properly. If the entire core is loose, for small generators, two iron plates smaller than the inner diameter of the stator winding end can be used, and double-ended bolts can be inserted to tighten the core. After the original shape is restored, tighten the original clamping bolts of the iron core. If the local core is loose, you can first apply silicon steel sheet paint between the loose pieces, and then inject hard insulating materials into the loose parts.
8. Short circuit between iron chips
(1) The core laminations are loose. When the generator is running, the core vibrates and damages the insulation. If the insulation in individual areas of the iron chip is damaged or the core overheats locally, causing insulation aging, it shall be handled in accordance with the methods stipulated in the original plan.
(2) The edges of the iron chip have burrs or are mechanically damaged during maintenance. Use a fine file to remove burrs, trim the damaged area, clean the surface, and then apply a layer of silicon steel sheet paint.
(3) If there is solder or copper particles short-circuiting the core, the metal welding points should be scraped off or chiseled off, and the surface should be properly treated.
(4) Arc short circuit in the winding may also cause short circuit in the core. The burned part should be removed with a chisel and the surface should be properly treated.
9. When the generator loses residual magnetism, it cannot generate electricity during startup
(1) The residual magnetism is often lost after the machine stops, which is because the material used for the magnetic poles of the exciter is close to soft steel, resulting in less residual magnetism. When there is no current in the excitation winding after the machine stops, the magnetic field disappears. A battery should be prepared and magnetized before power generation.
(2) If the magnetic poles of a generator lose their magnetism, a direct current larger than the rated current (for a very short time) should be passed through the windings to magnetize them, and sufficient residual magnetism can be restored.
10. The temperature of the excitation reactor in the automatic excitation device is too high
(1) If there is a local short circuit in the reactor coil, the reactor should be repaired.
(2) If the air gap in the reactor’s magnetic circuit is too large, the air gap in the magnetic circuit should be adjusted.
After the generator starts, the voltage cannot rise
(1) The excitation circuit is disconnected, preventing the voltage from rising. It is necessary to check whether there are any broken wires in the excitation circuit and whether the contact is good.
(2) Residual magnetism disappears. If the voltmeter of the exciter shows no indication, it indicates that the residual magnetism has disappeared, and the exciter should be magnetized.
(3) If the polarity of the magnetic field coil of the exciter is reversed, its positive and negative connection wires should be swapped.
(4) When conducting certain tests during generator maintenance, if the magnetic field coil is mistakenly supplied with reverse direct current, resulting in the disappearance of residual magnetism or reverse flow, it should be re-magnetized.
12. Oscillation loss of synchronization of the generator
Under normal circumstances, the power generated by a generator is balanced with the load power. When a short-circuit fault occurs in the system or the generator experiences a significant load drop, the power of the generator will be unbalanced with the user’s load. To adjust the load to balance it, due to the rotor inertia and governor delay, a process is required. During this period, the stable operation of the generator will be disrupted, causing the generator to oscillate. If the story is serious, it may even cause the generator to lose synchronization with the system. When the generator oscillates and loses synchronization, the on-duty personnel should create conditions for restoring synchronization by increasing the excitation current. It can also be appropriate.
Adjust the load of this machine to help restore synchronization.
13. Generator vibration
If the rotor is not round or the balance is not properly adjusted, the manufacturing and installation quality should be strictly controlled or the balance of the rotor should be readjusted.
(2) If the rotating shaft is bent, it can be corrected by methods such as grinding, heating and hammering.
(3) If the coupling is not properly connected, the clamping force of the mating bolts of the high-speed coupling should be re-adjusted. If necessary, the end face of the coupling needs to be reprocessed.
(4) Resonance of structural components can be altered by changing the support method of the structural components to change their inherent frequency.
(5) In case of interlayer short circuit of the excitation winding, the excitation winding should be inspected and repaired and insulated.
(6) If the fuel supply or oil pressure is insufficient, the nozzle diameter should be increased to raise the oil pressure. Increase the fuel supply port to reduce the clearance.
(7) If the fuel supply is too large or the oil pressure is too high, reduce the nozzle diameter, lower the oil pressure, increase the area pressure and enlarge the clearance.
(8) If the stator core assembly is loose, the core should be re-pressed.
(9) The bearing seal is too tight, causing local overheating and bending of the rotating shaft. The bearing seal should be inspected and adjusted to ensure an appropriate fit clearance with the shaft.
(10) If the ventilation system of the generator is asymmetrical, attention should be paid to the structural layout and size selection of the wind shields at both ends of the stator core and the wind shields of the rotor support to make the air path system symmetrical. The rigidity of the cover plate and the wind shield should be enhanced and they should be firmly fastened.
For more questions about the generator set, please call the Beidou Power team. More than ten years of professional production and sales of power generation equipment experience, more professional engineer team to serve you, choose Beidou power is to choose rest assured, welcome on-site factory inspection.
Post time: Jan-09-2026