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Troubleshooting for Generator No Electricity Output

Dec. 19, 2018

Fault diagnosis and troubleshooting method

Generator overheating

(1) The generator does not operate in accordance with the specified technical conditions, such as too high stator voltage, iron loss increases; if the load current is too large, the copper loss of the stator winding increases; if the frequency is too low, the cooling fan speed becomes slow, affecting the heat dissipation of generator; the power factor is too low, so that the rotor excitation current increases, resulting in the rotor heating. Check whether the indication of monitoring instrument is normal. If it is abnormal, necessary adjustment and treatment must be carried out to operate the generator in accordance with 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 of three-phase current exceeds 10% of the rated current, it is a serious phase current imbalance, and the three-phase current imbalance will generate negative sequence magnetic field, which will increase the loss and cause heating of components of magnetic pole winding and hoop. The three-phase load should be adjusted to keep the phase current as balanced as possible.


(3) The air duct is blocked by dust accumulation, and the ventilation is poor, which results in the difficulty of generator heat dissipation. Dust and oil dirt should be removed from the air duct.


(4) If the inlet air temperature is too high or the inlet water temperature is too high, the cooler will be blocked. The inlet or inlet temperature should be lowered to remove blockages in the cooler. Generator load should be limited to reduce the generator temperature before failure is eliminated.


(5) Grease should be added to the bearing according to the regulations, usually 1/2~1/3 of the bearing chamber (the upper limit of the low speed, the lower limit of the high speed), and not more than 70% of the bearing room is suitable.


(6) Bearing wear. If the wear is not serious, the bearing is partially overheated; if the wear is severe, the stator and the rotor may be rubbed, causing the stator and the rotor to overheat. The bearing should be inspected for noise. If friction between stator and rotor is found, generator should be stopped immediately to repair or replace the bearing.


(7) The insulation of the stator core is damaged, which causes short circuit between the sheets, resulting in local eddy current loss and heating, and the stator winding will be damaged if it is serious. Machine should be shut down immediately for maintenance.


(8) The parallel wires of the stator windings are broken, causing the current of other wires to increase and heat up. The machine should be stopped immediately for repair.


generator


2. The generator neutral line has abnormal voltage to the ground.

(1) Under normal circumstances, due to the influence of high harmonics or manufacturing process, the air gap under each magnetic pole is uneven and the magnetic potential is unequal, and the voltage is low. If the voltage is in the range of one to several volts, there will be no danger, do not have to deal with.


(2) The generator winding has short circuit or poor insulation to the ground, which leads to the deterioration of electrical equipment and generator performance, easy to heat. It should be repaired in time to avoid accidents.


(3) Neutral line has no voltage to ground at no load, and voltage occurs when there is load. It is caused by three-phase unbalance, and the three-phase load should be adjusted to make it basically balanced.


3. Generator current is too large.

(1) If the load is too large, the load should be reduced.

(2) If the transmission line has short circuit or grounding fault, the line should be overhauled and restored to normal after troubleshooting.


4. The generator terminal voltage is too high.

(1) If the grid voltage of generator parallel to the power grid is too high,  and the voltage of parallel generator should be reduced.

(2) If the fault of excitation device causes overexcitation, the excitation device should be repaired in time.


5. Insufficient power

Since the voltage source compound excitation compensation of the excitation device is insufficient, the excitation current required for the armature reaction cannot be provided, so that the generator terminal voltage is lower than the grid voltage and the rated reactive power cannot be delivered. The following measures should be taken:


(1) A three-phase voltage regulator is connected between the generator and the excitation reactor to increase the terminal voltage of the generator, so that the magnetic potential of the excitation device is gradually increased.


(2) Change the phase between the voltage magnetic-flux potential of the excitation device and the terminal voltage of the generator to increase the total magnetomotive force. Several thousand ohms and 10W resistors can be connected in parallel at  both ends of each phase winding of the reactor.


(3) The resistance of the varistor is reduced to increase the excitation current of the generator.


6. Stator winding insulation breakdown, short circuit

(1) The stator winding is damped. For generators that have been stopped for a long time or overhauled for a long time, the insulation resistance should be measured before putting into operation. Those who are not qualified are not allowed to put into operation. The damp generator should be dried.


(2) The winding itself is defective or improperly repaired, resulting in winding insulation breakdown or mechanical damage. The insulation material should be selected according to the specified insulation grade, the embedded winding and the dipping paint should be strictly carried out in accordance with the technical requirements.


(3) The winding is overheated. Insulation overheating will reduce insulation performance, and sometimes the insulation breakdown is quickly caused at a high temperature. Daily inspection should be strengthened to prevent the generator parts  from overheating and damaging the winding insulation.


(4) Insulation aging. Generally, generator runs for 15 ~ 20 years, winding insulation aging occurs, electrical performance changes, and even make insulation breakdown. If the insulation is found to be unqualified, replace the defective winding insulation in time to prolong the service life of the generator.


(5) Metal foreign matter enters the inside of the generator. After repairing the generator, do not leave the metal objects, parts or tools in the stator; tie the binding wire of the rotor and fasten the end parts so as not to be loosened by centrifugal force.


7. The stator core is loose.

The core is not fastened due to improper manufacturing and assembly. If the whole core is loose, for small generators, two iron plates smaller than the inner diameter of the stator winding end can be used to tighten the iron core by putting on double head bolts. After the original shape is restored, the original clamping bolt of the iron core is tightened. If the local iron core is relaxed, silicon steel sheet paint can be applied between the slack sheets, and then insert a hard insulating material into the slack parts.


8. Short circuit between iron chips

1) The iron core lamination is slack. When the generator is running, the iron core vibrates to damage the insulation; if the insulation of the iron chip is damaged or the core is partially overheated, it will cause insulation aging.


(2) There is a burr on the edge of the iron chip or mechanical damage during maintenance. Use a fine boring tool to remove the burrs, repair the damage, clean the surface, and then apply a layer of silicon steel paint.


(3) If there is solder or copper particles short iron core, the metal welding joint should be scraped or cut off to deal with the surface.


(4) The arc short circuit occurs in the winding, which may also cause the short circuit of the iron core. The burned part should be removed with a chisel and the surface should be treated.


9. The generator loses remanence and cannot generate electricity when starting.

(1) Remanence is often lost after shutdown, because the material used in the magnetic pole of the exciter is close to the soft steel, and the remanence is less. The magnetic field disappears when there is no current in the excitation winding after shutdown. A battery should be provided to magnetize before generating electricity.


(2) The magnetic pole of the generator loses its magnetism, and a DC current (in a short time) larger than the rated current should be applied to the winding for magnetization, that is, sufficient remanence can be restored.


10. Excitation reactor temperature of automatic excitation device is too high.

(1) The reactor coil is partially short-circuited, and the reactor should be repaired.

(2) If the air gap of the magnetic circuit of the reactor is too large, the air gap of the magnetic circuit should be adjusted.


11. When the generator starts, the voltage will not rise.

1) The excitation circuit is disconnected, preventing the voltage from rising. Check whether the excitation loop is broken and the contact is good.

(2) The residual magnet disappears. If the exciter voltmeter has no instructions to indicate that the residual magnet has disappeared, the exciter should be magnetized.

(3) The polarity of the field coil of the exciter is reversed, and its positive and negative connecting lines should be swapped.

(4) When performing some tests in the generator overhaul, the magnetic field coil is mistakenly connected to the reverse direct current, causing the residual magnet to disappear or reverse, and the magnetic field should be remagnetized.  

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