Why is the generator not generating electricity?
We are a Chinese supplier of generator sets – PowerSUM.
Today we share with you some common small problems of generator sets and solutions.
Why is the generator not generating electricity?
- Structure and principle
Synchronous generators are mainly composed of stator, rotor and other components. The stator part includes stator iron core, stator winding, and frame; the rotor part includes rotor iron core, excitation winding and slip ring (the hidden pole rotor also has ferrules and core rings, and the salient pole rotor has magnetic poles, yokes, and rotor brackets. ); other components include brush units, end caps, bearings, and fans.
- Working principle
The synchronous generator works according to the principle of electromagnetic induction. It converts mechanical energy into electrical energy through the relative motion of the rotor magnetic field and the stator winding. When the rotor is driven by an external force, the rotor magnetic field and the stator conductor move relative to each other, that is, the conductor cuts the magnetic field line, so an induced electromotive force is generated in the conductor, and its direction can be determined according to the right-hand rule. Since the position of the rotor magnetic pole causes the conductor to cut the magnetic field lines in the vertical direction, the induced electromotive force in the stator winding is large at this time. After the poles have turned 90 degrees. The magnetic pole is in a horizontal position, the conductor does not cut the magnetic field lines, and the induced electromotive force is zero. The rotor rotates 90 degrees again, and the timing stator winding cuts the magnetic field lines in the vertical direction, so that the induced electromotive force reaches a large value, but the direction is opposite to the previous one. When the rotor turns another 90 degrees, the induced electromotive force becomes zero again. In this way, the rotor rotates once, and the induced electromotive force of the stator winding also changes positively and negatively. If the rotor rotates continuously and uniformly, a periodically changing alternating electromotive force is induced in the stator winding. 2. Troubleshooting and troubleshooting
- Generator overheating
(1) The generator does not operate according to the specified technical conditions. For example, if the stator voltage is too high, the iron loss will increase; if the load current is too large, the copper loss of the stator winding will increase; if the frequency is too low, the speed of the cooling fan will slow down, which will affect the generator. Heat dissipation; the power factor is too low, which increases the rotor excitation current and causes the rotor to heat up. It should be checked whether the indication of the monitoring instrument is normal. If it is not normal, make necessary adjustments and treatments to make the generator operate 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 between the three-phase current exceeds 10% of the rated current, it is a serious phase current imbalance, and the three-phase current imbalance will produce Negative sequence magnetic field, thereby increasing losses and causing heating of components such as pole windings and ferrules. The three-phase load should be adjusted to keep the current of each phase as balanced as possible.
(3) The air duct is blocked by dust, and the ventilation is poor, which makes it difficult for the generator to dissipate heat. The dust and grease in the air duct should be removed to make the air duct unobstructed.
(4) If the inlet air temperature is too high or the inlet water temperature is too high, the cooler is blocked. The inlet air or inlet water temperature should be lowered to clear blockages in the cooler. Before the fault is eliminated, the generator load should be limited to reduce the generator temperature.
(5) Too much or too little grease is added to the bearing. Grease should be added according to the regulations, usually 1/2~1/3 of the bearing chamber (the upper limit for the low speed and the lower limit for the high speed), and should not exceed 1/2~1/3 of the bearing chamber 70% of the bearing chamber is appropriate.
(6) Bearing wear. If the wear is not serious, the bearing will be overheated locally; if the wear is serious, it may cause friction between the stator and the rotor, causing the stator and the rotor to overheat. The bearing should be checked for noise. If friction between the stator and the rotor is found, it should be stopped immediately for maintenance or replacement of the bearing.
(7) The insulation of the stator iron core is damaged, causing short circuit between sheets, resulting in increased eddy current loss in the iron core and heating, and in severe cases, the stator winding will be damaged. It should be stopped immediately for maintenance.
(8) The parallel wires of the stator winding are broken, which increases the current of other wires and generates heat. It should be stopped immediately for maintenance.
- The neutral line of the generator has abnormal voltage to the ground
(1) Under normal circumstances, due to the influence of high-order harmonics or the manufacturing process, the air gap under each magnetic pole is uneven and the magnetic potential is unequal, resulting in a very low voltage. If the voltage is one to several volts, there will be no danger. , do not have to deal with it.
(2) There is a short circuit in the generator winding or poor insulation to the ground, which leads to the deterioration of the performance of the electrical equipment and the generator, and it is easy to heat up. It should be repaired in time to avoid the expansion of the accident.
(3) When there is no load, the neutral line has no voltage to the ground, and when there is a load, there is a voltage, which is caused by the three-phase imbalance. The three-phase load should be adjusted to make it basically balanced.
- The generator current is too large
(1) If the load is too large, the load should be reduced.
(2) In case of phase-to-phase short circuit or grounding fault in the transmission line, the line should be overhauled, and it can be restored to normal after the fault is eliminated.
- The generator terminal voltage is too high
(1) The grid voltage of the generator parallel to the grid is too high, and the voltage of the parallel generator should be reduced.
(2) The failure of the excitation device causes over-excitation, and the excitation device should be repaired in time.
- Insufficient power
Due to the lack of compound excitation compensation of the voltage source of the excitation device, the excitation current required for the armature reaction cannot be provided, so that the terminal voltage of the generator is lower than the grid voltage, and the rated reactive power cannot be sent. 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 and gradually increase the magnetic potential of the excitation device.
(2) Change the phase of the voltage magnetomotive force of the excitation device and the terminal voltage of the generator to increase the combined total magnetomotive force, and a resistance of thousands of ohms and 10W can be connected in parallel at both ends of each phase winding of the reactor.
(3) Reduce the resistance of the varistor to increase the excitation current of the generator.
- Insulation breakdown and short circuit of stator winding
(1) The stator winding is damp. For generators that have been out of use for a long time or have been overhauled for a long time, the insulation resistance should be measured before being put into operation, and those that fail are not allowed to be put into operation. Wet generators should be dried.
(2) Defects in the winding itself or improper maintenance process, resulting in insulation breakdown or mechanical damage of the winding. The insulation material should be selected according to the specified insulation grade, and the winding installation and dipping and drying should be carried out in strict accordance with the process requirements.
(3) The winding is overheated. After the insulation is overheated, the insulation performance will be reduced, and sometimes it will quickly cause insulation breakdown at high temperatures. Routine inspections should be strengthened to prevent overheating of various parts of the generator and damage to the winding insulation.
(4) Insulation aging. Generally, the generator runs for more than 15 to 20 years, and its winding insulation is aging, the electrical performance changes, and even the insulation is broken down. It is necessary to do a good job in the overhaul and preventive test of the generator. If the insulation is found to be unqualified, the defective winding insulation should be replaced or the winding should be replaced in time to prolong the service life of the generator.
(5) Metal foreign objects enter the generator. Do not leave metal objects, parts or tools in the stator chamber after overhauling the generator; tie the binding wire of the rotor and fasten the end parts to avoid the centrifugal force. And loose.
(6) Excessive voltage 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 at no load. The generator should be boosted in strict accordance with the operating procedures to prevent misoperation. 3) For the internal overvoltage of the generator, including operating overvoltage, arc grounding overvoltage and resonance overvoltage, etc., the preventive test of the winding insulation should be strengthened, and the defects in the insulation of the stator winding should be found and eliminated in time.
- Stator core relaxation
Due to improper manufacturing and assembly, the iron core is not fastened properly. If the entire iron core is loose, for small generators, two iron plates smaller than the inner diameter of the stator winding end can be used, and stud bolts can be put on to tighten the iron core. After the original shape is restored, tighten the original clamping bolt of the iron core. If the iron core is loose locally, you can paint silicon steel sheet paint between the loose sheets first, and then drive hard insulating material into the loose part.
- Short circuit between iron chips
(1) The lamination of the iron core is loose, and the iron core vibrates when the generator is running, which damages the insulation; the insulation of individual parts of the iron core is damaged or the iron core is partially overheated, causing the insulation to age, so it is handled according to the method in the original plan.
(2) There are burrs on the edge of the iron core or mechanical damage during maintenance. Use a fine file to remove burrs, trim damage, clean the surface, and apply a coat of silicon steel sheet paint.
(3) If there is solder or copper particles short-circuiting the iron core, the metal welding joints should be scraped or chiseled, and the surface should be treated well.
(4) Arc short circuit occurs in the winding, which may also cause a short circuit of the iron core. The burnt part should be removed with a chisel, and the surface should be treated well.
- The generator loses its residual magnetism and cannot generate electricity when starting
(1) The remanence is often lost after shutdown, because the material used in the exciter magnetic pole is close to mild steel, and the remanence is less. When there is no current in the excitation winding after shutdown, the magnetic field disappears, and a battery should be prepared to be magnetized before generating electricity.
(2) When the magnetic pole of the generator loses its magnetism, a DC current larger than the rated current (for a short time) should be passed into the winding for magnetization, that is, enough residual magnetism can be restored.
- The temperature of the excitation reactor of the automatic excitation device is too high
(1) The reactor coil is partially short-circuited, and the reactor should be repaired.
(2) The air gap of the magnetic circuit of the reactor is too large, and the air gap of the magnetic circuit should be adjusted.
- After the generator starts, the voltage cannot rise
(1) The excitation circuit is disconnected, so that the voltage cannot rise. Check whether the excitation circuit is disconnected and whether the contact is good.
(2) The remanence disappears. If the exciter voltmeter has no instructions to indicate that the remanence disappears, the exciter should be magnetized.
(3) The polarity of the magnetic field coil of the exciter is reversed, and its positive and negative connection lines should be exchanged.
- When doing some tests in the generator maintenance, the magnetic field coil is mistakenly energized with reverse direct current, resulting in the disappearance or reverse of the residual magnetism, and it should be re-magnetized.