1. Keep the generator running and use a voltmeter to test the battery. The voltage reading at this time should be about 13 volts or a little higher. If different speed changes cause the voltage to fluctuate between 13 and 14 volts, Then the generator is in good condition; on the other hand, if the voltage remains the same or decreases, then the generator is indeed faulty.
2. Start the engine, turn it off after a few minutes, and touch the generator. If the generator is very hot, the bearings may have been worn or the insulating copper windings have been damaged, which indicates that the generator will soon Out of action.
3. Turn on the radio and start the engine. If the radio rattles or the sound quality is blurry whenever you step on the accelerator, then there is most likely a problem with the generator.
4. When the car does not start, use an electric meter to measure the V number of the battery and record it. Then start the car, use the meter to measure the V number of the battery, and record it. If the car's alternator is not broken, the battery V number will be higher when the car is started. About 13.7V, it depends on the car. But it will definitely be higher than the V number where the car won't start. The most obvious thing is that if the generator breaks down and the car is driven for 2-3 days, the battery will lose power and the car will not be able to start with electricity.
5. Turn on the car's headlights, check the brightness of the lights, and then start the car. The lights will dim and the car starts. Check the brightness of the headlights, then increase the accelerator and check the brightness. If there is no big difference between the lights before starting and after starting, it means the generator is not working. If the lights before and after starting are reflected and become very bright, then the generator is good but the battery is bad.
The generator does not operate according to the specified technical conditions. If the stator voltage is too high, the iron loss increases; the load current is too large, the stator winding copper loss increases; the frequency is too low, causing the cooling fan speed to slow down. , affecting 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. Check whether the indication of the monitoring instrument is normal. If it is abnormal, necessary adjustments and treatments must be made to make the generator operate according to the specified technical conditions.
References:
Can a car alternator be repaired if it is broken?
(1) Fault detection of alternator When the car alternator is found to be generating electricity When there is a fault such as the engine not generating electricity or insufficient power generation, you should first determine whether the fault occurs in the external circuit or inside the generator. If it is initially determined that the fault is inside the generator, the alternator should be removed from the vehicle and inspected and repaired. . The alternator should be tested as a whole first. The purpose is to determine whether the alternator is faulty and where the fault occurs, so that targeted repairs can be made. The whole machine test includes: measuring the resistance between each terminal,Conduct no-load voltage and load current tests on the universal test bench, and observe the generator output waveform with an oscilloscope. (2) Complete machine test of alternator (1) No-load test 1. Measure the resistance between each terminal (1) Measure the resistance between the generator’s output terminal B+ and the ground terminal E (shell or ground terminal). Through measurement, it can be determined whether the alternator rectifier is faulty. If there is a fault, the generator should be disassembled for further inspection. (2) Measure the resistance between the generator's positive brush F terminal and the negative brush E. If it is not possible to determine whether the alternator is faulty by measuring the resistance between each terminal, a test bench test should be performed. 2. Test bench test No-load test is a test when the alternator does not carry any load (no external current is output). The purpose of the no-load test is to initially determine whether the generator is faulty. (2) Load test The load test is a test when the alternator is under load (external output current). The purpose of the load test is to further determine whether the generator is faulty. Some faults of the alternator will not show up without current output, so if the no-load test of the alternator is normal, the load test should be performed again. 3. Use an oscilloscope to observe the output voltage waveform (if conditions permit). When the alternator fails, its output voltage waveform will be abnormal. Therefore, if conditions permit, you can use an oscilloscope to observe the output voltage waveform of the generator. According to The output voltage waveform can determine whether the internal fault of the alternator is a rectifier fault or a stator winding fault. 1. The reason why the ammeter indicates the discharge position when the silicon rectifier generator is running at medium speed 1. The connecting wire between the battery phase and the generator is broken, often Occurs at the armature terminal or at the turning point of the wire; 2. The generator does not generate electricity: the diode breaks down or the internal rectifier junction is detached and does not function as a rectifier; the brush is stuck in the brush holder, so that the generator cannot be excited; The excitation winding is open circuit; the stator winding is short-circuited or grounded; the excitation winding is short-circuited; the regulating voltage is too low, the contacts are ablated, and a wire end in the regulator is disconnected or open-welded, causing the excitation circuit of the generator to be blocked. 2. Charging is unstable, and the reason why the ammeter indicates charging sometimes and not charging 1. The generator transmission belt is too loose and slipping; 2. The wire between the battery and the generator armature terminal is not firmly connected or is about to break, causing the charging circuit to On and off; 3. Loose internal wiring of the generator, dirt on the slip ring, excessive brush wear, reduced brush spring pressure, etc., causing poor contact between the brush and the slip ring 4. Poor contact or spring tension in the internal connection part of the regulator Too weak and contact ablation cause poor contact, causing the regulator to work unstable. 5. Poor internal contact in the ammeter. 3. The charging current is too large, more than 10A for a long time, the electrolyte evaporates quickly and causes premature battery damage. 1. The regulating voltage is too high. Electricity should beThe positive test rod of the pressure gauge is connected to the armature terminal of the regulator, and the negative test rod is connected to the bottom shell of the regulator. If the measured voltage is higher than the specified value, the spring tension, movable contact arm and iron core need to be adjusted. gap; 2. The end of the regulator coil falls off and loses its regulating effect. 4. The charging current is very small, and the reasons for not charging at low speed are: 1. The diode in the rectifier is damaged; 2. One phase in the stator winding has poor contact or is disconnected; 3. The slip ring is dirty, and the brush and the slip ring are in poor contact; 4. The regulator voltage is too low or the pulley is slipping. Generators are constantly subjected to various mechanical and electromagnetic forces such as vibration, heat, and corona during operation. In addition, due to design, manufacturing, operation management, and system failures, the temperature of the generator often rises and the rotor winding is grounded. , stator winding insulation damage, exciter carbon brush sparking, generator overload and other faults. Some common faults in the operation of synchronous generators are analyzed as follows.
Common faults and measures for generators 2.1 Non-synchronous paralleling of generators
When generators are paralleled using the quasi-synchronous method, they should meet the three conditions of the same voltage, cycle and phase. If Due to improper operation or other reasons, if these three conditions are not met during paralleling, the generator will be paralleled asynchronously, which may damage the generator and cause a strong impact on the system. Therefore, attention should be paid to preventing such failures from occurring. When the voltage of the generator to be paralleled is different from that of the system, there is a voltage difference between them, and a certain inrush current will occur when the generator is paralleled. Generally, when the voltage difference is within ±10%, the inrush current is not too large and there is no danger to the generator. If the voltage difference is large when paralleling, especially when large-capacity motors are paralleled, if their voltage is much lower than the system voltage, then in addition to generating a large current impact, the system voltage will drop, which may amplify the accident. Generally, when paralleling, the voltage of the generator to be paralleled should be slightly higher than the system voltage. If the phase of the voltage of the generator to be paralleled is different from that of the system voltage, the impulse current caused by paralleling will produce a synchronous torque, causing the generator to be paralleled to be immediately synchronized. If the phase difference is within ±300, the generated impulse current and synchronous torque will not have serious effects. If the phase difference is large, the impact current and synchronous torque will be very large, which may reach twice the three-phase short-circuit current. This will cause the stator bar and rotating shaft to be subject to a large impact stress, which may cause serious deformation of the stator end windings. , the coupling bolts are sheared and other serious consequences. In order to prevent non-synchronous paralleling, some factories have installed a voltage difference checking device and a phase angle locking device in the manual quasi-synchronous device to ensure that the electrical difference and phase angle difference do not exceed the allowable value during paralleling. 2.2 Generator temperature rise (1) The stator coil temperature and inlet air temperature are normal, but the rotor temperature rises abnormally. At this time, the rotor temperature gauge may be malfunctioning and should be checked. When the three-phase load imbalance of the generator exceeds the allowable value, the rotor temperature will also rise. At this time, the load should be reduced immediately, and the system should be adjusted to reduce the imbalance of the three-phase load so that the rotor temperature drops within the allowable range. . (2) The rotor temperature and inlet air temperature are normal, depending onIf the stator temperature rises abnormally, the stator temperature gauge may be malfunctioning. The resistance value of the resistive temperature measuring element used to measure the stator temperature will sometimes gradually increase during operation, or even open circuit. At this time, the temperature at a certain point will suddenly rise. (3) When the inlet air temperature and the stator and rotor temperatures all rise, it can be determined that the cooling water system has failed. At this time, you should immediately check whether the air cooler is cut off or the water pressure is too low. (4) When the inlet air temperature is normal but the outlet air temperature rises abnormally, this indicates that the ventilation system has failed, and the machine must be shut down for inspection. Some generator sets are equipped with guide baffles in the ventilation ducts. Improper operation will block the air path. At this time, the position of the baffles should be checked and corrected. 2.3 Damage to the stator winding of the generator. The generator will cause grounding or phase-to-phase short circuit faults due to insulation breakdown of the stator bar and open welding of the joints. When a generator has a phase-to-phase short circuit accident or a generator running on a neutral point grounding system is grounded, a large amount of current will pass through the fault point, which will cause sudden fluctuations in the system. At the same time, a strong sound can often be heard next to the generator. Inspection The arc fire can be seen outside the window. At this time, the relay protection device of the generator will act immediately, causing the main switch, excitation switch and emergency breaker to trip, and the generator will stop running.
If there is a fire inside the generator, for the air-cooled unit, after confirming that the switches have tripped, open the fire hose and use water to extinguish the fire, while keeping the generator cranking at a low speed of about 200r/min. After the fire is extinguished, the generator should still be operated at low speed for a period of time, and then stop the generator after it has completely cooled down to prevent the rotor from bending the large shaft due to local heating. Hydrogen-cooled and water-cooled generators generally do not cause end fires. For a generator operating in a system with an ungrounded neutral point, when a stator winding ground fault occurs, only the generator's ground protection device will act and alarm. The operator should immediately identify the grounding point. If the grounding point is inside the generator, measures should be taken immediately to cut it off quickly. If the grounding point is outside the generator, the cause should be quickly identified and eliminated. For steam turbines with a capacity of 15MW and below, when the grounding capacitance current is less than 5A, the generator is allowed to run for a short time with the power grid grounded at one point before it is eliminated, but not more than 2h. For power generation with capacity or grounding capacitance current greater than the above regulations When the stator circuit is single-phase grounded, the generator should be decoupled from the power grid immediately and the excitation should be disconnected. When the generator is running, sometimes the operator does not notice sudden fluctuations in the system, and the turbine driver does not send an emergency signal. However, the main circuit breaker of the generator trips due to the differential protection action. At this time, the person on duty should check whether the excitation switch is also activated. has tripped. If it does not trip due to failure of the operating mechanism, it should be manually tripped immediately, the magnetic field rheostat should be adjusted back to the maximum resistance position, the automatic excitation adjustment device should be deactivated, and then the equipment within the differential protection range should be checked. , when the equipment is found to have burnout, flash soldering or other faults, it should be repaired immediately. When any abnormality is found, use a 2500V megger to measure the insulation resistance of the primary circuit. If the measured insulation resistance value isWhen the resistance value at the standard temperature is compared with the previously measured value, it has dropped by less than 1/5, and the cause must be identified and eliminated. If the measured insulation resistance value is normal, the generator can be boosted from zero and then connected to the grid for operation. 2.4 Generator rotor winding grounding When the insulation of the generator rotor is damaged, the windings are deformed, and the ends are severely dusted, it will cause a generator rotor grounding fault. The rotor winding grounding is divided into one-point grounding and two-point grounding. When the rotor is grounded at one point, an electrical circuit has not yet been formed between the wire turns and the ground, so no current flows through the fault point. Various meter indications are normal, and the excitation circuit can still maintain a normal state. However, the relay protection signaling device issues "rotor is grounded at one point". signal that its generator can proceed. However, after the rotor winding is grounded at one point, if any grounding occurs again in the rotor winding or excitation system, two points of grounding will occur.
After a two-point ground fault occurs in the rotor winding, part of the rotor winding is short-circuited. Because the DC resistance of the winding decreases, the excitation current will increase. If a large number of turns in the winding are short-circuited, the main magnetic flux will be greatly reduced, the reactive power output of the generator to the grid will be significantly reduced, the power factor of the generator will increase, and it may even become a phase-advance operation, and the stator current may also increase. , and at the same time, because part of the rotor winding is short-circuited, the symmetry of the generator's magnetic circuit is destroyed, which will cause the generator to produce severe vibrations, which is more significant in the salient-pole generator. When the rotor coil is short-circuited, the excitation current greatly exceeds the rated value. If the machine is not stopped in time and the excitation circuit is cut off, the rotor winding will burn out. In order to prevent the generator rotor winding from grounding, the on-duty personnel on each shift are required to measure the insulation resistance of the excitation circuit through an insulation monitoring meter during operation. If the insulation resistance is lower than 0.5 MΩ, the on-duty personnel must take measures. Purge the parts of the excitation circuit that may be cleaned during operation to restore the insulation resistance to above 0.5MΩ. When the rotor insulation resistance drops to 0.01MΩ, it should be considered that a ground fault has occurred. When a one-point ground fault occurs in the rotor, it should be eliminated immediately to prevent it from developing into a two-point ground fault. If it is a stable metallic ground fault and there is no condition to arrange maintenance at the moment, the rotor two-point ground protection device should be installed to prevent the rotor from being burned and the accident expanded after the two-point ground fault occurs. When an inter-turn short circuit accident occurs in the rotor winding, the situation is the same as that of the rotor being grounded at two points, but generally the number of short-circuited turns is not large at this time, and the impact is not as severe as the two-point grounding. If the rotor two-point grounding protection device is put in, its relay will also act. At this time, the main circuit breaker of the generator should be cut off immediately to decouple the generator from the system and stop. At the same time, cut off the excitation switch and put the magnetic field rheostat on The maximum resistance position, check the rotor and excitation system after shutdown. 2.5 Generator demagnetization
(1) Reasons for generator demagnetization. When a running generator trips due to vibration or misoperation of the excitation switch, poor contact of the magnetic field rheostat, disconnection of the exciter field coil or severe commutator sparking, automatic voltage regulator failure, etc., causing the excitation circuit to open circuit, will generate electricityThe machine loses magnetism.
(2) The situation will be reflected on the meter after demagnetization. After the generator loses excitation, the rotor excitation current suddenly drops to zero or close to zero, the excitation voltage is also close to zero, and there is a swing equal to the slip. The generator voltage and bus voltage are both lower than before, and the stator ammeter indicates an increase. The power factor meter indicates phase advancement, and the reactive power meter indicates negative, indicating that the generator absorbs reactive power from the system. The pointers of each meter swing, and the frequency of the swing is 1 times the slip rate.
(3) Effects caused by loss of magnetism. After the generator loses its magnetism, it changes from synchronous operation to asynchronous operation, and changes from outputting reactive power to the system to absorbing a large amount of reactive power from the system. The generator speed will be higher than the synchronous speed of the system. At this time, the rotating magnetic field generated by the stator current will induce an AC induced electromotive force on the rotor surface with a frequency equal to the slip rate, which generates an induced current on the rotor surface, causing the rotor surface to heat. The greater the active load carried by the generator, the greater the slip, the greater the induced potential, the greater the current, and the greater the loss on the rotor surface. At the moment when the generator loses excitation, there will be overvoltage at both ends of the rotor winding. When the rotor winding and the demagnetizing resistor are connected in parallel, the overvoltage value is related to the value of the demagnetizing resistor. The larger the value of the demagnetizing resistor, the greater the overvoltage value of the rotor winding. . Tests have shown that if the excitation resistance value is selected to be 5 times the rotor thermal resistance value, the overvoltage value of the rotor will be 2 to 4 times the rated voltage value of the rotor. (4) Allowable operating time and load after demagnetization. Whether the generator can continue to operate after it loses its excitation is related to the capacity of the generator operating in deexcitation and the system capacity. After a large-capacity generator loses its excitation, it should be immediately removed from the power grid and shut down. The generator capacity is small and the power grid capacity is large. The generator is generally allowed to operate with demagnetization under low load in a short period of time to handle the demagnetization fault. For generators that allow excitation operation, after a demagnetization fault occurs, the generator load should be reduced immediately to reduce the average stator current below the specified allowable value, and then check whether the excitation switch has tripped. If it has tripped, it should be closed immediately. If the excitation switch does not trip or the demagnetization phenomenon does not disappear after closing, the automatic adjustment excitation device should be deactivated, and the magnetic field rheostat handwheel should be turned to try to increase the excitation current. If the excitation still fails to be restored at this time, you can try to use a backup exciter to supply excitation. After these operations, if the demagnetization phenomenon still cannot be eliminated, it can be judged that the generator rotor has failed, and a shutdown must be arranged within 30 minutes. 2.6 The generator cannot raise the voltage. This type of fault often occurs in generators excited by self-excited coaxial DC exciters. (1)Fault phenomenon. After the generator speeds up to the rated speed, when the generator is excited, the excitation voltage and the generator stator voltage cannot rise, or the excitation voltage does not rise, but the generator voltage does not rise to the rated value. (2) Cause of failure. ① The residual magnetism of the exciter disappears; ② The wiring of the shunt coil of the exciter is incorrect; ③ The excitation circuit is disconnected; ④ There is a short circuit fault between the exciter commutator segments, the exciter carbon brushes are not in good contact or the installation position is incorrect; ⑤ Power generation The stator voltage measurement circuit of the machine is faulty. (3) oneHandled as usual. When the generator starts to the rated speed and then boosts the voltage, if the exciter voltage and the generator voltage do not rise, you should check whether the excitation circuit wiring is correct, whether there is any disconnection or poor contact, whether the brush position is correct, and whether the contact is good. wait. If all the above items are normal, but there is a very small indication on the exciter voltmeter, it means that the polarity of the exciter magnetic field coil is reversed, and its positive and negative connections should be swapped. If there is no indication on the exciter voltmeter, it means that the residual magnetism has disappeared and the exciter should be magnetized. 2.7 Generator overload operation The generator in operation should operate at or below the specified rated load. Otherwise, the temperature of the generator stator and rotor will exceed its allowable value, causing the generator stator and rotor insulation to quickly age and be damaged. Therefore When the generator is overloaded, adjustments should be made to reduce the load. When an accident occurs in the system, resulting in insufficient power or a sudden change in system operation that threatens the static stability of the system, the generator is allowed to operate overloaded in a short period of time. At this time, the personnel on duty should closely monitor the stator and rotor winding temperature, and its value shall not exceed Normally maximum allowed monitoring temperature. The rotor windings are also allowed to have corresponding overloads in the event of an accident. However, the use of these overload margins under normal conditions is prohibited for any generator.
Conclusion
Summarizing the common faults and treatment methods in the operation of synchronous generators is helpful to improve the daily maintenance level of generators in operation, and can also be used as a reference for peers.
If it is a minor fault in the generator, it can be repaired by replacing parts. However, if the copper winding in the generator is burned out, it is still recommended to repair it. Replace it.
Because the cost of replacing a generator is actually not very high. If you adopt the method of replacing internal parts, it will not only take time but also get a new generator with only some parts. In this way It's a bit unnecessary.
Methods to determine whether the alternator is broken:
1. Use a multimeter to measure the battery voltage before starting the vehicle and after starting the vehicle. Generally, when the generator is working normally, the battery voltage reading is generally between 13V-14V. If it is lower than this reading, it may prove that the generator is not working;
2. Feel the operating temperature of the generator , if the temperature of the generator is very hot after the engine has been running for a period of time, it may have malfunctioned;
3. Observe whether there is any abnormal sound or jitter when the generator is working. If such a situation occurs It is possible that the belt tensioner or bearing is faulty.
Of course, this is just a simple way to judge the fault by ourselves. If you want a more accurate judgment, it is best to find a professional repair shop or 4S shop for inspection.