The common problems of diesel alternators2018-10-14 10:54:30
The main rated parameters of synchronous alternators
(1) Rated power (pe): It is the maximum power output of the generator during the rated operation. The units are kilowatt (KW) or Megawatt (MW)
(2) Rated voltage (Ue): It is the line voltage of the generator during the normal operation. The units are volt (V) or kilovolt (KV)
(3) Rated currency (Ie): It is the line current of the generator during the rated operation. The units are ampere (A) or kilo-ampere (KA)
(4) Rated speed (nc): It is the required speed rate which keeps the frequency of AC 50Hz, The unit is r/min
(5) Rated efficiency (ηe): It is the efficiency under the rated operation of the generator.
(6) Rated frequency (fe): The definition under the rated frequency in our country is 50Hz
(7) Rated power factor (cosφe): It is the power rate during the rated operation of the motor.
(8) Rated temperature rise：it is the allowable rising temperature of generator stator winding and rotor winding than Environmental temperature, which is 40℃ of our country regulation.
What factors are related with electromotive force frequency of synchronous generator?
If the magnetic field of the rotor of a pair of poles in synchronous generator revolves around the space in full circle, the induced EMF of stator coil will alternate one time. If there are several magnetic poles with rotor, the induced EMF of stator coil will alternate for the same times when the rotor revolves one cycle. If the rotor revolves n times per minute, then the induced EMF of stator coil will alternate one time nP times per minute. Also the frequency is number of circles changing per second of alternating current. So f=nP/60 (n is the speed of generator rotor (r/min), and P is the number of poles).Therefore, the electromotive force frequency of synchronous generator are related to the speed of generator and the number of poles.
The definition of synchronization of synchronous generator
Since there are magnetic fields by the stator rotating and the rotor coil flowing through DC current in the air gap between the stator and the rotor, it is named as "synchronization” when the magnetic field of the stator and rotor rotating in the same direction and the same speed
What is the function of thrust bearing for hydrogenerator?
The function of thrust bearing for hydrogenerator is bearing the weight of generator rotor and turbine rotor and all axial driving force generated by water flow.
How reduces the heat from the end of stator core?
The heat from the end of stator core is due to the strong leakage flux in the end of stator core, which would cause large eddy currents in the end of iron core and partial overheating. The methods of reducing the heat: 1. Increase the air gap in the end of iron core to increase the reluctance and reduce the magnetic flux leakage. 2. Try to improve the cooling of the end of iron core and plate. 3. The pressing ring is made of non magnetic steel and nonmagnetic cast iron.
The reasons of synchronous generator insulation resistance lower than the standard, and the solutions
The reasons: the coil by damp causing transportation, storage, shutdown for a long time or coil damp by the water dropping into the generator.
Solution: Drying by the method of short circuit current,
The main reasons of generator with no producing electricity, and the solutions
Reason: wrong wiring connecting.
Solution: correct it with the right wiring diagram
Reason: too low speed of revolution.
Solution: measure the speed of revolution and keep rated number
Reason: There are sludge or oxide on connecting plug between the stator winding and generator power distribution equipment, or the wiring screws loosing, connecting line breaking, the stator winding disconnection.
Solution: check and find the breaking point by universal meter or lamp test method. Check the wiring screw connection and contact
Reason: the excitation circuit disconnection or poor contact.
Solution: check and find the breaking point by universal meter. Then weld and wrap by insulated material.
Reason: rectifier tube (including diode rectifier, SCR) damaged.
Solution: replace the damage components.
Reason: poor contact between the brush and slip ring or low pressure of brush.
Solution: Clean the surface and polish the brush, to make it anastomosis with the surface of slip ring, and increase the brush pressure
Reason: the brush rusts which leads the sliding brush failing to move up and down.
Solution: clean the inner surface of brush with emery cloth, or change it if damaged
Reason: the wrong location of exciter brush, brush damaged or low pressure of the spring.
Solution: Adjust the brush to the correct position, replace the brush and adjust the spring pressure
Reason: wrong rotating direction of the original motivation.
Solution: change the rotating direction of original motivation.
Reason: Error excitation winding connection, and reverse polarity.
Solution: correct the wearing connection and magnetize it by dry battery and battery.
Reason: disconnection of the exciter field rheostat.
Solution: find out and connect the place of breaking.
Reason: no excitation of the controllable silicon excitation device.
Solution: check whether the residual voltage exists in the main device, and magnetize the rotor excitation winding and check working condition of the trigger if not.
Reason: no working of the SCR trigger.
Solution: check the input AC power.
Reason: disappearing or too less of the remanence of generator.
Solution: magnetize it by DC power supply
The general reasons of the too low voltage of generators, and the solutions
Reason: too low speed of original motivation.
Solution: adjust the original motivation speed to the rated value
Reason: too high loop resistance of excitation.
Solution: decrease the resistance of the field rheostat to increasing excitation current, and check the additional winding connection broken or wrong for semiconductor excitation generator.
Reason: without the neutral position of exciter brush or too small pressure of the spring.
Solution: adjust the brush to the correct position, replace brush and adjust the pressure of spring.
Reason: breakdown of some rectifier diode.
Solution: check and replace the breakdown diode.
Reason: short circuit or ground fault of stator winding and excitation winding.
Solution: check the fault and remove it.
Reason: too small contact surface of the brush, low pressure and poor contact.
Solution: polish the surface of the commutator by emery cloth or adjust the pressure of spring under the low speed if it is caused by unsmoothed commutator surface,
The general reasons of too high voltage of the generator, and the solutions
Reason: too high revolution speed.
Solution: reduce the hydraulic turbine hydrofoil opening angle and reduce the speed of revolution
Reason: too large air gap of shunt reactor core.
Solution: change the thickness of reactor core shim, and adjust the air gap.
Reason: short circuit of the field rheostat, and failure of the voltage adjustment.
Solution: find out the short circuit point and remove it.
Reason: the galloping trouble of generators.
Solution: stop and deal with the accident emergency. What are excitation modes of small hydro generator, and what are their own excitation devices? There are two excitation modes of small hydro generators, excited and motivated modes, and motivated mode by DC exciter and excited modes by semiconductor excitation, such as silicon rectifier, SCR, three harmonic excitation and so on.
The advantages and disadvantages of DC exciter and semiconductor exciter
The advantages of DC exciter excitation as follows:
(1) It is simple and reliable, less cost of equipment investment and operation
(2) The exciter running only relates with original motivation of generators, and no relationship with external power grid, so the external power grid fault will not affect the normal operation of the exciter.
The disadvantages of DC exciter: repair work is heavy and the generators must be turned off in overhaul.
The advantages of semiconductor excitation:
(1) Small volume, light weight, small maintenance workload.
(2) Fast response, convenient adjustment, simplifying procedures, reducing the labor intensity of staff, and improving the quality of electric energy.
(3) Large excitation capacity. The disadvantage of semiconductor excitation: due to the power connected with grid, the influence by system is large, and system control is complex.
The general reasons of abnormal voltage of excitation, the solutions
(1) Reason: open circuit or short circuit of the reactor and a current transformer, or no working. Solution: find out the open circuit or short circuit and connect or replace a new coil. (2) Reason: too small setting resistance, and low voltage. Solution: adjust the setting resistance. (3) Reason: too small air gap of reactor, and low voltage. Solution: adjust the reactor air gap, and keep the rated voltage.
(4) Reason: too large air gap of reactor, and too high voltage. Solution: adjust the air gap reactor smaller, and keep the rated voltage.
The general reasons of the abnormal voltage of controlled silicon excitation generator, and the solutions
(1) Reason: breakdown or opened of the thyristor control board, and no electricity. Solution: check the thyristor by universal meter, and replace it if breakdown (2) Reason: too late for the opening of thyristor, and low voltage. Solution: adjust the opening angle of thyristor. (3)Reason: damaged of trigger link, and no electricity. Solution: remove the trigger link, check the fault, and eliminate it
The general reasons of unbalanced three-phase voltage of generator
(1) Reason: breakdown or opened of the thyristor control board, and no electricity. Solution: check the thyristor by universal meter, and replace it if breakdown
(2) Reason: too late for the opening of thyristor, and low voltage. Solution: adjust the opening angle of thyristor.
(3)Reason: damaged of trigger link, and no electricity. Solution: remove the trigger link, check the fault, and eliminate it
The general reasons of generator temperature rising too high, and the solutions
(1) Reason: too long loading time. Solution: reduce the load.
(2) Reason: friction of stator and rotor core. Solution: mostly reason is caused by the bearing damaged. Repair or replace bearing by shutdown the generator immediately.
(3) Reason: short circuit or electric leakage of the stator winding. Solution: check the stator winding.
(4) Reason: bad air cooling. Solution: check and confirm if the air duct is blocked, and the fan is damaged.
(5) Reason: bad rectification. Solution: for the silicon rectifier, check the silicon element. Check whether there is excitation loop grounding.
(6) Reason: damped motor. Solution: dry by short circuit current.
The possible reasons of smoking with burring smell from the inside of the generator, and the solutions
(1) Reason: the Interterm or interphase short circuit of stator winding. Solution: shut down the generator immediately and check.
(2) Reason: seriously overloaded of the generator. Solution: reduce the overload.
(3) Reason: breakdown of the excitation circuit. Solution: shut down the generator immediately, check the connection of each excitation loop leads, find out the problems and connect them firmly
(4) Reason: misoperation and non synchronization. Solution: solute column, stop the processing and check immediately
(5)Reason: generation galloping, too high voltage and damaged insulation. Solution: stop processing and check immediately.
The possible reasons of abnormal sound in generator operation, and the solutions
(1) Reason: bearing wearing, and frictional interaction between rotor and stator. Solution: replace the bearing.
(2) Reason: commutator copper rough or mica sheet bulge. Solution: polish the surface of the commutator with emery cloth at low speed, and scrap the protruding piece of mica sheet.
(3) Reason: too hard brush. Solution: replace with soft brush.
(4) Reason: too high pressure of the Brush. Solution: adjust the pressure of the spring.
The reason of too heavy vibration of generators, and the solutions
(1) Reason: misalignment between the generator rotor and turbine shaft center. Solution: adjust it again
(2) Reason: loose anchor bolts, or without a solid foundation, leading the uneven subsidence. Solution: tighten the screws, reinforce the foundation, and adjust it again.
(3) Reason: no round of the shaft neck bending. Solution: check the shaft bending, and adjust it.
(4) Reason: short circuit, grounding or connection error of the rotor excitation winding. Solution: check the ring and rotor winding insulation to ground by using DC voltmeter during the processing, and correct it,
(5) Reason: short circuit or grounded of the stator winding. Solution: shutdown the generator and check.
(6) Reason: non synchronization. Solution: shutdown the generator and checking immediately if the vibration is too strong.
(7) Reason: partial failure or lightning strike. .Solution: shutdown the generator and checking immediately if the vibration is too strong.
The general reasons of generator voltage instable, and the solutions:
(1) Reason: wiring loose or brush loose. Processing: connect the wiring tightly, and adjust the brush
(2) Reason: failure or particial connecting wrong of automatical voltage regulator.
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What factors are related with electromotive force frequency
