In the nationwide scale more than 20 month-long electric power supply short situations have become one which of continuously hot spots the society pays attention. Closes the supply and demand gap with difficulty in the short-term in the situation, some Local authority adopts to the installment supplies for oneself the power set or the dispersion-like electrical power system’s enterprise gives the action which in the policy, the technology supports, facilitated has supplied for oneself the power set or the dispersion-like electrical power system’s development, caused reaches many kW in the coastal economy developed area aggregate capacity the unit to put the operation one after another. The exciter is supplies for oneself the power set or the dispersion-like power source’s important component, not only its safe operation or not relates is exchanging power set’s steady operation, moreover relates enterprise’s economic efficiency. Supplies for oneself the power set engine off notification which initiates as a result of the exciter breakdown often to spread. Author two example exciter equipment failure which meets in view of the work in makes a brief analysis, refers for the related maintenance of equipment personnel, with the aim of resuming the breakdown equipment’s movement as soon as possible.
1 design and manufacture quality question initiation accident
1.1 accident processes
Some power plant #9 generator is QFS-125 (Ue is 13.8kV, rotor Ie is 1635A), its main exciter is ZLG-550-30 (550kW, 300V, the 1832A shunt excitation), was the Shanghai some electrical machinery plant 1974 annual products. The generator shoulders 120MW,75Mvar, rotor current 1500A. Some day, in any excitation adjustment’s situation, the idle work load has not swung large scale suddenly, from 75Mvar suspends to 50Mvar; The exciter air outlet braves the black smoke, the commutator spark to be serious, the spark long approximately 60~70mm, the carbon brush majority is destroyed, the unit is compelled emergency stop. The inspection discovered that the main exciter 84 carbon brushes have 81 to destroy, the commutator surface local overheating, the partial commutator segments lug. Has carried on under the cold clean criticality according to the overhaul regulations turning processing. Then starting, when the generator stator voltage climbs to 7kV, when rotor current 400A, presents the carbon brush to destroy once more phenomenon, creates two engine offs. After survey commutator bias 0.17mm (>0.05mm technology standard), and has the individual commutator segment bulge, the neighboring piece maximum height difference is 0.07~0.08mm.
1.2 reason analyses
Believed according to the phenomenon and the inspection analysis that this model exciter is designing and the manufacture aspect exists is congenitally deficient.
1.2.1 design aspects
the 550kW coaxial cocurrent exciter is the home maximum capacity the coaxial direct-current exciter. Its commutator diameter φ350mm, the circumferential velociy probably is 55m/s. According to the formula P=1.8×108/n(kW) computation, directs current exciter’s ultimate capacity is 600kW (common exciter capacity is generator capacity 0.25%~1%), the factory request use’s DS-74B carbon brush can only be suitable under the 50m/s circumferential velociy moves. But when is higher than under the 50m/s speed moves, will inevitably cause commutator surface temperature increment. Adds it, under the large diameter high speed moves the coaxial direct-current exciter, the commutator produces the mechanical stress is big, causes the commutator segment to have the distortion. Moreover, the 550kW exciter uses the coaxial fan cooling, the original design air flue moves toward unreasonable, in addition 3 solar halo’s influences, cause commutator surface various part to cool non-uniform, commutator various part of thermal deformation are inconsistent, as well as powdered carbon to commutator surface pollution and so on.
1.2.2 manufacture aspects
1) commutator segment material quality degree of hardness somewhat low (degree of hardness is 45 degrees), easy to wear, the distortion; 2) the fabrication technology is rough, between the commutator segment altitude error is big, between the piece mica breaker strip thickness is uneven, each piece of between tight strength has the difference, therefore after being heated, each piece distorts different;
3) wedge-shaped pushes the tight strength which pulls out not to stipulate explicitly, sometimes tight and sometimes lax, excessively tight possibly causes the commutator segment to haunch up, crosses the pine possibly to enable the commutator segment to rock;
4) commutator’s assembly uses the cold wrap cold-press craft, has not adopted thermal deformation processing, among them the stress has not released, but the group and the headgear start weld, causes magnetism not to be balanced is also another cause;
5) DS-74B carbon brush material quality bad, the product quality is unstable, brushes the tail easily to loosen creates the carbon brush overheated, in turn causes the carbon brush deactivation, to get angry;
6) the commutator center in exciter’s geometry neutral surface, the brush holder support is not away from waits for the influence commutation effect;
7) the commutator garden, the smooth finish is not low, the superficial oxide film cannot establish, between the piece the mica sheet protrudes, as well as commutator surface pollution and so on.
1.3 processing measures
According to the above inspection analysis, adopted the warming, the thermo-compression, the hot turning commutator’s method in scene to carry on processing, the entire technological process was as follows.
1) restores the standard craft, uses the hot jacket, the thermo-compression and 6h heating distortion processing to the exciter rotor and the commutator segment, so that stress-relieving. Before the warming, cold clean criticality back tight commutator. After exciter disintegration inspection cleaning, the inspection wedge-shaped pushes pulls out Zhang Quan the tight strength, generally is 13t, with the rap law, listens to the sound and the vibration, looked whether the back cocking nut does fasten. Stops the nail place in the back tight cap nut to open a skew notch, adds the horn important lock nut with 12 pounds hammers, and momentarily uses 2 pounds little hammers to inspect lock nut’s tight situation, until tightly up.
after 2) commutator cold clean criticality fastening, thrusts the drying room warming the armature whole, in the roasting the maximum temperature do not surpass 120℃; Maintains 120℃ (only heats up actually to 110℃) 6h, causes the commutator to distort as far as possible; Armature various part of temperatures must be balanced, prevent the partial excess temperature to cause the insulation damage. The commutator fastens under the heat condition. After heating up the thermal deformation, to wedge-shaped pushes pulls out the lock nut to carry on the fastening again, with the rap law inspection fastening situation, however the breech loading refreshes stops the nail. Stops nail’s weight to consider the lock nut reduces weight.
3) the commutator under the heat condition the turning, requests the commutator surface smooth finish to achieve △8; The commutator bias is not bigger than 0.01mm; The mica trough scrapes is lower than commutator surface 1.5mm, the commutator segment both sides pour 0.5×45° the bevel edge; After comparing cold, the heat and the turning commutator’s eccentric size, supplies the analysis processing.
Moreover, the carbon brush changes to the material quality to be even, degree of hardness is moderate, quality stable B374N.
1.4 processing results
After the above method processing, after the unit throws transports, moves normally, has not had the commutator serious spark, the carbon brush to destroy again the phenomenon, afterward also passes through tests many times, had not discovered that the commutator lugs the phenomenon.
2 greasy dirt sully initiation exciter rotor earth fault
2.1 breakdown phenomena
Some day, some factory #8 generator “the excitation return route earth” the signal sends out. The exciter is ZL105-3000 (105kW/230V/456A3000r/min). After the engine off, inspects, surveys the exciter and the generator armature coil. Surveys the exciter rotor dielectric resistance in the scene with the measuring range 500MΩ/500V megameter is zero. The disintegration inspection discovery decides, rotor’s carbon, the ash greasy dirt sully to be serious.
2.2 reason analyses
After the disintegration, first uses the compressed air to blow floats the ash. Then, after charged cleansing agent repeatedly spraying clean, carries on drying processing. After dry, with the measuring range 500MΩ/500V megameter survey exciter rotor dielectric resistance is still zero, with digital multitester survey exciter rotor dielectric resistance near 200Ω, surveys the commutator segment the resistance and carries on the comparison, all in qualified scope. Profits from the Brother unit to process the exciter rotor to insulate the low experience and the scene actual situation, judges the exciter rotor winding countershaft to have the carbon, the ash greasy dirt sully short circuit earth fault initially.
2.3 eliminate the method
After definite breakdown nature, the use self-restraint’s beak and the electrically operated spray gun, demolish the commutator end the epoxy resin shroud ring, after taking out elevates the complete insulation spacer between the piece, with the beak hook blows elevates the internal side clearance and the charged cleansing agent spraying cleaning up alternately repeatedly many times, after each time processes surveys its insulation with the avonmeter to have elevates the potential gradually, but still cannot achieve the rating (≮0.5MΩ). After on-spot check and the discussion, after searching the material, decided that with the throughflow burning through law determined the concrete ground point, might pass over the spot which like this through the observation the short-circuit current the size and the survey gave off heat to find the ground point, may also through the short-circuit current which passed over short-circuit earth medium burning through to be advantageous for the elimination. The concrete procedure is: (Commutator segment place) exerts an alternating voltage in the exciter rotor winding with the revolution axis between (electric current ≯5A), the slow booster tension causes the electric current which passes over by when 0 elevate gradually to 1.3A, discovers elevates between the piece to have many place belches smoke, continues to observe discovered that every belches smoke place all has the scaling sully powdered carbon, this namely for short circuit medium. Then the separation exerts the alternating voltage, belches smoke to the discovery place blows with the beak hook carries on repeatedly alternately after the charged cleansing agent spraying cleaning up, once more uses the digital multitester and the megameter survey, discovered that insulates the large scale rise to near 2.0MΩ. Again (commutator segment place) exerts when the exciter rotor winding with the revolution axis between the alternating voltage elevates to 250V, the ampere meter instruction is zero. Explained that the ground point eliminated. Then, carries on the 500V exchange pressure resistance and the leakage current experiment to the exciter rotor winding is qualified. The demolition test equipment amount used regulation 500MΩ/500V megameter survey exciter rotor dielectric resistance stabilizes in 1.5MΩ, hence, the exciter rotor winding earth fault eliminates. Carries on drying dipping lacquer processing the rotor, restores elevates between respectively the piece the crossover block, wraps up the commutator end the epoxy resin shroud ring, after other appendices make craft processing, the equipment restores completely to the readiness condition, also surveys its dielectric resistance ≯0.5MΩ, meets the regulations requirement.
2.4 processing results
After the above method processing, the equipment invests the movement already several years, until now is safe stably.
3 conclusions
Through the above two example exciter breakdown’s processing, made us to gain in the equipment overhaul experience, had the enhancement to the supporting facility important understanding, has provided the safeguard for the later unit’s safe operation.
