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The large generator used the fixed mode of regular pre test and planned maintenance, which has increasingly exposed its defects, mainly in the following aspects: one is the frequent overhaul, the two is insufficient maintenance, the three is overmaintenance, and the four is blind maintenance. With the development of the electric power industry, a new model of the generator state maintenance is put forward in the field of insulation supervision. On the basis of the preventive test, a new model which stands out from the mode of planned maintenance is presented. The basis of the maintenance is not limited to the data of the preventive test, but it is collected, mastered and analyzed. On the basis of various state information of generator, the comprehensive judgement is made to evaluate generator state and guide generator maintenance.
1 factors affecting the state of the generator
The state of the generator is a continuous and systematic concept, which refers to the situation of generator design, material selection, assembly, transportation, site construction, commissioning and operation, and the abnormal conditions that have occurred since the operation. For example, the overcurrent and overload caused by faults in the operation process of generator units will have an impact on the state of the equipment. There are a lot of factors affecting generator state, but the following main factors are: (1) manufacturing quality; (2) installation quality; (3) operation condition; (4) operation maintenance; (5) technical standard for maintenance; (6) life cycle of generator itself.
2 generator state assessment
The generator state assessment is based on the comprehensive analysis of the various state information gathered by the generator, and evaluates the health state of the generator.
2.1 state information
Generator status information includes: generator manufacturing quality, handover and installation acceptance, preventive test, on-line monitoring, operation condition, maintenance and elimination record. The test data include data obtained from power failure, electrification, on-line and off-line methods.
2.2 state information evaluation
According to the existing test technology level, the main data of generator state information have 6 aspects: manufacturing plant report, operation operation, monitoring disk and inspection situation; preventive test report; periodic maintenance report; stop inspection and temporary maintenance and infrared temperature measurement report; other online monitoring data. Based on the above information, the generator status can be divided into four levels: A: normal state; B level: suspicious state; C level: bad state; D level: dangerous state.
Main condition of normal state of 2.2.1 generator
Normal state: normal operation, normal test data or suspicious test data, but stable data. Generators with normal conditions must satisfy the following requirements simultaneously:
(1) the production and transportation of the generator are in good quality, in line with the technical agreement and the requirements of the relevant standards; there are measures to improve the insulation level, the ability to resist short circuit and adapt to the peak adjustment. The factory test, the handover test and installation test pass through one time, and the generator has no weak links and defects.
(2) the insulation resistance, absorption ratio and polarization index of the stator windings are stable and consistent with the standard during the cycle.
(3) the operation parameters of the generator are normal, and the vibration, noise and roving inspection of the unit are not abnormal.
(4) the temperature of each part of the generator is normal, the constant cold water conductivity, pH value, hydrogen purity and humidity are normal, the hydrogen leakage volume is not over standard, the oil system runs normally and the oil quality is qualified.
(5) no load characteristic, short circuit characteristic, core loss test, stator winding and end leakage current, withstand voltage test, 0.1Hz ultra-low frequency withstand voltage test qualified.
Main conditions for the suspicious state of 2.2.2 generator
Doubtful state: it is found that some parameters may reflect abnormal phenomena in the generator during the test and maintenance period, but there are still many uncertainties. All of the following factors belong to this state:
(1) for the first time in the test period, the insulation of the stator windings was reduced to less than 70%, but the absolute value (20 degrees) was greater than 500M, the polarization index was more than 2, and the absorption ratio was more than 1.6.
(2) the insulation test values of rotor winding insulation, bearing insulation, sealing support and middle ring insulation, center ring insulation, core screw insulation, end iron core and Bush thermocouple insulation and resistance temperature measuring element insulation are lower than 30% for the first time in the test period, but it is still above the standard limit.
(3) the temperature or temperature difference of each part of the generator is not up to normal, but it is still within the alarm limit.
(4) abnormal cooling water conductivity, pH value, hydrogen purity and humidity, which are more than the expected value but still less than the alarm value; the stator cooling water flow rate under the rated pressure is obviously lower, but still above the alarm value.
(5) the electrical insulation inspection of stator winding insulation is found to be abnormal but the value is within the allowable range.
(6) the DC resistance values of the phases or branches of the stator windings are different from each other, and the relative changes are more than 1% when compared with the measured values at the initial (factory or handover) time.
(7) when the stator core is tested, the maximum temperature rise of the magnetically sealed 1T is obviously increased, but it is still <25K, and the maximum temperature difference of the tooth is <15K.
(8) empty and short circuit characteristics and short circuit characteristic curves found in the test process of the short circuit characteristic and short circuit characteristic are lower than that of the factory or previous year, but it is still within the allowable range.
Main condition of bad state of 2.2.3 generator
Bad state: refers to previous periodic test or tracking test results analysis of the existence of failure, and basically determine the fault location and fault causes, to judge that this fault will not happen in the short term. One of the following factors belongs to the same state:
(1) the insulation of stator winding, rotor winding insulation, bearing insulation, seal bearing, middle ring insulation, core screw insulation, end iron core and axle bush thermocouple insulation, resistance temperature measuring element insulation, etc.
