In thermal power plant, there are many auxiliary high-voltage motors, which have a long running time. The motor leads run in a high temperature environment for a long time, which makes their insulation aging faster. The conventional test method can only measure the insulation to the ground, and the lead is fixed on the insulation board, so the routine test can not find the bad problem of interphase insulation (the motor is usually star internal dead connection). In this way, when the lead insulation is aged to a certain extent and the routine test is qualified, the phase to phase short circuit in operation will cause the high-voltage motor to stop running, and in serious cases, it will cause the boiler to stop running, which greatly endangers the safe and stable operation of the unit and even the system. The following describes several such events and their handling methods of our company as well as the application of heat shrinkable tubes.
Cases of motor inter phase short circuit accidents in operation
In August 2015, during the operation of No.5 boiler b air suction motor of a company, the blasting was conducted at high speed and low speed. It was found that the three-phase outgoing line of the low speed winding was bound and fixed due to inter phase short circuit, which caused serious local damage and class II assessment obstacles. It is found that the rubber insulation of the outgoing line is seriously aged, brittle and cracked, and the core of the wire is exposed. The rubber insulation will be broken as soon as it is pinched.
During the operation of No.2 boiler blower motor in a company, the No.2 boiler was forced to shut down, resulting in a kind of assessment obstacle. It is found that the phase to phase short circuit of the binding fixed part of the three-phase outgoing line is caused by the decomposition inspection of the motor, and the local damage is serious. The insulation aging condition of the outgoing line is the same as the above.
The outgoing lines of the motor are rubber insulated flexible wires, which are fixed in the hot air area. The operation environment is poor. The temperature in the hot air area is high (the maximum operation temperature in summer is 60-70 ℃). Under the long-term effect of the hot air, the rubber insulation is prone to aging and cracking. After investigation, it is found that after three years of operation of the motor, the insulation of the outgoing line is embrittled and cracked in varying degrees.
The three-phase outgoing lines of the motor are bound together and fixed, which is unreasonable. Once the insulation of the outgoing line is aged and cracked, because the metal exposed part is close to each other, the shot will be shot under the action of the phase-to-phase online voltage, and the motor will stop running.
The three-phase leads of the high-voltage motor are separated and fixed at a certain distance to solve the problem of inter phase short-circuit shooting.
The three-phase outgoing lines are respectively shrunk by high-voltage insulated heat shrinkable pipes to solve the insulation problems after aging and cracking. The high voltage insulation heat shrinkable tube is also heat shrinkable to prevent the aging of the lead insulation from cracking, so as to increase the ageing resistance of the rubber insulated soft wire and extend the aging period.
It is suggested that the manufacturer should separate the three-phase leads and fix them at a certain distance during production, and increase the protection of heating shrink tube to avoid inter phase short circuit and solve the problem of inter phase insulation from the source of production.
It is suggested that the manufacturer improve the operation environment of the outgoing line and solve the problem of aging and cracking of the lead.
It is suggested that brother units should strengthen the inspection of the outgoing line parts of high-voltage motors which have been operated on site for three years, and draw lessons from our company.