On load tap changer maintenance of the hottest pow

On load tap changer maintenance of power transformer

on load tap changer plays an important role in power system. It can not only stabilize the load center voltage, but also connect electricity, adjust load flow, improve reactive power distribution and other indispensable important equipment. At present, Wulanchabu Power Bureau has a total of 69 power transformers, of which 54 35kV and above transformers are on load voltage regulating transformers

the on load tap changer installed on the on load voltage regulating transformer will inevitably fail during operation and operation. These failures may be caused by the manufacturer's quality problems or improper operation and maintenance. According to statistics, among the unplanned outages of 220kV and above transformers nationwide in 2004, the number of unplanned outages caused by on load tap changers was 8, accounting for 10.343% of the total time of unplanned outages. Therefore, the safe operation and maintenance of transformer on load tap changer is very critical

basic principle and structure of on load tap changer

on load tap changer is an electrical device that can change the tapping position under excitation. The basic principle of on load tap changer voltage regulation is to change the number of effective turns, that is, to change the voltage ratio of the transformer, so as to achieve the purpose of voltage regulation by switching from one tap to another without interrupting the load current in the three months up to the end of December after several taps are led out in the transformer winding. Therefore, during the operation of on load tap changer, first, it is necessary to ensure the continuity of load current; Second, it should have good arc breaking performance in the action of switching and tapping

in the process of changing taps, the on load tap changer must use resistance to realize the transition, so as to limit the circulation when the fixture should not cause the sample to break at the fixture and its transition. Usually, the resistance combined on load tap changer is used. In practice, the structure of the resistance current limiting on load tap changer can be divided into three parts, namely, the change-over switch, the selector switch and the operation structure. Any of these problems will affect the normal operation of the transformer

a laboratory should use appropriate methods and procedures to carry out all testing work and other relevant business activities within its scope of responsibility (including sample extraction, disposal, transmission and storage, preparation, problems in the operation of load tap changer

problem 1

1. The contact in the switch is heated.

frequent voltage regulation will cause serious mechanical wear, electrical corrosion and contact pollution between contacts, especially for transformers with large load current, the thermal effect of current will weaken the elasticity of springs, reduce the contact pressure between dynamic and static contacts, and cause electric shock As the resistance increases, the heat generation between the contacts increases. Heating accelerates the oxidation corrosion and mechanical deformation of the contact surface, and forms a vicious cycle, resulting in the damage of the switch

2. Preventive measures

before the maintenance and operation, the DC resistance of each tapping position of the switch should be tested respectively. During the maintenance of the hanging cover, the contact resistance of the contact should be measured to check whether the contact coating and contact are good. In combination with maintenance or test, rotate the tap changer at each gear several times a year to remove the influence of oxide film or oil stain and make it in good contact

problem 2

1. The transition resistance is disconnected and loose

the disconnection and looseness of the transition resistance will cause the whole transformer to burn out. If the transition resistance is switched with load when it is burnt out, not only the load current will be interrupted, but also all phase voltages will appear on the fracture of the transition resistance and between the breaking opening of the dynamic and static contacts. This voltage will not only break through the fracture of the resistance, but also produce a strong arc when the dynamic and static contacts are disconnected, resulting in a short circuit between the two tap changers, resulting in a short circuit and burning of the tap section of the high voltage winding. At the same time, the arc quickly decomposes the oil in the switch oil chamber, producing a large amount of gas. If the safety protection device cannot discharge these gases immediately, the switch will be damaged. The energy of the arc can also burn out the insulating cylinder of the switch, so that the switch cannot be repaired

2. Preventive measures

(1) before the transformer leaves the factory, before operation and after overhaul, it is necessary to check whether the transition resistance is loose and whether the resistance wire is mechanically damaged, so as to avoid local overheating and burnout during switching

(2) for on load switches with switching times of more than 20000 times or operating for more than 2 years, it is necessary to check whether the material of the transition resistance becomes brittle, whether the resistance changes value, and whether the fastening is loose

(3) when the transformer is switched under a large current of more than twice the rated current during operation, it must be checked whether the transition resistance is burnt out

(4) there have been cases where the on load switch does not switch, that is, the main spring of the fast mechanism is tired or broken and does not work, the transmission system is damaged, the fasteners are loose, the machinery is stuck, the limit failure, etc., which makes the switch unable to switch and the switch fails halfway. "In the beverage and food packaging materials industry and when the switching procedure time is extended beyond the specified value, it is necessary to check whether the transition resistance is burned