In last few years, can use of ark of indoor switch of the rapid development of the enterprise and 35KV in great quantities as high cost, make cable gives increase of line proportion year after year, bring about leap of right capacitance electric current. Causes because 35kV system is only conterminously cable explosion is more and more, the pecuniary loss that brings from this and social impact are bigger and bigger also.
Only statistic of electric industry bureau discovers Wulanchabu since 2003, because 35KV system is only conterminous and caused accident many 10, some causes complete station power failure, affect principal user power supply, some causes burn down of ark of cable explosion, switch and lightning arrester explosion to wait.
Case study
(One) syntonic overvoltage
35kV system is not ground connection system, the voltage transformer of wiring of many star form exists in electrified wire netting, one of second winding are direct ground connection, become what electrified wire netting allows electric current of electric current, Gao Cixie wave to terrestrial electricity to fill discharge channel, when circuit ground connection, the core coil of voltage transformer is equivalent to as shunt-wound as capacitance of butt joint of blame fault line, formed a likelihood to produce syntonic parallel circuits, because opposite ground voltage is times more elevatory, make likely the core of voltage transformer appears saturated or adjacent saturated, impedance decrescent, the circumstance with capacitive reactance and equal impedance appears in circuit, produced shunt-wound resonance thereby, right now transformer the electric current of side is the biggest, make so likely the high-pressured side fusing of voltage transformer fusing, transformer of burned-out perhaps voltage, and cable explodes. This kind of case often is going electric place put into production is primary (route gives line return little) not be apparent, but the increase that gives line return as circuit (the equivalence capacitance to the ground increases each loop-line road, capacitive reactance increases) the circumstance of occurrence resonance is more. It is indoor switch ark as a result of 35KV system additionally, dot of 35KVPT ground connection is much, accept a place for 4 commonly, this also offerred a condition to produce syntonic overvoltage.
(2) overvoltage of arc ground connection
Below normal circumstance, 35kV neutral is nodded not ground connection system produces single-phase ground connection, allow to run 2h. But why to produce single-phase ground connection often to develop alternate with accident quickly, make accident broaden the scope? One of reasons are insulation of individual device existence is bit more fragile in the system, because electric current of 35kV system electric capacity is bigger,another main reason is, ground connection electric arc becomes the overvoltage of arc ground connection that cannot produce higher multiple from extinguish, according to domestic and international experience, overvoltage of arc ground connection can amount to 3-5 most times.
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