Research On Breaking Reasons And Preventive Methods Of Voltage Transformer Fuse In Distribution Network

The operation of a distribution power network is directly related to the vital interestsof users, so its safety, stability and reliability is essential. It is known, that fuse used toprotect voltage transformers (TV) blows and TV itself failures occur frequently, and theproblems is universal in distribution network. To solve this problem, study the cause ofthe fault and propose appropriate measures, is of great practical significance forimprovement of the distribution system for the safe and reliable operation.Results reflect, that most of fault TV are bus bar TV, and the failure often happenswhen the single-phase earth fault disappears, or during arc grounding period. The totallength of distribution network outlets is longer, the frequency of fault is higher. Thetransient process followed by single-phase grounding fault disappearance is detailedanalyzed, and come to a conclusion that the ferromagnetic resonance and low-frequencynonlinear oscillations have a certain consistency that they are two forms of the same kinddistribution network transient process with different parameters. And the over-currents inTV primary windings caused by them is the direct cause of the TV fuse blown.A10kV distribution network model is established by ATP-EMTP, four influencefactors for voltage transformer primary current are studied by the mathematical model:TV excitation characteristics, line length, zero sequence loop damping resistor, theoccurrence and disappearance moment of single-phase fault.For the existing suppressing fuse blown measures, corresponding mathematicalsimulation models are established, their application background, principles, advantagesand disadvantages, and inhibitory effect are detailed analyzed. The main measures are:the system neutral point grounded by arc suppression coil or low resistance, the primaryneutral point of TV grounded by single phase TV or harmonic eliminator.For the situation of existing elimination measures flawed, not better suppressing thefuse blown or applications constrained, this paper proposes a scheme of harmonicelimination switch based on synchronization control technology, precise control theswitching time. This can significantly reduce the interference produced during theswitching on the main system, effectively prevent the fuse blows; and remove thesingle-phase grounding fault coordinated with line relay. Moreover, vacuum circuitbreaker with permanent magnetic actuator has been matured to meet the relevantrequirements. The improved switch proposal has good practical value.