Harmonic elimination protector for electromagnetic potential transformer (PT) of three-phase electric network

Abstract

The invention discloses a harmonic elimination protector for an electromagnetic potential transformer (PT) of a three-phase electric network. The harmonic elimination protector comprises a resistor, particularly the resistor is connected in parallel with a resettable fuse (PPTC) to form the harmonic elimination protector (PTK) which is connected in series between a neutral point on the primary side of a three-phase electromagnetic PT and the ground so as to prevent ferromagnetic resonance overvoltage, wherein the PPTC is an REG-series product of American reychem Company; and the resistor is a linear resistor (R) or a nonlinear resistor (FR). The harmonic elimination protector can effectively eliminate ferromagnetic resonance caused by the use of the electromagnetic PT in an electric system, prevents generated overvoltage from damaging various types of equipment in the system, does not affect the normal operation of other protective devices in the electric system, has the advantages of simple structure, convenience of use and low manufacturing and using costs and can be widely applied to an electric system with the electromagnetic PT in a 3-35 kV three-phase electric network.

Description

technical field [0001] The invention relates to a voltage transformer harmonic elimination protector, in particular to a three-phase power grid electromagnetic voltage transformer harmonic elimination protector. Background technique [0002] At present in our country, based on economic reasons, the 3-35kV system in the three-phase power grid adopts the three-wire system with the neutral point not grounded. In order to monitor the insulation status of the system, three-phase voltage transformers are connected to the power plant, substation, and generator bus. When connecting, the primary side (high voltage) winding of the three-phase voltage transformer is connected in a star shape, and the neutral point of the star shape is directly grounded. For cost considerations, three-phase voltage transformers basically use electromagnetic voltage transformers. This kind of power system using three-phase electromagnetic voltage transformers has some changing factors to the ground whe...

AI Technical Summary

Problems solved by technology

However, although this three-phase electromagnetic voltage transformer with a primary resonance eliminator can eliminate the ferromagnetic resonance problem of the system, it also has shortcomings. First, due to the existence of the resistance value, the voltage transformer primary The neutral point on the side of the voltage transformer is not directly grounded. When the system is running normally, this resistance will cause the neutral point of the voltage transformer to be unbalanced, so that the open delta winding of the voltage transformer will generate a zero-sequence voltage, thereby affecting the protection of the relay protection device in the system. Normal operation; Secondly, when a single-phase ground fault occurs in the system, the existence of the resistance will cause the neutral voltage of the voltage transformer to shift, which will reduce the zero-sequence voltage induced by the open delta winding of the voltage transformer, thereby affecting the relay protection normal operation of the device

In short, it also brings unstable factors to the power system and brings hidden dangers to the safe operation of the power system.

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