Discussion on Causes and preventive measures of TV

2022-06-14
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Discussion on the causes and preventive measures of TV ferromagnetic resonance fault

TV applied in electricity has many no harmonic elimination devices and only uses fuse protection. Due to its inherent characteristics, it is easy to excite ferromagnetic resonance without bubbling voltage under the induction of sudden changes in system parameters, such as line grounding, single-phase grounding of distribution transformer, switching of compensation capacitor, pulling and closing knife switch and drop fuse, switching of no-load line and transformer, increase and decrease of load and other factors

2 fault hazard

when ferromagnetic resonance occurs in TV, the three-phase voltage often rises at the same time, resulting in non power frequency overvoltage, which can reach 2 ~ 3 times the rated value, seriously damaging the voltage quality, endangering or damaging the stability of the system, resulting in TV fuse fusing, insulation breakdown and burning; In severe cases, it will also cause power collapse and large-area power failure

3 preventive measures

(1) anti harmonic equipment shall be adopted. Select TVs with good excitation characteristics and not easy to magnetic saturation, such as jsjw, jdzx, jdjj2 and jdx series TVs

anti ferromagnetic resonance TV and jszg 10 three-phase five column epoxy resin casting insulated TV are selected, which will greatly improve the ability of anti resonance, overvoltage resistance and burning prevention

four sets of jdzj TV combinations are selected, that is, the windings on each side of the fourth set are connected in series in the middle line of high voltage and low voltage side and open triangular circuit respectively. During normal operation, there is almost no voltage in the neutral winding. During frequency division resonance, because the series input L of the neutral winding is doubled, the primary reactance is basically maintained, the magnetizing inrush current is limited, and the magnetic saturation is prevented, so as to prevent frequency division resonance

(2) adopt harmonic elimination device. Rxq harmonic eliminator is selected and connected in series on the middle line of the primary side of three-phase TV to damp ferromagnetic resonance; However, the annual production capacity exceeds 200000 pieces; During the same year frequency resonance, the potential on the middle line of the primary side is not high, which is equivalent to a series of large resistance grounding, and the harmonic elimination effect is poor

WNx Ⅲ/B and KFX thyristor frequency division and harmonic elimination devices are selected to selectively conduct by the frequency selection function of the trigger circuit; Thyristor is a harmonic elimination actuator, which shortens the open triangular winding instantaneously. Under this strong damping effect, ferromagnetic resonance can be eliminated quickly; However, if the excitation factor causing resonance exists for a long time, TV may be damaged by overload

fxg1 (xxg 10 or 35) harmonic eliminator is selected, which is composed of frequency discriminator and harmonic eliminator. When resonance occurs, the frequency discriminator acts to connect the resistance of the harmonic elimination tube less than 1 to the open triangular winding circuit for harmonic elimination; If the resonance exists for a long time, the action of the thermal switch inside the harmonic elimination tube is transferred to the resistance of 10 to 100 to avoid TV overload

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