Effectiveness of antiresonant voltage transformer insulation monitoring in networks with isolated neutral

Abstract

In the paper the problem of ferroresonance in isolated neutral. The results of investigation of subharmonic ferroresonance processes with voltage transformers traditional design. It is shown that the regime most likely to occur after the disappearance of single-phase ground fault and lead to thermal degradation of high voltage winding of the transformer. The basic concept of the protection of isolated neutral of ferroresonance phenome-na. Analyzed the structure and function of the modern antiresonance voltage transformer types such as NAMI. and NAMIT. The effectiveness of their work in networks with isolated neutral.
  Transient simulation packageimple mentedin MATLAB\Simulink. inMATLAB\Simulink. Calculations showed that all commercially available voltage transformers are able to enter into ferroresonance and damaged. Revealed that the trans-former type NAMIT has low sensitivity built-in protection, which is not able to effectively operate at subharmon-ic ferroresonance oscillations. As a result, this type of transformer is similar antiresonant transformer type NTMI therefore also able to enter into subharmonic ferroresonance and damaged.
In addition, the identified modes in which there is a loop protection voltage transformer, which is accompa-nied by dangerous overvoltage, and thermal damage to the transformer in this mode does not occur. In the study of modes of operation of the transformer type U.S. also revealed the possibility of instituting ferroreso-nance with his participation. Occurrence of ferroresonance occurs during switching network sites with low total capacitance, transformer itself in such regimes are usually not damaged.
  The problem of the accuracy of accounting in networks 6-35 kV, and also the problem of compatibility of modern electricity meters with antiresonance voltage transformers. It is shown that for a more accurate ac-counting of electricity meters should be fed from ungrounded voltage transformers that are devoid of residual voltage, and therefore the transients do not distort the evidence.