Resistance-capacitance type transformer direct current magnetic bias suppression device

Abstract

A resistance-capacitance type transformer direct current magnetic bias suppression device includes an isolation device and a magnetic bias monitoring device. The isolation device comprises a capacitor, an adjustable resistor, a bypass switch, a current limiting resistor, a switchover disconnecting link and a mechanical switch. The magnetic bias monitoring device comprises two sets of control units, one for controlling the bypass switch and the other for controlling the adjustable resistor; and a mutual inductor and an isolation transformer which are connected with the two sets of control units. According to the invention, by adjusting the adjustable resistor, a direct current passing through the device can be reduced within an allowable range, changes in neutral line direct currents of transformers affected by the operation of the device within 300km around a grounding transformer to which the device of the invention is installed can be minimized, the neutral line direct currents of these transformers are enabled to stay still within their respective allowable ranges to the greatest extent, and the device has the characteristics of being simple, economical and effective.

Description

Technical field [0001] The invention relates to a DC bias suppression device for a resistance-capacitance transformer. Background technique [0002] With the development of modern technology, especially the breakthrough of high-power power electronic device technology, DC transmission has gained more and more advantages due to its large transmission capacity, low cost, low loss, resistance to aging, long life, and unlimited transmission distance. development of. HVDC transmission has played an increasingly important role in long-distance large-capacity transmission and regional power system interconnection. Due to the many advantages of DC transmission, with the development of my country's power grid, more and more DC transmission lines have been put into operation in the power system, but at the same time it has also brought some new problems. The actual operation found that the grounded unipolar operation mode of the DC transmission system will cause DC current to flow into t...

AI Technical Summary

Problems solved by technology

The actual operation found that the ground unipolar operation mode of the DC transmission system will cause DC current to flow into the neutral point grounding transformer of the AC grid, resulting in DC bias phenomenon, causing the main transformer harmonics to increase, the noise to increase, and the temperature to rise. In severe cases, it may cause Damage to transformers and capacitor banks will affect the safe and stable operation of the power grid

[0003] At present, the engineering solutions are to make a fuss in the grounding circuit of the transformer. The main methods to suppress the DC current at the neutral point of the transformer are: 1. Capacitive blocking method: suppress the current by connecting a capacitor in series with the neutral point of the transformer. The advantages of this method are: It can completely suppress the DC current. The disadvantage is that the DC current is completely repelled to other grounding equipment, which may cause harm to other equipment; The effect of DC current must be suppressed, but when the DC current is large, the neutral point current of the transformer in the system may also exceed the standard; 3. DC current reverse injection method: apply and generate a neutral point around the neutral point of the transformer The counter electromotive force of direct current suppresses the direct current at the neutral point. This method is complex in installation, consumes more power, and cannot completely suppress the direct current; 4. Resistance-capacitance method: take a capacitor and a fixed resistance in parallel and connect it to the neutral point Connect in series to suppress the DC current. This method can only reduce its own DC current to the allowable range, and cannot minimize the changes in the DC current of other transformers within a certain range that are affected by the operation of the device. It is very likely that these transformers will The DC current exceeds the limit

Regardless of the above methods, it is necessary to consider the overvoltage problem at both ends of the series device when a single-phase grounding asymmetric short circuit fault occurs in the transformer. The larger the short circuit current, the higher the overvoltage, and if the overvoltage protection element is connected in parallel, its current Capacity is also a problem that has to be considered. Therefore, the current solution is acceptable for small short-circuit currents. For large-capacity giant transformers with a peak short-circuit current of tens of kiloamperes or even hundreds of kiloamperes, the only way to improve the withstand voltage level of series devices , resulting in higher cost

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