Principle and function of single phase grounding transformer
Writer： Hengfeng you electric Time：2023-04-14 views：times
The three-phase power supply system of grounding transformer layer adopts grounding transformer to provide manual service neutral line for the system software, which can be grounded or grounded immediately according to inductance, resistance or arc suppression coil. Efficiency and basic principle of transformer. The grounding objectives are summarized as follows: single phase electrical grounding at the bottom voltage side of the transformer.
1. Transfer the magnetically induced positive charge on the route to the road surface to prevent damage to the route and mechanical equipment.
2. Minimize the high voltage oscillation in the neutral insulation system software.
3. Cooperate with the arc suppression coil to compensate the capacitive current caused by single-phase electrical grounding by using the induced electromotive force of the arc suppression coil, so as to automatically extinguish the intermittent arc. Single phase electrical grounding at high voltage side of transformer.
4. Immediately grounding and supporting facilities of full-automatic protection equipment. Some common faults can be protected at the beginning of common faults.
The grounding transformer can be used for the secondary side of the subway station.
The function of grounding transformer is that when the neutral line connected by △ or y cannot be led out, the arc suppression coils are connected to each other.
Basic principle: the grounding transformer adopts Z-type connection. The difference from the general transformer depends on that each phase electromagnetic coil is wound on two magnetic columns. Therefore, the advantage of this connection is that the zero sequence magnetic flux can flow along the magnetic column, while the zero sequence magnetic flux of general transformer flows along the relative path of magnetic leakage, and the zero sequence characteristic impedance of Z-type grounding transformer is small (10 ω， Generally, the transformer is much larger. Therefore, when selecting general transformer with arc suppression coil, the volume of arc suppression coil shall not exceed 20% of the transformer volume, while Z-type transformer can be equipped with 90% - 100% arc suppression coil, which can save project investment. Basic principle of transformer efficiency. In China, Z-type connection (or zigzag connection) is generally adopted for grounding transformer to save project investment and indoor space of distribution station. The third winding resistance is added to the general grounding transformer, and the common transformer is replaced to supply power to the common mechanical equipment of the distribution station. According to the national industry standard of reactor in China, the grounding method of grounding transformer can be divided into immediate grounding. Grounding according to series reactor, resistor and arc suppression coil. At present, immediate grounding has not been applied in China, but some power engineering research units have begun to discuss it. Foreign grounding transformers generally adopt Z-type connection, which is used for 10kV ungrounded system software to form the grounding maintenance of distribution network. When common grounding faults occur in the system software, the grounding transformer has high resistance to positive and negative sequence current and low resistance to zero sequence current, so as to ensure reliable grounding maintenance.
According to the relevant safety operation regulations of China's power enterprises, the requirements for the operation state of connecting the neutral line of the transformer and connecting the arc suppression coil are as follows:
(1) The volume of arc suppression coil shall not exceed 20% of the short-circuit capacity of transformer;
(2) The zero sequence current generated in the transformer according to the zero sequence current of arc suppression coil shall not exceed 10% of the rated phase voltage;
(3) The total output of three-phase zero sequence current through the arc suppression coil shall not exceed 60% of the rated phase voltage of the transformer. It is required that the partial overtemperature mainly caused by zero sequence magnetic flux shall not exceed the maximum temperature limit of the hot spot of transformer winding resistance network. It can be seen from the above that the volume of the grounding transformer connected by ynyn has not been applied, and its zero sequence resistance is also very large.
