The role of grounding transformer


The grounding transformer is specially designed for the […]

The grounding transformer is specially designed for the arc suppression coil. Generally, the arc suppression coil is installed on the triangle side of the transformer of the small current grounding system to compensate for the grounding capacitance current when the power grid is single-phase grounded. But there is no neutral point on the triangle side of the transformer, and the grounding transformer is to provide an artificial neutral point for installing the arc suppression coil.
In our country's power system, the 6kV, 10kV, and 35kV power grids generally adopt the operation mode of neutral point ungrounded. The distribution voltage side of the main transformer in the power grid is generally delta connection, and there is no neutral point for grounding resistance. When a single-phase ground fault occurs in a neutral point ungrounded system, the line voltage triangle remains symmetrical, which has little effect on the user's continued work, and when the capacitive current is relatively small (less than 10A), some transient ground faults can disappear by themselves. It is very effective to improve power supply reliability and reduce power outages. Due to its simple operation and low investment, it has been used in the initial stage of my country's power grid and has played a very good role. However, with the increasing growth and development of the electric power industry, this simple method no longer meets the current needs. Now the increase in cable circuits in the urban power grid and the larger and larger capacitive current (over 10A), the grounding arc cannot be extinguished reliably at this time , It will have the following consequences.
1) The intermittent extinguishment and reignition of a single-phase grounding arc will produce an arc grounding overvoltage, the amplitude of which can reach 4U (U is the normal phase voltage peak) or higher, and the duration is long, which will cause damage to electrical equipment Insulation causes great harm, forming breakdown in weak insulation; causing heavy losses.

2) Due to the dissociation of air caused by the continuous arc, the insulation of the surrounding air is broken, and short circuit between phases is easy to occur;

3), produce ferromagnetic resonance overvoltage, it is easy to burn out the voltage transformer and cause damage to the arrester or even explosion of the arrester;

These consequences will seriously threaten the insulation of power grid equipment and endanger the safe operation of the power grid. In order to prevent the occurrence of the above accidents and provide enough zero-sequence current and zero-sequence voltage for the system to make the grounding protection work reliably, it is necessary to artificially establish a neutral point to connect the grounding resistance at the neutral point. In order to solve such a solution. The grounding transformer (referred to as grounding transformer) is produced under such circumstances. The grounding change is to artificially create a neutral grounding resistance, and its grounding resistance is generally very small (generally required to be less than 5 ohms).

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