The role of reactors in box-type substations.

Release time:

2021-09-30

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Abstract

After using reactors in box-type substations, in the event of a short circuit, the voltage drop across the reactor is significant, which results in smaller voltage fluctuations on the bus. This helps to maintain the bus voltage level and ensures the stable operation of user electrical equipment on non-faulty lines.

The reactors used in the State Grid's power system are essentially air-core coils without magnetic permeability, which can be assembled into vertical, horizontal, or zigzag forms according to layout requirements. During power generation and transmission operations, when a short circuit occurs in the power system, a large short-circuit current is generated. If not controlled, it can lead to damage to electrical equipment in the power system and may evolve into an accident in severe cases. Therefore, even when a short circuit occurs in the power system, it is necessary to maintain the dynamic stability and thermal stability of electrical equipment as much as possible. As a result, the power department often installs series reactors at the outgoing circuit breaker to increase short-circuit impedance and limit short-circuit current to meet the breaking capacity requirements of various circuit breakers.

　　Box-type substationAfter using reactors, once a short circuit occurs, the voltage drop across the reactor is significant, resulting in smaller voltage fluctuations on the busbar. This helps maintain the bus voltage level and ensures stable operation of user electrical equipment on non-faulty lines.

High-voltage reactors in box-type substations can be divided into series reactors and parallel reactors.

The role of parallel reactors in box-type substations:

1. Mitigate the increase in power frequency voltage caused by the capacitive effect of unloaded or lightly loaded lines;

This voltage rise is caused by the voltage drop of line capacitance (for low capacitance and inter-phase capacitance) current on line inductance during unloaded or lightly loaded conditions. It can cause line voltage to exceed supply voltage. In severe cases, typically, the longer the line, the greater the capacitive effect and the larger the increase in power frequency voltage.

For ultra-high voltage long-distance transmission lines, the charging power of line capacitors during unloaded or lightly loaded conditions is significant. Generally, charging power increases sharply with voltage levels. The enormous charging power not only causes the aforementioned increase in power frequency voltage but also increases line power and energy losses, leading to self-excitation and synchronization difficulties. Installing parallel reactors can compensate for this portion of charging power.

2. Improve voltage distribution along box-type substations and reactive power distribution on lightly loaded lines, reducing line losses;

When the power transmitted on a line does not equal natural power, the voltage at various points along the line will deviate from its rated value, sometimes significantly. For example, based on compensation from parallel reactors, line voltage can be reduced or increased.

3. Reduce potential supply current within box-type substations, accelerate extinguishing potential supply arcs, and improve the success rate of automatic reclosing;

The so-called secondary current refers to the residual current in the arc light at the fault point after disconnecting both sides of the fault phase during a single-phase instantaneous ground fault. The neutral point of parallel reactors compensates for secondary current through a small grounding resistance to accelerate extinguishing secondary arcs.

4. Parallel reactors are connected in parallel on the low-voltage side busbar of the main transformer to transmit reactive power to the system through the main transformer, compensating for capacitive current in transmission lines and preventing voltage rise at lightly loaded line ends, thus maintaining stable transmission system voltage.

 

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