Three forms of reverse switch connection in photovoltaic system

In photovoltaic system, electrical switch has two functions

One is to cut off the circuit function: when the photovoltaic system is not required to generate power, it is necessary to cut off the electrical connection between photovoltaic modules, inverter, distribution cabinet and power grid;

Second, safety protection function: when the electrical system occurs over-current, over-voltage, short-circuit and leakage current, it can automatically cut off the circuit to protect personal and equipment safety.

Three forms of reverse connection of air switch

1. N neutral line and phase line are reversed

This happens in 4-pole and N-pole switches. Due to different power grid structures, the functions of neutral line (N-pole) are also different. There are four common types:

Type A: N pole is not equipped with over-current release, and N-pole is always connected and not combined with other three poles; type B: N-pole is not installed with over-current release, and N-pole is closed and opened with other three poles; type C: N-pole is installed with over-current release, and N-pole is closed and opened together with other three-pole; type D: N-pole is installed with over-current release, and N-pole is always connected and not combined with other three-pole.

Among them, a is suitable for three-phase balance system, and the isolation transformer of photovoltaic system is star connected. For example, Hong Kong requires photovoltaic system with isolation transformer. B is suitable for three-phase balance, TN-C power grid structure, and distributed low-voltage grid connected photovoltaic systems in China are suitable for application of type B. C and D are suitable for three-phase unbalanced off grid system.

If the 4-pole circuit breaker is selected for the grid connected system, the over-current release is not installed on the N-pole. If the N-pole and the phase line are inversely connected, it may lead to the failure of the circuit detection or false alarm.

2. Reverse connection of incoming and outgoing lines

The circuit breaker is usually the upper end of the incoming line, the lower end of the outgoing line. The over-current action characteristics of the molded case circuit breaker are independent of the voltage, only related to the current size, and independent of the current direction. AC has no direction, so theoretically, the connection mode has nothing to do with the over-current protection function.

According to the Convention, the power grid supplies power to the load. The power grid is the energy output end, which is connected above the circuit breaker. The energy receiving end of the load is connected below the circuit breaker. The energy flows from the upper end to the lower end. However, in the photovoltaic system, the inverter is the energy output end, and the grid is the receiving end of energy. Should the inverter be above the circuit breaker? In fact, according to the principle of safety first, whether the energy flows into or out of the grid, the top of the circuit breaker is always connected to the grid.

The wiring of the electronic residual current operated circuit breaker (RCCB) with overload and short-circuit protection can only be connected to the upper line, but not to the lower line. This is because the tripping coil of the electronic residual current operated circuit breaker is installed close to the load side. When the input line is connected, the release coil will make the circuit breaker trip in case of leakage, because the dynamic and static contacts are open and there is no voltage at the moving contact; If the current line is changed to the lower incoming line, the circuit breaker will be opened after the leakage action, and there will be voltage from the original load end (because the load end of the lower incoming line becomes the power supply end) to the release coil and moving contact. If the line voltage has surge phenomenon and other faults, the coil will be burned and the residual current operated circuit breaker will lose its due function.

3. Air switch inverted

The third is that the air switch is inverted. The power supply is still the upper incoming line and the lower outgoing line. Just reverse the air switch. This connection method can also be used normally, and all kinds of protection are normal. However, it violates a kind of human operation habit. Under normal circumstances, when the air switch is pushed upward, it is closed, and it is opened when it is pulled down. However, it is just the opposite, which is easy to cause human error operation It's strictly forbidden.