In the photovoltaic system, the electrical switch has two main functions: one is the electrical isolation function, which cuts off the electrical connection between the photovoltaic module, the inverter, the power distribution cabinet and the grid during installation and maintenance, and provides the operator with a In a safe environment, this action is actively realized by the operator; the second is the safety protection function, when the electrical system has overcurrent, overvoltage, short circuit, overtemperature and leakage current, it can automatically cut off the circuit to protect the safety of people and equipment. This action is realized automatically by the switch.

Therefore, when a switch trip occurs in a photovoltaic system, the reason is that the switch may have overcurrent, overvoltage, overtemperature, and leakage current. The following analyzes the solutions to the causes of each situation.

1 Cause of current

This kind of fault is the most common, the circuit breaker selection is too small or the quality is not good enough. When designing, first calculate the maximum current of the circuit. The rated current of the switch should exceed 1.1 times to 1.2 times the maximum current of the circuit. Judgment basis: do not trip at ordinary times, and only trip when the weather is good and the power of the photovoltaic system is high. Solution: Replace a circuit breaker with a large rated current or a circuit breaker with reliable quality.

There are two types of miniature circuit breakers, C type and D type. These are trip types. The difference between C type and D type is the difference in short-circuit instantaneous trip current, and the overload protection is the same. The C-type magnetic trip current is (5-10)In, which means it trips when the current is 10 times the rated current, and the action time is less than or equal to 0.1 second, which is suitable for protecting conventional loads. The D-type magnetic trip current is (10-20)In, which means it trips when the current is 20 times the rated current, and the action time is less than or equal to 0.1 seconds. It is suitable for protecting equipment with high inrush current. When there are electrical equipment such as transformers before and after the switch, and there is an inrush current after the power is cut off, type D circuit breakers should be selected. If the line does not have inductive equipment such as transformers, it is recommended to select type C circuit breakers.

2 Cause of voltage

This kind of fault is relatively rare. There is a rated voltage between the two phases of the circuit breaker, generally 250V for a single pole. If this voltage is exceeded, it may trip. There may be two reasons: one is that the rated voltage of the circuit breaker is selected incorrectly; the other is that when the power of the photovoltaic system is greater than the power of the load, the inverter increases the voltage to send power. Judgment basis: Use a multimeter to measure the open circuit voltage, which exceeds the rated voltage of the circuit breaker. Solution: Replace the circuit breaker with a higher rated voltage or a cable with a larger wire diameter to reduce the line impedance.

3 Causes of temperature

This kind of fault is also common. The rated current marked by the circuit breaker is the maximum current that the device can pass for a long time when the temperature is 30 degrees. The current is reduced by 5% for every 10 degrees increase in temperature. The circuit breaker is also a heat source because of the presence of contacts. There are two reasons for the high temperature of the circuit breaker: one is the poor contact between the circuit breaker and the cable, or the contact of the circuit breaker itself is not good, and the internal resistance is large, which causes the temperature of the circuit breaker to rise; the other is the environment where the circuit breaker is installed. Enclosed heat dissipation is not good.

Judgment basis: When the circuit breaker is in action, touch it with your hand and feel that the temperature is too high, or you can see that the temperature of the terminal is too high, or even the smell of burning.

Solution: re-wiring, or replace the circuit breaker.

4 Cause of leakage

Line or other electrical equipment failure, other electrical equipment leakage, line leakage, component or DC line insulation damage.

Judgment basis: low insulation resistance between the positive and negative poles of the module and the AC phase wire, between the positive and negative poles of the module, the phase wire and the ground wire.

Solution: detect and replace faulty equipment and wires.

When a trip is caused by a leakage fault, the reason must be found out and the fault removed before re-closing. Forcible closing is strictly prohibited. When the leakage circuit breaker breaks and trips, the handle is in the middle position. When re-closing, the operating handle needs to be moved downwards (breaking position) to re-lock the operating mechanism, and then close upwards.

How to choose a leakage protector for a photovoltaic system: Since photovoltaic modules are installed outdoors, the DC voltage is very high when multiple circuits are connected in series, and the modules will have a small amount of leakage current to the ground. Therefore, when selecting a leakage switch, adjust the leakage current protection value according to the size of the system . Generally, a conventional 30mA leakage switch is only suitable for installation in a single-phase 5kW or three-phase 10kW system. If the capacity is exceeded, the leakage current protection value should be appropriately increased.

If the photovoltaic system is equipped with an isolation transformer, it can reduce the occurrence of leakage current, but if the isolation transformer wiring is wrong, or there is a leakage problem, it may trip due to leakage current.

تلخيص

A switch trip event occurs in a photovoltaic system. If it is a power station that has been installed for a long time, the reason may be the wiring problem of the circuit or the aging problem of the switch. If it is a newly installed power station, there may be problems such as improper selection of switches, poor line insulation, and poor transformer insulation.