Foreword
Photovoltaic systems are generally composed of components, inverters, grid-connected cabinets, and power grids. As a form of low-voltage power distribution, the leakage current of photovoltaic systems is a non-negligible problem. Current measures for preventing leakage hazards in photovoltaic systems are: Leakage protectors are installed, but frequent tripping and burning of the leakage protection switch (marking light during editing) also occur from time to time. The document will start with the principle of the leakage protector, focusing on how to select and install the leakage protector for the photovoltaic system.
How Leakage Protectors Work
Residual current protector full name residual current action protector, mainly consists of three parts: the detection element, the intermediate amplifier and the operating mechanism. Electrical equipment will exhibit abnormal current and voltage signals when it is leaking. The leakage protection device detects the abnormal current or abnormal voltage signal, and after signal processing, prompts the actuator to operate, and quickly cuts off the power supply through the switchgear to implement leakage protection. Figure 1 is a general wiring diagram of a leakage protection switch in a three-phase four-wire system.
Among them: TA zero sequence current transformer, GF is the main switch, TL is the main switch GF shunt release coil.
When the circuit is leaked or there is electric shock, due to the existence of leakage current, the phasor of the load current of each phase passing through the primary side of the TA is no longer equal to zero, that is, IL1+IL2+IL3+IN≠0 generates a residual current. TA2 The secondary coil has an induced electromotive force. This signal is processed and compared by the intermediate link. When the predetermined value is reached, the main switch shunt release line TL is energized, the main switch GF is automatically tripped, and the protected circuit is quickly cut off. Power supply for protection.
Leakage protector main parameters
The leakage protector has the function of breaking the circuit, and the internal circuit needs to supply power. Therefore, when selecting the leakage protector, firstly ensure that <frequency><rated voltage><rated current> meets the needs of the distribution network.
At the same time, the leakage protector needs to operate according to the magnitude of the leakage current, so it has three unique parameters:
1. Rated leakage current
2. Rated leakage action time
3 rated leakage current
Leakage protector classification
Leakage protectors can be divided into several types based on structure classification, working method, and working time. In photovoltaic systems, classification is based on sensitivity and leakage current DC component types.
1. According to the leakage current DC component type
AC type leakage protector: AC type leakage protector is designed for industrial frequency sinusoidal leakage current and can reliably protect sinusoidal leakage current applied abruptly and slowly.
A-type leakage protector: A-type leakage protector and AC-type leakage protector are basically the same in the working principle (measurement of leakage value through zero-sequence current transformer), but the magnetic characteristics of the transformer have been improved, except for sinusoidal leakage. The signal can be reliably protected, and it can also reliably protect the leakage signal containing the pulsating DC component.
B-type leakage protector: B-type leakage protector can reliably protect sinusoidal AC signal, pulsed DC signal and smooth signal.
2. Classification according to sensitivity
According to the rated leakage current, leakage protection switches can be divided into three categories:
High sensitivity: leakage current is below 30mA;
Medium sensitivity: leakage current at 30~1000mA;
AC type leakage protector: AC type leakage protector is designed for industrial frequency sinusoidal leakage current and can reliably protect sinusoidal leakage current applied abruptly and slowly.
A-type leakage protector: A-type leakage protector and AC-type leakage protector are basically the same in the working principle (measurement of leakage value through zero-sequence current transformer), but the magnetic characteristics of the transformer have been improved, except for sinusoidal leakage. The signal can be reliably protected, but it can also reliably protect the leakage signal containing the pulsating DC component.
B-type leakage protector: B-type leakage protector can reliably protect sinusoidal AC signal, pulsed DC signal and smooth signal.
Photovoltaic system leakage current generation
When the inverter is started, in order to ensure the reliable and normal operation of the inverter, the internal relay needs to be detected because of the common-mode capacitance of the inverter to the ground and the leakage capacitance of the PV panel to ground and the common-mode capacitance of the inverter and the earth. A loop is formed between them and instantaneous leakage power is generated.
Leakage Protector Frequently Asked Questions in Photovoltaic System
Leakage protector escapes
Photovoltaic systems, especially those with a relatively large capacity, have a large tiled area. After an early morning or rainy day with heavy dew, the inverter will close the internal relays during the self-test process. During this process, the component-to-ground leakage current is greater than the leakage current. The leakage protector can escape when the protector operates. This situation is characterized by randomness, that is, when there are multiple leakage protectors in the system, the escape is random; when the air is dry, the system can work normally.
For this situation, the recommended solution is:
Check the frame grounding of the component is good;
Replace the leakage protector with larger <rated leakage action current>. For example, for a system with low power, it is possible to select the DZ47LE-63 leakage protector with an operating current of 100mA. Considering sensitivity and price, TYPE-A is Relatively good choice.
Leakage protector burned
The main reason for the leakage of the leakage protector is that the rated current of the leakage protector is less than the circuit current of the line, or the damage of the leakage protector leads to the internal inspection device being damaged in the long-term overload state;
The cable connected to the leakage protector is too thin, and the overheating causes the leakage protector port to burn out;
The input and output are reversed. The leakage protector must be connected strictly according to the above connection. The upper end is connected to the power grid, and the lower end is connected to the inverter, otherwise it is extremely easy to burn.
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