Leakage protection switch is divided into two types: voltage type and current type. In view of the fact that voltage type leakage protection can only be used for total protection, low reliability of safety supply and limitation of protection, it has been eliminated in China. Here, the current type leakage protection switch is mainly introduced. . According to the structure and action principle, the switch can be divided into three types: pulse type, electromagnetic type and electronic type.
The working principle of the pulse leakage protection switch is to use the sudden change of current. Although there are current and time action dead zones, each branch can have the disadvantage of malfunction when it is put into operation, but the pulse leakage protection switch has the recognition. It can be developed into an intelligent leakage protection switch. As the total protection of the distribution transformer, the main line is protected by level 1 and the current value and time value of the setting action are large. The above disadvantages can be completely overcome in multi-level protection.
The characteristics of the electromagnetic leakage protection switch are not affected by the power supply voltage, the ambient temperature has little influence on the characteristics, the pressure shock resistance is strong, the external magnetic field interference is small, and the structure is simple, the inlet and outlet lines can be inverted, etc.; but the mechanical shock resistance Poor vibration capability, meeting the requirements of delay inverse time characteristics is difficult, manufacturing requirements are precise, the price is more expensive, and the sensitivity is limited to 30mA. It is only suitable for small-capacity load, so it has been replaced by electronic leakage protection switch.
Although the electronic leakage protection switch has the influence of the power supply voltage and the ambient temperature on the characteristics, the lightning resistance is poor, the external magnetic field is weak, the structure is complicated, and the ingress and egress lines are not reversible, but it is easy to meet the delay inverse time characteristic. Simple to manufacture, high sensitivity and low price. For the above shortcomings, the power supply, temperature compensation, and overvoltage absorber are separately installed, and the electronic circuit can be completely prevented by taking anti-interference measures, so it is widely used. In particular, the rapid development of electronic technology, the widespread use of integrated circuits and integrated blocks, the protection switch volume is getting smaller and smaller. According to the user's requirements, it can be made into a quick-break type, or it can be made into a time-delay type, and can be matched with various capacity switches (small several amps, several hundreds of amps) to meet various user requirements. It can be used as a kind of leakage protection switch for direct protection of the user's end backup (such as power switch socket, hand-held, mobile power tools, water pump, machine tool, etc.), and can be made into user indirect protection (such as residential total protection, low-voltage main, branch Various leakage protection switches for lines, total distribution transformer protection, etc., thus have a broad development prospect.
Leakage protector structure principle When the electrical equipment leaks, an abnormal current or voltage signal will be presented. The leakage protector will cause the actuator to act by detecting and processing the abnormal current or voltage signal. The leakage protector that operates according to the fault current is called a current-type leakage protector, and the leakage protector that operates according to the fault voltage is called a voltage-type leakage protector. Due to the complicated structure of the voltage type leakage protector, the stability of the external disturbance action characteristics is poor, and the manufacturing cost is high, and it has been basically eliminated. At present, the research and application of leakage protectors at home and abroad are dominated by current-type leakage protectors. The current-type leakage protector is a part of the zero-sequence current in the circuit (usually called residual current) as the action signal, and the electronic component is used as the intermediate mechanism. The sensitivity is high and the function is complete. Therefore, the protection device is more and more widely used. Applications. The composition of the current leakage protector is divided into four parts:
1. Detection component: The detection component can be said to be a zero-sequence current transformer. The protected phase and neutral wires pass through the toroidal core and form the primary coil N1 of the transformer. The winding wound on the toroidal core forms the secondary winding N2 of the transformer. If no leakage occurs, then the current flows. The current vector sum of the phase and neutral lines is equal to zero, so the corresponding induced electromotive force cannot be generated on N2. If a leakage occurs, the current vector of the phase and neutral lines is not equal to zero, so that the induced electromotive force is generated on #$, and this signal is sent to the intermediate link for further processing.
2. Intermediate link: The intermediate link usually includes an amplifier, a comparator, and a trip unit. When the intermediate link is electronic, the intermediate link also assists the power supply to provide the power required for the operation of the electronic circuit. The function of the intermediate link is to amplify and process the leakage signal from the zero-sequence transformer and output it to the actuator.
3. Actuator: This structure is used to receive the command signal of the intermediate link, implement the action, and automatically cut off the power at the fault.
4. Test device: Since the leakage protector is a protection device, it should be checked regularly for its integrity and reliability. The test device simulates the leakage path by connecting the test button and the current limiting resistor in series to check whether the device can operate normally.
Leakage protection switch in use problems In the two network transformation, a large number of residual current action leakage protector, a few years have passed, it turns out that the leakage protector is damaged, artificially relieved is very serious. The problem of power consumption is still serious. There are many reasons for correcting it, but the direct cause is the frequency and refusal of the leakage protector, which seriously affects the normal use of electricity, so that the pipe and power personnel lose confidence in the leakage protector and even give up.
The frequency of the leakage protector includes two aspects:
A leakage protector First, when the grid is grounded, the leakage protector operates normally. In this normal operation, due to the aging of the power grid and the change of the climatic environment, the actions caused by the grounding point of the power grid account for the majority, and the actions caused by the human body electric shock are very few. It is conceivable that the normal use of electricity is the first demand of people. In order to prevent frequent electric shocks caused by the extremely low probability of personal electric shock, affecting normal production and life will certainly cause people's troubles.
Second, the grid has not been grounded, but the leakage protector may be mishandled under the following conditions:
1. Since the leakage protector is triggered by the signal, the signal will be triggered to trigger the leakage protector under other electromagnetic interference, resulting in malfunction.
2. When the power switch is turned on and off, an impact signal will be generated to cause the leakage protector to malfunction.
3, the sum of multi-branch leakage can cause over-level misoperation.
4. Repeated grounding of the neutral line may cause the stream to malfunction.
5, with the inverter or other components that are prone to interference, the use of malfunctions from the technical principle analysis, the leakage protector also has technical misunderstandings that may cause refusal.
1. When the neutral line is repeatedly grounded, the leakage protector will be shunted, and the neutral grounding point is difficult to find.
2. When the power supply is out of phase, and the missing phase is exactly the working power of the leakage protector, it will be rejected.
The neutral point grounding of the earth leakage protector is essential for use
1Because the neutral point is grounded, the support of the phase line of the power grid is subjected to the phase voltage for many years, so the support is broken down to form the grounding point of the power grid, causing leakage and causing the leakage protector to fluctuate.
2Because the neutral point is grounded, when the phase line is occasionally grounded, a large leakage current will be generated immediately, which not only increases the electric loss, but also causes a fire, and will further aggravate the frequency of the leakage protector.
3Because the neutral point is grounded, when the person is exposed to electricity, it will immediately generate a large electric shock flow, which is very threatening to human life. Even if there is a leakage protector, it will be shocked first, then action protection, if the action is slow or malfunction, the consequences It will be more serious.
4. Since the neutral point is grounded, the distributed capacitance of the grid to the ground is connected in the loop, which will increase the grounding current when the switch is closed and cause misoperation.
5. Since the neutral point has been grounded, it is difficult to find the repeated grounding of the neutral line. Repeated grounding of the neutral line will cause shunt rejection and stream misoperation of the leakage protector.
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