Leakage protector safe use knowledge - Database & Sql Blog Articles

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First, the role of leakage protector
1. What is a leakage protector?
A: The leakage protector (leakage protection switch) is an electrical safety device. The leakage protector is installed in the low-voltage circuit. When leakage and electric shock occur, and the operating current value defined by the protector is reached, the power supply is automatically disconnected for protection within a limited time.
2. What is the structural composition of the leakage protector?
Answer: The leakage protector is mainly composed of three parts: the detection component, the intermediate amplification section, and the operation actuator. 1 detection component. It consists of a zero-sequence transformer that detects the leakage current and sends a signal. 2 zoom in. The weak leakage signal is amplified, and the electromagnetic protector phase electronic protector is formed according to different devices (the amplifying component can be mechanical or electronic). 3 executive agency. After receiving the signal, the main switch is switched from the closed position to the open position, thereby cutting off the power supply, which is the tripping component of the protected circuit off the grid.
3. What is the working principle of the leakage protector?
Answer: 1 When electrical equipment leaks, there are two kinds of abnormal phenomena: First, the balance of the three-phase current is destroyed, and the zero-sequence current appears; Second, the normal-time uncharged metal casing appears to the ground voltage (normal time) The metal casing and the earth are both zero potential). 2 Zero-sequence current transformer function The leakage protector obtains an abnormal signal through the current transformer detection, and transmits and transmits through the intermediate mechanism to make the actuator act and disconnect the power through the switch device. The current transformer is similar in construction to a transformer and consists of two coils that are insulated from each other around the same core. When the primary coil has residual current, the secondary coil induces a current. 3 leakage protector working principle The leakage protector is installed in the line, the primary coil is connected with the line of the power grid, and the secondary coil is connected with the trip unit in the leakage protector. When the electrical equipment is operating normally, the current in the line is in equilibrium, and the sum of the current vectors in the transformer is zero (the current is a vector with direction, such as "+" in the direction of the outflow and "-" in the return direction. The currents flowing back and forth in the transformer are equal in magnitude and opposite in direction, and the positive and negative offsets each other). Since there is no residual current in the primary coil, the secondary coil is not induced, and the switching device of the leakage protector is in a closed state. When the equipment casing leaks and someone touches it in time, a shunt is generated at the fault point. The leakage current flows through the human body-earth-work ground, and returns to the neutral point of the transformer (without current transformer), causing the transformer to flow in and out. The current is unbalanced (the sum of the current vectors is not zero) and the primary coil is applied to generate residual current. Therefore, the secondary coil is sensed. When the current value reaches the operating current value defined by the leakage protector, the automatic switch trips to cut off the power.
4. What are the main technical parameters of the leakage protector?
Answer: The main operational performance parameters are: rated leakage current, rated leakage operation time, rated leakage non-operating current. Other parameters are: power frequency, rated voltage, rated current, etc. 1Rated leakage current The current value of the leakage protector under specified conditions. For example, a 30 mA protector, when the current value reaches 30 mA, the protector is disconnected from the power supply. 2 The rated leakage operation time is the time from the sudden application of the rated leakage current to the time when the protection circuit is cut off. For example, a protector of 30 mA x 0.1 s does not exceed 0.1 s from the current value of 30 mA until the main contact is separated. 3 rated leakage current does not work under the specified conditions, the current value of the leakage protector does not work, generally should choose one-half of the leakage current value. For example, a leakage protector with a leakage current of 30 mA should not operate when the current value reaches 15 mA or less. Otherwise, the sensitivity is too high and it is easy to malfunction, which affects the normal operation of the electrical equipment. 4 Other parameters such as: power frequency, rated voltage, rated current, etc., when using the leakage protector, should be compatible with the line and electrical equipment used. The working voltage of the leakage protector should be adapted to the rated voltage of the normal fluctuation range of the power grid. If the fluctuation is too large, it will affect the normal operation of the protector, especially for electronic products. When the power supply voltage is lower than the rated working voltage of the protector, it will refuse to operate. The rated working current of the leakage protector should also be consistent with the actual current in the circuit. If the actual working current is greater than the rated current of the protector, it will cause overload and malfunction of the protector.
5. What is the main protective effect of the leakage protector?
Answer: The leakage protector mainly provides indirect contact protection. Under certain conditions, it can also be used as supplementary protection for direct contact to protect against potentially fatal electric shock accidents.
6. What is direct contact and indirect contact protection?
Answer: When the human body comes into contact with a charged body and has a current through the human body, it is called an electric shock. According to the cause of human body electric shock, it can be divided into direct contact electricity and electric contact electricity. Direct electric shock refers to the electric shock caused by the direct contact of the human body and the charged body (such as touching the phase line). Inter-contact electricity refers to the electric shock caused by the human body touching the metal conductor that is not charged under normal conditions and charged under the fault condition (such as the outer casing of the leakage device). Depending on the cause of the electric shock, the anti-shock measures taken against the electric shock are also divided into: direct contact protection phase indirect contact protection. Direct contact protection generally adopts measures such as insulation, protective cover, fence, and safety distance; indirect contact protection generally adopts measures such as protective grounding (zero connection), protection cutoff, and leakage protector.
7. What is the danger of human body shock?
Answer: When the human body is exposed to electricity, the greater the current flowing into the human body, the longer the phase current lasts and the more dangerous it is. The degree of danger can be roughly divided into three stages: perception - get rid of - ventricular fibrillation. 1 perception stage. Since the current is small, the human body can feel (generally greater than 0.5 mA), which does not pose a hazard to humans; Refers to the maximum current value that people can get rid of when the electrode is electrically touched (generally greater than 10 mA). Although this current is dangerous, it can be rid of itself, so it is basically not fatal. When the current is increased to a certain extent, the electric shock will be contracted by the muscles, causing the sputum to cause the gripping of the charged body, and cannot get rid of it by itself. 3 ventricular fibrillation stage. Increasing the current and increasing the time of the electric shock (generally greater than 50 mA and ls) will cause ventricular fibrillation, which will result in death if the power is not immediately disconnected. It can be seen that ventricular fibrillation is the most important cause of death from human electrocution. Therefore, the protection of humans is not commonly used to cause ventricular fibrillation, as a basis for determining the characteristics of electric shock protection.
8. What is the safety of "30mA•s"?
A: Through a large number of animal experiments and studies, it has been shown that ventricular fibrillation is related not only to the current through the human body (I), but also to the duration of the current in the human body (t), that is, the safe electrical energy through the human body Q=I• t to determine, usually 50mA•s. That is to say, when the current is not more than 50 mA and the current duration is within ls, ventricular fibrillation generally does not occur. However, if controlled by 50 mA•s, there is still a risk of ventricular fibrillation when the energization time is short and the current is large (for example, 500 mA × 0.1 s). Although less than 50 mA•s will not cause the consequences of electric shock, it will also cause the electric shock to lose consciousness or secondary injury. Practice has proved that using 30 mA•s as the action characteristic of the electric shock protection device is suitable for both safety and manufacturing, and has a safety ratio of 1.67 times compared with 50 mA•s (K=50). /30=1.67). From the safety limit of "30mA•s", it can be seen that even if the current reaches 100mA, as long as the leakage protector operates within 0.3s and cuts off the power supply, the human body will not cause a fatal danger. Therefore, the 30mA•s limit has also become the basis for the selection of leakage protector products.
9. Which electrical equipment needs to install a leakage protector?
Answer: The "Safety Technical Specifications for Temporary Electricity Use at Construction Sites" stipulates that "all electrical equipment on the construction site, except for protection and zero connection, must be provided with leakage protection devices at the head end of the equipment load line." Aspects: 1 All electrical equipment on the construction site must be equipped with a leakage protector. Because of the open construction of the building, the humid environment, the changing personnel, and the weak management of the equipment, the danger of electricity consumption is high, requiring all power equipment including power and lighting equipment, mobile and stationary equipment. Of course, equipment that is powered by a safe voltage supply and an isolation transformer is not included. 2 The original protection zero (grounding) measures according to the regulations are still unchanged as required. This is the most basic technical measure for safe use of electricity and cannot be removed. 3 The leakage protector is installed at the head end of the load line of the electrical equipment. The purpose of this is to protect the load line while protecting the electrical equipment to prevent electric shock accidents caused by line insulation damage.
10•Why do you need to install a leakage protector after the protection is connected to zero (ground)?
A: Regardless of whether the protection is connected to zero or grounded, the scope of protection is limited. For example, “protection to zero” means connecting the metal casing of the electrical equipment to the neutral line of the power grid and installing a fuse on the power supply side. When a fault occurs in the electrical equipment (a phase touches the outer casing), a single-phase short circuit of the relatively neutral line is formed. Since the short-circuit current is large, the fuse is quickly blown and the power supply is disconnected for protection. The working principle is to change the "cracking fault" to "single-phase short-circuit fault", so as to obtain a large short-circuit current cut-off insurance. However, electrical faults on the construction site are not frequent. Frequently, leakage faults, such as equipment moisture, excessive load, long lines, and aging insulation, are small. These leakage currents are small and cannot be quickly cut off. Therefore, the fault does not automatically disappear and exists for a long time. However, this leakage current poses a serious threat to personal safety. Therefore, it is necessary to install a more sensitive leakage protector for supplementary protection.
Second, the choice of leakage protector
11. What are the types of leakage protectors?
A: Leakage protectors are categorized in different ways to suit the type of use. According to the action mode, it can be divided into voltage action type and current action type; according to the action mechanism, there are switch type and relay type; according to the number of poles and lines, there are single pole two-wire, two-pole, two-pole three-wire and so on. The following is classified according to the action sensitivity and the action time: 1 According to the action sensitivity, it can be divided into: High sensitivity: leakage current is below 30mA; medium sensitivity: 30~1000mA; low sensitivity: above 1000mA. 2 According to the action time can be divided into: Fast type: leakage operation time is less than 0. ls; Delay type: action time is greater than 0.1s, between 0.1-2s; Inverse time type: with leakage current increase, leakage operation time is reduced small. When the rated leakage current is running, the action time is 0.2~1s; when the action current is 1.4 times, it is 0.1, 0.5s; when the action current is 4.4 times, it is less than 0.05s.
12. What is the difference between an electronic and an electromagnetic leakage protector?
Answer: The leakage protector is divided into two types: electronic type and electromagnetic type according to the different tripping methods: 1 Electromagnetic trip type leakage protector, with electromagnetic tripping device as the intermediate mechanism, when the leakage current occurs, the mechanism trips and disconnects the power supply. . The disadvantages of this protector are: high cost and complicated manufacturing process requirements. The advantages are: the electromagnetic component has strong anti-interference ability and impact resistance (overcurrent and overvoltage impact); it does not need auxiliary power supply; the leakage characteristics after zero voltage and phase failure are unchanged. 2 electronic leakage protector, with transistor amplifier as the intermediate mechanism, when the leakage occurs, the amplifier is amplified and transmitted to the relay, and the relay controls the switch to disconnect the power. The advantages of this protector are: high sensitivity (up to 5 mA); small setting error, simple manufacturing process and low cost. The disadvantages are: the transistor has weak impact resistance and poor environmental resistance; it needs auxiliary working power (electronic amplifier generally needs more than ten volts DC power supply), so that the leakage characteristics are affected by the fluctuation of working voltage; when the main circuit is out of phase, the protector Will lose protection.

13. What are the protection functions of the leakage circuit breaker?
Answer: The leakage protector is mainly used to provide protection when the electrical equipment is leaking. When installing the leakage protector, an overcurrent protection device should be installed separately. When using a fuse as a short-circuit protection, the specification should be selected in accordance with the on-off capability of the leakage protector. Leakage circuit breakers that integrate leakage protection devices with power switches (automatic air circuit breakers) are widely used. This new type of power switch has short-circuit protection, overload protection, leakage protection and undervoltage protection. The installation simplifies the wiring, reduces the size of the electrical box and facilitates management. The nameplate type of the leakage circuit breaker has the following meanings: It should be noted during use, because the leakage circuit breaker has multiple protection performances. When a trip occurs, the cause of the fault should be clearly distinguished: When the leakage circuit breaker is disconnected due to a short circuit, the cover must be opened to check whether the contact is There is serious burnt or pit; when it is tripped due to line overload, it cannot be reclosed immediately. Since the circuit breaker is equipped with a thermal relay as an overload protection, when the current is greater than the rated current, the bimetal is bent to separate the contacts, and the contact must be re-closed after the bimetal is naturally cooled and restored to its original state. When tripping due to a leakage fault, it is necessary to find out the cause and eliminate the fault before re-closing, and forcibly closing is prohibited. When the leakage circuit breaker breaks off, the L-like handle is in the middle position. When re-closing, the operating handle must be pulled down (disconnected position) to re-close the operating mechanism and then close upward. Leakage circuit breakers can be used for switching appliances with large capacity (greater than 4.5kw) and infrequently operated power lines.
14. How to choose the leakage protector?
Answer: Select the leakage protector according to the purpose of use and according to the operating conditions: According to the purpose of protection: 1 to prevent personal electric shock. Installed at the end of the line, use a high-sensitivity, fast-type leakage protector. 2 For the purpose of preventing electric shock and grounding the equipment, use a medium-sensitivity, fast-type leakage protector. 3 For the purpose of preventing fires caused by electric leakage and for protecting the lines and equipment, a medium-sensitivity and time-delay type leakage protector should be used. According to the power supply mode: 1 When protecting single-phase lines (equipment), use a single-pole two-wire or two-pole leakage protector. 2 When protecting three-phase lines (equipment), use a three-pole product. 3 When there are three-phase and single-phase, choose three-pole four-wire or four-pole products. When selecting the number of poles of the leakage protector, it must be compatible with the number of lines of the protected line. The number of poles of the protector refers to the number of wires that can be disconnected by the internal switch contacts. For example, a three-pole protector means that the switch contacts can disconnect three wires. The unipolar two-wire, two-pole three-wire, three-pole four-wire protector has a neutral wire that directly passes through the leakage detecting component without being disconnected, and the connector terminal of the protector is marked with an "N" character to indicate the connection. Work the neutral line, this terminal is strictly prohibited to connect with the PE line. It should be noted that the three-pole leakage protector should not be used for single-phase two-wire (or single-phase three-wire) electrical equipment. It is also not advisable to use a four-pole leakage protector for three-phase three-wire electrical equipment. It is not allowed to replace the three-phase four-pole leakage protector with a three-phase three-pole leakage protector.
15. According to the requirements of graded power distribution, should there be several settings for the electrical box?
Answer: The construction site is generally divided into three levels, so the electric box should also be set according to the classification. That is, under the main distribution box, the distribution box should be set, and the switch box should be set below the distribution box. The switch box is the electric equipment below. . The distribution box is the central link in the distribution system, the power transmission and distribution between the power supply and the electrical equipment. It is an electrical device specially used for distributing electric power. The power distribution at all levels is carried out through the distribution box. The main distribution box controls the distribution of the entire system, and the distribution box controls the distribution of each branch. The switch box is the end of the power distribution system, and the next is the power equipment. Each power equipment is controlled by its own dedicated switch box, and one machine is used. Do not use a single switch box to prevent accidents; do not put power and lighting control in a switch box to prevent lighting from being affected by power line failure. The power supply equipment connected to the power supply on the switch box is frequently operated and dangerous, and must be taken seriously. The selection of electrical components in the electrical box must be compatible with the line and the electrical equipment. The electrical box is installed vertically and firmly, and there is room for operation around it. There is no water or debris on the ground. There is no heat source or vibration nearby. The electric box should be protected from rain and dust. The distance between the switch box and the controlled fixture should not exceed 3m.
16. Why use hierarchical protection?
A: Because low-voltage power supply and distribution generally use hierarchical power distribution. If the leakage protector is installed only at the end of the line (in the switch box), the faulty line can be disconnected even if there is leakage, but the protection range is small; similarly, if it is only in the branch trunk (in the distribution box) or the trunk line (the main distribution box) Inside) installing the leakage protector, although the protection range is large, if a certain electrical equipment leaks, it will cause the entire system to be completely powered down, which will affect the normal operation of the fault-free equipment, and it is not convenient to find the accident. Obviously, these protection methods are insufficient. Where. Therefore, different requirements such as line and load should be connected, and protectors with different leakage action characteristics are installed at the low-voltage trunk line, branch line and line end to form a hierarchical leakage protection network. When grading protection, the protection scope of each level should be matched to ensure that the leakage protector does not move in the event of a leakage fault or personal electric shock. At the same time, when the lower protector fails, the upper protector acts to remedy the lower level. Unexpected accident. The implementation of hierarchical protection enables each electrical equipment to have two or more levels of leakage protection measures, which not only creates safe operating conditions for the electrical equipment at the end of all lines of the low-voltage power grid, but also provides multiple direct and indirect contact for personal safety. Protection, and can minimize the scope of power outages in the event of a fault, and easy to find and find fault points, which has a positive effect on improving the level of safe power consumption, reducing electric shock accidents, and ensuring the safety of operations.