With the continuous development of my country's low-voltage electrical system and economic construction scale, people have also put forward higher requirements for improving power supply capacity and safety. Especially in some places where electricity is used, supervision is weak and the safety of maintenance personnel cannot be guaranteed. Hidden safety hazards and economic losses such as fire accidents often occur due to line equipment contact, leakage accidents, and grounding short-circuits. Therefore, innovative smart leakage protection devices are imminent. The residual current action relay is a better protection device to prevent the above accidents. Its main function is to protect people from electric shocks and deaths, and to prevent fires caused by large leakage of electrical equipment or lines.
1. The principle of residual current relay
The basic principle of the residual current operated relay is shown in Figure 1. When the circuit is in normal operation, using the current theorem of circuit theory, the magnitude of the current flowing in and out of one end of the network, etc., the direction is opposite, that is, the sum is zero. Therefore, in the schematic diagram, the sum of the currents on the right side of the leakage protector should be zero, that is, IL1+IL2+IL3+IN=0; at this time, the contact and leakage protector are in a static working state. In this diagram, the zero sequence current The transformer is used as the detection element of this device. The vector sum of each phase current is equal to zero (it is assumed that the unbalanced current is not considered for the zero-sequence current protection). Therefore, the secondary winding of the zero-sequence current transformer has no signal output, and the operating actuator has no action.
When a ground fault occurs, the vector sum of the currents of each phase is not equal to zero, the zero-sequence current transformer generates magnetic flux in the toroidal core due to the fault current, and the induced voltage on the secondary side of the zero-sequence current transformer makes the operating actuator do the corresponding Actions, such as tripping of universal circuit breakers or molded case circuit breakers, to achieve the purpose of ground fault protection; when someone is electrocuted, as a conductor, part of the current IK will flow through the human body and lead into the ground, causing the shock and leakage The sum of the current on the right side of the protector is not zero, that is, IL1+IL2+IL3+IN ≠ 0. When the leakage current reaches the operating current, the operating actuator of the touch and leakage protector will act, so that the current flowing through the human body It is very small, controlled within 30mA, which protects the personal safety of the person who gets an electric shock, and can achieve the effect of uninterrupted electricity. If someone gets an electric shock in the same phase now, it can also protect the safety of the shocked person, because the current flowing through the shocked person is controlled within 30mA through the reactance R of the operating actuator; if the second electric shock occurs in the out-of-phase, then perform the operation The processing link of the mechanism drives the universal circuit breaker or molded case circuit breaker to trip to protect the personal safety of the person who gets an electric shock. At the same time, the electric shock and leakage protection device can monitor the leakage current value of the line in real time. As long as the leakage current is greater than the dangerous value, the protection The device immediately issued an audible alarm, and promptly and automatically reminded the electrician management personnel to investigate the leakage of related lines and equipment through the GSM communication network telephone and short message notifications, so as to prevent problems before they occur.
Two, the main purpose of the residual current relay
2.1 Indirect contact electric shock protection
The measure of indirect contact electric shock protection is to automatically cut off the power supply. GB 13955 "Protection against indirect contact electric shock accidents" stipulates: "The main measure of indirect contact electric shock accident protection is to adopt a protection method that automatically cuts off the power supply to prevent damage accidents due to insulation damage to electrical equipment. Ground faults occur when the circuit is damaged. When the fault current value is less than the operating current value of the overcurrent protection device, a residual current protection device should be installed.” Research shows that the safe value of the human body contact voltage is 50 V. To ensure personal safety, when an insulation failure occurs in any part of the electrical installation, once the contact voltage exceeds 50 V, the power supply of the faulty part needs to be automatically cut off within the specified time. The overcurrent protection device is limited by the electric circuit and equipment and its own action value, and cannot automatically cut off the power supply. The residual current protection device is not affected by the load current, and can be used in conjunction with the overcurrent protection device for indirect contact electric shock protection.
2.2 Ground fault protection
Grounding is the contact between a live conductor and the ground, a grounded metal shell, or a component connected to the ground. Its failure may lead to personal injury and death, equipment damage, and electrical fires in severe cases. In the past, ground fault protection usually used overcurrent protection devices for protection. When the ground fault current was greater than the set value of the overcurrent protection device, the overcurrent protection device would cut off the fault circuit. In the TT system with large rated current and long power distribution lines, the ground fault current of the live conductor in the TN system, unsafe metallic ground fault, and arc ground fault may occur when the ground fault current is less than the overcurrent protection When the setting current is activated, the overcurrent protection device does not operate. Residual current protection devices, or circuit breakers with ground fault protection, can reliably perform ground fault protection.
2.3 Electrical fire protection
Electrical fires are usually caused by electrical short circuits. Electrical short circuits include metallic short circuits and arc short circuits. The former is a short circuit between live conductors (such as between phase and phase, between phase and N wire), mostly with high-temperature welded metal as the path, and the fault current is in kiloamperes. High temperature is likely to cause the insulation to oxidize and spontaneously ignite. Although the fire hazard is great , But it can be protected by a circuit breaker and fuse with short-circuit protection, and the power supply can be cut off by the instantaneous action of the circuit breaker to avoid fire. The latter is a short-circuit of the charged conductor to the ground, mostly using the arc as the path. Although the fault current is small, on the one hand, the arc continues for a long time and the local temperature is high. It is easy to ignite the surrounding combustible materials and cause a fire. Generally, the circuit breaker trips and cuts off the power supply. Therefore, the fire hazard caused by arc short circuit is far greater than that caused by metal short circuit. The circuit breaker with residual current operation protection function can cut off the protection circuit when the overcurrent protection device does not operate to prevent electrical fires caused by arcing short circuits.
Grounded.
