Similarities and differences between the hottest z

The similarities and differences between zero sequence current protection and residual current protection

Abstract: in order to prevent personal contact with electricity and the damage of distribution lines due to various reasons, resulting in fire and other accidents, and to ensure the thermal stability of equipment and lines, China's current electrical design, construction and other relevant specifications have proposed the need to set up grounding fault protection in low-voltage distribution lines. Article 4.4.10 of the national standard gb50054-95 code for design of low voltage power distribution clearly points out two methods of ground fault protection, zero sequence current protection and residual current protection (also known as leakage current protection). The basic working principle of these two kinds of current protection is the same, but the application scope, installation and other requirements are different)

key words: zero sequence current protection residual current protection Untitled Document in order to prevent personal contact with electricity and distribution lines from being damaged due to various reasons, causing fire and other accidents, and ensure the thermal stability of equipment and lines, China's current electrical design, construction and other relevant specifications have proposed the need to set up grounding fault protection in low-voltage distribution lines. Article 4.4.10 of the national standard gb50054-95 code for design of low voltage power distribution clearly points out two methods of ground fault protection, zero sequence current protection and residual current protection (also known as leakage current protection). The basic working principle of these two kinds of current protection is the same, but the application scope, installation and other requirements are different)

the specific application of zero sequence current protection can install a current transformer (C.T) on three-phase lines, or let three-phase conductors pass through a zero sequence C.T together, or install a zero sequence C.T on neutral line n. these C.T can be used to detect the current vector sum of three phases in the series of seminars on "utilization of rubber and plastic materials", that is, zero sequence Current IO, ia+ib + ic=io, When the three-phase load connected to the line is completely balanced (there is no grounding fault, and the leakage current of the line and electrical equipment is not considered), io=0; When the three-phase load connected to the line is unbalanced, io=in, and the zero sequence current at this time is unbalanced current in; When a phase grounding fault occurs, a single-phase grounding fault current ID must be generated. At this time, the detected zero sequence current io=in+id is the vector sum of three-phase unbalanced current and single-phase grounding current

the specific method of residual current protection is to install a C.T on the tested three-phase conductor and neutral n respectively, or let the three-phase conductor and N wire pass through a zero sequence C.T together, and obtain the current vector sum Ia + IB + IC + in of the three-phase conductor and neutral n. when a single-phase grounding fault occurs, regardless of whether the three-phase load is balanced or not, the vector sum is zero (strictly speaking, it is the normal leakage current of the line and equipment); When a phase ground fault occurs, the fault current will pass through the protective line PE and the metal components related to the ground, that is, Ia + IB + IC + in ≠ 0. At this time, the value is the ground fault current ID plus the normal leakage current

from the above analysis, it can be seen that the basic principles of zero sequence current protection and residual current protection are based on Kirchhoff current law: the algebraic sum of the complex current flowing into any node in the circuit is equal to zero, that is Σ I=0, and zero sequence C.T is used as the sampling element. Under normal conditions of circuit and electrical equipment, the vector sum of each phase current is equal to zero (it is assumed that unbalanced current is not considered for zero sequence current protection). Therefore, the secondary winding of zero sequence C.T has no signal output (avoiding unbalanced current during zero sequence current protection), and the actuator does not act. When the ground fault occurs, the vector sum of each phase current is not zero, the magnetic flux is generated in the annular iron core of the zero sequence C.T of the fault current, and the induced voltage at the secondary side of the zero sequence C.T makes the actuator act, drives the tripping device, switches the power supply network, and achieves the purpose of ground fault protection

zero sequence current protection is generally suitable for TN grounding system. Because when one phase grounding occurs, the loop impedance to TN-S system ID includes phase line impedance Z1, PE line impedance ZPE and contact impedance ZF, that is, ZS = z1+zpe+zf; For TN-C system, ID loop impedance includes phase line impedance Z1, pen line impedance zpen and contact resistance ZF, that is, ZS = z1+zpen+zf; For TN-C-S system, ID loop impedance includes phase line impedance Z1, pen line impedance zpen, PE line impedance ZPE and contact resistance ZF, that is, ZS = z1+zpen+zpe+zf, and the generated single-phase grounding fault current id = 220/zs, which is significantly greater than the three-phase fault free. For details, please call Jinan new era gold Testing Instrument Co., Ltd. to balance the current. As long as the setting is appropriate, the zero sequence current at the time of grounding fault can be detected to cut off the fault loop. For it systems, generally, three-phase three wire distribution lines without neutral lines in industrial and mining enterprises that have high requirements for power supply reliability, do not need to cut off the power supply circuit immediately for single-phase grounding, but need to send insulation damage monitoring signals to maintain continuous power supply for a period of time are used. When the single-phase is grounded, the zero sequence current flowing through the fault line is the sum of the capacitive current of the whole system non fault system, so it is easy to detect the ground fault current, so the zero sequence current protection device can be used to monitor the first phase to ground fault. TT grounding system is often used in the three-phase four wire distribution system of lighting and power hybrid power supply in industrial, agricultural and civil buildings. It is often found that the three-phase unbalanced current is large. When one phase grounding occurs, the ID loop impedance includes phase line impedance Z1, PE line impedance ZPE, load side grounding resistance RA and power side grounding resistance Rb, contact impedance ZF, that is, zs=z1+zpe+ra+rb+zf, grounding fault current id=220/zs, because ra+rb ＞ z1+zpe+zf, And ra+rb values are generally large. Obviously, the fault loop impedance of TT system is large, and the single fault current ID generated is far less than the unbalanced current, so it is difficult to detect the fault current, so it is not suitable for TT grounding system

according to the analysis of the working principle of residual current protection, its protection action setting current can range from Ma level to a level, which has quite high action sensitivity. Therefore, the residual current protection device can be applicable to TN, TT and it grounding systems. However, residual current protection is applicable to TN-S system in TN grounding system, and cannot be used for feeder trunk line protection of TN-C grounding system. Because the protective line PE and neutral line n in TN-C grounding system share one line, pen and pen flow through three-phase unbalanced current during normal operation, and the grounding fault current ID generated when single-phase grounding also flows through the pen line. 3. According to the scope of utilization, it can be divided into warning tape, grounding tape, electrical tape, protective film tape, winding tape, sealing tape Residual current protection devices such as die-cutting tape cannot detect whether it is unbalanced current or grounding fault current at all, that is, the single