什么是零序电流、什么是剩余电流、零序电流保护与剩余

什么是零序电流、什么是剩余电流、零序电流保护与剩余 The vector of each phase current and zero magnetic flux ring core C.T zero sequence fault current in two secondary side induction voltage of zero sequence C.T so that the actuator action drives the tripping device, switching power supply network, to achieve the purpose of grounding fault protection. Zero sequence current protection is generally suitable for TN grounding system. Because when there is a ground, the Id loop impedance TN-S system including phase impedance Z1, PE line impedance ZPE and contact impedance Zf, Zs = Z1+ZPE+Zf; Id for TN-C system, including the phase loop impedance impedance Z1, PEN line impedance ZPEN and contact resistance Zf, ZS = Z1+ZPEN+Zf; on TN-C-S system the Id loop impedance including phase impedance Z1, PEN ZPEN PE line impedance, line impedance and contact resistance of Zf ZPE, ZS = Z1+ZPEN+ZPE+Zf, the single phase grounding fault current of Id = 220/ZS, significantly greater than when no fault three-phase unbalanced current, as long as the appropriate setting, it can detect the occurrence of zero sequence current grounding fault when, in order to cut off the fault circuit. The IT system is generally used for the power supply reliability, higher requirements of single-phase grounding unnecessary immediately cut off the power supply circuit, but need to send the monitoring signal, in order to maintain the insulation failure to supply power for a period of time in the industrial and mining enterprises deserve a three-phase neutral line three line distribution line. When the single-phase grounding fault line, the whole system is zero sequence current flowing through the capacitor current and non fault system, thus it is easy to detect the fault current, it can be used to monitor the zero sequence current protection device relative to ground fault first. TT grounding system often used in industry and agriculture, civil building lighting, power supply three-phase four wire distribution system, often found in three-phase unbalanced current is larger, when there is a ground, including the Id loop impedance phase impedance Z1, PE line impedance ZPE, load side grounding resistance RA and power supply side joint the resistance of RB, Zf or ZS=Z1+ZPE+RA+RB+Zf, contact impedance, ground fault current due to Id=220/ZS, RA+RB > > Z1+ZPE+Zf, and the RA+RB number are generally larger, fault loop impedance obviously TT system, the single fault current of Id, far less than the unbalanced current, it is difficult to fault detection, it does not apply TT grounding system. From the analysis of the residual current protection principle, protection of its current setting from grade mA to grade A, has very high sensitivity, so the residual current protection device for TN, TT, IT grounding system can be applied. But the TN-S system, residual current protection for TN grounding system, cannot be used for protection of TN-C grounding system of trunk line feed. Because the TN C grounding system PE protection line and neutral line N with a line of PEN and PEN in normal work through the three-phase unbalanced current when single-phase grounding occurs when the ground fault current from flowing through the Id PEN line, residual current protection device can not detect the unbalanced current or the ground fault current, that is to say, has lost the detection function of single-phase grounding fault. When used in the sub line and end line, if the TN-C grounding system, it should be according to the TN-C-S or local TT earthing, action current residual current protection setting value (I n) to escape the normal leakage current, can avoid misoperation. In our selection, for I, Delta, n values can be based on JGJ/T16-92 "civil building electrical design specifications" article 14.3.11 to choose, in order to adapt to a variety of occasions and use requirements. "According to the" code for design of low voltage distribution, phase of nominal voltage of 220V TN three-phase four wire distribution line grounding fault protection for when overcurrent protection can not meet the personal shock, the maximum allowable cut off the fault time, should adopt the zero sequence current protection, but the protection setting value should be less than the maximum unbalanced current in the power supply circuit, when the overcurrent protection and the zero sequence current protection can not meet the above requirements, should use the residual current protection. For the grounding protection of low voltage distribution lines of the TT system, when used over current protection devices can not meet the operating characteristics of the ZSIA is less than or equal to 50V, should use the residual current protection. For the grounding protection of low voltage distribution lines of the IT system, when the exposed conductive part of the ground alone, second different grounding faults, the fault loop cut should be consistent with the requirements of the protection of grounding fault in TT system, when the exposed conductive part of the common ground, then occurred second times out of phase grounding when the fault cut off the fault circuit grounding fault protection shall comply with the requirements of TN system. For zero sequence current protection, the zero sequence C.T installation must comply with the relevant process standards. For the IT grounding system, the single-phase grounding fault occurs, the grounding current may not only along the conductor surface to cable failure, but may also along the conductor surface to the non fault of the cable, the installation must be cable head grounding through zero sequence C.T, so as to ensure the capacitive current of fault phase and non fault phase through the ground, which can prevent the misoperation of protection device in the external fault, and can guarantee the reliability of fault fashion. For the IT grounding system, generally use the installation of zero sequence C.T in neutral line N, on the bus in low voltage side of the zero sequence C.T must be installed on the N and neutral grounding (or repeated grounding) between the bus bar. If the zero sequence C.T installed in the screen of the N distribution line bus, because the distribution of metal screen directly with the general grounding busbar connected when grounded fault occurs, the fault current Id generated along the distribution screen, metal shell, transformer neutral point connected wire flow, but not through the zero sequence C.T, not up to the protection function required to achieve this point, the construction site is very easy and vegetables. From the sensitivity of protection and safety, residual current protection higher than zero sequence current protection, zero sequence current protection and not as application of residual current protection in single-phase power line, so for the three-phase power supply system if the zero sequence current protection sensitivity enough, and also suitable for occasions of the protection device, in order to save money, can be used zero sequence protection. For the TN� C system, the single-phase earth fault is usually installed on the PEN with zero sequence current protection device. Due to the protection of current setting should be spared the maximum PEN on the unbalanced current in single-phase grounding fault current is less than the setting current, zero sequence current protection maloperation, may cause electric shock and fire, from this point, in fact concerned has canceled the zero sequence current protection in IEC standard grounding protection of low voltage distribution line, China's current norms or the introduction of this protection. Whether zero sequence current protection or residual current protection is one of the measures of ground protection, and it must be used in combination with equipotential bonding, so as to achieve perfect anti electric shock effect.