Lightning is a strong atmospheric overvoltage. Damaged equipment can be divided into two situations. One is direct lightning strike. The probability of directly hitting the station equipment is very low; most of the damage is caused by induction, and the interference voltage is induced through the coupling secondary circuit. The route has indirect harmful effects on the equipment. The cable port connecting the wire and the device is the main transmission route of electromagnetic interference, which is transmitted by power lines, ground lines, and signal lines. Through inspection, it was found that the power line has anti-interference low-pass filter capacitors, the power module uses a high-frequency switch, the shell metal grounding wire and protective grounding are all intact, and initial suspicion is introduced by the signal control line. After further investigation on site, the cable trenches were not laid in a multi-layered manner. Due to site constraints, many control cables were densely arranged in the cable trenches, and the control cables in the cable trenches were closely attached to the grounding wires and the fixed cables. Together, and the shielded cable is not grounded. According to field operation personnel measurements, the voltage of the shielded control cable after lightning strike reached 200 V. Therefore, it is concluded that there are many microelectronic devices in Shenghua Thermal Power Plant, various lines and cables are complicated and most of them are laid in the cable trench and in close contact with the ground wire. When the control cable and grounding wire are arranged in the same cable trench, the ground wire suffers. After a lightning strike, a strong electromagnetic field will be generated around the control cable to cause an overvoltage between the control cable cores and between the core and the ground, which may cause false letters, malfunctions, and even damage the microcomputer protection equipment.
Main transmission route of substations
Substation's electromagnetic interference (EMI) channels are divided into conductive and radiative interference categories by medium. Conducted interference refers to interference that propagates through power lines, ground lines, and signal lines; radiated interference refers to interference that propagates through space. According to the nature can be divided into capacitive coupling, inductive coupling. Electromagnetic interference exists in the form of electromagnetic fields, mainly through the electric field, magnetic field, electromagnetic field and other ways to affect signal transmission lines and equipment signals.
Capacitive coupling
Due to the distributed capacitance between the electrical equipment, the voltage on the substation high voltage bus and the equipment generates a disturbance voltage in the control cable system through the distributed capacitance.
The higher the voltage, the stronger the resulting capacitive coupling strength, and the closer the high voltage part is to the secondary device, the stronger the capacitive coupling strength.
Inductive coupling
Substation high-voltage bus and other primary devices will flow alternating current and will generate alternating magnetic field in the control cable laying space. Due to the change of magnetic field, induced voltage will be generated in the control cable. The magnitude of the interference voltage is determined by the mutual inductance and is determined by the spatial position of the primary device and the secondary cable.
In the actual production, the coupling modes of various interference sources to the secondary loop are very complicated, and the same interference source often acts on the secondary loop in a variety of interference modes. According to different sources of interference, take appropriate anti-jamming measures, summarize the experience of anti-interference, and gradually meet the requirements of substation electromagnetic compatibility.
The effect of shielded cable and the comparison of shielding layer grounding
At present, most of the substations use protective shielding against electromagnetic interference. The control and signal cables are mostly made of a braided layer made of a fine copper wire braid with a coating layer. The shielding layer can generally cover 90%. In view of the primary equipment's interference to the secondary control cable in the substation, at present, the main anti-jamming method we use is the grounding of the cable shield. There are two methods: one end of the cable shield is grounded, and the other end of the cable shield is grounded. The characteristics and applicable conditions of the two anti-jamming methods are discussed now.
1. Prevent capacitive coupling
The unshielded shield has no shielding effect on the electric field, and the shield at one end and the other at both ends has the same shielding effect on the electric field. If the shield is well grounded, the electric field ends with the shield directly coupled to ground.
The metal shielding layer of the shielded cable has an electrostatic shielding effect, so that the strong power line of the high-voltage power supply of the primary line is terminated in the metal shield, and the internal electric field intensity is zero, so that the core line in the shielding layer is protected from external strong electric field. From the perspective of electrostatic shielding, in order to make the shield surface a fixed equipotential surface, one end of the shield should be grounded.
2. To prevent inductive coupling
When the shielding layer is grounded at both ends, electromagnetic induction can be effectively suppressed.
The induced potential generated by I1 on the cable core is E 21 = jωM12I1
The induced potential generated by I1 on the shield is Em = jωM1mI1
When one end of the shielding layer is grounded, there is an induced voltage on the shielding layer, but it does not constitute a loop, and no current flows through the shielding layer and does not change the spatial magnetic field distribution.
There is no effect on the induced voltage generated by inductive coupling on the secondary cable core.
When the shield is grounded at both ends, the induced current flowing through the shield is Im = E m/(jωLm + Rm)
Im induced potential on the secondary cable core is E 2m = jωM2mIm
Inductive potential E2 = E 21-E 2m generated on the secondary cable core
The induced current flowing in the shield layer is induced by the external electromagnetic field. Its actual function is to cancel the interference of the external electromagnetic field. Therefore, the cable shield is grounded at both ends, which can effectively suppress electromagnetic induction.
The mkvv mining control cable shield grounding method shall be analyzed in detail according to the specific environment and conditions of the substation, and shall be implemented in a corresponding manner. The DC resistance and metal armored cable with high magnetic permeability for reducing the metal shielding layer and the compact and reasonable Structure, in a good grounding network to take pressure, diversion and other supporting measures to effectively eliminate interference and provide a reliable guarantee.
Mechanical Parts Package Of Cargo Elevator
Mechanical Parts Package Cargo Elevator, Mechanical Parts Package Freight Elevator, Mechanical Parts Package Goods Elevator
OTIS Mechanical
Parts Package Of Complete Cargo Elevator, Thyssen Mechanical
Parts Package Of Complete Cargo Elevator, KONE Mechanical Parts Package Of Complete
Cargo Elevator, GiantKONE Mechanical Parts Package Of Complete Cargo Elevator,
ThyssenKrupp Mechanical Parts Package Of Complete Cargo Elevator, Schindler Mechanical
Parts Package Of Complete Cargo Elevator, XJ Schindler Mechanical Parts Package
Of Complete Cargo Elevator, Xizi OTIS Mechanical Parts Package Of Complete
Cargo Elevator, Mitsubishi Mechanical Parts Package Of Complete Cargo Elevator,
Shanghai Mitsubishi Mechanical Parts Package Of Complete Cargo Elevator,
Fujitec Mechanical Parts Package Of Complete Cargo Elevator, Hitachi Mechanical
Parts Package Of Complete Cargo Elevator, Toshiba Mechanical Parts Package Of Complete
Cargo Elevator, Hyundai Mechanical Parts Package Of Complete Cargo Elevator, LG
Mechanical Parts Package Of Complete Cargo Elevator, Sigma Mechanical Parts Package
Of Complete Cargo Elevator, Express Mechanical Parts Package Of Complete Cargo
Elevator, GUANGRI Mechanical Parts Package Of Complete Cargo Elevator, FUJI Mechanical
Parts Package Of Complete Cargo Elevator, BLT Mechanical Parts Package Of Complete
Cargo Elevator, CANNY Mechanical Parts Package Of Complete Cargo Elevator, SJEC
Mechanical Parts Package Of Complete Cargo Elevator, KOYO Mechanical Parts
Package Of Complete Cargo Elevator, IFE Mechanical Parts Package Of Complete
Cargo Elevator
Mechanical Parts Package Cargo Elevator, Mechanical Parts Package Freight Elevator, Mechanical Parts Package Goods Elevator
CEP Elevator Products ( China ) Co., Ltd. , https://www.zjsmartcommercialescalators.com