Anti-interference design is an important part of the safe operation of power telecontrol monitoring system. In the process of developing integrated automation system, if the reliability problem is not fully considered, it is easy to make mistakes under the interference of strong electric field, which will make the whole electrical telecontrol monitoring system unable to operate normally or make mistakes (false trip accidents, etc.). ), unable to supply power to stations and sections, affecting railway traffic safety.
First, the causes and characteristics of electromagnetic interference
(a) Conducted transients and high-frequency interference
1. Surge and high-frequency transient voltage or current caused by lightning strike, circuit breaker operation and short circuit fault enter the remote terminal equipment through the secondary side of transformer (distribution station), which will interfere with the normal operation of the equipment and seriously damage the circuit. 2. The transient interference voltage caused by electromagnetic relay is high in amplitude, short in time and high in repetition rate, which is equivalent to a series of pulse groups. 3. In the railway power supply, especially the modern high-speed railway, the demand for electricity is relatively high. Generally, it is powered by several power sources, with frequent bus switching and more oscillation waves.
(2) On-site interference
1. There are two kinds of static magnetic field under normal conditions and transient magnetic field during short circuit accident, especially the magnetic field during short circuit accident has great influence on the display. 2. Pulse magnetic field caused by circuit breaker operation or short circuit accident, lightning strike, etc. 3. The transient process of damping oscillation caused by isolating switch and high-voltage cabinet handcart in substation also produces a certain magnetic field. 4. The electromagnetic fields radiated by radio communication and walkie-talkie will cause certain interference to the telecontrol terminal. Railway relay stations are usually located in the same place as communication stations, and communication towers have great interference to the power telecontrol terminal equipment of relay stations.
(3) Interference with communication lines
1. The data of the railway substation telecontrol terminal enters the station communication station through twisted-pair serial communication, and then is converted into optical signals, which are sent to the electric power telecontrol dispatching center along the special communication optical cable of Tietong. In the process from substation to communication station, telecommunication and remote control data are in the form of electrical signals. Because there are many high and low voltage cables entering and leaving the substation, it has great interference to the telecontrol terminal. 2. The relay station is generally close to the railway, and the vibration when the train passes has certain interference to the telecontrol terminal equipment.
(d) the relay itself
The relay itself may not be in place at one time for some reason, resulting in interference vibration signals, or the secondary side such as load switch, circuit breaker and disconnector may produce vibration signals.
Second, the influence of interference on power telecontrol system
Whether AC power supply or DC power supply, there are relatively many coupling channels between power supply and interference sources, which are easy to affect telecontrol terminal equipment, including key CPU；; The interference of analog input may cause errors in sampling data, affect the accuracy of precision and measurement, and may also cause misoperation of microcomputer protection, damaging telecontrol terminal equipment and some components of microcomputer protection; The interference of switch input and output channels may lead to misjudgment of microcomputer and telecontrol terminal, and data error of telecontrol debugging terminal. The interference of remote terminal CPU may lead to the abnormal operation of CPU, and may also lead to the damage of remote terminal program.
Third, anti-interference design analysis
Shielding measures
1. The input and output of high-voltage equipment and telecontrol terminal adopt cables with armor (shielding layer), and both ends of the steel armor of the cable are grounded, which can greatly reduce the coupling induced voltage. 2. When selecting power supply equipment for substations and relay stations, try to choose transformers with special shielding layers, which is also beneficial to prevent high-frequency interference from entering telecontrol terminal equipment. 3. Connecting a small capacitor with high voltage resistance to ground at the input end of the telecontrol terminal equipment can effectively suppress external high-frequency interference.
(2) System grounding design
1. Primary system grounding is mainly used for lightning protection, neutral grounding and equipment protection. Proper grounding system can effectively ensure the safe operation of equipment. For the grounding position of circuit breaker cabinet, the number of grounding flat iron and grounding electrode should be increased, and the interconnection lines of grounding network should be increased to reduce the transient potential difference in grounding network, improve the electromagnetic compatibility of secondary equipment and reduce the interference to remote terminals. 2. The grounding of the secondary system is divided into safety grounding and working grounding. Safety grounding is mainly to avoid the risk of electric shock when the insulation of the equipment is damaged or reduced, and to ensure the safety of the equipment. The equipment shell is grounded, and the grounding wire adopts multi-strand copper flexible wire, which has good conductivity and reliable grounding. The safety grounding grid can be connected with the grounding grid of primary equipment; The purpose of working grounding is to provide a potential reference for electronic equipment, microcomputer control system and protection device, so as to ensure their reliable operation and prevent the interference of earth circulation. 3. Because the high and low voltage cabinets themselves are mostly galvanized steel plates, they also have shielding effect, and the high and low voltage cabinets are reliably grounded. 4. The power ground and digital ground of the telecontrol terminal microcomputer are not connected with the shell, which can reduce the distributed capacitance between the power line and the shell, improve the anti-interference ability of * * * mode, and obviously improve the safety and reliability of the electric telecontrol monitoring system.
(3) Take good isolation measures.
1. In order to avoid the power interference of the telecontrol terminal itself, an isolation transformer is adopted. The high-frequency noise of the power supply is mainly coupled by the primary and secondary parasitic capacitances of the transformer, and the primary and secondary of the isolation transformer are isolated by the shielding layer, so the distributed capacitance is small, which can improve the ability of resisting * * * mode interference. 2. The switch input of power telecontrol monitoring system is mainly the position of auxiliary contact of circuit breaker, disconnector, load switch and tap of power regulator. , and the output of the switch is mainly to control the tap of the circuit breaker, load switch and power regulator. 3. The signal cable shall be kept away from the power cable as far as possible, and mutual inductance shall be avoided when wiring the telecontrol terminal circuit board. 4. Using photoelectric coupling isolation, the input impedance of photoelectric coupler is very small, but the internal resistance of interference source is very large, and the distributed capacitance between input/output circuits is very small and the insulation resistance is very large, so it is difficult for interference from one side of the circuit to be sent to the other side through optical coupling, which can effectively prevent interference from entering the main CPU from the process channel.
(4) Design of filter
1. Use low-pass filtering to remove higher harmonics. 2. Double-ended symmetrical input is used to suppress the interference of * * mode, and the software adopts discrete acquisition mode and corresponding digital filtering technology.
(5) Power is supplied by independent functional blocks, and each functional block has a separate voltage overload protection, so that the whole system will not be damaged due to the failure of the regulated power supply, and the mutual coupling between the public impedance and the public power supply is also reduced, which greatly improves the reliability of power supply.
(6) Anti-interference design of data acquisition
1. When collecting information, cancel the special transmitter cabinet, encapsulate the transmitter part in RTU, and reduce the intermediate links, which can reduce the length of the weak current loop output by the transmitter part. 2. Telecommunication is a false telecommunication interference signal caused by primary closing failure or secondary side vibration, which will also produce sharp pulse signals and may also interfere with telecommunication circuits.
(7) Anti-interference design of process channel
(8) Design of printed circuit board. In the design of printed circuit board, digital circuit grounding and analog circuit grounding should be separated as far as possible; The input end of the power supply is connected across the electrolytic capacitor of10 ~100μ f.
(9) Interference design of control status bits
Anti-interference design of (10) abnormal program operation
Anti-interference design of (1 1) single chip microcomputer software
(12) When the digital communication cable from the terminal to the communication station passes through the steel pipe, especially when it crosses other power cables, it should be avoided to be laid in the same trench with other power cables and keep a certain crossing distance.
(thirteen) special substation (distribution station) or interval signal station environment.
(14) Improve the reliability of telecontrol information transmission, and establish error retransmission technology between the power dispatching center and the telecontrol terminal until the confirmation information remains.