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Secondary prevention device signal interference
Release time:2015-01-21   Click times:19910

1 source of interference


Complex and poor working conditions are the source of electromagnetic interference. Electrical equipment may directly or indirectly to external influences, such as welding spark work, equipment operating over-voltage, over-voltage atmosphere, wireless intercom equipment high-frequency radio waves, large capacity motors and switching equipment. Another example is the more than 35kV disconnector switching operation booster station and stop investment and operating direct supply feeder; the system ground fault, power failure frequency current flows between the ground will show a larger potential difference between two different medium; lightning bad weather and other external interference . Sometimes disturbed internal electrical equipment itself, such as the machine-side rectifier excitation or excitation system, the output of higher harmonic interference protection of the rotor; voltage fluctuation, the system multi-point grounding potential difference (without battery) substation relay electric power supply filtering protection is not good, poor quality power supply or floating charge of internal interference.


Due to the different electromagnetic disturbances, but also it will be referred to the radiation interference. For example, welding operations around electrical equipment, wireless radio links, high-pressure test, etc. formed electromagnetic interference generated by the device directly. Further, since the equipment layout, wiring unreasonable, adjacent or connected equipment exists among capacitance, inductance coupling type interference or weak insulation leakage and the like. Practical experience has demonstrated that only 1V, 2V; interfering signal and measurement signal are superimposed the measuring apparatus substantial deviation of the actual value of the differential mode interference, etc. These should focus on prevention.


2 Prevention and Control Measures


Quarantine measures: for example, the use of optical couplers, electrical measurement signal switch completely isolated in the electrical, can be achieved in isolation potential for common mode interference suppression is more effective; the use of isolation transformers, such as voltage, current, DC power inverter, wire protection, to avoid the telecommunications lines and power lines in the same cable line, signal cables, control cables, power cables laying stratification; avoid measurement circuit and power circuits using the same ground lines.


Take the shield: the electric field shielding, grounding the Faraday cage made of a good conductor is good, in order to ensure zero potential, shielding devices to prevent the electric field outside the shield into the inside of the body. Magnetic shielding, to be used in the low range of the magnetic material is preferably a metal such as silicon steel shield, so that the interference-magnetic field along the magnetic reluctance smaller shield by shielding to reduce interference to the magnetic field penetrating the body; in the above-described high band two screens mode, use the shield to block high-frequency electromagnetic field propagation in space; the use of metallic conductors for the electromagnetic wave attenuation and reflection attenuation, when the electromagnetic wave incident on the metal shield, due to the different wave impedance part is reflected, another part eddy currents in the metal shield loss, namely the absorption loss. Such as the use control cables with a lead sheath armored shield, which shield the booster station control room and grounded at both ends, can effectively reduce the interference of ground potential rise instrumentation and protection devices; intermediate cable when the transition or relay connectors, handle the shield continuity layer; do not think that the signal cable is low-voltage equipment, while ignoring its insulating state, to ensure a good measuring cable insulation and dry environment; the second plug-in measuring circuits shield to be grounded in the protection of the screen; prohibit grounding cable core at both ends, as anti-jamming measures.


Ground: for example, the ground voltage transformer secondary neutral point and ground current transformer secondary current loop, in the control room should choose the ground; ground high-frequency protection secondary voltage cable circuit, and a ground wire ground has 3 ~ 5m distance sometimes has to use a plurality of wires grounded; protection of the AC voltage, AC and DC current into the line, and sometimes to eliminate high frequency interference, before entering the measuring device via the first capacitor ground, after anti after the interference, the device should also be introduced into the traces away from the DC operating power lines and high-frequency circuit wire, do not habitually bundled into the line in the same direction together.


Other measures: the measure of protection relays, to be 1MHz burst disturbance test, electrostatic discharge test (test voltage 8kV general election), electromagnetic radiation Fast transient disturbance test; it is possible to use protection devices around the walkie-talkie place, radio signal interference test, otherwise prohibit the use of radios around it or improve shielding measures; secondary cable laying to choose the right location, far away from the high voltage bus and avoid parallel, as far as possible away from the capacitive voltage transformers and other equipment capacitance power cables and control cables do not put the same cable shelves, the weaker the signal voltage cable, in particular, away from power cables or signal voltage strong, reasonable arrangement and organization of cable run, to reduce and eliminate parasitic interference voltage; increase anti-jamming performance of the device itself, the use of reliable filter device, the output voltage ripple factor rectified less than 5%; copper grounding strengthen maintenance.

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