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Method for anti-interference of digital time relay

With the continuous development of digital technology and related majors, relay protection technology has also developed greatly. As a basic component, digital time leakage relays have been widely used in various relay protection and automatic control circuits, making controlled equipment or The action of the circuit obtains the required delay and is used to realize the selective coordination of the main protection and the backup protection.


Digital time leakage relay is used for relay protection, first used to replace electromagnetic type and transistor type time leakage relay. It can shorten the step of overcurrent protection, reduce the maintenance amount, and improve the correct rate of protection action. Safe and stable operation of main system and main equipment is protected. Because it has the characteristics of high accuracy, good stability, convenient setting, intuitive, no need to verify the setting value change, wide setting range, etc., it is welcomed by users. Therefore, the digital time leakage relay is widely used in power systems.


Zhenghong Technology specializes in the production of ZHRT1 series digital micro-core technology time leakage relays. In terms of anti-interference performance, it focuses on suppressing the main sources of interference, making the product more reliable, stable and more accurate.


The leakage relays in the operation of the power system are mainly electromagnetic interference, and the sources are as follows


(1) When the DC low voltage circuit disconnects inductive loads (such as contactors, intermediate leakage relays, etc.) or electromagnetic current, voltage leakage relay contacts, the fast transient pulse group radio waves are often generated;


(2) Inductive interference generated when the high-voltage substation is operating near high-voltage electrical equipment;


(3) FM electromagnetic waves generated by mobile phones, portable walkie-talkies and adjacent or nearby equipment and high-frequency electromagnetic radiation generated during arc discharge;


(4) The electromagnetic energy propagating through space in the equipment such as pulse circuits, clock circuits, switching power supplies, transceivers, etc .;


(5) A discharge occurs when a charged operator touches the conductive parts of the equipment.


(2) General anti-interference measures for digital circuits


① The clock frequency should be selected as low as the work permits; ② The power line and control line must be decoupled to prevent external interference from entering; ③ Decoupling capacitors should be added between the power supply and ground of each integrated circuit. Requires high-frequency performance of the capacitor; ④ Add decoupling capacitors on the signal lines that are not fast.


(3) Reasonably design the printed circuit board. ① The power and ground wires on the printed board should be wired in a "Well" shape to equalize the current and reduce the line resistance. ② When wiring, separate the high and low voltage wires and separate the AC and DC wires. ③ Input, The output line should not be close to electromagnetic hot lines such as clock generator and power line, and should not be close to fragile signal lines such as reset line and control line. Reduce electromagnetic coupling; ⑥ The wiring of adjacent layers should be perpendicular to each other; 不要 Do not have branches in the wiring to prevent reflections and harmonics; ⑧ Correctly connect the bypass capacitor. When the digital circuit is working, the current changes suddenly, and a strong noise signal will be generated. The bypass capacitor should be correctly connected to the power line according to Figure 4; 集中 The ground point is concentrated.


(4) Reasonable wiring ① The input power line and ground line should be as short as possible; ② the wiring between the boards or the connector should be as short as possible. Separate the line from the line; ③ When wiring, the power line and the contact lead should be separated; ④ The positive and negative power lines should be twisted with each other to reduce common mode interference.


(5) Adopting new technology ① Adopting surface-mount packaging technology with surface-mounting technology, which can significantly reduce stray parasitic capacitance and inductance due to the longer lead of the device, and simplify the design of the shield, so to a large extent Reduced electromagnetic interference and radio frequency interference. ② The use of multi-layer circuit boards from a 2-layer printed circuit board to a 4-layer printed circuit board can greatly improve the emission and immunity performance.


The problem of anti-interference of the digital time leakage relay is analyzed above. After practical application, the interference problem of the previous digital time leakage relay has been solved, and the operational reliability has been greatly improved. The field application in a certain power system has also been confirmed.