Monday, December 27, 2010

Weak current College】 【digital time relay anti-interference method analysis】.

As digital technology and professional development, the protection technology also has a great development, such as static relay application in power systems, including digital time relay as the base component, has been widely applied to various kinds of relay protection and automatic control loop, the control device or circuit of actions for the desired time delay, and to achieve the main protection and selective backup protection.

Digital time relays for relay protection, firstly to replace the electromagnetic type and transistor-time relay. It can shorten the over-current protection gaps, reduce maintenance, improving protection for accuracy. Protect the master system and master of security and stability. Due to its high precision, good stability, setting convenient, intuitive, change the setting value does not require validation, tuning range, and other characteristics, warmly welcomed. The resulting digital time relays for electric power system has been widely used.

But in recent years, digital time relay in power system malfunction occurs multiple times, giving users a great loss. The cause of the malfunction, such as the system environment, use the maintenance issues, product quality problems, the device is damaged, anti-jamming performance, and so on, but the most intractable problem is the digital time relay anti-jamming performance, this article here for digital time relay anti-jamming performance, put forward their opinions, for reference.

1 improve the antijam capability method

The main source of interference 1.1

In the electric power system running relay disruption is electromagnetic interference, sources have the following

(1) DC low-voltage circuit disconnect inductive load (e.g. contactor, intermediate relay, etc.) or electromagnetic current, voltage relay contact jitter, regular produce fast transient burst group radio;

(2) high-voltage substation near high-voltage electrical equipment operation of inductive interference;

(3) mobile phone, portable walkie-talkies and adjacent or nearby devices FM waves and arc discharge when the high-frequency electromagnetic radiation;

(4) the device clock pulse circuitry, circuits, switching power supply, transceiver transmitter through space-borne electromagnetic energy;

(5) with charge of operations personnel touch devices have conductive part discharge.

1.2 transmission of electromagnetic interference

Electromagnetic interference in the transmission mainly two kind of forms, namely the conduction and radiation. Transmission by wire for current or voltage function in the form of relay. Radiation through space to electromagnetic fields on the form to the relay. For digital time relay main pathway for power cables. Therefore inhibit the major part of conducted noise in digital time relay power part.

1.3 improve the antijam measures

According to the sources of electromagnetic interference and noise and digital time relay characteristics of work, on digital time relays enhance anti-interference ability to adopt measures primarily from the following aspects of the solution.

(1) power input EMI filter added. EMI filter is a low-pass filter, passive components of multi-port network. Not only does it spread by conduction disturbance attenuation caused by interference, but also how the radiation interference interference suppression of significantly. Such a filter for low-frequency (20-100kHz) is especially effective. Then, through the selection of suitable ferrite cores, it inhibits the frequency range can be increased to 400 MHz.

As digital timer relay's small size, structure, forming of EMI filter General volume is large, do not apply.
And Relay operating frequency is not high, design and technology of relative requirements, while also reducing cost, thus directly in the circuit design EMI filter is very feasible.
Accessories through strict screening,optional to close to ideal, but in fact exist.

Filter media, capacitors, inductors can change, appropriate changes during coupling, circuit switches, contactors, implementing agencies, contact jitter generation of transient disturbances can play a full role of inhibition.

(2) a antijamming General measures of digital circuits

① clock frequency should work permit under the conditions of the lowest selection; ② need for power cables, control cables decoupling to prevent outside interference into; ③ each IC power and ground between Canada decoupling capacitor. Requirements of high-frequency capacitance; ④ a good performance in speeds fast signal cable with decoupling capacitor.

(3) rational design of printed circuit board ① printing plate on the power supply and ground to is "well" glyph wiring to balance current, reduce line resistance; ② wiring separation of high and low-voltage cable, AC, DC separately; ③ input and output lines does not matter on clock generator, power lines, and other electromagnetic hotline, no problem by resetting the line, control line and other fragile signal lines; ④ adjacent plate cross wiring; ⑤ minimize power line alignment of effective surround the area, which can reduce the electromagnetic coupling; ⑥ adjacent layer wiring should be mutually perpendicular; ⑦ alignment of don't have a branch in case lead to reflection and produce harmonics; ⑧ correct access bypass capacitor. Digital circuit in the work, the current mutations in larger, it will have a very strong noise signal should be Figure 4 in the power cord correctly access bypass capacitor; ⑨ Earth point set.

(4) reasonable wiring ① enter power cable and the ground should be as short; ② plate and the plate of the line or connector line should be as short. And cable and wire separation between; ③ wiring, power supply lines and contact pin separately; ④ positive and negative power cable should be stranded one another to reduce EMI.

(5) the introduction of new technology adoption ① SMT surface mount Assembly seal technology, can significantly reduce device lead long and spurious parasitic capacitance, inductance, simplifies the design of the shield, greatly reduces electromagnetic interference and radio frequency interference. ② the use of multi-layer PCB printed circuit boards from Layer 2 to 4 layer printed circuit board, can significantly improve the performance of emission and immunity.

> 2 conclusion

The above analysis a antijamming digital time relays. The actual application, solved the previous digital time relay interference problems that exist, actions have greatly improved reliability, in particular in the field of power systems, is also confirmed.

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