Two Examples of Solving Electromagnetic Interference with Clever Methods

The discipline of electromagnetic compatibility was developed on the basis of simple anti-interference methods in the early days. The goal is to make equipment and systems not interfere with each other in a coexisting environment and maximize their working efficiency. As we all know, measures such as shielding, filtering, reasonable grounding, and reasonable layout to suppress interference are very effective and are widely used in engineering practice. Technical treatments such as avoidance and diversion can also be adopted, such as spatial orientation separation, frequency division and avoidance, filtering, absorption and bypassing. Sometimes these avoidance and diversion techniques are simple and ingenious, and can replace expensive and bulky hardware measures, achieving twice the result with half the effort. The following are two typical examples of Baiyun Telecom Branch cleverly handling electromagnetic interference failures.

2 Typical Case 1

2.1 Fault phenomenon

The fuses of the newly replaced capacitor compensation cabinet in the Xinshi machine building often burn out.

2.2 Fault Analysis

(1) Replace the fuse and capacitor with a normal capacitor compensation cabinet to make sure there is no quality problem with the fuse and capacitor.

(2) Detect the working current of the capacitor. When only one group of capacitors is used, the working current exceeds the rated current by 50%, causing the fuse to burn out.

(3) The harmonic content in the power grid was detected, and it was found that the 11th and 17th harmonic content was as high as 28%, which was seriously exceeded. Due to the high content of harmonic current and the high frequency, the heat destructive energy was extremely large, so the harmonic heat burned the insulation matrix before the fuse could be blown.

(4) The power supply of the system is mainly supplied by NEC phase-controlled rectifiers, Intercontinental high-frequency switching rectifiers, and Yida high-frequency switching rectifiers. These rectifier systems are the main source of interference.

(5) The actual detection of the system capacitance compensation is small. The capacitor cabinet originally has 8 30KVar/450V capacitors, and usually only 2 to 3 are used. It is considered to be replaced with 8 15KVar/450V capacitors to reduce the harmonic current.

Divide the load into multiple paths to reduce heat generation and avoid resonance points as much as possible.

2.3 Solution

Reduce the capacity of a single group of capacitors, replace 30KVar with 15KVar capacitors. Replace 100A fuse with 63A. The measured working current of the capacitor is normal.

3 Typical Case 2

3.1 Fault phenomenon

The analog data monitored by the SPARTON monitoring equipment next to the inverter in Tongde and Jiangcun machine buildings are inaccurate.

3.2 Fault Analysis

(1) By shutting down the high-frequency energy saver, it was determined that the source of the interference was the high-frequency energy saver, and the main interference target was the monitoring analog data part of SPARTON, while the switch quantity part was not affected.

(2) The grounding and line shielding of the equipment are in good condition, and there is no direct power supply and control line relationship between SPARTON's monitoring equipment and high-frequency energy saver. The interference is mainly transmitted through space.

(3) Considering that the solutions to suppress the generation of interference in the high-frequency energy saver and improve the anti-interference capability of SPARTON's monitoring equipment are relatively complicated, the monitoring line has adopted shielded cable, which rarely causes crosstalk interference.

The interference is mainly caused by the SPARTON monitoring rack itself. Now the SPARTON monitoring rack is too close to the high-frequency energy saver. Properly extend the monitoring line to keep the SPARTON monitoring rack away from the interference source.

3.3 Solution

The SPARTON monitoring rack was moved to a nearby location without interference, and the monitoring data returned to normal.

Through the analysis and testing of these two cases of electromagnetic interference failure, the causes of the failures were addressed and solved by ingeniously using relatively economical and convenient means.