Improvement of Reliability of Large-Sized Ceramic Capacitors and Dummy Resistors for the High Power Transmitter

Tohru MIZOKAMI  Hiroki TAKAZAWA  Eiichi KAWABATA  Yuzi OGATA  Haruo OHTA  Kazuaki WAKAI  Kazuhisa HAYEIWA  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E77-A   No.1   pp.220-227
Publication Date: 1994/01/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Reliability)
Category: Evaluation of Reliability Improvement
ceramic capacitor,  dummy resistors,  transmitter,  exfoliation,  plating,  UV sensor,  

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This paper describes the effective countermeasures for exfoliation of large-sized ceramic capacitors, deterioration of dummy resistors and developement of a spark sensor with UVtrons at 300-500 kW transmitting stations. Cracks and exfoliation were found at the electrode of large-sized ceramic capacitors in the output circuit of the 500 kW transmitter. The exfoliation was caused by the temperature rise and the thermal fatigues at the electrode with the Nickel plating including Irons. A pure Nickel-plated electrode including no Irons and a new soldering method using disk-typed solder with a large adhesive area are employed in order to reduce the temperature rise. The temperature rise of the improved capacitor was 18 lower than the conventional one. Deterioration of ELEMA resistors of the 300 kW dummy antenna was discovered. The damage of the resistor was caused by the concentration of the electric current followed by the thermal stress cycle which made mechanical exhaustion at the electrode. Therefore, oval-shaped type resistors with much longer electric current path (20% up) to suppress the concentration of current flow and much slower temperature rise are newly developed. In case that sparks occurred at DC or RF high voltage impressed sections of the high power transmitting equipment, the discharged points could be seriously damaged by the transmitter energy itself. In orded to prevent this, a spark detector using UV (Ultra violet) trons is developed and installed at the matchign circuit of the 500 kW transmitter. Conventional UV sensors with only one UVtron could not detect feeble discharges and sparks with a duration time of less than 150 ms because of false outputs by the back ground noise. Since choosing three out of four UV trons system is employed, possibility producing a false output will be just one to 445 years theoretically. This means extremely reliable and sensitive spark detection system are constructed. These countermeasures have improved reliability of the transmitting equipment greatly. No damages have been found in the transmitters ever since.