To protect the power component of electric welding machine,overtension and undertension protection are circuit designed.

为保护焊机的功率器件设计了过压欠压电路。

Moreover, the proposed control system is of some fault diagnosis and protection functions, such as overcurrent, overvoltage-undervoltage, overtemperature and parameter overrun.

，该电源控制系统还有过流、过欠压、过热、限等故障诊断与保护功能。

The causes are presented as follows: packer unloading pressure, formation damage, oil tool plugging, formation voidage, the worst formation physical properties and the effect from vicinage wells.

地层污染或工堵塞;地层欠压;地层物性极差;邻井影响等。