Product Overview
The protective threshold device (ZPU (Ex) SHIK) (hereinafter referred to as PU) is a method and means for protecting metal structures and equipment from corrosion and overvoltage during AC short circuits caused by lightning strikes or switching transients. The PU operates by utilizing a semiconductor switch and a capacitor connected in parallel. This design expands its scope of application, enabling simultaneous DC isolation of cathodic-protected equipment from the public power grid grounding system and protection of equipment from overvoltage during AC short circuits caused by lightning strikes and switching transients.
The electrical circuit of the control unit is illustrated by drawings: in Fig. 1; in Fig. 2, a diagram explaining its operation.
The device contains a diode switch, electrically connected between the ground and the protected metal structure (main pipeline).
In the PU, the diode bridge is made using a counter-parallel connection scheme of diodes.
The PU additionally contains an electric capacitor (capacitance) connected in parallel to the diode bridge.
The PU is used to provide AC grounding and DC isolation of electrical equipment of a main pipeline where electrochemical protection potential is present.