Rectifiers.  Main Components

	Switching surge protection Power semiconductor devices are protected against internal and external switching surges. Diodes are protected against both internal and external switching surges by filtering circuits and varistors.
	Power Diodes Pill power diodes manufactured by VISHAY (formerly International Rectifier) are utilised in rectifiers. Two diodes in series are connected in each arm of rectifier.
	Galvanic isolatition boards  Galvanic isolation boards provide protection against overvoltage by in-built RC- circuits. In addition boards convert and supply data for diagnostic system.e connected in each arm of rectifier.
	Diagnostics and Control System Rectifiers are equipped with microprocessor control and diagnostics system. This system captures following information about condition of each diode and visualise it on HMI panel: «normal operation», «parameters de-rating», «failure», and diodes temperature. Monitoring of each diode parameters is happening constantly during rectifier operation. Diagnosis of these criteria can forecast potential failures and significantly improve maintenance cycle.

In case of diode parameters got deteriorated, the power diode can be replaced eliminating its imminent failure. In-built redundancy allows normal operation of the rectifier even if one diode is failed.

HMI is a modular type industrial controller PP65 with colour LCD screen produced by Bernecker&Rainer (Austria). 

Information about state of the rectifier and its elements can be observed on visualisation panel or computer monitor through supplied software. Mnemonic symbols of rectifier diodes, graphs of reverse voltage distribution between diodes and arms temperature are displayed on the panel along with the following data:

• rectifier single-line diagram; 
• events log;
• diodes temperature;
• diodes temperature diagram;
• voltage distribution between two diodes in series;
• signals: 
  - transformer overheating;
  - doors condition;
  - rectifier overheating;
  - diode parameters deterioration. 

The rectifier diagnostic system constitutes and integral part of medium voltage switchgear protection device and SCADA system.