How to Operate Telecom Power: Wear Proper Protection

Rectifier Operation Procedures

Sustainability seems to be the latest buzzword, and cathodic protection (CP) is an important component of sustainability for many metal structures. What better way to protect and maintain infrastructure than by mitigating corrosion? Some CP systems consist of sacrificial anodes that naturally corrode to protect less active metals, such as steel.

Others require a power source to drive the protective current in the correct direction. The most common impressed current voltage source is a rectifier, which can break down. A well-maintained rectifier can provide uninterrupted CP, thereby reducing repair costs and labor/technician time. This article discusses the basic principles of rectifier operation and maintenance as well as basic recommendations.

Sustainability is the ability to endure. The fundamental purpose of any cathodic protection (CP) system is to mitigate corrosion. By preventing corrosion damage, a pipeline or other metal structure is protected and made to last. Therefore, corrosion mitigation leads to sustainability.

CP is most often achieved through galvanic (sacrificial) or impressed current systems. Galvanic CP systems consist of sacrificial anodes, usually made of active metals (aluminum, magnesium, or zinc), that corrode to provide protective current to less active metals such as pipeline steel. Impressed current CP (ICCP) systems utilize an external power source in the form of a rectifier or other voltage source to drive impressed current anodes (e.g., cast iron, graphite, and mixed metal oxide) to corrode in order to distribute protective current to the structure (cathode).

A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. Rectifiers must be kept in continuous operation. Since a rectifier is an electrical device, it is susceptible to power surges. A nearby lightning strike may cause circuit breakers to trip or diodes to short. Therefore, routine inspection and monitoring are necessary to keep rectifiers operating properly and enduring.

Safety is the most important aspect of all inspections. The goal of any task related to rectifier operation is to perform the work safely, which includes wearing proper protective equipment.

Operation

A rectifier has three main components: transformer, stack, and cabinet. The purpose of the transformer is to safely isolate the incoming alternating voltage (primary side) from the secondary side, which is adjusted to control the output voltage of the rectifier. Typically, these adjustments are made through tap rods connected at intervals to the secondary side windings, which provide multiple setting options.

The stack is the actual rectifier, consisting of a bank of silicon diodes or selenium plates that act as one-way current valves. The configuration of the diodes or plates causes the cyclic alternating current to flow in one direction and be blocked in the other, resulting in both directions of the AC wave flowing in the same direction. The cabinet includes a test panel, safely houses these components, and allows for monitoring and other advanced operations.

Other items in a typical rectifier include circuit breakers, voltage and current output meters, lightning arresters, surge suppressors, transformer taps, and fuses.