Voltage Clamping Devices:
This is a device that conducts once a predetermined voltage has been attained. Once conducting, they maintain the predetermined volt drop across the device. The voltage clamping devices will “soft turn on” as the threshold approaches have a partial turn on bleeding more and more current off of the pipeline as the voltage threshold is approached. Once at the predetermined threshold, the voltage will be clamped whilst the conduction will be at maximum. The Voltage clamping devices truly comply with NFP 70 & Eskom guidelines as they do not ”Short Circuit” both the current as well as the voltage off of the pipeline. These types of devices can have AC Mitigation circuits in parallel to decouple AC steady-state interference from overhead powerlines on the pipe to cater for AC voltage below the Cathodic Protection DC fault threshold level. Once “on” current flowing through the device will not keep the device conducting if the voltage falls below the predetermined threshold. Disadvantages of Voltage clamping devices are heat generation (ignition temperatures in Hazardous zones) and relative physical size whilst they fully comply with NFP 70 and Eskom guidelines. Typical discharge currents are 1,2kA, 3,7kA, 5kA and 14kA. Hazards can be mitigated by suitable enclosure and application selection.
CE VLD 70 EX – Voltage Limiting Device – Dc transient protection and voltage limiting devices for test points, ground mats, earth spikes and rebar connections.