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Surge Suppression for Drilling Rigs

CONTRELEC have designed a more effective and reliable Surge Suppression Unit for use on DC Drilling Rigs


Typical MOV Device

It is a fact that SCR systems on Oil Rigs (which have a number of high-power, 6-pulse thyristor drives) suffer from spikes and notches on the AC waveform caused by the commutation of the thyristor bridges.

It is standard practice for a Surge Suppression circuit to be connected to the AC supply to suppress the spikes. Historically this consisted of a rectifier and a capacitor reservoir which provides a low impedance trap for transients. In the first instance, this was to protect the thyristors from damaging voltages. As thyristors evolved the voltage ratings improved to a point where MOV (Metal Oxide Varistor)devices could be used which clip the voltage spikes to a level which is within the specification of the thyristors. However, MOVs have a distinct disadvantage over the rectifier/capacitor circuit. Every time an MOV clips a voltage spike it is degraded, up to a point where the MOV (literally) explodes.

This led to SCR system manufacturers pushing the clipping voltage up so that the MOVs were working as infrequently as possible in order to just protect the thyristors. However, the voltage level of the spikes is now at a point where other sensitive circuits on the rig might be damaged or degraded.

CONTRELEC re-visited the original rectifier/capacitor design and engineered a new version which can be fitted to the 600V and 480V rig supplies. This circuit does not degrade and therefore there is no danger of parts failing explosively, and can be connected alongside an MOV circuit if preferred. Two versions are available: a single, large enclosure which can be bulkhead mounted or installed in the main switchboard, or a more flexible two-panel version for in-panel installation where space is more limited.


Panel 1 of a Dual Panel Surge Suppressor

Panel 2 of a Dual Panel Surge Suppressor

Single Enclosed Version

Assembly Drawing