Submarine cable systems employing switchable, powered branching units can be hazardous to repair as the system power could be re‐applied under certain fault conditions, thus endangering the lives of the repair personnel. Global Marine’s Protection Grounding Unit (PGU) technology enables cable systems to be repaired safely and without risk to personnel.
Global Marine provide a number of services associated which include: cable qualification, kits and equipment, supporting manual as well as frequent updates and training opportunities.
Switchable branching units allow the power path of a system to be reconfigured such that a faulty segment of a system can be de‐powered while the rest of the system remains powered and carrying traffic. This enables a vessel to repair the faulty segment without further loss of traffic. If during the repair, one of the working segments is interrupted or the branching unit fails, there is a real risk of power being connected to the faulty segment and therefore a risk of electric shock to shipboard personnel.
As the remaining segments of the system are powered from the terminals, the vessel has no physical control over the power feed equipment and thus, in the event of the faulty segment becoming live, the ship would receive a high power level on the recovered cable. To minimise the risk of electric shock the recovered cable is therefore earthed before it is handled by ship personnel. The ship’s Power Safety Officer will take control of power safety for the entire system during a PGU repair.
The primary function of the Protection Grounding Unit (PGU) is to provide the earth path and, secondly, it will warn personnel should power come onto the cable by visual and audible alarms. It is imperative that good communication between the ship and all terminal stations is available during such an operation. If significant current (beyond normal earth currents) is detected, then there is a serious system defect and all personnel should immediately stop working on the cable and stand clear of the cable whilst all terminals are contacted to identify and resolve the problems before work is restarted.
The PGU Manual (or PGUM) is published annually on an Explorer CD, or more frequently when there are important changes. It is distributed to all Global Marine customers who have successfully trained in PGU. The manual is very detailed and contains step‐by‐step instructions for carrying out PGU repairs on every qualified cable. The manual also stipulates when resistance measurements must be carried out and what the maximum values must be. The manual is used in conjunction with the Universal Jointing Construction Manual (UJCM) when standard jointing procedures are required.
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