Electricity is transmitted and distributed from generation plants to users, it goes through various sections of low voltage which is below 1000 V, and the high voltage more than 1000 V cables. Additionally, these transmission cables are used to connect secondary outputs of current transformers located at both ends of the transmission stations.
In order to protect critical equipment and avoid the increase of faults that can impact the entire transmission network, the pilot cable’s purpose is to monitor any unbalances between the corresponding pairs of CT, which signify fault conditions. While only one pair of wire is needed to complete the connections, operation, and redundancy planning call for a minimum of three functional pairs of wire at any one time.
It is not possible to have a single cable that spans the distance between substations. As result, various joints are formed to connect different sections of cables together. These joints are the weakest links in the system, for they are prone to failures caused by environmental factors such as thermal stress and moisture absorption. The failures will show up when current readings taken at the secondary of CT deviate from the proportional primary current readings
When a failure is detected, the utility team is called to fix the problem. They go through the sub-station from one end to another in order to isolate the affected CT and pilot cable located at the substation. Then they need to travel to the sub-station at the other end to check the insulation resistance of the pilot cable. The wires that were used must be checked as well as the remaining 4 or 9 pairs of wires in the same bunch of pilot cable and make sure at least three pairs are functional. Because some wires may have permanent damage, there are chances that different color wires are mixed in order to achieve the minimum 3 functional pairs. Therefore, the team must verify the exact inter-connect pairs and they term this work as phasing. When a joint is detected as faulty it will be cut out and a shorter jumper cable will be added and two new cable joints are formed.
Time is one of the most important things to consider when repairing because the maintenance team is always hard-pressed to finish troubleshooting and repairs in a short period of time. If you are looking for a versatile tool that can perform insulation resistance as well as voltage measurements and continuity checks Fluke 1587 Insulation Multimeter is the solution. Visit https://presidium.ph/ to learn more about our products.
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