Use of Distance Protection in EHV Submarine Cable Network in Oil and Gas Industry

摘要

Objective: Present trend around the world is to power up the Offshore Oil and Gas facilities by power from shore. The popular choice is to use Extra High Voltage submarine cables for handing these large quantities of power. The objective of this presentation is to focus and explain how the EHV cables and offshore facilities can be protected by Distance Protection. Application of Distance Protection in Oil and Gas Industries: The efficient protection of the costly submarine cables and the offshore facilities from the electrical fault is extremely important. One of the most efficient ways to protect these types of electrical network is by using Distance Protection. EHV Interconnected grid network often involves bidirectional flow of power. If a fault in one interconnecting cable is not identified and isolated fast, it can cause substantial damage to the equipment and system. Also it is necessary to identify the faulty section correctly and ensuring the continuity of the service for the healthy section. Benefits of Distance Protection in EHV Submarine Cable Network: 1. Fast and correct isolation of the faulty section: The Distance Protection enables the correct circuit breaker to operate instantaneously for clearing a fault same time it ensures the blocking of unnecessary tripping of the other circuit breakers. This improves overall availability of the healthy system. 2. Concept of forward and reverse zone and back up protection for bus bar in reverse zone: Distance protection are inherently directional for it's MHO characteristics which endowed it with an added advantage to segregate between forward and reverse zone. This feature provides a facility to include backup protection of the substation bus bars in zone 2 or zone 3 while in zone 1 forward direction, the interconnecting cable can be protected. 3. The special challenges in submarine cable and how to overcome them: The cables have substantial capacitances which need to be properly taken into consideration while selecting the MHO characteristics of the relay so that it can identify the faulted section correctly. 4. The challenges faced in short length of cables and how to overcome them: For a short length of cable the fault arcing resistance occasionally becomes comparable with the load impedance which hinders correct identification of a faulty zone. Special types of characteristics are to be selected for the same. 5. Communication requirement between the sending and receiving end: Distance protection is a unit type of protection in an interconnected transmission line or cable network. Communication is very important between the substations at the two ends for proper location of zone and tripping decision of the circuit breakers. Novelty focused on this paper: This paper provides comprehensive ideas about effective use of Distance Protection in EHV submarine cable network. This is utmost important because offshore oil and gas facilities are increasingly powered up from shore power using EHV submarine cable. Effective use of the Electrical System will both reduce downtime of the plant and save cost of operation.