11kV cable protection to permit an increase in distributed generation

• Main Author: Chilvers, Ian Michael
• Published: University of Manchester 2005
• Subjects: 621.319
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595837

The UK government have set ambitious targets for future energy supply from renewable energy schemes and combined heating and power plants. In order to meet these targets a large amount of distributed generation is expected to be connected to medium voltage distribution networks. The connection of large quantities of distributed generation causes technical problems with existing medium voltage feeder protection schemes. These problems can limit the installed capacity of distributed generation. This work concentrates on the development of an 11kV cable protection scheme in order to minimise or remove the problems with existing cable protection schemes. In the UK, faults on 11kV cable circuits contribute significantly to the total number of customer interruptions. The development of 11kV cable protection can minimise the number of these customer interruptions. This work begins with studies to determine the types of problems encountered with existing 11kV cable protection schemes when distributed generation is connected directly to the 11KV circuit. Based on the results of these studies, the investigation of an 11kV cable protection scheme using distance relays is carried out. In the UK, voltage transformers and communication schemes are seldom installed at 11/0.433 kV distribution substations. The distance relay voltage is measured at the secondary winding of the local 11/0.433 kV distribution transformer, avoiding the cost of installing a voltage transformer at the distribution substation. The performance of the distance scheme is then studied using an electromagnetic transient simulation package. The feasibility and benefits of the new protection scheme are then discussed.