England, Cannon Bridge, London

1. Site Location: Euronext-Liffe Cannon Bridge, London

Plant Description: The electricity supply to Liffe Cannon Bridge is from the LE system at 11 kV, 50 Hz, 3-phase, 3 wire. The maximum 3-phase fault level quoted for the supply at the 11 kV LE switchboard is 13.12 kA (250 MVA). The existing 11 kV power distribution system at Liffe has six switchboards. The main Intake Switchboard has two utility incomers from LE, two incomers from generators Gen-1 and Gen-2, two ring main feeders, and the DT1 and DT2 transformer feeders. The other existing switchboards are as follows:

  • Bush Lane Atrium Substation - one LE incomer and supplies transformers ADT1, ADT2 and ADT3.
  • Bush Lane Caged Substation - two incomers from Generators Gen-3 and Gen-4.
  • Atrium Level 1 Substation - supplies transformers DT5 and DT6.
  • Transfer Deck East Substation - supplies transformers DT3 and DT7.
  • Transfer Deck West Substation - supplies transformers DT4 and DT8.

Under the normal mode of operation, supply to the system is through the two LE feeders connected to the 11 kV Intake Switchboard, which is normally run with its bus-section circuit breaker B5 open. The Bush Lane Atrium Substation is fed separately through its LE incomer, with circuit breaker B25 open. The ring main breaker B12 is also normally open. This configuration was taken into account when performing the maximum fault level calculations.

Scope of Work: To perform fault level calculations for the purpose of determining protection settings and verifying operation of the protection systems after proposed substantial modifications to the distribution network had been implemented. The main objective of the study was to check the co-ordination of the overcurrent and earth fault protection, taking into account the new switchboards and transformers.