Variable speed drives as applied to the London Water Ring Main

The London Water Ring Main (LWRM) is an integrated system of deep tunnels supplementing the capital´s ageing surface distribution system. With up to 1300 megalitres of water per day fed in and carried round the ring by gravity from the major treatment works in the Thames and Lee Valleys, pumping stations are only required at strategic positions where it is necessary to link in to the existing surface system. This form of water distribution is more efficient than pumping direct through surface mains with high frictional losses. With localised shaft pumping stations using a mixture of fixed and variable speed pumps with ratings up to 700 kW, there is better operational flexibility for pressure or flow control. Here, the author describes the variable speed drives applied to the pumping stations described.