132kV and 22kV busbar protection schemes of the new Hong Kong Electric’s stations

132kV busbar protection system

The Hongkong Electric Co., Ltd. (HEC) generates electricity at Lamma Power Station on Lamma Island and transmits the electricity from Lamma Island to various parts of Ap Lei Chau Island and Hong Kong Island where the load centres reside.

The voltage levels of the transmission networks are 275kV and 132kV. At primary zone substations, i.e. the load centres, the transmission voltage is stepped down to 11kV or 22kV for feeding the distribution networks nearby.

Electricity is then distributed from the primary zone sub stations to over 3,600 distribution substations on Hong Kong Island, Ap Lei Chau Island and Lamma Island through the 11 kV and 22 kV distribution networks.

In this connection, new zone substations are designed to distribute electricity at 22kV level.

To cope with the load growth in the Central and Wan Chai areas, following the commissioning of the new MRS 275kV Switching Station in 2008, a new 132kV switching station and a new 275/22kV zone substation are required to be put into service in the Wan Chai area in 2010.

Due to scarcity of land, the two new substations are housed together with the MRS 275kV Switching Station in a multi-storey building.

The following sections describe the protection schemes to be used at these two new substations with new busbar configurations.

2. MRS 132KV Switching Station

The new MRS 132kV Switching Station injects power to the existing 132kV transmission network in Wan Chai area so as to relieve the load congestion in adjacent areas.

Due to the crucial role and special location of this switching station, it was decided to adopt a design with higher fault tolerant capability for the 132kV busbar configuration and the associated busbar protection.

MRS 132KV GIS Busbar Configuration

MRS 132kV Switching Station comprises a 6-busbar GIS with 20 bays (viz. 12 outgoing circuits, 2 275/132kV interbus transformer circuits, 4 bus-sections and 2 bus-couplers) in double-busbar configuration as shown in Figure 1 above.

In HEC’s existing 132kV switching stations, GIS with separate isolators and earth switches have been adopted with proven reliability and performance.

During the market search inquiry for the supply of MRS 132kV GIS, it was found that most GIS manufacturers only offered 3-position switches (see Figure 2), which integrate an isolator with an earth switch, as their standard products in the 145kV class GIS.