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Zambia: Kafue gorge power station moves on after the mudslide

The Utility Wide Safety Committee (UWSC) comprising officials from Energy Regulation Board (ERB), ZESCO Limited, University of Zambia, and Copperbelt Energy Corporation (CEC) recently visited Kafue Gorge Power station to check on the rehabilitation works being undertaken at the power station following the mudslide of 2005.
The committee was constituted in May 2005 and was tasked to look at major happenings in the Zambian Electricity Sector, one of which was the Kafue Gorge mudslide of 2005.

During the inspection, the committee established that the culverts were being replaced and works would soon be concluded. Water from the main gallery was now being directed to the right channel without disturbing the operations.

The committee further established that the drainage system which had been blocked had been opened and the entrance door to the power house replaced. The mudslide had severely threatened the operations of the power station.

Geological experts at the University of Zambia and Konkola Copper Mines were then contracted to assess the mudslide and advise on remedial measures.

A ZESCO task team and external experts identified remedial actions to be undertaken in the medium to long term in order to reduce or eliminate the risk of a similar disaster in the future. Some of these measures have already been embarked upon. The measures include slope stabilization and re-design of the culverts and other civil works to improve the drainage so as to cater for flood waters and debris.

On Saturday 24th December 2005, Zambia’s principal power station mudslide following a heavy downpour. The mudslide caused by torrential rains in the Namalundu area besieged the power station leading to its shut down.

As a result of the mudslide, the generator flow and the pumping station were flooded with water and mud. The slurry pump could not pump as it was chocked by roots, and muddy water. At the pothead yard, the wire fence on the hill side was damaged and the pothead platform was filled with sediment deposits leaving the pothead drains blocked.

The power house entrance and access tunnel road surface and shoulders were severely eroded and the cable trenches were seriously undercut in several areas. The three drains at the entrance, surge gallery, and access door were completely chocked, meanwhile, the power house door was damaged and there was a lot of sediment deposited on the road, blocking accessibility.

In the power house, the four units that were in service tripped. Unit 1 and 2 tripped on differential protection whilst unit 5 and 6 tripped on flood protection, leading to loss of production. As a result five battery chargers were partially submerged in the mud and the newly supplied 135MVA transformer that was temporarily stored in the transformer repair bay was contaminated with sediments.

Generator 1 and 2 and associated turbine equipment were contaminated with sediments and rendered in-operational, but for unit 5 and 6, only turbine equipment at valve floor was contaminated, however, this could still be put back into service with minimal amount of work.

All drains in the powerhouse including transformer pits and drain pits were overwhelmed with sediment and the lubrication system on unit 1 was contaminated, leading to loss of over two thousand liters of oil. Meanwhile, tools and equipment that were left in various work areas under rehabilitation, (i.e. Turbine floor, valve flow, transformer hall etc) were damaged.

The power house lift (elevator) was rendered in-operational due to flooding in the lift sump. This meant that all forms of transportation had to be done by way of the 8 kilometer road route to the surface. The findings showed that some control cards of the elevator were damaged as a result of the flooding.

Fortunately, the station did not record any incident of injury or accident both during the mudslide and the works leading to the restoration of the plant. To restore the power station, the station team was mobilized to the power house entrance to divert the water that was rushing down the power house access tunnel. The station emergency ejectors were started; however, their effectiveness was slow due to the closure of the generator cylinder gates (station flood protection).

Over 200 workers were contracted to commence physical removal of sediment, unblocking of access ways, de-slugging and restoration of drains, general cleaning and other tasks. Immediate mobilization of station technical staff to assess and carry out immediate works to restore whatever generation was possible was part of the immediate remedial actions taken.

Several submersible pumps were also deployed in various areas to control flooding, as the drains were not functional. To supplement ZESCO’s own equipment at the power station and expedite the physical removal of sediment, heavy equipment was hired and mobilized from various organizations like the Zambia National Service, Dana Services Ltd, and KCM.

The Kafue Gorge power station - Zambia’s largest Power Station is Located on the Kafue River and has been in operation since 1971. The power station has an installed capacity of 900MW with 6 generators of 150MW each.

Additional information:
News date: 01/01/2006

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