The Volta River Authority, VRA, was created in 1961 by an act of parliament (the Volta River Development Act 46). The VRA is responsible for generation of electric energy in Ghana by developing the hydro potential of the Volta River and also the operation of the transmission system. Since 1987 the VRA has also been responsible for the distribution of electricity to customers in the Brong Ahafo, Northern, Upper East and Upper West regions.
The Volta River Development
The Volta River Development initially involved the construction of the Akosombo Hydroelectric Plant comprising the power generating station and the Akosombo dam. The Kpong Hydroelectric Plant was later constructed downstream the Akosombo dam. The construction of the Akosombo dam resulted in the creation of the Volta Lake , which is described below:
The Volta Lake and River
The Volta River is the main fresh water source for Ghana . The Volta River is formed by the confluence of the Black Volta and the White Volta rivers at Yeji in the central part of the country. The river flows in a southerly course through Lake Volta to Ada on the Gulf of Guinea . The total length, including the Black Volta is 1, 500 km (930 miles).
Lake Volta , the head pond of Akosombo dam has a surface area of 8500km 2 and a live storage capacity of 148X10 9 m.
Effect on the Environment
The formation of man made lakes e.g. in tropical countries create environmental changes resulting in propagation of water borne diseases. The three water related diseases common to the project were: Onchocerciasis (river blindness), Schistosomiasis (bilharzias) and Malaria. The VRA in this regard provides healthcare services to the affected villages and also has a medical boat (Onipa Nua), which also provides health care services to the communities along the Volta Lake.
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KPONG HYDRO ELECTRIC DAM
TECHNICAL DATA
Design Station Capacity - 148MW
Design Annual Energy - 1000GWh (avg. flow of 1160m3/s)
Turbine
Unit output - 40MW (55,500hp) @11.75m
Synchronous speed - 62.5 Rev/Min
Type of Turbine - Fixed Blade Propeller
Manufacturer - Boving , UK
Generator
Type - Vertical Shaft, Umbrella Type
Rating - 4.4MVA
Cooling - OFAF
Manufacturer - Toshiba , Japan
Unit Transformer
Type - Outdoor 3phase
Rating - 51MVA at 13.8/161KV, 09PFM
Manufacturer - OyStromberg , Finland
Exciter
Type: - Static
Manufacturer - Toshiba , Japan
Governor
Type - Electronic/Hydraulic
Manufacturer - ASEA ( Sweden )
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In the Akosombo Plant, water is allowed to fall at a height of about 60m unto the turbine at a considerable speed through the penstocks. The energy in the falling water is made to drive the turbine and the turbine in turn drives the magnet in the generator (rotor) since they are coupled. The movement of the magnet, relative to the stationary conductors (stator) in the generator causes electricity to be produced at the voltage of 14.4kilovolts. The electricity is then transformed to a higher voltage of 161kilovolts by the use of a power transformer and transported through cables throughout the country.
RETROFIT PROJECT
After 30 years successful operation of the generating units at Akosombo, VRA in looking ahead to the next 30 years of trouble-free reliable and economic operations embarked on the retrofit project in 1992. The project was suspended after the first unit retrofit in 1993, and resumed again in1999, with a new scope to replace the exiting turbine runners. The objective of the project was to modernize, upgrade and improve the performance, reliability, maintenance and operations of the Plant.
The major activities were:
- Replacement of the existing runners with a more efficient ones;
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Modification in the water passages to improve flow (i.e. stay vanes, wicket gates and insertion of a splitter vane in the draft tube);
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Rewinding of the generators with higher class insulation to up rate and restore their integrity;
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Replacement of the electromechanical governors with electronic governors;
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The rotary exciters were replaced with static exciters;
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The station auxiliaries were also replaced and/or refurbished.
Guaranteed peak efficiency of 93.5% was met during efficiency test after the retrofit of the first Unit. Click here for information on Akosombo Retrofit Project.
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