Shiroro Hydroelectric Power Station is situated on the Kaduna River in the Niger State, Nigeria. It comprises of four turbine-generator units referred to as Unit 1, Unit 2, Unit 3 and Unit 4. Each unit has a capacity of 150MW, giving the station an installed capacity of 600MW.
Sometime in 2010, a loud and frightening noise was heard from the water intake structure and shortly afterwards it was observed that the output of unit 4 had reduced drastically. Upon investigation, engineers at the power station found a large piece of concrete measuring about 6 metres by 2 metres in the Scroll Case of the Unit. It therefore became clear that the noise heard was a result of structural failure at the water intake of Unit 4. This piece of concrete was removed from the scroll thereby restoring the output of Unit 4 to 150MW.
However, the damage resulted in failure of the unit’s maintenance gate to close as required when carrying out certain types of maintenance on the unit. Consequently certain aspects of Unit 4 have not been serviced since then and may well never be able to be serviced. Furthermore the damage occurred about 60 meters under zero visibility water and was therefore difficult to assess and repair. This raised concerns about the possibility of further catastrophic failure. These factors cast a shadow on the viability of Unit 4, and there was a real possibility that Unit 4 would soon or later have to be decommissioned, which would have resulted in reduction of Shiroro’s Hydro Plant Power output from 600MW to 450MW.
The North South Power Company Limited took over the operation of Shiroro Hydroelectric Power Station on 1st November 2013 under a 30 year concession agreement with the Federal Government of Nigeria. Shortly afterwards the company became aware of this problem with Unit 4 and decided to address it. This problem was never in any of the information space at the time of bidding for the plant nor was the company aware before taking over the plant.
North South Power employed Tetra Tech Inc. of USA in 2014 to assess all structures at Shiroro including the water intake of Unit 4. Tetra Tech was able to assess the damage through use of deep water “sona” technology and confirmed that the damage was to the lintel of Unit 4 Maintenance Gate.
North South Power proceeded to commission Tetra Tech for the design and specifications for the repair work. In April 2015, a Nigerian construction company, Precon Smith Construction Ltd was contracted to fabricate a 100 tonne bulk head divided into five segments. A United States underwater construction company was then contracted to create an access for the bulkhead in the trash rack, floated each of the 26 tonne bulk head segments on the reservoir using airbags technology with exceptional engineering equipment to tow them to the intake tower and lowered them approximately 60 metres into position on the intake of Unit 4 in a zero visibility environment close to the diving limit of humans. However, due to a number of challenges including unexpected variations in the shape of underwater structures, the bulkhead could not hold the pressure of water at those depths. The bulkhead had to be taken out for modifications and was reinstalled. In August 2015 the level of water had risen to such a level that divers would not work safely at the bottom of the intake, and the project had to be suspended.
The US construction company remobilised in April 2016 when the water level had fallen to a safe level and managed to get the bulkhead to hold the water pressure as required for the repair of the lintel but had to be disengaged from the work at this stage when negotiations for them to complete the works collapsed. Consequently NSP approached and engaged PowerChina Company in conjunction with Sinohydro of China to complete the Project. Another US company, Apex Diving, provided practical advice to PowerChina and Sinohydro on the use of the American made high-tech equipment that were acquired by North South Power (NSP) for the work. Under the arrangement we have been able to repaired the structural damage on the lintel of Unit 4, removed the bulk head and on Wednesday 6th July 2016 bolted down the last trash rack segments to mark the successful completion of the Project.
We have therefore cast away the shadow that was hanging over one quarter of Shiroro’s generation capacity. In order to achieve this, we have had deploy the ingenuity of an engineering feet, overcome enormous safety and technical challenges and show the value that a true private entrepreneur space came bring to bare on our economy.
We thank Tetra Tech for designing the solution and providing engineering support service solutions, PowerChina and Sinohydro for completing the works and Apex Diving for their practical continuity support services. We also wish to thank North South Power employees of all categories who participated in many ways including providing management, engineering and administrative inputs to the Project.
We must not go without thanking the Board of North South Power Company limited for financing this Project. To date North South Power Company limited has spent relatively US$8.5 million on the project, particularly under the escalating cost of Dollar.
Finally, we must appreciate the patience of the regulators and participants within the Power industry for their patience and understanding during the course of the work, in particular, the National Control Centre (NCC) Oshogbo. Commendation also goes to the Nigerian Electricity Regulatory Commission (NERC) for their faith in us in spite of some shortcoming.
It will be unwholesome not to extend our gratitude to the Hon. Minister of Power, Works and Housing for his support, the Power Team of the Office of the Vice President for their continuous follow up on the project status and the comforting acknowledgment of their understanding of the challenges faced with the project.
Thank you for your audience.
Engr. Olubunmi Peters, PhD
Executive Vice Chairman
North South Power Company Limited