Imst Small Hydropower Plant
Country: Austria
Project period: 05/2006 - 12/2008
Client: Private Investor
Investment amount: EUR 5.0 Million
Description:
Development and realization of a rehabilitation concept for the SHPP Imst, which consisted of 4 small units along the Pigerbach river, including application for the revised water right permits and limnological impact assessment.
The rehabilitation concept consisted of the rehabilitation of the first upper unit and an improvement of the existing design, with the replacement of the three lower units with one new unit.
In the upper unit the three existing Francis Turbines were improved, as well as the intake structure, the headrace channel and the surge tank. A new steel frame storage and maintenance building was constructed alongside the upper unit, and a new bypass installed so that the upper unit could be shut down. The tailwater channel of the upper unit was also newly built, using precast concrete components.
For the new lower unit, a 2000m long penstock of GRP diameter 1800 (50% of the distance) and diameter 1600 (50% of the distance) was intstalled. This replaced an existing open channel.
Services provided:
For the operation of the hydro power plant water was taken from the Pigerbach stream and after the final stage the water was discharged through a tunnel directly into the River Inn.
Following the closure of the textile company, the power plants were bought by the company WEB Windenergie AG, who contracted Posch & Partners to design and supervise the rehabilitation and optimization of the plants. The main upper stage has now been rehabilitated and the three lower stages have been replaced by a single new small hydro power plant.
A new by-pass was also constructed for the upper stage to facilitate maintenance works and additional storage space was created by the construction of a new storehouse besides the existing plant.
Additional works included the installation of an automatic water level turbine control system and renewal of the energy supply and switchgear. The side walls of the stream channel behind the power house were also raised. Following the rehabilitation works the power production was enhanced and the maximum turbine power of the upper stage is 512 kW.
The automatic turbine control system for the upper stage was supplied by Andritz AG and the automatic turbine control system for the lower stage was supplied by Siemens AG. A challenge for our electrical engineers was the installing of a network between the upper- and lower stage so that automatic control was possible.
The existing water intake of the upper stage, which was built in 1912, also acts as the water intake for the lower stage. This was redesigned to ensure a (dynamic) residual flow is maintained in the stream below the water intake and a fish ladder was installed.
A base amount of 160 l/s flows through the new installed fish ladder. The discharge of the remaining base amount, which is 340 l/s during the months of May to July, flows over a newly installed roller gate. The required dynamic residual flow (15% of the water allocation) is achieved through a hydraulically controlled flushing gate at the weir. The determination of the river water flow is derived from a newly constructed residual water discharge measurement station below the surge tank and an IDM-measurement in the penstock below the surge tank. The hydraulically controlled flushing gate is operated via the PLC system installed in the power house.
The retention water level elevation is at 736.2 m.a.s.l. The consensus water amount of 5 m³/s for the existing upper stage is unchanged. The unlimited water right already conferred was not affected and remains as per the original approved form.
At the power house of the upper stage a by-pass was constructed so that in case of maintenance works on the turbines the water flows through the by-pass to the lower stage. In the power house there are three Francis turbines installed (Andritz AG, 1951). These were completely refurbished, including replacement of the guide vanes, sandblasting and repainting of the entire housing and restoration of the vane regulation.
The tailrace channel of the upper stage has a length of about 176 m, which was originally constructed as a natural, open channel. This tailrace channel was rebuilt with prefabricated concrete elements and a building at the reversal gate on the spillway was also newly constructed. This arrangement provides increased protection from floods and also permits the entire water flow to be discharged into the Pigerbach for maintenance work on the lower stage.
The water from the upper stage flows over a height of about 13 m through an 850 m long headrace to the newly constructed lower stage. (About 1595 m total length, including the upper stage) Below the lower stage water is discharged through the existing tunnel directly into the Inn.
The headrace of the lower stage consists of an existing inverted siphon under the Pigerbach, a 72 m long existing tunnel under the so-called Brennbichl and an approximately 780 m long newly constructed penstock made of fiberglass.
Before the new inverted siphon two closing gates were installed that permit the discharge of the entire water flow via the reversal gate into the Pigerbach so as to allow maintenance work on the lower unit.
The penstock is DN1800 between the end of the tunnel and the hotel Neuner and it follows over a length of 368 m the existing headrace channel (former lower stages 2 and 3). Under the hotel Neuner the penstock was installed as an inliner in an existing steel pipe DN 2200.
The penstock route between the hotel Neuner and the new powerhouse follows for a length of 366 m the existing headrace (former lower stage 4). This penstock section was constructed with GRP pipes, DN 1600. Due to the new design level of the penstock the base of the existing channel had to be removed at certain sections.
Since the existing inverted siphon is an insurmountable obstacle (smooth surface, drop height) fish could not pass this section. For this reason the existing disused by-pass channel was adapted to create a fish pass for this section.
The new power house was built at the same location as the former powerhouse of stage 4, within the municipality of the town of Imst. The exterior dimensions of the powerhouse are 13 x 10 m with a maximum height of 7 m. The shape of the roof of the powerhouse is designed in a waveform, symbolizing the energy of the water. The machine sets are 9 meters below ground level, which was necessary so as to make a connection to the existing underground discharge tunnel that leads to the River Inn. Under the current Danger Zone Plan for the Pigerbach stream the power house is located entirely within the yellow danger zone. The Pigerbach can dissipate in this section a water amount of 50 - 60 m³. In a one hundred-year flood event, which would correspond according to the hazard mapping of 120 m³/s, widespread flooding would be expected in this area. For this reason the ground level was raised around the power house and the entire engine house was also designed so that no hazard is created by groundwater or flood events.
During the construction period the dewatering of the excavation for the lower stage was very difficult due to the high groundwater level resulting from the proximity of the Pigerbach and the River Inn. Evidence for the fact that the entire project is in an area vulnerable to flooding is also substantiated by flood events in the years 2001 and 2005.
The powerhouse contains not only the turbine room, but also space for the switchgear and transformer, a workshop / storage room, a rest room for staff, a kitchen, a wash area and space for maintenance works in the turbine room. There is also a small museum which is used to exhibit the old power plant equipment of the former three lower stages.
The electromechanical equipment of the newly constructed lower stage consists of a Kaplan bulb turbine at 712.40 m.a.s.l. (turbine shaft) and a three-phase synchronous generator (rated output ~ 700 kVA). The turbine was developed by Kössler, the generator was supplied from the company Hitzinger and the control system comes from the Siemens AG.
Discharge water flows through the existing tunnel from the former lower stage 3 (Length 348 m, constructed in 1918) directly into the Inn. The tunnel ends at a level of 709.5 m.a.s.l.
In front of the tunnel a new stilling basin was built with a ventilation shaft. This ventilation shaft also allows access to the tunnel from above.
- Limnological and ecological impact assessment
- Detailed design
- Production of tender documents
- Construction supervision
General:
The Imst small hydro power plant originally consisted of four small hydro power plants, arranged as one main upper stage and three lower stages. It was operated by an adjacent textile company, the former Textilverarbeitungs- und Vertriebs GmbH.For the operation of the hydro power plant water was taken from the Pigerbach stream and after the final stage the water was discharged through a tunnel directly into the River Inn.
Following the closure of the textile company, the power plants were bought by the company WEB Windenergie AG, who contracted Posch & Partners to design and supervise the rehabilitation and optimization of the plants. The main upper stage has now been rehabilitated and the three lower stages have been replaced by a single new small hydro power plant.
Upper Stage:
The upper stage was completely rehabilitated, which mainly comprised concrete repair works at the weir, the water intake and the head race channel, the electrical mechanization of all the existing gates and the full automation of the existing rack cleaner.A new by-pass was also constructed for the upper stage to facilitate maintenance works and additional storage space was created by the construction of a new storehouse besides the existing plant.
Additional works included the installation of an automatic water level turbine control system and renewal of the energy supply and switchgear. The side walls of the stream channel behind the power house were also raised. Following the rehabilitation works the power production was enhanced and the maximum turbine power of the upper stage is 512 kW.
The automatic turbine control system for the upper stage was supplied by Andritz AG and the automatic turbine control system for the lower stage was supplied by Siemens AG. A challenge for our electrical engineers was the installing of a network between the upper- and lower stage so that automatic control was possible.
The existing water intake of the upper stage, which was built in 1912, also acts as the water intake for the lower stage. This was redesigned to ensure a (dynamic) residual flow is maintained in the stream below the water intake and a fish ladder was installed.
A base amount of 160 l/s flows through the new installed fish ladder. The discharge of the remaining base amount, which is 340 l/s during the months of May to July, flows over a newly installed roller gate. The required dynamic residual flow (15% of the water allocation) is achieved through a hydraulically controlled flushing gate at the weir. The determination of the river water flow is derived from a newly constructed residual water discharge measurement station below the surge tank and an IDM-measurement in the penstock below the surge tank. The hydraulically controlled flushing gate is operated via the PLC system installed in the power house.
The retention water level elevation is at 736.2 m.a.s.l. The consensus water amount of 5 m³/s for the existing upper stage is unchanged. The unlimited water right already conferred was not affected and remains as per the original approved form.
At the power house of the upper stage a by-pass was constructed so that in case of maintenance works on the turbines the water flows through the by-pass to the lower stage. In the power house there are three Francis turbines installed (Andritz AG, 1951). These were completely refurbished, including replacement of the guide vanes, sandblasting and repainting of the entire housing and restoration of the vane regulation.
The tailrace channel of the upper stage has a length of about 176 m, which was originally constructed as a natural, open channel. This tailrace channel was rebuilt with prefabricated concrete elements and a building at the reversal gate on the spillway was also newly constructed. This arrangement provides increased protection from floods and also permits the entire water flow to be discharged into the Pigerbach for maintenance work on the lower stage.
Lower Stage:
For the lower stage the consensus water of 2.5 m³/s (consensus of the former small hydro power plants 2, 3 and 4) was increased to 5.0 m³/s.The water from the upper stage flows over a height of about 13 m through an 850 m long headrace to the newly constructed lower stage. (About 1595 m total length, including the upper stage) Below the lower stage water is discharged through the existing tunnel directly into the Inn.
The headrace of the lower stage consists of an existing inverted siphon under the Pigerbach, a 72 m long existing tunnel under the so-called Brennbichl and an approximately 780 m long newly constructed penstock made of fiberglass.
Before the new inverted siphon two closing gates were installed that permit the discharge of the entire water flow via the reversal gate into the Pigerbach so as to allow maintenance work on the lower unit.
The penstock is DN1800 between the end of the tunnel and the hotel Neuner and it follows over a length of 368 m the existing headrace channel (former lower stages 2 and 3). Under the hotel Neuner the penstock was installed as an inliner in an existing steel pipe DN 2200.
The penstock route between the hotel Neuner and the new powerhouse follows for a length of 366 m the existing headrace (former lower stage 4). This penstock section was constructed with GRP pipes, DN 1600. Due to the new design level of the penstock the base of the existing channel had to be removed at certain sections.
Since the existing inverted siphon is an insurmountable obstacle (smooth surface, drop height) fish could not pass this section. For this reason the existing disused by-pass channel was adapted to create a fish pass for this section.
The new power house was built at the same location as the former powerhouse of stage 4, within the municipality of the town of Imst. The exterior dimensions of the powerhouse are 13 x 10 m with a maximum height of 7 m. The shape of the roof of the powerhouse is designed in a waveform, symbolizing the energy of the water. The machine sets are 9 meters below ground level, which was necessary so as to make a connection to the existing underground discharge tunnel that leads to the River Inn. Under the current Danger Zone Plan for the Pigerbach stream the power house is located entirely within the yellow danger zone. The Pigerbach can dissipate in this section a water amount of 50 - 60 m³. In a one hundred-year flood event, which would correspond according to the hazard mapping of 120 m³/s, widespread flooding would be expected in this area. For this reason the ground level was raised around the power house and the entire engine house was also designed so that no hazard is created by groundwater or flood events.
During the construction period the dewatering of the excavation for the lower stage was very difficult due to the high groundwater level resulting from the proximity of the Pigerbach and the River Inn. Evidence for the fact that the entire project is in an area vulnerable to flooding is also substantiated by flood events in the years 2001 and 2005.
The powerhouse contains not only the turbine room, but also space for the switchgear and transformer, a workshop / storage room, a rest room for staff, a kitchen, a wash area and space for maintenance works in the turbine room. There is also a small museum which is used to exhibit the old power plant equipment of the former three lower stages.
The electromechanical equipment of the newly constructed lower stage consists of a Kaplan bulb turbine at 712.40 m.a.s.l. (turbine shaft) and a three-phase synchronous generator (rated output ~ 700 kVA). The turbine was developed by Kössler, the generator was supplied from the company Hitzinger and the control system comes from the Siemens AG.
Discharge water flows through the existing tunnel from the former lower stage 3 (Length 348 m, constructed in 1918) directly into the Inn. The tunnel ends at a level of 709.5 m.a.s.l.
In front of the tunnel a new stilling basin was built with a ventilation shaft. This ventilation shaft also allows access to the tunnel from above.
Technical Characteristics of the lower stage:
- Catchment area: 188.4 km²
- Design flow: 5000 l / s
- Specific water expansion: 22.8 l / s.km²
- Gross head: 13,32 m
- Net head at QD: 11.36 m
- Max. turbine power : 501 kW
- Max. generator power: 474 kW
- Annual energy production: 3.5 GWh