Stonebyres and Bonnington Hydro Stations

These are both run-of-river hydro schemes; the river passes through a weir and then into a slightly sloped tunnel ending with an open-air tank. At Bonnington the tunnel is 150m and at Stonebyres it is shorter, only 50m. The tank is known as the surge-tank as it absorbs sudden changes, so if the plant is shutdown suddenly the water pressure in the tunnel doesn’t increase as dramatically and cause any damage to the pipeline.

Some water doesn’t pass through the weir but only a fairly small amount, as when it was built the Clyde was much dirtier so they didn’t need to worry about migratory fish. Nowadays, when planning a new hydro scheme, you’d have to have compensation water and possibly fish ladders. The Clyde is cleaner now so they do get migratory fish, but they are naturally prevented from coming as far as the stations by steep waterfalls.

From the tank it splits into two routes, one for each turbine. The entrance to these can be automatically closed if there is a malfunction, or for controlled shutdown. To make the water enter the turbine uniformly it is forced in a snail-shell shape.

We went inside the section beneath the generator and saw the guiding vanes which are adjusted to control the volume of water. It starts with the vanes at 20% to get the turbine up to the correct speed to connect to the grid. Once it reaches that speed it locks so that any further increase will produce load.

The amount that the guide vanes are opened is also controlled by a water level detector in the weir, so that if the level increases above the optimal 50mm below the top of the weir, the vanes are opened more to keep the water level where they want it. If the water level continues to rise the water will spill over the top of the weir. Once it reaches over 200mm above the top of the weir, there is a danger of flooding the upriver land and so the weir angles to let more water spill over, keeping the head above the turbines the same so that optimal power is still produced. Each generator can produce up to 3MW. Once the weird is completely flat, there is nothing more that can be done and it is as if the station is not there.

Guide vanes

Pipeline

At Bonnington, one of the generators has a vibration problem so they operate that one manually and allow the second generator to automatically handle water level etc.

These stations were build around 1927 but most of the major components have been replaced since then. Originally it was operated at 25Hz, before voltage frequency was standardised across the UK.

50mm below the top is optimal water level

Inside the generator outer casing

Weir

We also drove up to see the Stonebyres intake, which was currently de-watered enabling us to clearly see the weir mechanism and other parts of the intake.

Control panels

Originally it would have

been someone’s job to control the

oil by turning this wheel.

Intake filter

Here are some old photos from when Stonebyres was built.