HPP's Anatomy

HPP's Anatomy

The mankind learned to use the power of water flow hundreds of years ago: In the Middle Ages the river rotated the impeller of the mill, and in the 19th century the first hydro power plant appeared, which allowed to convert the water flow energy into electricity.

And though each of us can imagine the general idea of these structures, rarely anyone manages to look inside.

Hydroelectric Generating Unit

Hydroelectric generating unit of a power plant looks like an iceberg, most of it is located in water, and from the above in the turbine hall we only see a kind of oiler which is the top part of the working machine.

The huge scale of the main equipment, thanks to which the energy of the water flow is converted into electricity, can be estimated only during a major overhaul — the concentration of efforts of dozens of people.

Major repairs rarely last less than a couple of months. First the generator should be dismantled. It is fixed on a massive spider which takes the weight of all equipment.

Generator spider is a visible part of the hydroelectric generating unit in the turbine hall.

A huge rotor is located under the spider's cover. It is here that electricity is born: The rotor rotates in the magnetic field of the stator, there is an electromotive force that causes electric current.

The rotor is removed and sent to a special repair site located in the turbine hall for inspection and maintenance.

The impeller is then excavated. This huge "fan" takes on all the power of the river.

Impeller and turbine shaft

Under the influence of pressure, the impeller rotates the shaft on which the generator rotor is fixed. This is the schematic diagram of the HPP operation.

The mine of the hydroelectric generating unit can reach a depth of 18 meters
Generator windings. Here the voltage of 10 kilovolts is released and directed to the transformer on coloured tyres

The weight of the rotor can reach a few tens of tons, so it is impossible to do without a crane when installing the rotor.

Rotor (at the top) and stator (at the bottom) of the power generator
Moving the rotor with a gantry crane from the repair site to the installation site

Any assembly and disassembly of the hydroelectric generating unit requires a lot of mechanic work.

Installation of the rotor

There is no little thing: each screw must comply with regulations and tolerances. Therefore, there is a locksmith site at the HPP where employees work that is called “on quality”.

Machine in the locksmith workshop

By the way, turbines are different, too. For rivers with a slight difference of heights and accordingly pressure, adjustable-blade turbines (Kaplan turbines) are used. They are similar to the propeller of the ship. As the name suggests, their blades can be adjusted, which allows changing the operating range.

Adjustable blade or Kaplan turbine

Radial-axial turbines are the second common type. They are used on rivers with high pressure, allow for more power, and can operate in a narrower range of modes.

Radial-axial or Francis turbine, Volkhovskaya HPP

The impeller weighs a few tens of tons and can serve for decades. For example, Volkhovskaya HPP's turbine has worked for about 90 years and now has become a monument near the hydroelectric power plant.

The monument in honour of the builders of Volkhovskaya HPP
The turbine monument at Iovskaya HPP

Spiral Case

For the HPP to work effectively, it is not enough simply to put the turbine in the river — water needs to be brought in a special way — through a supply channel and a spiral case. This is necessary in order to ensure that the water flows evenly on the impeller blades.

Spiral case, archive photo of Knyazhegubskaya HPP

You can see the spiral case only during construction, as it is located in its base of the hydroelectric power plant. But sometimes during capital repairs the spiral case is drained and there you can go to carry out inspection and perform routine work.

Inside the spiral case of the HPP: the diameter of the supply pipeline is about 6 meters, like a subway tunnel!

There is another important element here: A distributor. It is a system of fixed and movable blades on the water path to the turbine.

Stator columns of the distributor, archive photo

Static plates lamininirise, that is “calming” the flow so that it does not damage the impeller, and the movable ones open and close the entrance windows, thereby regulating the amount of incoming water. The management task is simple: It is necessary to achieve optimal relations between the openings of the distributor and the angles of rotation of the blades.

Servo motors for the distributor control


The last two decades have dramatically changed the practice of operating these amazing machines. Digital computer technologies have replaced analogue devices, which have become an integral part of power plant management.

The duty station controls the entire power plant from a computer

Today, many HPPs can even operate autonomously — one person gives commands to a whole cascade of hydroelectric power plants, and all actions on equipment management are performed by automation. It also monitors the parameters: As soon as something goes beyond the acceptable values, the system generates a signal or enables protection.

All telemechanics and automation are placed in several cabinets.

Equipment of the automated control system of technological processes (ACS TP)
Installation and adjustment of electronic control systems
In the machine room touch control screens are installed

Working with modern digital equipment places special demands on the staff. They are engineers with higher education and the highest qualification. Each of them took several exams before they got a job permit!

Water Discharge

Any hydroelectric power plant is a complex of artificial structures, with the help of which a person reliably established control over the elements of the river. Due to regulation on many rivers it has been possible to stop destructive floods, and with the help of locks even to provide navigation.

Many HPPs in the North-West of Russia (the firstborn of Lenin's electrification plan of the country) are already 80–90 years old, which often means that their project did not the development of modern technologies. For example, it is unlikely that power fathers could assume that a huge flow of cars will move through the dams of HPPs.

There is a need to modernise the design in such cases. The peculiarity of work on hydraulic structures is the impossibility to decommission the facility. It is impossible to turn off, to dry and to easily reconstruct water discharge. Each step must be strictly taken according to the project. Dismantling of old structures takes place with surgical accuracy.

Dismantling concrete of the water discharge's old load-bearing structure

New steel beams will be able to withstand the required loads.

In addition, the updated water discharge will have its own crane for repair work.

Could not do Without a Diver

River carries a lot of foreign objects that clog intake screens. Water itself is an aggressive environment. It is necessary to constantly monitor the condition of concrete dam and supply channel. How can we do without divers?

Diving work at the HPP. Preparation takes up to two hours

In recent years, hydropower engineers has used innovative equipment: A real robot immerses instead of divers!

Preparation of the underwater robot takes a few minutes

Operator controls its movement from the shore, and cameras transmit the picture to the terminal in real time.

They use a joystick to control the device, like with the game console.

In a matter of minutes it is possible to inspect the screens or the underwater camera.

Robot at work

Electric drive motors allow for manouvering in all directions and resisting the river flow. The future is here!


From time to time, hydropower engineers face challenges that no robot can cope with. What if...... an island appeared on the horizon in the upstream flow of the river? And it is approaching fast!

It turns out that floating islands are not so rare. In the upstream flow there are extensive wetlands. A carpet of grass grows on the surface of the water for years and even trees take root. In the multiwater years, after heavy rains or melting of snow, the water level in the river rises, areas of the swamp emerge and go downstream.

Islands can be quite extensive, and even with occasional passengers: amphibians and small rodents. It is not necessary to say that such “surprises” bring power engineers a lot of trouble.

A regular boat comes to the rescue, which allows you to take the island aside and begin its liquidation.

Towing a floating island to a safe place

In a few hours power engineers manage to divide it into parts. Next, the pieces of the island should be directed exactly into the open water discharge window.

Obstacles successfully passed through the water discharge

The Rib of a Coin

The main task of hydropower engineers is safe operation of hydraulic structures and equipment. All this complex system works thanks to the work of outstanding engineers of the past and competent engineers, operatives, and repairmen of the present.

When a large-scale repair is completed, the turbine is in place, and the generator is ready to start the electron flow into the network. There is one simple test.

You need to put a coin on its rib on the cover of the working hydroelectric generator. If the enormous power of the river rotates a multi-ton rotor with such ease and tenderness that the coin does not fall, then the work is performed qualitatively.

As power engineers usually do.