Supply of pumping units for wet footway of Volzhskaya HPP

LLC «EnergoFront» expands its presence in energy complex of the Russian Federation. Having ten years of experience in thermal energy, our company has started to develop a new direction – hydropower. 

Hydroelectric power stations of Russia, at 40% load, provide more than 18-19% of electricity in the country. The most powerful stations and hydroelectric chains of power plants are located in Siberia and the far East on rivers such as the Yenisei and Angara. One of the largest HPP chains is the Volzhsko-Kamskaya power chain located, accordingly, on the Volga and Kama rivers.  This chain is the largest transport, water and energy system in Europe. Consists of more than 20 HPPs, eleven of which are in the ownership of JSC «RusHydro», including Zhigulyovskaya HPP, Rybinskaya HPP, Nizhegorodskaya HPP and the largest hydroelectric power plant in the European part of Russia – Volzhskaya HPP.

At the time, the commissioning of Volzhskaya HPP has played a crucial role in the energy supply of the Lower Volga region and the Donbass, and in the alliance of huge power systems of the Center, the Volga region, the South of the country. The economic region of the Lower Volga region also received a powerful energy base for further development of the national economy. HPP is also playing an important role in the creation of a deep-sea route throughout the Lower Volga - from Saratov to Astrakhan. Constructions of a hydrosystem are used for installation on them a permanent crossing of the Volga railway and road transport. They provide the shortest connection between the Volga regions. In addition to its main function — electricity generation — Volzhskaya HPP creates the opportunity for irrigation and watering of large areas of dry lands of the Trans-Volga region.

Volzhskaya HPP, located near the city of Volgograd, plays a crucial role in the power supply of the Lower Volga region and combines large power systems of the Center, the Volga region and the South of the country. HPP capacity - 2671 MW, average annual output - 11.1 billion kWh.

Pressure structures of HPP, with a total length of the pressure front of 4.9 km, form the Volgograd reservoir.

One of the most important elements of the HPP is its drainage system, designed to drain the flow of the hydraulic parts of the units for the period of maintenance, as well as to collect and remove leaks at the HPP.

Water from inferred for repair hydroelectric unit, as well as all leaks, is discharged into the «wet» footway – gallery, located in the lower part of the dam, passing along its entire length (650 m) at the level of minus 33 m from the lower reaches of the river. The water accumulated in the wet footway is removed by the pumping station, located in the «dry» footway at minus 30 m. The pumping station pumps the water accumulated in the wet footway back into the river to the downstream. This scheme of drainage of HPP is the standard for the same HPPs such as Zhigulyovskaya and Saratovskaya.

Now the wet footway pumping station is equipped with two vertical centrifugal pump units of 600V-1,6/100 brand released in 2006 , capacity 3600 m3/h, 500 rpm, pressure 44 m and two similar pumping units of 28B-12V brand released in 1956, with the same parameters. These pumping units have low protection against moisture and are not designed for operation under flooding.

The reliability of the drainage system ensures its stable operation and the safety of the staff.

In 2009 at Zhigulyovskaya HPP, located upstream of the Volga, has occurred an emergency situation at the pumping station of wet footway. At that time, the HPP was also equipped with vertical centrifugal pump units of V type. During the repair of one group of the pumps, the water level in the dry footway began to sharply rise, it was flooded. Pumping units and electrical equipment of the dry footway were flooded, and could not get back to work. Serious problems were avoided thanks to coordinated work of the staff and the rapid installation of an additional pump. Hereinafter, the pumping station of wet footway Zhigulyovskaya HPP was upgraded, pumping units were replaced by submersible pumps with a degree of protection from dust and moisture IP68.

Due to the risk of flooding of equipment of dry footway and the whole station, the management of Volzhskaya HPP made a decision on modernization of the pumping station of wet footway. The main objective of the modernization was to transfer the work of the pumping station to automatic operation, as well as the installation of equipment operating under flooding.

Section of Volzhskaya HPP:
Blue shows wet footway, red - dry footway

The development of the modernization project was conducted by the scientific research Institute «Gidroproekt» named after S.Y. Zhuk, being part of the structure of JSC «RusHydro» and the developer of the projects of the majority of HPPs in Russia, including Volzshkaya HPP. This project involved the installation of four submersible polder pumps with their placement in sealed pressure columns. Operation of pumping units is provided in automatic mode, for which the pump station is equipped with ACS. The pumps are connected to 10 kV network, the type of their work is variable. To reduce the negative impact of frequent starts on electric motors, soft starters must be installed on each pump.

The general contractor of this modernization is the Scientific Research Institute of electric machine building JSC «NIIelektromash» which is also engaged in development and production of systems of excitation.

Submersible polder pumping units are widely used in water disposal, lowering the level and the oil industry, but have a complex structure and high cost. Pumps are installed only in the shaft (column) or well. These pumps had a mass of more than 10 tons, which would require an increase in the capacity of existing crane beams and hoists to 12.5 tons. In addition, the layout of pumping units in sealed pressure columns made their maintenance much more difficult. In this regard, JSC «NIIelektromash» together with Volzhskaya HPP decided to abandon the designed pumping units and search for new solutions that meet all the requirements of the station. Several options were worked out, including the possibility of supplying submersible downhole pumping units of Chinese production, but all the proposed solutions did not meet the requirements of HPP for performance, reliability, ease of operation, etc.

In 2017, «EnergoFront» company has started its work on this project. The company got the task to find complex technical solution, which includes not only the selection of the particular pump unit that meets the requirements of HPP, but also the solution to the problem of filling the pump with water (aeration), cooling of the motor and the organization of water intake of the pump.

The basic requirements for the pump unit:

In addition to these requirements, pumping units must have an independent motor cooling system, a set of sensors and protections that ensure their trouble-free operation, as well as a simple design and high maintainability.

The specialists of LLC «EnergoFront» considered several types of pumping units and schemes of their placement. The main problem was the requirement for the voltage of the electric motor 10 kV, as well as the presence of the engine cooling system.             

Because of the technical analysis of the equipment options, the customer was offered a solution based on four centrifugal pump units KSN4.100.600.4500.8.M manufactured by LLC «Grundfos», fully complying with the requested requirements while maintaining the existing installation scheme.

KSN pumps feature optimized hydraulics, thereby achieving a high efficiency value of 84%. Moreover, the presence of SmartTrim system provides easy and quick adjustment of the slit gap, maintaining high efficiency of the pump throughout the service life. The engine is cooled by the pumped medium through the cooling jacket. The movement of water through the jacket is due to the pressure drop created by the impeller of the pump. The impeller is located on one shaft with an electric motor. The electric motor is mounted directly on the spiral pump housing by means of a flange connection.

A feature of this pump unit is a high-voltage motor with a power of 450 kW, with a rotation speed of 735 rpm, a voltage of 10 kV, having an integrated cooling system with pumped liquid and a degree of protection IP68, which allows the pump unit to operate both in dry condition and in flooding. Double face seal of cartridge type shaft.

Two humidity relays provide continuous monitoring of the stator housing and terminal box, ensuring automatic shut-off in case of liquid ingress.  The motor is fitted with temperature sensors of windings Pt100 with triple redundancy of sensors (on demand of HPP) and bimetallic thermal overload relay, which protects the motor from overheating. The rolling bearings of the electric motor are also equipped with temperature sensors.

The pump unit is equipped with a combined power and control submersible cables 10 m long. Cable gland has plastic design, made of stainless steel with sealing rings, which allows protecting the cable from damage and prevents leaks. The cable gland has a convenient design that helps to disconnect the cable very fast. To remove the cable gland it is simply necessary to unscrew two bolts.

The spiral housing and impeller of the pump are made of high-strength cast iron, which provides additional strength when large solid inclusions enter the pumped medium. The self-cleaning impeller with 200 mm free passage ensures efficient pumping and reduces the risk of jamming. There are hatches for maintenance and cleaning on the spiral housing, as well as on the pressure pipe on demand of HPP will be placed an additional fitting for connecting the standard air removal system.

The weight of the pump unit does not exceed 7 tons, which is 3.5 tons less than the designed polder pump unit and does not require an increase in the load capacity of regular crane beams and hoists.

KSN pumping units are installed in the places of existing pumping units at minus 30 m with the alteration of foundations and suction pipes. Water intake is carried out from a depth of minus 33 m, thus there are strict requirements for the pump for cavitation reserve that should not exceed 4 m. To optimize the suction pipe and reduce its hydraulic resistance, mathematical simulation of the pump operation was performed, on the results of which were given recommendations on the profile and technical device of the suction pipe. The pressure line of pumping units Du600 are equipped with return valves. Start-up of pumps will be carried out through SCP on open latches, which in turn, will be retrained into repaired. The air-conditioning system of the spiral pump housings is maintained. The air is removed from the pumps by means of water ejectors. This scheme is well established for more than 50 years of operation, it is simple and not whimsical.

In general, the proposed option of the pumping equipment and the installation scheme in addition to lower the cost of the equipment itself significantly reduces the cost and time for SIW, and also preserves worked-out, common to the maintenance personnel operating principles of the pumping station of wet footway.

In the course of several meetings with the representatives of Volzhskaya HPP, JSC «NIIelektromash», «EnergoFront» and JSC «Institute Gidroproekt» current technical decision was approved by all of the participants for the implementation at Volzhskaya HPP.

The technical solution developed by LLC «EnergoFront» is the most optimal for HPP of a similar design, in terms of efficiency and the achieved effect-increase of the safety and reliability of the station.

Project achievements