alstom pump turbine

7/27/2019 ALSTOM Pump Turbine

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DERIAZ pump-turbine for the NAUSSAC 2 plant in

France

By : JB. HOUDELINE, JM. VERZEROLI and J. CLERIN

PowerHydro Turbines


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INTRODUCTION

EPALA, the owner, has entrusted SOMIVAL, the project manager, and ALSTOM Power Hydro Neyrpic with theconstruction of the hydroelectric part of the second phase of the NAUSSAC installation, ensuring additional

reservoir filling by pumping. The choice of DERIAZ pump-turbines was fundamental to obtaining the flexibilityrequired for using the Allier water resources. These machines are able to operate over a relatively wide range ofdischarge and upstream levels and so can adapt to the site's variable hydrological conditions.

The owner wanted to maintain the best possible quality of pumped water, which meant installing "green" machineswith a number of innovations.

1. THE NAUSSAC INSTALLATION

1.1. Installation characteristics

The NAUSSAC installation, near LANGOGNE (Lozre department), on the high basin of the Allier, is intended

for drought management of the Allier and the Loire. It was designed in two phases in 1973.

The first phase, commissioned in 1983, provided a reservoir with a capacity of 190 Mm3, by creating a dam on the

Donozau. This reservoir is fed by the Donozau's hydraulic basin (20 Mm3

average annual supply) and the

Chapeauroux tributary hydraulic basin through a 2 km tunnel (60 - 70 Mm3

average annual supply). This phasewas completed by SOMIVAL, State concession holder.

The second phase (NAUSSAC 2) consisted of completing reservoir filling by pumping water from the Allier. Thisrequired construction of inlet works on the Allier with water transfer to the downstream foot of the dam, where apumping basin had been provided. (See overall installation plan in appendix 1).

A pit shaped power-station constructed at the immediate foot of the dam holds three identical DERIAZ machines,3 MW each, of variable discharge and head, designed and manufactured by ALSTOM Power Hydro Neyrpic

(See

overall cross-section of the machine in appendix 2).

According to an alert graph based on the guarantee of 90% total filling of the reservoir on June 1st, and according

to Allier discharge, the pumps are put into operation.

The machines are reversible, enabling drought management releases to be turbined, thereby reducing installation

running costs.

The particularities of the second phase of the installation are :

the choice of machine type the oil-free operation of certain devices.

1.2. The choice of DERIAZ machines

The name DERIAZ comes from the inventor of this specific type of pump turbine. It is a reversible diagonal flow

turbo-machine with adjustable distributor and blades, able to adapt its discharge and accommodate largevariations in head thanks to these mobile blades. The main feature of the blades distinguishing them from those ofa traditional KAPLAN type machine, is that their axes are sloped, like the frame of an umbrella, and not in a

horizontal plane. They also have a hydraulic profile which enables them to operate safely in both turbine and pumpmodes, under a wide head range.


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NAUSSACInside view

2.2. General characterisrics

The three identical reversible hydroelectric units of the NAUSSAC 2 power station have a unit power of 3MW in pump mode and 2.65 MW in turbine mode. Each unit is coupled with a traditional asynchronous motor-generator. The three units supply one transformer of 5.5 kV / 63 kV of 12 MVA.

A single penstock is linked to the three machines by a trifurcation at the downstream foot of the dam, immediatelyupstream of the power station pit. The existing penstock under the dam is currently connected by means of a

cylindrical distributor changing flow direction by 90.

This original structure has built-in grids to prevent foreign matter entering the machines during turbine operation.

These grids do not have a trash rake, but can be cleaned during pumping by the counter-current, with debrisevacuated by the deviation chase pipe.

Upstream, a stop log enables isolation of the power station without having to drain the whole penstock up to thewater intake, and thus guarantees drought management without turbining.

Each machine has a butterfly valve upstream and a roller gate downstream. These two inlet valves are controlledby water servomotors. Just one hydraulic station is used per unit, and is shared by the butterfly valve and thedownstream gate.

The three draft tubes are gathered in a shared draft pit downstream of the power plant, which is also equipped withgrids and stop logs.

To prevent a unit's draft tube being accidentally pressurised upstream, the downstream valve operation is tightlylinked to that of the inlet butterfly valve : the closure of the downstream valve is only authorised after detection oftotal closure of the inlet butterfly valve. If the butterfly valve leaks while the downstream valve is closed, the

pressure increase in the draft tube pushes the gate leaf downstream. The clearance thus created between the valveseals and the fixed parts is sufficient to allow the leak flow to pass without the pressure difference between thetwo sides of the valve exceeding 5 mWC.

3. HYDRAULIC CHARACTERISTICS

3.1 General

The main performances of NAUSSAC 2 double regulated DERIAZ pump-turbines is their capability to operateover a wide range of both net head and discharge. We show on the tables below the operation data in pump and

turbine mode.

Pump mode operation data

In spring 1998, all tests necessary for

the industrial commissioning of themachines were performed.Hydrological conditions only allowed

operation of two units, with amaximum discharge of 10 m

3/s and an

upstream reservoir level 4.5 m less thanthe normal reservoir level.Consequently, additional tests remainto be undertaken with the three units

operating simultaneously under allheads, in particular in pump mode, withthe highest head.


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Maximum input per unit 3 MW

Discharge range per unit from 2 to 5.5 m3/s

Net head range from 32 to 56 mWC

Turbine mode operation data

Maximum available output per unit 2.65 MW

Discharge range per unit from 1.5 to 6.0 m3/s

Net head range from 25 to 56 mWC

Of course, this should be achieved both with a satisfactory energetic efficiency and good behaviour regardingcavitation.

Moreover part of the plant was existing, thus transient phenomena during load rejection both in pump and turbinemode of operation where also importance in order to preserve the structural integrity of the upstream conduit.

As usual for hydraulic power plant, the theoretical hydraulic development of NAUSSAC 2 machines was verifiedon laboratory by a model test. This model was geometrically fully homologous with NAUSSAC 2 units fromspiral case entrance to draft tube exit.

3.2 Performances

During model test, the efficiency of the machines was derived both in turbine and pump modes of operation over

the complete range of expected discharges and heads. The achieved model results were exceeding the preliminarytheoretical estimate both regarding efficiency and range of operation.

Moreover, the model test was used to determine accurately the on cam relationship for operation of the units bothin pump and in turbine. These relationships give for any given head the optimal guide vane setting as a function ofthe runner blade setting. On cam is essential to preserve the level of efficiency obtained at the model, thus theserelationships are incorporated in the governing electronic system.

During commissioning, the proper behaviour of the governing system was verified implementing a relative flow estimate associated in turbine mode with an ultrasonic flow measuring device. We show hereafter the check

of NAUSSAC 2 on cam relationship (net head 49 mWC).

0,92

0,94

0,96

0,98

1,00

-0,5 0 0,5

Blade angle []

Effic

iency

On cam 0

0,92

0,94

0,96

0,98

1,00

-5,5 -5 -4,5

Blade angle []

Efficiency

On cam -5

The above results indicate clearly that efficiency is maximum for the on cam position of the runner blade opening.

Moreover, the S shaped pump characteristics under low discharge was believed to introduce some difficultiesduring the stating process. A careful determination of the respective guide vane and runner blade openings during

the starting process was defined and a starting relationship inserted in the governing system. This particular

arrangement has been prove to be very effective and no problem were encountered during commissioning.Operating tests carried out in the S shaped pump characteristics have shown that the pump was not particularly


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noisy, nor unstable in this part of its characteristic. The problem with pumping in this zone, if it was authorised,would be deteriorated production, only authorising very low pump discharge compared to the power absorbed bythe generator-motor.

3.3 Cavitation

Cavitation was carefully observed at the model. The model tests indicate as expected that the pump operation is

more critical.

In turbine mode, the machine is particularly quiet no cavitation or low frequency pressure pulsation linked to

cavitation has been observed at site, this is fully in accordance with the model.

In pump mode, the low discharge range (


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Inlet diameter of the spiral case 1 140 mm

Number of stay vanes 12

Number of wicket gates 24

Height of the distributor at the inlet runner (in turbine) 257 mm

Axis distributor level 871.0 NGF

Distributor pitch diameter 1 286 mm

Runner diameter 950 mm

Number of runner blades 8

Width of the draft tube outlet 2 592 mm

Height of the draft tube outlet 1 130 mm

Level of the draft tube low point 868.9 NGF

Normal level of the NAUSSAC reservoir 945.0 NGF

Normal level of the pumping basin 890.4 NGF

The small size of these machines, far from simplifying manufacturing, actually makes it more complex. The mereheight of the draft tube is sufficient to convey the difficulties of constructing its fabricated draft tube outlet, and

when you look at the runner, it is hard to understand how all the control mechanisms for the 8 blades managed tofit inside such a small space.

Added to these difficulties, inherent to the size of the machines, are those linked to their prototype nature. Theseare the first DERIAZ pump-turbines manufactured by ALSTOM Power Hydro Neyrpic

.

The blade control mechanism with a water servomotor built into the runner hub represents a technological feat.Moreover, the water operation of this blade control is an innovation, and required adaptation of the traditionalsystem of distributing heads with a ceramic coating on the fixed and mobile parts in contact.

Finally, the main hydrostatic bearing-combined seal of the pump, designed to prevent all risk of oil pollution ofthe pumped or turbined water, was created on the same basis as that of the TRUEL unit in EDF's POUGET powerstation (Aveyron department).

5. CONTROL-MONITORING SYSTEM CHARACTERISTICS

Speed governing of each unit is managed by a Neyrpic DIGIPID 1500. Speed is measured using inductiveoscillator sensors and a toothed wheel. Over-speed is detected by the governor based on the speed informationthus obtained. Rotation direction is detected from the indications of two specific sensors. In the start up phase in

turbine mode, the governor brings the machine to around the nominal synchronous speed, and maintains it there,enabling coupling with the network. When the unit is coupled with the network, the governor manages thefeedback system of the pumped or turbined flow through a set-point supplied by the automated system.

The governor has two adjusting cams, one for pump operation and one for turbine operation, which ensureoptimal cam-relationship between the blades and wicket gates. This corresponds to the best possible production

for all ranges of discharge and power under all pump and turbine heads.

The NAUSSAC installation is intended for drought management of the Allier and the Loire. The operation of the

machines has therefore been optimised in pump mode in order to favour filling of the reservoir, and nothydroelectric production, which is a by-product.

6. FUTURE POSSIBILITIES

The implementation of the DERIAZ pump-turbines at NAUSSAC 2, suggested by SOMIVAL to EPALA, enabledrespect of the requirements of adaptation to local hydrological conditions, while respecting the natural beauty of


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the site. This concern for integration into the landscape was a major requirement for the project, imposed by theowner and project manager.

Other sites, similar to NAUSSAC, could be equipped in France and abroad. Water transfers, similar to that createdat NAUSSAC, may be considered each time drought management problem or evenflood problems have to be solved. The use of DERIAZ pump-turbines is perfectly suited to these cases. This type

of machine may also be integrated in any energy production project where operation must fit the river discharge.An old hydroelectric installation project in the French Alps, which was abandoned for ecological reasons, includedequipment integrating DERIAZ turbines.

Today, the NAUSSAC-LANGOGNE installation forms a French showcase for demonstrating the feasibility ofprojects with environmental characteristics. All those involved in NAUSSAC are prepared to welcome on the siteany French or foreign investors interested in using DERIAZ pump-turbines, to observe all the operation qualities

and perfect site integration in real life.


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APPENDIX 1

NAUSSAC INSTALLATION

Fish and canoepasses

Allier water intakehydraulic sill: 890.30

upstream head works

on the Allier

Transfer Tunnel 2.60m

Transformationstation

Hollow jet

Control Building

Water intaketower

NAUSSAC DAMheight: 50mridge length: 240mreservoir capacity: 190Mm3Downstream head

works DONOZAU

Pumping bassinR.N. 890.40

Pumping station (3 pumps)maximumgross head: 58M

Donozau sill890.40

Control areamobile flap

OVERALL PLAN OF THE INSTALLATION


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ABCD

Alstom

Rotation to the rightin turbine operation

750 tr/min

Rotation to the left inpump operation

distributor

runner 950

Pit 1660

NAUSSAC II

Overall cross-section ofthe machine

Max. power 3 MW

APPENDIX 2

Publication : Hydropower & Dams, Autriche - 1999


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ALSTOM Power Hydro - 82 avenue Lon Blum - BP 75 - 38041 Grenoble Cedex 9

Tl. 33 (0) 4 76 39 30 00 - Fax 33 (0) 4 76 39 30 01

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LSTOM

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