Electro Mechanical Equipment Selection

ELECTRO-MECHANICAL EQUIPMENT – SELECTION,

BEST PRACTICE AND USE OF CHECKLISTS

CONTENTS

1 INTRODUCTION 1

2 TURBINES 2

2.1 TURBINES TYPE 2 2.2 ARRANGEMENT 5 2.2.1 AXIS ARRANGEMENT 5 2.2.2 BEARING ARRANGEMENT 5 2.3 NUMBER OF UNITS 6 2.4 GEARBOX 6 2.5 EXPECTED ENERGY OF THE PROJECT 6 2.6 MAIN TURBINE TYPES: DRAWINGS AND PICTURES 7

3 GENERATORS 14

4 GEARBOXES 15

5 VALVES 16

6 ELECTRIC PANELS 17

7 ADDITIONAL REMARKS AND CONCLUSIONS 18

8 REFERENCES 19

NF-S3-RevA.doc Section 3 Page 1

1 Introduction The main choices for the SHP electromechanical equipments are related to the following top-ics.

1. Turbine 2. Gear 3. Generator 4. Gates and valves 5. Control panels

6. Switch boards

7. Transformers

8. Crane

9. Screen cleaner

In the present paper we discuss only the first 4 items, which constitute the more relevant ones.


2 Turbines The turbines are the heart of the hydroelectric plants, as they transform the hydraulic energy in the mechanical one, which is a more easily usable form of energy. The choice about the turbines is related to:

• type; • arrangement; • number of units; • gear; • expected energy of the project: • others peculiar aspects of the designed plant.

The table resumes the above mentioned items and the main factors involved in the choice. In the following chapters each item will be discussed more deeply.

Factors

Type H; Qmax; Qmin

Arrangement Power station; maintenance facilities

Nr. units Qmin

Gear Rotation speed; cost

Expected energy Total investment

Others Transport facilities; delivery time; waterhammer problems, etc.

2.1 Turbines type In the long history of the hydroelectric technology, a small number of turbine types survived to the field tests, so the choice is practically restricted in a small list, depending from the net

head (H) and the rated flow (Q) of the installation. Although each turbine is designed taking into consideration both head and flow rate - which are the nominal data of the machine - a first classification is traditionally given by the head only.

Turbine Type Head Classification

High (>50m) Medium (10-50m) Low (<10m)

Impulse Pelton Crossflow Crossflow

Turgo Turgo

Multi-jet Pelton Multi-jet Pelton

Francis (open-flume)

Reaction Francis (spiral case) Propeller

Kaplan

A more scientific approach comes from the theory of the models which leads to the specific

speed function of head and flow rate.


H

P

H

nnc =

where:

• n [min-1] • H [m] • Q [m3/s] • P [kW]

The choice process starts from the nominal value of the net head and flow rate, and it needs to state the rotation speed of the genera-tor, based on technical/economical considerations. Using the specific speed value, the turbine type comes from the following table

Type ns

Pelton 1 jet 4-20

Pelton multi-jets 20-70

Low speed Francis 50-100

Normal Francis 100-200

High speed Francis 200-300

Very high speed Francis 300-400

Kaplan 400-900 The same approach is quoted in a graphic form, where nQe is calculated the SI values [1].

Nr. poles Frequency

2 3.000,0

4 1.500,0

6 1.000,0

8 750,0

10 600,0

12 500,0

14 428,6

16 375,0

18 333,3

20 300,0

22 272,7

24 250,0

26 230,8

28 214,3

30 200,0

32 187,5

34 176,5

36 166,7

38 157,9

40 150,0

42 142,9

43

H

QnnQe =

0.01

0.1

1

10

1 10 100 1000

Hn = E/g

Kaplan

Propeller

Bulb

Francis

Pelton


A general diagram with the utilisation field of each turbine type is quoted in the IEC 1116 In-ternational Standard 2.

Very often the turbine manufacturers supply diagrams H/Q of its own production, making it easier to chose the turbine type


2.2 Arrangement

2.2.1 Axis arrangement

Many types of turbine accept the 3 possible arrangements: vertical, horizontal and inclined axis. If there aren’t any constraints (typically from existing civil works or from site geomor-phology), the choice depends on the maintenance facilities and on the impact on the power

station shape.

Vertical Horizontal Inclined

Turbine type Pelton; Francis; Kaplan;

Axial; Cross-flow

Pelton (max 2 jets); Francis;

Axial; Cross-flow

Axial

Maintenance Difficult Simple Medium

Power station Narrow Large Medium

2.2.2 Bearing arrangement

The SHP plants allows some simplifications and cost saving solutions in the bearing arrange-ment and type, while the large hydro machines use only plane bearing oil lubricate (typically with oil injection). The bearing type has a significant impact on the generator, which can be standard if it sup-ports only its own loads, or customized if it must sustain the turbine loads too.

Number Generator Coupling Delivery time Erection

2 Special design Rigid Longer Easy alignment

4 or more Standard Elastic Standard Careful alignment


As regards the lubrication, the small machine can use grease, easier to manage.

Installed capacity Lubrication

Roller < 1.000 kW Grease

Plane >3.000 kW Oil

Both 1.000 - 3.000 kW Oil

2.3 Number of units

The number of units basically depends of the design minimum flow which we want to exploit in efficient and safe (from the equipment point of view) way. Each turbine type has a typical range.

Turbine type Acceptance of Q variation Acceptance of H variation

Pelton 1 jet 20% Qmax Low

Pelton multi-jet 10% Qmax Low

Francis 50% Qmax Low

Kaplan double regulated 20% Qmax High

Kaplan single regulated 50% Qmax Medium

Cross-flow 20% Qmax Medium

Propeller Qmax Low

2.4 Gearbox The gear is a device installed between the turbine and generator increasing the rotation speed of the generator in order to reduce its cost. Form the other side, the total unit efficiency decreases of a couple of point at least and the maintenances are more expensive and difficult, especially in the vertical axis arrangement. Moreover the gearbox usually increases the noise of the unit in a significant way. Additional details on the gearbox are presented in the § 0.

2.5 Expected energy of the project The plant performance, as annual energy production, is directly connected with the unit ex-pected efficiency, which could be a choice parameter.

Turbine type Best efficiency

Kaplan single regulated 0.91

Kaplan double regulated 0.93

Francis 0.94

Pelton multi-jet 0.90

Pelton 1 jet 0.89

Turgo 0.85

Cross-flow 0.80


Moving from the design point (H and Q with the best efficiency), the turbine efficiency de-creases following curves which are typical of each machine type [1].

2.6 Main turbine types: drawings and pictures In the following pages are presented drawings and pictures of typical arrangement of the main turbine types.

Pelton

Francis

Kaplan

Main turbines types


Pelton turbine

[1]

Multi-jet Pelton : vertical arrangement

3


Multi-jet Pelton: horizontal arrangement

4

Francis turbine: vertical arrangements

5


Francis turbine: horizontal arrangements

[5]e 6

Pelton inlet flow

needle

water jet

Runner blades

Turgo inlet flow

[1]


Francis flow

Cross-flow (Banki)

water flow

distributor

runner

blades

[1]

Francis and Banki

horizontal arrangement

[5]


Kaplan turbine

[1]

Small Kaplan (1 MW) draft tube

[3]


Small Kaplan (1 MW) spiral case

[3]

Small Kaplan (1 MW) runner


3 Generators In comparison with the turbines, the generators of the SHP are usually a more standard prod-uct. Nevertheless some option is possible to better adjust the machine to the specific charac-teristics of the designed plant. The first choice is between the asynchronous (also called induction) generators and synchro-

nous ones. Basically, the induction generators, which are less expensive and easier to manage, don’t have any own excitation device so they are suitable only for plant connected with large electric grid and under additional conditions, quoted in the table, where other options are rep-resented.

Type Pi <500 kW 500 kW<Pi <1.500 kW Pi >1.500 kW Stand alone

Asynchronous suitable suitable not suitable not suitable

Synchronous only stand alone suitable suitable suitable

Voltage (V) 400 600 - 3.200 >3.200

Free wheel not necessary suggested suggested mandatory The expected efficiency depends mainly on the machine size, and on the rotation speed for a little percentage.

Rated power [kW] Best efficiency

10 0.910

50 0.940

100 0.950

250 0.955

500 0.960

1.000 0.970 We presented in the § 2.2 the unit axis and bearing arrangement: referring to the cooling sys-tem, the basic option is the forced air arrangement. Nevertheless, the water cooling option (closed circuit) is becoming more usual then in the past, for its advantages from the cooling efficiency point of view and, mostly, to reduce the unit noise, cutting the noise emission and/or allowing the installation of acoustic insulation boxes without affecting the thermal ex-change.

Air Water c.c.

Small power house not suitable suitable

Interred power house not suitable suitable

Noise constraints not suitable suitable

Very high air temperature not suitable suitable

Standard situation suitable possible


4 Gearboxes The gearbox is an optional chance to reduce the unit cost, which can affect the project feasi-bility in a significant way, mostly in case of very small plant (so called micro-hydro). The more common kinds of gearboxes are:

1. belt; 2. conical (orthogonal axis) or bevel gears; 3. parallel axis.

The choice can be carried out as shown in the table.

Type Capacity Turbine speed Maintenance Noise

No gear > 3.000 kW > 500 rpm = =

Belt < 300 kW every Weekly Low

Conical (bevel gear) < 1.000 kW every Expensive High

Parallel axis < 3.000 kW every Cheap High Although the gearboxes allow some money saving, we must not forget that they add an effi-ciency penalization to the generation unit.

Type Efficiency

Belt 95%

Parallel 98%

Bevel gear 96%


5 Valves As they are very simple mechanical tools, the valves can play critical roles in the hydroelec-tric schemes both during the normal plant management and during extraordinary events. The table shows the main criteria in choosing the valves types.

Type Head losses Diameter [mm] Pressure [m w.c.] Cost

Gate 0.2xV2/2g <500 <20 2

Butterfly 0.6xV2/2g >200 <400 3

Globe (only rotation) 0.05xV2/2g <300 no limits 1

Rotary (with translation 0.05xV2/2g 400-1.000 no limits 5 where: 5: more expensive 1: less expensive


6 Electric panels Although the electric panels topic isn’t in the index of the present paper, nevertheless we like to spend some words about a special toll which represents a great facility for the micro-hydro plants. We refer to the electronic control load device, that changes dramatically the approach to regu-lation of the off-grid schemes, but also provides important services to the small plants operat-ing in parallel with a grid. In the isolated installations (off-grid plants), a well known problem is to maintain the fre-quency and the voltage at their nominal values when the electric loads change. The traditional way, adapting the output power to the instantaneous power request by means of electromechanical and hydraulic devices (so called governors), is quite expensive for the small installations and not so efficient, because of the inertial delay and of the tolerances in positioning of the mechanical actuation. The load control panel works on the loads site by means of electronic devices (very rapid and accurate), adding a ballast load to equilibrate perfectly the output power (kept constant at the rated value of the unit) to the instantaneous load request. In the on-grid plants, the load control device helps a lot to manage the parallel operation of small units, which are strongly penalized in the speed regulation by the low value of the mo-mentum of inertia of the rotating components. The graphic represents in a schematic way the results of a control load regulation.

0

10

20

30

40

50

60

70

80

90

100

0 6 8 12 16 20 24

Hours

Cap

aciy

Dissipation area

Load


7 Additional remarks and conclusions The Indian sub-continent presents two typical situations, which are at the opposite site for many characteristics.

Canal based schemes Himalayan schemes

Head Low High

Flow rate High Low

Water availability fluctuation Small, with low gradient Large seasonal variation

Flood versus rated flow Significant Extremely high

Access facilities Good/Excellent Poor/very difficult

Grid connection facilities Good Expensive/not suitable

Operating facilities Good Difficult

Maintenance facilities Good Very difficult

Typical capacity range 200 ÷ 5.000 kW 10 ÷ 500 kW Taking into account what we’ve written in the above paragraphs, the more suitable units for the two typical mini-micro hydropower plants in the Indian sub-continent can be summarized as follow.

Canal based schemes

Rated flow Head Turbine

> 50 m3/s >3 m Kaplan

10 ÷ 50 m3/s 3 ÷ 20 m Kaplan/Kaplan derived

< 10 m3/s > 4 m Kaplan derived

< 10 m3/s < 4 m Pit/Archimedean screw The generators can be asynchronous or synchronous depending on the rated power, as we suggested in the § 3

Himalayan schemes

Head Turbine

> 200 m Pelton (single jet or multi-jet)

100 - 200 m Turgo; Pelton multi-jet

50 - 100 Cross-flow, Francis In the Himalayan schemes, the basic option is the synchronous generators, as these plants generally work off-grid: the load control device is strongly recommended as much as possi-ble.


8 References 1 Layman’s Guidebook on how to develop a small hydro site - ESHA - 2004 http://www.esha.be 2 IEC International Standard - http://www.iec.ch 3 KÖSSLER Ges.m.b.H. - http://www.koessler.com 4 Studio Frosio - http://www.studiofrosio.it 5 Cink Hydro-Energy k.s. - http://www.cink-hydro-energy.com 6 Andriz VA TECH HYDRO - http://www.andritz.com

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Electro Mechanical Equipment Selection