A. Tessarolo

HYDRO-POWER

A. Tessarolo

Fuel shares in

world electricity production in 2011

IEA – Renewable Energies Information 2013

Today’s scenario

2

Our times (world)

IEA data (2000-2011), 2DS Projections (2012-2020)

3In 2020 renewables should grow from 20% to 28% at least.

Share Trend

•Hydropower is (going to be) the main renewable energy source

•Other sources are growing faster (hydro is mature….)

•Wind power has the main share among other sources

4

History: Wind and Hydro power

• Both used from Europe to Far East since ancient times

• In 19th century steam power and the modern Francis hydraulic turbine were developed

• In the late 19th century the first electric generators were coupled with wind ad hydraulic turbines

5

Typical Plant Layout

6

Head

Electricity

Transformer

Generator

Turbine

Penstock

Dam

Intake

Discharge

Reservoir

Hydraulic power plant classification

• Turbine Type

• Head – Flow

• Rated power

• Reservoir – Run of River – Pumped storage

7

Turbines and Head

8

Flow rate

Head Pelton

(50-1300m)

Francis

(10-400m)

Kaplan

(10-80m)

Power

Micro Hydro Turbines

Gorlov Turbine η=35%

Gravitation water vortex

η=70%

Archimedes Screw η=80% Banki cross-flow turbine η=85%

Type : Impoundment plant (reservoir)The most common type of hydroelectric power plant is an impoundment facility. An

impoundment facility, typically a large hydropower system, uses a dam to store water in a

reservoir. Water released from the reservoir flows through a turbine, spinning it, which in

turn activates a generator to produce electricity. The water may be released either to meet

changing electricity needs or to maintain a constant reservoir level.

A diversion, sometimes called run-of-river, facility channels a portion of a river through a

canal or penstock. It may not require the use of a dam.

Type : Diversion or run-of-river plant

When the demand for electricity is low, a pumped

storage facility stores energy by pumping water

from a lower reservoir to an upper reservoir.

During periods of high electrical demand, the

water is released back to the lower reservoir to

generate electricity.

Type : Pumped storage

Large Hydropower

Although definitions vary, DOE defines large hydropower

as facilities that have a capacity of more than 30

megawatts.

Small Hydropower

Although definitions vary, DOE defines small

hydropower as facilities that have a capacity of 100

kilowatts to 30 megawatts.

Micro Hydropower

A micro hydropower plant has a capacity of up to 100

kilowatts. A small or micro-hydroelectric power system

can produce enough electricity for a home, farm, ranch,

or village.

Size

Development

• Large Hydro is mature:

– Turbines: Francis 1848 , Pelton 1880, Kaplan 1913

all over 90% efficiency

– Large synchronous generators 1882

– First hydropower plant 1881 (DC), 1891 (AC)

• Today locations fit for new large hydropower

plants (with reservoirs) are few

18

Italian Hydropower

GSE – Rapporto Statistico 2011 – Impianti a fonti rinnovabili 2011

Power rating trend

NUMBER POWER [GW] Avg Power

<1MW 1-10MW >10MW <1MW 1-10MW >10MW [MW]

2000 8.5

2001 8.7

2002 8.5

2003 8.5

2004 8.4

2005 8.4

2006 8.3

2007 8.2

2008 8.1

2009 1270 682 297 465.6 2189.6 15066.3 7.9

2010 1727 700 302 523.5 2210.5 15142.2 6.6

2011 1858 743 301 567.7 2328.3 15196.2 6.2

0

1

2

3

4

5

6

7

8

9

10

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

Average Power

Hydro plants with reservoir Run off river plants

Safety and

environmental impact

issues

Main sites are already

exploited

Large initial investment

(long pay-back time)

Low investment

(short pay-back time)

Safety and small

environmental impact

Very suitable for distributed

generation

Emphasis on mini- and micro -

hydroelectricity• Building of new plants

• Revamping of existing plants

1929

Computing the energy that can be

delivered by a Hydropower plant

• This is an essential task to evalutate if a certain site is

suitable for fulfiling energy demands

• It enables to estimate the revenues to be expected

• Is serves as a check to compare various design and sizing

solutions from an economic point of view (given the

investment, what is the pay-back time?

(an an yearly basis)

(an daily basis)

Depend on Q !!

Pn

Design flow

FIRST CASE: PLANT

CONNECTED TO CENTRAL

GRID

SECOND CASE

Available power

Daily delivered power

load

TO BE

COMPUTED

FOR ANY n !

THIS WILL BE

INTEGRATED

OVER n TO

FIND THE

DELIVERED

POWER

Example: calculation of G75

Emphasis on mini- and micro -

hydroelectricity• Building of new plants

• Revamping of existing plants

1929

% del totale degli

impianti idro

none

Adriatic

sea

Monfalcone

Canale

Valentinis Monfalcone

Power

plant

Underground

stream

Harbour

Outlet

Upstream

fllow

Downstream

flow

Plant

Underground stream

to the sea

Vista da sopra

Upstream

flow

Plant

UPSTRAM VIEW

Downstream

flow

DOWNSTREAM VIEWPlant

PREVALENZA

Upstream

level (rains)

Downstream level

(tides)

STRONGLY

VARIABLE TIDES

VARIATION OF HEAD

UPSTREAM DOWNSTREAM

Physical layout of the plantBefore revamping

Induction

generator

226 kVA

6 poles

380 V

50 Hz

1000 rpm

Kaplan turbine

210 kW

Q = 6.8 m3/s

H = 3.5 m

200 rpm

Adjustable

blades

2 ×

Outlet ducts

Penstock

Induction generatorGearbox

90°

Physical layout of the plantBefore revamping

SPM generator

305 kVA

32 poles

170÷240 rpm

45.3÷64 Hz

Turbina Kaplan

Q = 6.8 m3/s

n = 170÷240 rpm

Adjustable blades

Induction generator SPM generator

226 kVA 305 kVA

6 poli 32 poli

1000 rpm 170÷240 rpm

50 Hz 45.3÷64 Hz

Turbine before

revamping

Turbine after

revamping

Q = 6.8 m3/s Q = 7.4 m3/s

n = 200 rpm n = 170÷240 rpm

Physical layoutAfter revamping

SPM generators

Physical layoutAfter revamping

Functional layoutBefore revamping

Induction generator

Functional layoutAfter revamping

SPM generator

~200 rpm

~1000 rpm

≡50 Hz

170÷240 rpm

45÷64 Hz DC link

PWM Rectifier PWM Inverter

≡50 Hz

SPM generators

Requirements for direct coupling:

• Axial compactness

• High torque density (low weight)

• Low speed (200 rpm) � high pole count (32)

Hypothesis of salient pole solution

L

D

N

S

N

S

Fractional slot

winding

Design

optimization

with genetic

algorithms

High

performance

magnets

Highly efficient

cooling system

SPM solution

Cooling system

Heat exchanger with water pipes

integrated in the frame

Project results

PMG IG

Weight kg 4200 1700

Torque kNm 13.9 2.0

Torque to weight ratio Nm/kg 3.7 1.2

Efficiency % 98.1 93.5

Generatore SPM

170÷240 rpm

45÷64 Hz DC link

PWM Rectifier PWM Inverter

≡50 Hz

Advantages of variable frequency design

Turbine characteristic curves

n [rpm]

Q [m3/s]

α1

α3

η ↑ α2αopt

nopt

Qopt

Head = H1

n [rpm]

Q [m3/s]η ↑

αopt

nopt

Qopt

Head = H2

Turbine characteristic curves

H

α

Plant

automationn*

Speed

control

n

HEAD

System factory test

ωη

T

ivoutout

3=

%5.93=>IGη

+ GEAR-BOX !!

Conclusions so far

� Importance of hydroelectricity

� Importance of mini and micro- hydroelectric

run-of-river plants

� A case of revamping of an existing plant.

� Fixed-frequency geared induction generator

replaced by direct-drive SPM alternator

connected to a power converter

� Benefits obtained

� Installation and plant layout

� Higher efficiency

� Better turbine exploitation thanks to the variable-

speed control for efficiency maximization

Further

experience with

micro-

hydroelectricity

Despite in many regions the hydroelectric potential has

been greatly exploited, the contribution of small hydro is

still considerable scope for development.

Until a few years ago, the small hydro has been

neglected, even because of the market conditions and

the main business operators who did not encourage the

development of the sector.

Since several years, there are good overall conditions

for the revitalization of the small hydro and the PM

technology established to give satisfactory solutions

Small hydro PM technology

HOWTHE NEW TECHNOLOGY CAN BE

ENVIRONMENTALLY BETTER ACCEPTED ?

Especially for low speed small machines, the permanent magnet technology

(Permanent Magnet Generator PMG) gives optimal solutions to the small

hydro by providing high-polarity, rugged, compact and highperformance

generators.

These features match in a natural way some of the increasingly stringent

environmental constraints that are now

required in most small hydro plants:

- limited oil/grease in the vicinity of the river water and low maintenance

costs with direct drive installation (no gear-box);

- well adapted to the surrounding with minimum visual impact and reduced

noise level thanks to the compactness;

- adjustable to different heads and flows with variable speed operation.

HOW THE NEW TECHNOLOGY (PM) CAN MAKE BETTER

PERFORMANCES

The high torque density and the PM’s on the rotor in place of the wound excitation,

naturally give to the PM generators particular good performances and a high efficiency.

Furthermore, small machines can easily allow low speed applications with direct drive

solutions, with the very big benefit of an installation without the gearbox.

A PM machine can be manufactured in several modes, in particular the arrangement of

the magnets determines certain characteristics of machine:

- magnets fixed superficially to the rotor (SPM)

- magnets disposed inside the rotor (IPM).

Taking into consideration the long life generally request to hydro power

plants (never less than a few tens of years), for an absolute guarantee on

the preservation of the performance of PMG over time, is important

during design steps to accurately manage external stresses potentially

affect the physical properties of the magnets. In particular, the

temperature of the magnets and the cooling system are critical to the

good operation of the machine on long and very long term.

The best solution is a cooling system integrated in the frame, type water

jacket.

This method has several benefits:

- high efficient cooling system

- best protection the machine from the environment due to the

totally enclosed construction

- very compact solution

- sound proof.

PMGENERATORS AT FIXED SPEED - Direct Grid Connection

The direct connection of the PMG to the distribution grid (PMG dol = direct on line) is

possible but, depending on the parameters of the grid and the prime mover, the turbine,

the PMG is asked to give a special response in terms of sub-transient reaction and/or a

damping capacity. This is critical because PMG machines are typically not equipped with

dampers.

In principle, the excitation of a PMG is constant, due to the magnets on the rotor.

In reality, it depends on the operating temperature, which may be very contained thanks

to a goodelectromagnetic design.

It means that for a given speed/frequency, the PMG makes available a practically constant

electromotive force: the generator cannot independently control the reactive power flow

to the grid, which is determined only by the grid voltage and the load.

However, the PMG can be design so that the power factor is:

- very high (almost unity in the vicinity of the nominal conditions)

- such as the reactive power compensation can be virtually avoided (if the mains voltage is

stable and thedegree of load always greater than 50%).

Damper cage

In case a power factor control is required, the insertion of an

electronic static compensator, connected to the same bus bars of the

generators, is an efficient solution to:

- control the overall reactive power flow from the power plant;

- set the power factors operating points, even lagging and leading, to

comply with the imposed conditions to parallel with the mains;

- react quickly to load changes practically nullifying the effects of over

and under voltage, even on weak distribution systems.

A good joint sizing of PMG DOL and compensator can allow a very

reduced reactive load on the compensator, if grid is close to nominal

voltage.

When grid is close to max and min allowed limits, the compensator

must to supply the entire reactive power.

In both cases, the losses on the power electronics are still very

modest: the compensator is designed in fact for the amount of

reactive power that the PMG naturally not be able to deliver

because of the discrepancy between its no load voltage and the

grid voltage, and this is normally only a part of the rated output.

For this reason, the combination of PMG DOL and static

compensator guarantees maximum efficiency

(maximum productivity) at the same time to guarantee the

stability of the network, in consequence both of transient

perturbations and/or daily variations.

Moreover, the static compensator can even be only one in a power

plant with several PMG DOL, or be sized in order to stabilize and

control the grid voltage when other loads are connected, allowing a

great flexibility of the project from the system integration point of

view, not only of the generating

Efficiency comparison

PM GENERATORS AT VARIABLE SPEED - connection to the grid through a Variable

Speed Drive, Full Converter

In the conversion of the potential energy of water into electricity, the

turbine is the most critical component from the efficiency point of

view: consequently in the engineering compromise is always trying to

put the turbine in the best conditions of operation and fit the other

components accordingly.

Therefore, we have always been used to think that fix grid frequency

50Hz (60Hz) = constant turbine operating speed

Different generator’s polarity always helped us to adapt the speed to

the nominal speed of the turbine: still the design of the turbine is a

compromise between the imposed synchronised speed and the

optimal speed, suggested by the most probable conditions of

head/flow.

A certain runner profile has a typical hill curve.

For some head H1, there will be different possible openings of the distributor an but the

point of maximum efficiency will fixe the optimum speed nopt1.

For some changed head H2, we will also have different possible openings of the distributor

but still the point of maximum efficiencywill fixe the optimum speed nopt2 , different from

the previous.

We need to match the different speeds in order to maximize the efficiency for different

conditions of operation.

However, variable speed on mini hydro is not a general approach.

When specific hydraulic conditions occur, a site with a variable operating points,

especially head variations, it helps us:

- to solve some problems, (noise, vibrations, oil/lubrication, …)

- to make better performances

- to make economies (no gear box, reduced maintenance, no synchro devices, wide

operation range, increased global efficiency, …) on new installations or rehabilitation of

existing plants.

The solution at variable speed, with direct driven inverter controlled PMG+VFD (PM

generator + Variable FrequencyDrive) gives the best global performances.

The control operates by:

- the inverter INV : it manages the speed of the turbine and the voltage on the DC bus

- the Active Front End AFE : it manages actively the interface with the mains (available

four quadrant operation, bidirectional energy flow).

Once the Inveter and the AFE are activated and the turbine begins to rotate, it is

possible to start to produce.

The ENERGY PRODUCTION CAN START SINCE VERY LOW SPEED (10% of the nominal

speed).

A smart control automatically manages the input head/flow, to match the imposed

ondition of operation, and gives a speed/torque output to match the best condition of

efficiency.

The Speed/Torque reference can be supplied by:

- a look-up table, integrated in the system and matched during operation, based on

level measurement;

- a automatic Maximum Power Point Tracking MPPT wich provides by itself to find the

point of maximum power production.

The focus of both systems is to maximize the global efficiency in the widest expected

range of operation.

A breaking resistor is available on option for continuity of production in case of grid

power failure.

No difficulty to put in parallel with the mains since the AFE works constantly

synchronized with the grid and decoupled from the speed/frequency of the turbine by

means of the dc bus.

The waveform is particularly clean: the harmonic distortion is within 1%.

The power factor is near to the unit and adjustable according to requirements.

The result of the solution is a maximum exploitation of the hydraulic conditions, therefore

an increased global efficiency for a final INCREASED ENERGY PRODUCTION.

The comparison between a solution with PMG + VFD and with brushless synchronous

conventional generator (fixed speed) can not be done in a direct way, since the exploitation

of water conditions is not the same, the head/flow is not always the same.

Therefore, the comparison between the efficiency values can not be direct.

Even if a first comparison might show similar and comparable efficiency in the operating

range, in fact the solution PMG+VFD allows the water exploitation even in extreme

conditions of head/flow.

Thanks to the variable speed, still good performances of the turbine are possible whereas

under fixed speed conditions would be unacceptable or even impossible (downtime).

In this case, THE COMPARISON doesn’t make sense for specific efficiency but must be done

ON THE BASIS of MEAN ANNUAL EFFICIENCY or of ENERGY ANNUAL PRODUCTION, which

can greatly increased.

CASE HISTORY

The Lake of Paneveggio (1460 m asl) is part of the Natural Park of Paneveggio-Pale di San

Martino, a protected naturalistic environment, in the heart of the Trento Dolomites.

The lake is formed by the dam of Forte Buso, more than 100 meters high and with a

reservoir of about 30 million cubic meters, mainly exploited by a historic and important

hydroelectric power plant.

The small hpp of Forte Buso have been built practically at the base of the dam, to exploit the

reserved flow, previously released in a free way.

Whereas a hydraulic turbine generally manages with difficulty an important head variation,

the variable speed control is an optimum solution for hydroelectric exploitation of the

ecologic flow of a dam, subject to significant changes in the water level.

The solution technically advanced, shows excellent performance, the base of which there is

the best operating the power plant at highest/lowest water levels.

A quick comparison can give some idea of the difference between a possible solution at synchronous

speed and the adopted solution at variable speed

On the basis of the diagrams seen so far, in particular:

- the daily records of reservoir levels, as a result of the net head,

- the seasonal values imposed for the reserved flow, as a result of the available flow discharge,

- a plant shutdown for not applicable conditions of operating of the turbine below a minimum head of

77 meters (see Figg. 17 and 18) (See also HYDRO 2013 - Session 4a: “Variable speed Pelton turbine …”),

- the efficiencies of an equivalent system at synchronous speed and the adopted solution at variable

speed, both for the mechanical part (turbine, see Figg. 17 and 18) and the electrical part (generator and

power electronics; see Fig. 6 and 9), it is interesting to draw up two tables to compare the average

annual results of:

- overall efficiency

-annual mean power output

-Energy production

CONCLUSIONS

The new technologies applied to the established and traditional solutions on small hydro, can provide

good

solutions.

It is not a general approach, but where conventional technology (brushless synchronous generators and

asynchronous) can be constrained, the direct driven permanent magnet generators PMG give

performing

solutions in terms of:

- compact footprint

- reduce weight

- more acceptable noise level

- less construction constraints

- high performances

The power electronics for variable speed operation, already integrated since longtime in industrial

applications and renewable energy sources (PV, wind, …), is a further integration to traditional

schemes, for

- a smart exploitation of the entire operating range (avoiding some limitations of operation)

- the cost-effective use of a single performing machine (avoiding schemes with more machines in back-

up

each other)

- simpler mechanics with less moving parts, in particular with Kaplan turbines.

The case history of the Forte Buso shpp is proof, but many other situations.

Some pictures of the built

generator