1. business and industrial
2. energy
3. electricity

ICHPSD-2015
GENERATING EQUIPMENT
G.P.Patel, MD, UJVN Ltd., Dehradun
Purushottam Singh, Director (Operations), UJVN Limited
Pankaj Kulshreshtha, DGM (RMU), UJVN Limited
Vivek Atreya, DGM (Tech.), UJVN Limited
Jaipal Singh, EE (Monitoring), UJVN Limited
ABSTRACT
This paper describes the generating equipment of hydroelectric power plants and how they
work to convert energy from water into electricity.
Water flowing from the penstock is allowed to enter the power generation unit, which houses
the turbine and the generator. When water falls on the blades of the turbine the kinetic and
potential energy of water is converted into the rotational motion of the blades of the turbine.
The rotating blades cause the shaft of the turbine to rotate thus converting the energy into
mechanical form which produces alternating current in the coils of the generator.
Moving water spins a turbine, the turbine spins a generator and electricity is produced with the
energy already within the flowing water.
Before discussing the generating equipment let us have a brief of power of water and other
important parts of hydro power generating system.
1.
The Power of Water
When watching a river roll by, it's hard to imagine the force it's carrying. If you have ever
been white-water rafting, then would have felt a small part of the river's power. White-water
rapids are created as a river, carrying a large amount of water downhill, bottlenecks through a
narrow passageway. As the river is forced through this opening, its flow quickens. Flood is
another example of how much force a tremendous volume of water can have.
Hydropower plants harness water's energy and use simple mechanics to convert that energy
into electricity.
Hydropower is based on simple concepts. Flowing water spins a turbine, the turbine spins a
generator and electricity is produced in the generator. Many other components may be in a
system, but it all begins with the energy already within the flowing water.
What Makes Water Power
Water power is the combination of head and flow. Both must be present to produce electricity.
Water is diverted from a stream into a tunnel/power channel and is directed downhill through
the turbine (flow) in a typical hydro system. The vertical drop (head) creates pressure at the
bottom end of the penstock. The pressurized water emerging from the end of the penstock
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creates the force that drives the turbine. More flow or more head or both produces more
electricity. Electrical power output will always be slightly less than water power input due to
turbine and generator and water conductor system efficiencies.
Head is water pressure, which is created by the difference in elevation between the water
intake and the turbine. Head can be expressed as vertical distance (meters) or as pressure viz.
kg/cm2. Net head is the pressure available at the turbine when water is flowing and will always
be less than the pressure when the water is turned off (static head) due to the friction between
the water and the water conductor system called penstock or valves etc. Penstock diameter has
an effect on net head.
Flow is water quantity, and is expressed as “volume per time,” such as gallons per minute
(gpm), cubic meter per second (Cumecs), or liters per minute (lpm). Design flow is the
maximum flow for which hydro machines are designed. It will likely be less than the
maximum flow of stream (especially during the rainy season), more than minimum flow, and
a compromise between potential electrical output and economics related.
Head and flow are the two most important things about the hydro power station site. We must
have these measurements before discussing a project.
Power Conversion & Efficiency
The generation of electricity is simply the conversion of one form of energy to another. The
turbine converts the energy in the flowing water into mechanical energy at its shaft, which is
then converted to electrical energy by the generator.
Energy is never created; it can only be converted from one form to another. Some of the
energy will be lost through friction at every point of conversion. Efficiency is the measure of
how much energy is actually converted. The theoretical power (P) available from a given head
of water is in exact proportion to the head and the quantity of water available.
P= Q × H × e × 9.81(kW)
Where
P
H
Q
e
- Power at the generator terminal, in kilowatts (kW)
- The gross head from the pipeline intake to the tail water in meters (m)
- Flow of water, in cubic meters per second (m3/s)
-The efficiency of the plant, considering head loss in the penstock/power
channel/hydraulic system and the efficiency of the turbine and generator,
9.81 is a constant and is the product of the density of water and the acceleration due to gravity
(g)
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Net Energy = Gross Energy x Efficiency
While some losses are inevitable as the energy in moving water gets converted to electricity,
they can be minimized with good design. Each aspect of hydro system—from water intake to
turbine-generator alignment to transmission wire size—affects efficiency. Turbine design is
especially important, and must be matched to specific head and flow for best efficiency.
A hydro power system is a series of interconnected components. Water flows in at one end of
the system, and electricity comes out the other. Here is an overview of these components;
2.
Dam/ Water Diversion (Intake)
The dam is the most important component of hydroelectric power plant. The dam is built on a
large river that has abundant quantity of water throughout the year. It should be built at a
location where the height of the river is sufficient to get the maximum possible potential
energy from water.
3.
Water Reservoir
The water reservoir is the place behind the dam where water is stored. The water in the
reservoir is located higher than the rest of the dam structure. The height of water in the
reservoir decides how much potential energy the water possesses. The higher the height of
water, the more its potential energy. The high position of water in the reservoir also enables it
to move downwards effortlessly.
The height of water in the reservoir is higher than the natural height of water flowing in the
river. This helps to increase the overall potential energy of water, which helps ultimately
produce more electricity in the power generation unit.
The intake is typically the highest point of hydro system where water is diverted from the
stream into the tunnel/penstock/power channel that feeds the turbine. A diversion can be as
simple as a screened pipe dropped into a pool of water, or as big and complex as a dam across
an entire creek or river. A water diversion system serves two primary purposes. The first is to
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provide a deep enough pool of water to create a smooth, air-free inlet to pipeline. The second
is to remove dirt and debris.
Trash racks and rough screens can help stop larger debris, such as leaves and limbs, while an
area of quiet water will allow dirt and other sediment to settle to the bottom before entering
the pipeline. This helps reduce abrasive wear on the turbine. Another approach is to use a fine,
self-cleaning screen that filters both large debris and small particles.
4.
Intake or Control Gates
These are the gates built on the inside of the dam. The water from reservoir is released and
controlled through these gates. These are called inlet gates because water enters the power
generation unit through these gates. When the control gates are opened the water flows due to
gravity through the penstock and towards the turbines. The water flowing through the gates
possesses potential as well as kinetic energy.
5.
Surge Tank/Surge Shaft
A surge tank is an additional storage space or reservoir fitted between the main storage
reservoir and the power house (as close to the power house as possible). Surge tanks are
usually provided in high or medium-head plants when there is a considerable distance between
the water source and the power unit, necessitating a long penstock. Surge shaft is located at
the end of tunnel.
It is a well type structure of suitable height and diameter to absorb the upcoming and lowering
surges in case of tripping and starting of the machine in the power house. The surge shaft is
provided with gates to stop flow of water to the penstock if repairs are to be carried out in the
penstock or inlet valves
6.
Penstock Protection Valve
The Penstock protection valves are provided after the surge shaft to facilitate maintenance of
the penstocks. The valves are of butterfly type. The BF valves are operated hydraulically with
provision of pressure accumulators in case of power failure.
7.
The Penstock
The penstock is the long pipe or the shaft that carries the water flowing from the reservoir
towards the power generation unit comprising of the turbines and generator. The water in the
penstock possesses kinetic energy due to its motion and potential energy due to its height.
Penstocks are the water conductor conduit of suitable size connecting the surge shaft to main
inlet valve. It allows water to the turbine through main inlet valve. At the end of the penstock
a drainage valve is provided which drains water from penstock to the draft tube. In case of
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long penstock and high head, butterfly valve is provided just before the penstock. It takes off
from the surge shaft in addition to spherical valve at the end of the penstock acting as the main
inlet valve.
The total amount of power generated in the hydroelectric power plant depends on the height of
the water reservoir and the amount of water flowing through the penstock. The amount of
water flowing through the penstock is controlled by the control gates (Wicket gates).
8.
Main Inlet Valves
Main inlet valve works as the gate valve/isolating valve in the water conductor system. It is
located before turbine and allows water flow from penstock to turbine. MIV acts as closing
valve and cuts the flow of water during an emergency trip. They are of following type:
•
•
9.
Butterfly valve (upto 200 m head)
Spherical valve (more than 200m head)
Generating Unit
Water Turbine, Generator, Generator Transformer
9.1
Water Turbines
Water flowing from the penstock is allowed to enter the power generating unit, which houses
the turbine and the generator. When water falls on the blades of the turbine the kinetic and
potential energy of water is converted into the rotational motion of the blades of the turbine.
The rotating blades cause the shaft of the turbine to rotate. In most of the hydroelectric power
plants there are more than one power generating unit.
There is large difference in height between the level of turbine and level of water in the
reservoir. This difference in height, also known as the head of water, decides the total amount
of power that can be generated in the hydroelectric power plant.
The turbine is the heart of the hydro system, where water power is converted into the
rotational force that drives the generator. For maximum efficiency, the turbine should be
designed to match specific head and flow. There are different types of turbines and proper
selection requires considerable expertise.
Turbines can be divided into two major types.
•
Reaction turbines use runners (the rotating portion that receives the water) that operate
fully immersed in water, and are typically used in low to moderate head systems with
high flow. Examples include Francis, propeller, and Kaplan.
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•
Impulse turbines use runners that operate without being immersed, driven by one or
more high-velocity jets of water. Pelton turbine is an example of Impulse Turbines.
Impulse turbines are typically used with moderate-to-high head systems, and use
nozzles to produce the high-velocity jets.
Figures of Reaction and Impulse Turbines
Kaplan Turbines
Tubular Turbines
Francis Turbines
Inclined jet Turbines
Tubular Turbines
Pelton Turbines
Each turbine type can be designed to meet vastly different requirements. The turbine system is
designed around net head and design flow. These criteria not only influence which type of
turbine to use, but are critical to the design of the entire turbine system.
Minor differences in specifications can significantly impact energy transfer efficiency. The
diameter of the runner, front and back curvatures of its buckets or blades, casting materials,
nozzle (if used), turbine housing, and quality of components all affect efficiency and
reliability.
9.1.1
Reaction Turbines
Reaction turbine uses the pressure energy and kinetic energy of water flow, is divided into
Kaplan, Propeller, Francis, Tubular (bulb turbines, pit turbines, etc.) according to the water
flow movement direction inside the runner area. Its components and parts: flume (spiral
casing), water distributor, runner, draft tube, shaft and bearing etc.
Kaplan turbine
The Kaplan turbine is an inward flow reaction turbine, which means that the working fluid
changes pressure as it moves through the turbine and gives up its energy. Power is recovered
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from both the hydrostatic head and the kinetic energy of the flowing water. The design
combines features of radial and axial turbines. Its main parts usually include Blades, hub, main
shaft, runner cone, and rotating mechanism.
Kaplan turbines are now widely used throughout the world in high-flow, low-head power
production. The Kaplan turbine was an evolution of the Francis turbine. Its invention allowed
efficient power production in low-head applications that was not possible with Francis
turbines. Application scope of heads: 10m~70m. According to whether the runner blade is
movable or not in operation, it is divided into two categories: axial movable-blade type and
axial fixed-blade type.
The blades of axial fixed-blade turbine are fixed on runner hub is also called as Propeller
Turbine. The place angle of blades cannot be changed in operation. As its efficiency curve is
relatively steep, it is suitable for small load change or the station to adjust the running amount
of the units in order to adapt to the load variation. It has the advantages of simple structure and
low cost, while the disadvantage is that its efficiency will decline sharply when deviating from
the design condition. According to its characteristics, the axial fixed-blade turbine is
commonly used in the hydropower station with small output, low water head and small head
variations. The axial fixed-blade turbine has larger flow capacity and the improved cavitation
performance than axial movable-blade turbine, but it cannot meet the requirements of the
hydropower stations whose head and load change is too big.
Axial movable-blade turbine is also called Kaplan Turbine, its blades are usually operated by
the oil pressure relay installed in the runner hub and can be turned according to head and load
changes in order to keep the optimal coordination between the activity of the guide vane angle
and the blade angle to enhance average efficiency. The maximum efficiency of this kind of
turbine has been more than 94%. It has the advantages of small size and light weight, while
the disadvantage is limited flow capacity when available head increases, large cavitation
coefficient, complicated structure, high cost. The axial movable-blade turbine is commonly
used in the large and medium-sized hydropower station where output and head vary widely.
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Francis turbine
Francis turbine can be designed for a wide range of heads and flows and is the most common
water turbine in use today. The Francis turbine has the characteristics of simple structure,
small size, low cost, high efficiency at full capacity (typically over 92%) and stable in
running, applicable to a wide range of water heads. Francis turbines generally are the most
efficient solution for heads ranging from 40 to 600 meters; Runner diameters ranges from 1.0
m ~ 10.0m, Installable capacity ranges from 200 kW ~ 800000 kW.
The Francis turbine is a type of reaction turbine, a category of turbine in which the working
fluid comes to the turbine under immense pressure and the energy is extracted by the turbine
blades from the working fluid. A Francis turbine consists of the following main parts: Spiral
Casing, Guide & Stay Vanes, Runner Blades, Draft tube, etc., Wicket gates around the outside
of the turbine's rotating runner adjust the water flow rate through the turbine for different
water flow and power production rates. In addition to electrical production, Francis turbines
may also be used for pumped storage, where a reservoir is filled by the turbine (acting as a
pump) driven by the generator acting as a large electrical motor during periods of low power
demand, and then reversed and used to generate power during peak demand. These pump
storage reservoirs act as large energy storage sources to store "excess" electrical energy in the
form of water in elevated reservoirs. This is one of only a few ways that temporary excess
electrical capacity can be stored for later utilization.
Main parts of Francis turbine
Spiral casing: It makes the water flow to produce circular motion, guides the water flow
evenly and axis symmetrically into the turbine.
Top Cover& Pivot Ring: It is located in the periphery of the runner, consists of the upper and
lower ring and the upright column. It is the skeleton of turbine, bears the loads of turbine pier
and external parts, transmitting them to the lower foundation and supporting the movable
guide vane.
Stay Vane: Streamline shape to guarantee strength and stiffness. Its numbers are half of the
movable guide vane.
Water distributor: It adjusts the discharge of turbine and changes the output according to the
load change of the Unit. It also guides the water flow into the runner as tangent direction to
form speed-torque.
Draft tube: The function of draft tube is to guide water flow into downstream channel and
recycle part of kinetic energy and potential energy.
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Tubular turbine
The Tubular type turbine is usually the best choice for exploitation of tidal power and
hydraulic power with extremely low heads and extremely large flow rates. This has the
advantages such as large discharge, high flow speed, high efficiency and less excavation, etc.
The variations are Bulb, Pit, Siphon and S types according to their structural types. The water
diversion parts, runner and water drainage parts of Tubular turbine are on one axial line. The
water flows directly and straightly through the runner without spiral casing. The water flow is
axial from the pipe inlet to the draft tube outlet. Application scope of heads: 2m~25m, Runner
diameters: 1.0m ~ 7.2m, Installable capacity: 200 kW ~ 200000 kW.
Tubular turbine generally has two categories: fully tubular and half tubular. The half Tubular
turbine is divided into bulb, pit and shaft extension types, etc.
The generator’s rotor of the full tubular type unit is on the outer circle of turbine’s runner,
whose application is less because of its difficult sealing.
For half Tubular turbine, the generator is separate from the hydro turbine.
9.1.2
Impulse turbines
Impulse turbine use the kinetic energy of water flow, is divided into pelton type, inclined-jet
type and cross-flow type. The inclined-jet type and cross-flow type turbine only applies to
small turbine. Its components and parts: spray pipe, baffle plate, runner, housing casing, shaft
and bearing etc.
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Pelton turbine
The Pelton type turbine is usually the preferred turbine for hydropower, when the available
water source has relatively high hydraulic head at low flow rates, where the Pelton wheel is
most efficient. They have the advantages such as compact structure, small size, low operation
maintenance cost, low cost because of less excavation and less investments, etc. and
disadvantages like inadequate energy recovery and lower efficiency than other types of
turbines. Application scope of head: 80m~1200m, Runner diameter: 0.6 m ~ 3.5m, Installable
capacity: 200KW ~ 20000KW. Their shaft arrangements are either vertical or horizontal and
they may have single nozzle, twin or multi-nozzles.
Main parts of Pelton turbine
Nozzle, runner, support parts and deflector parts. Major components: rotating parts (runner,
main shaft etc), nozzle parts (nozzle and related control), seat parts (seat, cover, spiral casing
etc), pipeline parts (distributing pipe, brake piping, expansion joint etc), bearing parts and
others. Core part is the runner and nozzle for structure.
Inclined-jet turbine
Inclined-jet turbine: The pressure energy of water flow is changed to velocity energy by the
nozzle, since leaving the nozzle, the water flow is not in a closed system, but forms the free jet
in the spiral casing filled with atmosphere, and at the same time there are 3-4 buckets
receiving the free jet from the same nozzle with unequal-sized discharge. There was a fixed
angle (usually take 22.5 degree) between the jet center of nozzle exit and the inlet water plane
of runner.
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Characteristics and application scope of Inclined-jet turbine
Application scope of heads: 15m~300m, Applicable discharges: Q=0.089~8.30m3/s, Runner
diameters: 0.05m ~ 5m, Installable capacity: 500KW ~ 6000KW, Types and Structures of
Generators: Vertical, Horizontal; Bearing, Bearing Bush, Adjustment and governing methods:
Automatic, Manual and Electric. Suitable for small hydropower stations which are of high
water head and small water flow.
Features: Simple structure, easy installation and maintenance, sufficient output, low noise,
normal running, and reliability quality. Disadvantages: Low efficiency.
9.2
Drive System/ coupling between the turbine and generator.
The drive system couples the turbine to the generator. At one end, it allows the turbine to spin
at the rpm that delivers best efficiency. At the other, it drives the generator at the rpm that
produces correct voltage and frequency—frequency applies to alternating current (AC)
systems only. The most efficient and reliable drive system is a direct, 1:1 coupling
between the turbine and generator.
This is possible for many sites, but not for all head and flow combinations. In many situations,
especially with AC systems, it is necessary to adjust the transfer ratio so that both turbine and
generator run at their optimum (but different) speeds. These types of drive systems can use
either gears, chains, or belts, each of which introduces additional efficiency losses into the
system. Belt systems tend to be more popular because of their lower cost.
9.3
Generators
It is in the generator where the electricity is produced. The shaft of the water turbine rotates in
the generator, which produces alternating current in the coils of the generator. It is the rotation
of the shaft inside the generator that produces magnetic field which is converted into
electricity by electromagnetic field induction. Hence the rotation of the shaft of the turbine is
crucial for the production of electricity and this is achieved by the kinetic and potential energy
of water. Thus in hydroelectric power plants potential energy of water is converted into
electricity. The capacity of hydro generator normally ranges from 100 kW to 800 MW and the
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range of its voltage is 0.4-13.8 kV; The insulation class includes B/F-grade. Hydropower
generator is driven by hydro turbine.
Types of hydro generator: According to its axis location, hydro generator is usually divided
into two types: horizontal and vertical. Large and medium-sized units usually adopt the
vertical type layout, whose max. speed can reach 750 rpm. While horizontal type usually is
used for medium and small capacity units, whose max. speed can reach 1500 rpm.
Horizontal type generators
Vertical type generators
As per its excitation mode, Hydro generator can be classified as brushless excitation unit and
excitation with brush generator.
Structure of hydro generator
Hydro generator usually consists of the following major parts: Rotor, stator, frame, thrust
bearings, guide bearings, cooler, brake, etc. The rotor and stator are the main parts of the
generator for electromagnetic effect. Other parts are for support or subsidiary use. The rotor is
the main part for transforming energy and delivering torque, which consists of the main shaft,
rotor frame, magnet yoke (torus) and pole, etc.. Stator consists of base, iron core and threephase winding coil, etc.. Stator core is made of cold-rolled silicon steel, which can be made
into an entirety and split structure as per the manufacturing and transportation requirements.
The type of cooling for Hydro Generator usually uses closed loop air cooling (ONAN). The
huge capacity unit is suitable to use water cooling to cool the stator directly. If both the rotor
and stator need to be cooled at the same time, it should be dual cold water cooling inside
turbine generating unit.
The installation structure of the hydro generator
The installation structure of the hydro generator is confirmed by the type of turbine. It mainly
includes the following styles:
Horizontal structure Usually, the horizontal hydro generator drives by Pelton turbine.
Horizontal turbine usually uses two or three bearings. The structure of two bearings is short in
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its axial length, compact structure, and easy to install. But when the combined critical speed
can’t meet the requirement or the bearing load is large, three bearing structure should be used.
Vertical structure The domestic hydroelectric generating units widely use vertical structure.
Usually, the vertical hydro generator drives by Francis or Kaplan turbines. It also can be
classified as hanging and umbrella type. It is called hanging type that thrust bearing of
generator is upper on the rotor. While it is called umbrella type, its thrust bearing of generator
is under the rotor.
Head, Flow, & Efficiency
Whether a hydro system generates a few watts or hundreds of megawatts, the fundamentals
are the same. Head and flow determine how much raw water power is available, and the
system efficiency affects how much electricity will come out of the other end. Each
component of a hydro system affects efficiency, so it’s worthwhile to optimize the design at
every step of the way.
9.4
Transformers Associated with Generating Equipments
Generator Transformer
Generator Transformer is employed in power plant for stepping up the voltage for transmitting
the power to the grid. Electrical power is generated in the power plant at lower voltages
(typically generation voltage will be between 0.4kV/6.6. kV/11kV /33kV). In order to transmit
the power to long distances voltage has to step up to reduce the losses. Hence in power plants,
generation transformer is employed.
Rating of the generation transformers will be almost equal to the rating of the generator
(11.25MW generating unit will have generating transformer rating about 12MVA).
Connection between the generator transformer and power plant generator will be through
isolated Phase Bus Duct (IPBD).
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Generator transformers are provided with on-load tap changing mechanism to regulate the
terminal voltage. Generator transformer will be Delta (LV side) and Star (HV side) connected
with star connection is connected to earth through resistor to reduce the fault currents and
protecting the transformer.
If Generator Circuit Breaker (GCB) is provided at the generator terminals, power from the
grid can be supplied to plant auxiliary loads through generator transformer by opening the
GCB when generating unit is not in operation.
Some of the points about generator transformer are given below:
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This is the main transformer of generating unit used for stepping up the voltage
from generating station for the transmission
In a generating plant for every generating unit one generating transformer is
required
Rated voltage on LV side corresponds to the rated generating voltage
Rated voltage on the HV side corresponds to rated voltage of the HV bus
Usually these transformers are outdoor type
LV terminals are connected to the generating terminals via isolated phase bus
systems
HV terminals are connected to the outdoor busbar by flexible ACSR conductors
via overhead flexible bus
Unit auxiliary Transformer (UAT)
Power plant is provided with Unit Auxiliary Transformers (UAT) connected to the generator
terminals through Isolated Phase Bus Duct (IPBD). Unit Auxiliary Transformers provides
electrical power to power plant distribution buses by stepping down the voltage from 11kV to
6.6kV/0.4 kV (example).
Unit Auxiliary Transformers are rated based on the rating of the loads it has to supply. Onload tap changing mechanism is provided to UATs. They are usually Delta (HV side) and Star
(LV side) connected transformers. The neutral of the star point is connected to earth through
resistor to limit the fault current during ground faults and to protect the transformer.
Some of the points associated with Unit Auxiliary Transformers are listed below:
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The Purpose of Unit auxiliary Transformer is to feed power to generator
auxiliaries of that unit
These transformers are connected to generators and are used as stepping down
transformers. The HV side transformer voltage corresponds to the voltage of the
generating unit and the LV side voltage is stepped down to 6.6 kV or 0.4 kV
Rated KVA of Unit Auxiliary Transformers is not more than 1% of the
generating capacity of the machine
These transformers may be outdoor/indoor type transformers
One Unit auxiliary transformer is present normally for every generating unit.
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Station Service Transformer
Station Transformers are employed for supplying power to plant auxiliary loads during the
event of starting of the plant or when generating unit is not generating power. Station
Transformers are connected to the switchyard bus. LV side of the station transformer is
connected to the auxiliary load buses.
Station transformer is normally rated for supplying power to the auxiliary loads. On-load tap
changing mechanism is provided to regulate the terminal voltage of the transformer. The star
point of the station transformer is grounded through resistor.
Some of the points related to station transformer are given below:
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In general station service transformer is used for supplying power to auxiliary
equipment in the power plant when the plant is not generating any power.
Rated HV voltage corresponds to the rated voltage of the outer busbars
Rated LV voltage corresponds to the auxiliary bus voltage
Rated KVA corresponds to the load of common auxiliaries of the station. This
corresponds to the 10% to 15% of the rating of the generating power.
These transformers are normally outdoor type.
REFERENCES
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www.addnew.com
www.brighthubengineering.com
www.homepower.com
www.ieeexplore.ieee.org.in
www.srpnet.in
www.bhel.com
www.homepower.com
http://www.slideshare.net/prasadvejendla/basic-terms-of-hydro-power-plant
http://kiran111.hubpages.com/hub/Differenet-Transformers-in-PowerStationhttp://en.wikipedia.org
www.fwee.org/nw-hydro-tours/walk...a-hydroelectric.../5-transformer
UJVNL’s own experience
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