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R. Shankar Raju

Roll No: 07915A0211IV / IV II Semester

EEE, V.J.I.T

POWERFORMER

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INTRODUCTION

Powerformer is a 3 phase AC

generator which is capable of

generating output voltage ranging from

30 kv to 400 kv that can be directlyconnected to the high voltage

transmission grid by replacing the

generator and step-up power

transformer used in todays powerplant.

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FEATURES

It can produce high output voltage rangingfrom 30 kv to 400 kv

High efficiency, Highly reliable

Improves reactive power output andoverload capacity of the system

Robust in construction

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Schematic Diagram

a) Conventional plant with step uptransformer

b) Same plant Using power former

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Design Powerformer has a rotor design similar to a

conventional generator

The difference in design of stator of aPowerformer and a conventional generator

lies in its stator windings

Powerformer stator uses a high voltage

cables instead of a square cross section

wires for its winding.

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Cables Used In Stator Winding Of

Powerformer The power cable

consists of a stranded

conductor, solid

insulation and two

semi conducting layers

The insulation material

is cross-linked

polyethylene (XLPE), a

material successfully

used in high-voltage

power cables

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Electric Field Distribution

The two semi

conducting layers, one

surrounds the

conductor and the

other outside theinsulation, the semi

conducting layers

serves as an equi-

potential surface thatforces the electric field

to be uniform around

the circumference

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Stator ViewSectional View

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Type Faults And Their Behaviour

There are mainly two type of faults internal andexternal

For a conventional system the internal fault refers

to a fault that occurs at the terminals of thegenerator, and an external fault is a fault thatoccurs at the high-voltage side of the step-uptransformer

For a Powerformer system, internal and externalfaults are basically the same as a Powerformer thatis connected directly to the high-voltage bus-bar inthe generating station

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External Faults

The fault currents from a Powerformer at externalthree-phase short circuits will be of the samemagnitude as the fault current from theconventional unit.

External single-phase ground faults will be lowerthan that from the conventional unit. The reason isthat the neutral point of a Powerformer is isolatedfrom ground while the neutral point of the step-up

transformer of the conventional generator is solidlygrounded.

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Internal Faults

The internal three-phase short-circuit current of aPowerformer is less than that of the conventionalgenerator due to its higher output voltage.

In the case of the internal two-phase-to-groundand the internal phase-to-phase faults, the faultcurrent in a conventional generating unit will besubstantially higher than the fault current in thePowerformer.

For the internal single phase-to-ground internalfault, the fault current in a conventional generatingunit is much lower than that of the Powerformerdue to the high impedance grounding of theneutral of the conventional generator

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Comparision Of Fault Currents

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Cooling System

The cooling system of the Powerformer stator core is alsobased on a new concept . This is due to the low current in thecables of the stator winding and the lower ratio betweenohmic and iron losses than that for a conventional generator.Accordingly, most of the heat is generated in the stator core,which is grounded. This fact greatly simplifies the cooling

system. The new cooling system is an indirect system thatcools the stator core by axially inserted water pipes made ofhigh density XLPE. Thus, the stator has no radial air coolingducts, and this leads to a homogeneous stator core. Thismakes the gross length of the stator shorter, the efficiencyimproves, and the stator assembly is more convenient,

especially with respect to the cable installation through theslots. As the water cooling is carried out at ground potential,there is no need for de-ionized water as in the conventionalwater-cooled stator windings. Ordinary tap water may beused for the cooling of the Powerformer stator core.

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First Powerformer Installation

The worlds first powerformer was installed

at porjus hydropower centre on the lule

river in northern Sweden rated at 11 MVA,

45 kV, and 600 rpm

The data from the two units installed at

porjus is shown below

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Compared Parameters Generator Powerformer

App. Power (MVA) 11 11

Voltage (kV) 10 45Current (A) 635 141

Speed (rpm) 429 600

Length (mm) 750 1450

Stator Outer d (mm) 3100 3050No of Cables per Slot - 12

Weight of Stator (ton) 11.5 34.5

Weight of Rotor (ton) 23.0 22.8

Xdi 0.98 0.79Xdu 0.25 0.22

Xdu 0.16 0.17

Efficiency 97.2% 97.6%

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Development Of Powerformer Rated

Voltage

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Existing Powerformer Generators

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Advantages

High efficiency.

Reactive power capability.

Low maintenance cost.

Reduced environmental impact.

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Efficiency

Powerformer plants have 0.5-1.5 % less activelosses than conventional plants.

In general, a power plant with Powerformer has

0.5-1.5 % higher efficiency than a conventionalpower plant.

For example a 120 MW plant with Powerformerplant with 1.5 efficiency will produce 1.8 MW morepower than a conventional plant which increasesthe overall economy of the plant.

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Reactive Power Capability

The generation of reactive power is needed

to compensate for the reactive power losses

in the transmission networks. WithPowerformer the reactive power losses in

the step-up transformer is eliminated.

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Low Maintenance Cost

With Powerformer, every thing tothe right of plane A-A can beeliminated, leading to powerplants with fewer components,For example Powerformer

technology eliminates the step-uptransformer, the handling of oils,generator circuit breaker andpart of the bus-bar system. Fewercomponents means fewer sourcesof potential faults and thusconsiderably lower maintenanceand maintenance costs.

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Reduced Environmental Impact

A 150 MVA Powerformerversus a conventional 136MVA generator, breaker andtransformer system. Alifetime of 30 years wasassumed, the environmental

impact is expressed inEnvironmental Load Unit(ELU), a high impact on theenvironment gives large ELUnumber. The results areshown in Figure (6), whichshows that the Powerformersystem has lowerenvironmental impact than atraditional system during allof its life time phases, this ismainly because Powerformerhas less energy losses.

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Comparison between a conventional

system and a power former systemConventional system Powerformer system

Transformer None

MV bus-bar None

Generator switches None

Space & volume = 1 Space & volume < 1

Many parts Few parts

Weight = 1 Weight < 1

Overload capacity = 1 Overload capacity > 1

Reactive power capability = 1 Reactive power capability > 1

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Disadvantages

Powerformer output voltage is limited by the

AC power cable and the cable accessories

(terminations and joints) used in stator

winding

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Conclusion

Powerformer (high-voltage generator) has

been studied through out this seminar; this

new concept provides the possibility to

directly connect a rotating machine to thehigh-voltage power grid without going via a

step-up transformer resulting in higher

efficiency. Powerformers enable very clean

and compact power plants that are not onlyeconomical, reliable, and environment

friendly but also more efficient than

conventional ones.

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ThankYou