Abstract- This paper shows the various aspects such as geometry

and applications of High Temperature Superconducting (

transformers. The conventional transformer had some drawbacks

so our design shifted to HTS transformer. The comparison of both

is shown in this paper. Windings, core and cryogenic systems are

essential parts of HTS which are discussed here. The major use

HTS in power system is as power transformer, fault current limiter

and many more which are discussed. Insulation of parts is also kept

in mind while studying the tests and results. Efficiency of HTS with

different winding material is compared. So it is

transformer considering the various parameters.

I. INTRODUCTION After the development of High temperature superconducting

materials by Georg Bednorz and Alex Muller developments have been made in the field of transformer design. The high temperature superconducting transformer have their windings made from HTS materials while in conventional transformers, the windings are made from copper. The transformers made from HTS materials have various advantages over conventional transformers. Construction wise, HTS transformers are lighter in weight and smaller in size. They have higher efficiency and are capable of overloading with no thermal ageing. HTS transformers are economical as they have lower life-cycle costs. Losses are substantially reducedthe use of HTS materials and hence increased energy savings. HTS transformers are also environment-friendly as they cause reduced pollution and no contamination with fewer hazards. Back in 1986, Georg Bednorz and Alex Muller developed

HTS material that had Tc of 30K [1]. But with the improvements in technology Tc has increased above the liquid nitrogen temperature of 77K. Till date, the highest Tc superconductor is mercury-barium-calcium-copper oxide (ceramic with a Tc of 135 K [2]. Although researches are being carried out for further increasing the Tc for thecooling system and to reduce AC losses.

Study of High Temperature Superconductor Based

Deepak Jain, Umang Lahoty, Gaurav Path

Vellore Institute of Technology, Vellore

This paper shows the various aspects such as geometry

High Temperature Superconducting (HTS)

transformers. The conventional transformer had some drawbacks

so our design shifted to HTS transformer. The comparison of both

is shown in this paper. Windings, core and cryogenic systems are

essential parts of HTS which are discussed here. The major use of

HTS in power system is as power transformer, fault current limiter

and many more which are discussed. Insulation of parts is also kept

in mind while studying the tests and results. Efficiency of HTS with

different winding material is compared. So it is a review of HTS

High temperature superconducting by Georg Bednorz and Alex Muller in 1986, various

developments have been made in the field of transformer design. The high temperature superconducting transformer have their windings made from HTS materials while in conventional transformers, the windings are made from copper. The

rmers made from HTS materials have various advantages Construction wise, HTS

transformers are lighter in weight and smaller in size. They have higher efficiency and are capable of overloading with no

sformers are economical as they have are substantially reduced due to

increased energy savings. friendly as they cause

ation with fewer hazards.

norz and Alex Muller developed first ut with the improvements

has increased above the liquid nitrogen superconductor is

copper oxide (HgBa2Ca2Cu3O8) Although researches are being

for the stability of the

In USA, the HTS transformers were1 MVA to 5/10 MVA to 30/60 MVA [basically consist of three parts: HTS windings, a cooling system and the core. HTS transformers can be used for various applications such as for quenching tecsystem. Because of its advantages, HTS transformers are expected to be installed in future on commercial basis. Various research institutes and power companies are carrying out development programs to develop HTS technology in transformers [4]-[8].

II. PARTS OF HTS TRANSFORMER

Constraints to commercialization of HTS transformers are the

cost of HTS wires used to make windings and cost of cooling system. Therefore for the commercialization proper design of the following parts have to be kept in

A. HTS wires and HTS windings

With the development of first high temperature

superconducting material in 1986, various developments are being done in the field of HTS materials. perovskite structure Lanthanum-Bariumdeveloped [1].

Fig. 1 Multi-filament HTS tape

The HTS material used in transformers are divided in two

parts: 1st generation and 2nd generation HTS wires.1st generation: BSCCO (Bismuth Strontium Copper Oxides)2nd generation: YBCO (Yttrium Barium Copper Oxides)

Study of High Temperature Superconductor Based

Transformer

, Gaurav Pathak, Vishwas Vats and R. Sudha(Assistant professor, VIT)

Vellore Institute of Technology, Vellore-632014, India

transformers were developed in three stages. MVA to 5/10 MVA to 30/60 MVA [3]. HTS transformers

of three parts: HTS windings, a cooling system HTS transformers can be used for various

such as for quenching techniques and in traction Because of its advantages, HTS transformers are

expected to be installed in future on commercial basis. Various research institutes and power companies are carrying out development programs to develop HTS technology in

RANSFORMER

Constraints to commercialization of HTS transformers are the cost of HTS wires used to make windings and cost of cooling

Therefore for the commercialization proper design of the following parts have to be kept in mind [9].

st high temperature superconducting material in 1986, various developments are

he field of HTS materials. In 1986, the Barium-Copper oxide at 30K is

filament HTS tape[1].

The HTS material used in transformers are divided in two generation HTS wires.

generation: BSCCO (Bismuth Strontium Copper Oxides) YBCO (Yttrium Barium Copper Oxides)

Study of High Temperature Superconductor Based

ak, Vishwas Vats and R. Sudha(Assistant professor, VIT)

The most promising known HTS materials for high current

applications are given below, with their common numerical reference names in brackets [10]: Yttrium compounds (YBCO)

Y1Ba

2Cu

3O

7-x (123) T

c

Y2Ba

4Cu

7O

15-y (247) T

c

Bismuth compounds (BISCCO)

Bi2Sr

2Ca

1Cu

2O

y (2212) T

c

Bi2-xPb

xSr

2Ca

2Cu

3O

y (2223) T

c

Thallium compounds (TlPb)

1Sr

2Ca

2Cu

3O

9 (1223) T

c

Tl2Ba

2Ca

2Cu

3O

10 (2223) T

c

Mercury compounds

Hg1Ba

2Ca

2Cu

3O

10 (1223) T

c

The mostly used HTS is 1G Bi-2223 with T2223 wires are made using powder-in tube (PIT) technique which uses silver for sheathing of the wires. Bimore than Bi-2212 as it has Tc 20K more than that of BiThe second generation HTS is YBCO also known as ‘123’. It is the first HTS to be developed above liquid nitrogen temperature 77K. Its Tc is found to be 93K. While developing and commercializing HTS transformers

cost is the major challenge. Increased production and increase in automation cause cost to be lower. There are many benefits to HTS applications if the cost of BSCCO is $50/kAm as studied in[11]. While, YBCO provide same benefits at the cost of $10/kAm with potential of further reduction of price as studied in[12]. Due to anisotropic properties of HTS materia

axial magnetic field is different which causes AC loss in transformer. For studying the AC loss in Bisuperconductors an AC loss model is developed and studied [13]. Basic reason for AC loss in HTS is due to the strong electromagnetic coupling due to the normal component of AC field between the filaments of the HTS winding. This is due to the low resistivity of Ag-matrix as Bi-2233 is developed from PIT techniques. This phenomena lead to the hysteric loss which is the major contributor of AC loss. Reduction of AC loss in Bi2223 tapes can be done by introducing inter-filamentary oxide barriers which is analyzed in [14]. YBCO wires allow larger critical current density than BSCCO

and hence YBCO are much more economical as they largehelp in reducing AC loss in HTS transformer. of HTS transformer has been developed using YBCO roebel cable which considerably reduced AC loss in windings [15]. In this model, low voltage winding is made up of YBCO Roebel cable for handling high current while high voltage winding is

The most promising known HTS materials for high current applications are given below, with their common numerical

c = 92 K

c = 95 K

c = 80 K

c = 110 K

c = 120 K

c = 125 K

c = 153 K

2223 with Tc of 110K. Bi-in tube (PIT) technique

which uses silver for sheathing of the wires. Bi-2223 is used 20K more than that of Bi-2212.

The second generation HTS is YBCO also known as ‘123’. It is he first HTS to be developed above liquid nitrogen temperature

HTS transformers, cost is the major challenge. Increased production and increase in

e are many benefits to $50/kAm as studied

While, YBCO provide same benefits at the cost of $10/kAm with potential of further reduction of price as studied

Due to anisotropic properties of HTS materials, the radial and axial magnetic field is different which causes AC loss in transformer. For studying the AC loss in Bi-2223 superconductors an AC loss model is developed and studied in 13]. Basic reason for AC loss in HTS is due to the strong

netic coupling due to the normal component of AC field between the filaments of the HTS winding. This is due to

2233 is developed from PIT techniques. This phenomena lead to the hysteric loss which

butor of AC loss. Reduction of AC loss in Bi-filamentary oxide

larger critical current density than BSCCO and hence YBCO are much more economical as they largely

One such model of HTS transformer has been developed using YBCO roebel cable which considerably reduced AC loss in windings [15]. In this model, low voltage winding is made up of YBCO Roebel

g high current while high voltage winding is

made up of YBCO wires which reduce AC losses. Roebel cable also improved mechanical and winding strength.Another method of reducing AC losses in the HTS

transformers is to reduce the radial component of the leamagnetic field. The radial component of leakage magnetic field heavily reduces critical current and as a result increased AC losses as compared to axial component of leakage magnetic field. Hence, the influence of core structure and winding configuration on leakage magnetic design to reduce radial magnetic field is studied in

B. Core

Core is the heart of the transformer. It used to carry the magnetic flux from primary side to secondary side with low reluctance. There are two types of core in HTS transformer, i.e.,

“C-Core” or core-type and “E-Core”

Fig. 2 Typical core forms for single-phase transformer. (The white quadrangles

represent the primary coils, and black ones represent the secondary core” core-type. (b) “E-core” shell

Core –type transformer consist of two windings and one core whereas shell-type transformer consist of one winding and two cores. Core-type transformer provides better insulation between both the winding because of two winding present while shelltype transformer provides high degree of mechanical protection because it is surrounded by core. Based on the research, it is found that shell-type core is more cost efficient and it is 5% less than its core-type counterpart. Shell but 21% less conductor material than coreAnother type of core that is extensively used in HTS

transformer is partial core transformer (PCTX) [difference between full core transformer andin partial core outer limbs and connecting yokes is absent.magnetic circuit for PCTX consists of core and the surrounding air which results in high magnetic reluctance. Due to high magnetizing current the efficiency is poor and cmore. The introduction of HTS eliminates the issues, i.e. low conductor losses and low cross-sectional area gives very compact and low weight PCTX.

made up of YBCO wires which reduce AC losses. Roebel cable also improved mechanical and winding strength. Another method of reducing AC losses in the HTS

transformers is to reduce the radial component of the leakage magnetic field. The radial component of leakage magnetic field heavily reduces critical current and as a result increased AC losses as compared to axial component of leakage magnetic field. Hence, the influence of core structure and winding

field and to optimize the design to reduce radial magnetic field is studied in [16].

Core is the heart of the transformer. It used to carry the magnetic flux from primary side to secondary side with low

are two types of core in HTS transformer, i.e.,

” or shell-type [17].

phase transformer. (The white quadrangles

represent the primary coils, and black ones represent the secondary coil). (a) “C-core” shell-type[17].

transformer consist of two windings and one core e transformer consist of one winding and two

type transformer provides better insulation between ing because of two winding present while shell-

type transformer provides high degree of mechanical protection because it is surrounded by core. Based on the research, it is

type core is more cost efficient and it is 5% less ype counterpart. Shell –types uses 18% more core

but 21% less conductor material than core-type. Another type of core that is extensively used in HTS

transformer is partial core transformer (PCTX) [18]. The main difference between full core transformer and partial core is that in partial core outer limbs and connecting yokes is absent. The

circuit for PCTX consists of core and the surrounding air which results in high magnetic reluctance. Due to high magnetizing current the efficiency is poor and copper loss is more. The introduction of HTS eliminates the issues, i.e. low

sectional area gives very

Fig.3 Cross-sectional view of the differences between full core and partial coreTransformers[19].

Another type of core that is usually used in HTS transformer is air-core transformer due its dual nature i.e. absence of iron core and acts as a shunt reactor due to high magnetizing current [19]. HTS air-core transformer is very useful in ctransmission and UHV transmission lines. C. Cryostat and Cryogenic System

The transformers which were designed earlier had many problems with layered winding in the insulation and distribution of the surge voltage under the high voltage. This AC lossgenerated from the strong magnetic field density perpendicular to the surface of the HTS tapes which can be seen in [20improve this we arrange the pancake type winding concentrically using BSCCO-2223 and increasewindings up to the height which cryostat permit to reduce the AC loss seen in [21], [22]. To achieve this success we need to remove eddy current so

the cryostat is made of FRP (Fiberglass Reinforced Plastic). Cross section view of FRP can be seen in Fig. 3and the location of the windings from the center is shown. Another method to reduce AC loss is by implementing continuous disk winding for high voltage winding and layered winding for low voltage side. A cryostat is made of GFRP with a room temperature bore for

a transformer. Vacuum jacket and super insulation layer at the side and the bottom of cryostat are introduced to reduce the heat penetration by radiation from outside. Secondary cryostat isused to supply 65 K, 1 atm liquid nitrogen as the HTS windings are supposed to be cooled down to 67 K. This secondary is made of stainless steel with cryo-cooler, cryo-pump and the heat exchanger. Graphical explanation of the liquid nitrogen from and to the

cold box inside the FRP cryostat can be seen in Fig. 4. Heat exchanger of secondary cryostat brings down the temperature of liquid nitrogen to 65 K which flows through the 1straight pipe and can be studied in [23]. The number of the holes

sectional view of the differences between full core and partial core

Another type of core that is usually used in HTS transformer core transformer due its dual nature i.e. absence of iron

core and acts as a shunt reactor due to high magnetizing current core transformer is very useful in cable

The transformers which were designed earlier had many layered winding in the insulation and distribution

of the surge voltage under the high voltage. This AC loss is generated from the strong magnetic field density perpendicular

which can be seen in [20]. To the pancake type winding

2223 and increase the number of windings up to the height which cryostat permit to reduce the

To achieve this success we need to remove eddy current so Reinforced Plastic).

Fig. 3 and the number ation of the windings from the center is shown.

Another method to reduce AC loss is by implementing for high voltage winding and layered

GFRP with a room temperature bore for a transformer. Vacuum jacket and super insulation layer at the side and the bottom of cryostat are introduced to reduce the heat penetration by radiation from outside. Secondary cryostat is

iquid nitrogen as the HTS windings are supposed to be cooled down to 67 K. This secondary is

pump and the heat

Graphical explanation of the liquid nitrogen from and to the yostat can be seen in Fig. 4. Heat

exchanger of secondary cryostat brings down the temperature of liquid nitrogen to 65 K which flows through the 1-inch diameter straight pipe and can be studied in [23]. The number of the holes

Fig. 4. Concentric arrangement of windings

has to be numerous enough to achieve the equal upward flow rate circumferentially. Warmed liquid nitrogen is sent back to secondary cryostat. So finally the sum of AC loss, the radiation from the wall and the heat conduction through thecan be removed to keep the winding under the design temperature.

Fig. 5. Graphics of the liquid nitrogen supply

To keep temperature below the critical temperature in cryogenic system we need to insulate achieved by composite winding. Composite winding is concentrically arranged windings which are primary (high), secondary (low) and tertiary (high). Fig. 6of turn-to-turn (part A), layer-to-layer (part B), main in(part C), and coil-to-ground (part D).A depends on kapton film, of part B depends on FRP, of part C depends on LN2 and barrier and that of part D varies with voltage. So the insulation strength of different parts dependifferent aspects as expressed in [24]. The other insulation which can be seen in cryogenic system is

using two layers of “NOMEX T-410

which occur when the transformer is operated

ement of windings[23].

has to be numerous enough to achieve the equal upward flow rate circumferentially. Warmed liquid nitrogen is sent back to secondary cryostat. So finally the sum of AC loss, the radiation from the wall and the heat conduction through the current lead can be removed to keep the winding under the design

and return at the main cryostat[23].

To keep temperature below the critical temperature in cryogenic system we need to insulate it. Insulation can be achieved by composite winding. Composite winding is concentrically arranged windings which are primary (high),

gh). Fig. 6 shows the insulation layer (part B), main insulation

ground (part D). Insulation strength of part A depends on kapton film, of part B depends on FRP, of part C depends on LN2 and barrier and that of part D varies with voltage. So the insulation strength of different parts depends on different aspects as expressed in [24]. The other insulation which can be seen in cryogenic system is

410” tape. During failure, is operated too close to the

HTS tape’s critical current density in a magnetic fieldof nitrogen gas is created heating the conductors. The

Fig. 6. Insulation construction of HTS transformer with composite winding

emergency venting rupture disc prevents build up of nitrogen gas in the LN2 chamber. A model and its inspection can be seen in [18]. For having a proper insulation we need to know the voltage

time and breakdown characteristics especially for turnHTS transformer [25]-[27]. For the surface contact geometry breakdown voltage is lower than that of the point contact geometry, because the contact area is larger than that of the point contact geometry as shown in Fig.7. The slope of thevoltage–time characteristics increases with the number of layers, which agrees with the result of [28].

Fig. 7. (a) Surface contact geometry ;(b) point contact geometry[28].

III. APPLICATIONS

The most exciting feature of superconducting materials is its ability to carry significant current that can be reached with liquid nitrogen 77K. These materials are called HTS and are most frequently made up of Bismuth, Copper, Strontium,

ensity in a magnetic field, the surge heating the conductors. The

nsformer with composite winding[18].

build up of nitrogen its inspection can be seen

For having a proper insulation we need to know the voltage-time and breakdown characteristics especially for turn-to-turn

For the surface contact geometry lower than that of the point contact

geometry, because the contact area is larger than that of the The slope of the

with the number of layers,

point contact geometry[28].

The most exciting feature of superconducting materials is its ability to carry significant current that can be reached with

These materials are called HTS and are most frequently made up of Bismuth, Copper, Strontium,

Calcium and oxygen [29],[30]. HTS wires are most commonly

applied in developing Power transformer,

and it can be also used as Fault current l

A. Power Transformers

The most important application of HTS technology is its use to develop a Power transformer. With the advancement of HTS technology various types of power transformers are fabricated and tested in recent times. A single phase

have been developed since 1998 [31]

alpha prototype was developed [32].

30/60 design can be easily accomplished by installing more turns of improved HTS wires on the same frame. These HTStransformers have been manufactured using BSCCO wires. More development in HTS materials has lead us to development of 100 MVA power three phase power transformer in 2011.advantages of HTS transformer compared to transformers with lower conductivity include lighter and smaller units and increased efficiency. Initially the theoretical prototype of 10 KVA and 5 MVA HTS technology has the globe. The ultimate aim is development of a threeMVA HTS transformer. Before then the idea of 5 MVA transformers has been proposed and has been fabricated successfully. The impact of development of these types of high temperature superconducting transformers on development and modernization of power system will be felt soon in the near

future [33],[9].

B. Traction Transformers

One of the major applications of HTS is its use as electric locomotive traction transformers. In 1996 Siemens and GBC Alsthom LINDE cooperated to carry out research to develop 10 MVA electric locomotive traction transformers with aapply it in high speed railways system. The prime motive was to reduce the weight of the traction transformer from 12 t to 7.7 t using HTS technology. With the help of HTS technology the efficiency of traction transformers would increase from 94%99% and the volume could reduce from 30% to 40% as compared to normal traction transformers. A nominal single phase 100 KVA (5.5kV/1.1kV) transformertested until January 1999. In 2005, a 4MVA HTS traction transformer was developed in Japan. This traction transformer has a primary winding; four secondary wwinding. The four secondary windings

each other [9]. The total weight of the transformer was 1.71 t

excluding the refrigerators and compressors. The maximum output of 4 MVA HTS traction transformer maintaining the superconductivity was 3.5 MVA with a value of AC loss about 6.3kW. It is able to allow 750A of current to flow in secondary winding corresponding to a total output of 4 MVA, and the calculated AC loss is about 7.9kW at 4 MVA output. The HTS

HTS wires are most commonly

developing Power transformer, Traction transformer

and it can be also used as Fault current limiter.

The most important application of HTS technology is its use to develop a Power transformer. With the advancement of HTS technology various types of power transformers are fabricated and tested in recent times. A single phase 1 MVA transformer

] and in 2004 the 5/10 MVA

. Extension of 5/10 MVA to

can be easily accomplished by installing more turns of improved HTS wires on the same frame. These HTS transformers have been manufactured using BSCCO wires. More development in HTS materials has lead us to development of 100 MVA power three phase power transformer in 2011. The advantages of HTS transformer compared to transformers with

include lighter and smaller units and Initially the theoretical prototype of 10

KVA and 5 MVA HTS technology has been developed across The ultimate aim is development of a three-phase 100

MVA HTS transformer. Before then the idea of 5 MVA transformers has been proposed and has been fabricated successfully. The impact of development of these types of high

ormers on development and of power system will be felt soon in the near

One of the major applications of HTS is its use as electric locomotive traction transformers. In 1996 Siemens and GBC

INDE cooperated to carry out research to develop 10 MVA electric locomotive traction transformers with an aim to apply it in high speed railways system. The prime motive was to reduce the weight of the traction transformer from 12 t to 7.7 t

With the help of HTS technology the efficiency of traction transformers would increase from 94% to

and the volume could reduce from 30% to 40% as compared to normal traction transformers. A nominal single phase 100 KVA (5.5kV/1.1kV) transformer was constructed and tested until January 1999. In 2005, a 4MVA HTS traction transformer was developed in Japan. This traction transformer

four secondary winding and one tertiary The four secondary windings are independent from

The total weight of the transformer was 1.71 t

excluding the refrigerators and compressors. The maximum output of 4 MVA HTS traction transformer maintaining the superconductivity was 3.5 MVA with a value of AC loss about

le to allow 750A of current to flow in secondary winding corresponding to a total output of 4 MVA, and the calculated AC loss is about 7.9kW at 4 MVA output. The HTS

wires could not decrease AC loss, the AC loss therefore become larger and was anticipated to be over 6 kW. The application of HTS wires had marked a new beginning in development of more

efficient and reduced weight traction transformers

C. Fault Current Limiters

The Fault current limiter (FCL) is a power apparatus that suppress the fault current by generating limiting impedance when any fault occurs in power system. For fault current limiter it is important to choose optimum limiting impedance properly

[36],[37]. Fault-current problems are the most common problem

that is faced by the electric power designers while expanding the buses. Larger transformers results in higher faultforcing the replacement existing bus-bar and switchgear not rated for the current fault duty. The problem of fault current, bus capacity and system stiffness has persisted for decades now. The introduction and development of HTS enables the development of economical FCL. The concept of superconducting fault current limiters were first studied about 20 years ago. These fault-current limiters based on high temperature superconductors offers a solution for controlling the problem of faultlevels at utility distributions and transmission networks. Unlike reactors or high impedance transformers these faultlimiters will limit fault current without adding impedance to the circuit during normal operations. This kind of FCL finds numerous application as it provides various benefits like avoiding equipment damage, avoiding equipment replacement,

higher breaker rating and avoiding split buses

enhances the grid stability. In order to improve the total efficiency of power system Superconducting fault current limiting transformer has already been proposed. It will help to reduce the leakage impedance of the HTS transformer and it also help to improve system stability in normal operating

conditions as well as in fault-conditions.

IV. COMPARISION OF TRANSFORMERS

If we see the different possibilities of making of power transformer’s windings, then there will be three ways; First generation (1G) BSCCO, Second generation (2G) YBCO and conventional way of paper-oil. The transformer which is environmental-friendly and for critical issues in the environmental profiles is to be found out by comparingtalking about conventional and HTS, to reduce the loadthe copper windings of the transformer could beinnovative conductor based on HighSuperconductors (HTS). HTS includes 1st and 2available in long lengths 1G BSCCO tapes with silver mand 2G YBCO coated conductors. In particular, 2G HTS results in large current density in external magnetic fields which is several times greater as compared to copper [39]allows a very compact device hence reduction in volume and

wires could not decrease AC loss, the AC loss therefore become The application of

HTS wires had marked a new beginning in development of more

efficient and reduced weight traction transformers [34],[35].

The Fault current limiter (FCL) is a power apparatus that ault current by generating limiting impedance

when any fault occurs in power system. For fault current limiter it is important to choose optimum limiting impedance properly

current problems are the most common problem

electric power designers while expanding the buses. Larger transformers results in higher fault-level duties

bar and switchgear not rated for the current fault duty. The problem of fault current, bus

stiffness has persisted for decades now. The introduction and development of HTS enables the development

The concept of superconducting fault current limiters were first studied about 20 years ago. These

high temperature superconductors offers a solution for controlling the problem of fault-currents levels at utility distributions and transmission networks. Unlike reactors or high impedance transformers these fault-current

without adding impedance to the circuit during normal operations. This kind of FCL finds numerous application as it provides various benefits like avoiding equipment damage, avoiding equipment replacement,

higher breaker rating and avoiding split buses [38]. It also

enhances the grid stability. In order to improve the total efficiency of power system Superconducting fault current limiting transformer has already been proposed. It will help to reduce the leakage impedance of the HTS transformer and it will also help to improve system stability in normal operating

RANSFORMERS

If we see the different possibilities of making of power transformer’s windings, then there will be three ways; First

ation (1G) BSCCO, Second generation (2G) YBCO and transformer which is most critical issues in the

is to be found out by comparing. First and HTS, to reduce the load losses,

the copper windings of the transformer could be replaced by innovative conductor based on High Temperature

and 2nd generation 1G BSCCO tapes with silver matrix

conductors. In particular, 2G HTS results in external magnetic fields which is

as compared to copper [39],[40]. This device hence reduction in volume and

weight. The goal was to search critical issues and the identification of the most environmentalwith 1G, 2G HTS windings and which are designed for 150 kV/20 kV substations with a nominal rating of 25 MVA.

Fig. 8 Dimensional comparison for the three different ttransformers[41].

TAB. 1: MAIN TECHNICAL CHARACTERISTICS OF THETRANSFORMERS

Bscco

Rated power (MVA)

Power frequency (Hz)

Primary winding voltage (V)

Secondary winding voltage (V)

Connection type

Total height (mm) 2613

Total width (mm) 3105

Winding diameter (mm)

No-load losses (kW)

Total load-losses (kW)

Total weight (kg) 38453

With the help of the table and example of a modal tested in [41] we conclude the HTS YBCO transformer is the most environmental-friendly solution under all considered stress factors. The reason being is mainly due to its reduced energy losses in the use. Only improvement that anyone would suggest is the search of a material with lower energy consumption in production and recycling phases to replace the fiberglass reinforced resin. The conventional transformer because of its

goal was to search critical issues and the of the most environmental-friendly transformers

conventional transformers, which are designed for 150 kV/20 kV substations with a

Dimensional comparison for the three different types of considered transformers[41].

TAB. 1: MAIN TECHNICAL CHARACTERISTICS OF THE TRANSFORMERS

Bscco Ybco Conv.

25 25 25

50 50 50

150 150 150

20 20 20.8

Y/Y Y/Y Y/Y

2613 2199 2800

3105 2383 7000

1032 791 1500

21.5 10.8 17

22.5 13.6 118

38453 17949 54150

With the help of the table and example of a modal tested in ] we conclude the HTS YBCO transformer is the most

friendly solution under all considered stress factors. The reason being is mainly due to its reduced energy losses in the use. Only improvement that anyone would suggest

terial with lower energy consumption in production and recycling phases to replace the fiberglass reinforced resin. The conventional transformer because of its

higher weight and energy losses shows the worst environmental profile.

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