electronic instrument transformer

8/18/2019 Electronic Instrument Transformer

1/6

Electronic Instrument T ransformers

for Integrated Substation Systems

M. S a i t oh ,

T.

K i mur a , Y. Minami,

N.

Yamanaka,

S.

Maruyama,

T. Nakajima, M.

Kosakada, Member, IEEE,

Abstract-In orde r to integrate prima ry equipm ent to digitized

integrated substation systems, the digitizing procedure of

instrument transformers is indispensable.

Electronic current transformers (ECTs) and electronic voltage

transformers Ems)have achieved high performance with a very

small size. The ECTs and

EVTs

play a sensing and digitizing role

for current and voltage information offered by Rogowski coils

and capacitive voltage dividers respectively with the processing

capabilities

of

digital electronics, and link up with protection

relays and bay control units via process level

LAN.

The sensed

current and voltage signals are transmitted as digital signals.

This paper discusses the system construction of the electronic

instrument transformers, which are applied for digitized

substation systems integrated with primary equipment. The

results

of

performance that can be achieved by the electronic

instrument transformers are evaluated.

Index Terms-Electronic CTs, Electr onic VTs, Process BU S,

Rogowski coil, Capacitive Voltage divider, Sensing Unit, M erging

Unit.

I. INTRODUCTION

Being encouraged by recent progress in information

technology and requirements of the com petitive power market,

it is proposed to make a substation information-terminal in

which precise and sophisticated d ata from substation primary

equipment can be acquired. These data are needed not only for

operational, engineering, maintenance staff in the operation

center but also for sales, marketing, quality engineering, and

management people at remote places. Digital information

technology assures realization of this scheme. Current and

voltage information in the main high-voltage circuits are one

of the most important information dealt with substation system,

so the digitizing procedure of instrument transformers is

indispensable to integrate primary equipment to digitized

integrated substation system, that

is

to make a substation

information-terminal.

Today, electronic current transformers (ECTs) and

electronic voltage transformers (EVTs) have achieved high

performa nces with a very small size In addition their

digital output com plies with the m ost stringent requirement of

the digitized integrated substation system. The ECTs and

EVT s play a sen sing and digitizing role for current and voltage

M. Saitoh, T. Kimura, Y Minami, N. Yarnanaka,

S.

Maruyarna, T.

Nakajima, and M. Kosakada are with Toshiba Corporation, Tokyo, Japan

(e-mail: [email protected]).

information with the processing cap abilitie s of digital

electronics. The designs of ECTs and EVTs are based on IEC

60044-8 and IEC 60044-7 respectively, and take into account

the harshest environm ental cond itions of temperature,

vibrations, and electromagnetic compatibility. On the other

hand the designs of the digital output interfaces of the digital

electronics are based on IEC

61850-9.

The ECTs and EVTs

link up with protection relay units, Bay C ontrol Units (BCUs),

Control and Monitoring Units (CMUs) mounted on primary

equipment instead in the local co ntrol cubicle, via the process

level

LAN.

The sensed current and voltage information are

transmitted to them as optical digital signals. By do ing this, the

primary equipment and substation system wiring can be

simplified due to the extensive use of optical fibers for

communication of current and voltage information, operating

commands, state condition of primary equipment, and

so

on.

This also lead to important savings in civil engineering at the

time of installation. In addition, the compactness and

economics of the substation facilities are improved, which is

always an advantage.

This pa per discusses the electronic instrument transformers,

which are applied for digitized substation systems integrated

with primary equipment. The optimum system configuration

and the reliability of the electronic instrument transform ers are

described. T he results of performance that can b e achieved by

the electronic instrument transformers are evaluated.

11. GENERALONFIGURATION OF ELECTRONIC T S AND

VTS

A . The System Configuration

o

Electronic CTs and

VTs

Fig. 1 shows an example of the system configuration of

electronic CTs and VTs. The ECT is based on the principle of

a Rogowski coil by taking into account of saturation free

characteristics and economical efficiency. As for the voltage

detection se nsor of EVT , a capacitive voltage divider of high

reliability a nd simple insulated construction was applied.

Sensing Units (SUS) are arranged near the Rogowski coil

and the capacitive voltage divider on each bay, respectively,

and one Merging Unit (MU) is provided. Each SU is

connected to the MU by optical fiber, and the MU is

connected to the process bus by optical fiber. In order to

secure high reliability, all Rogowski coils,

SUS,

MUS, and

process bus are duplicated, except for the capacitive voltage

divider. The E CT and EV T are designed based

on

I E C 60044-

8 and IEC

60044-7 ,

respectively.

0-7803-7525-4/02/$17.00 002 IEEE. 459


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Time

Synchronizat ion

Signal

Fig. 2 The View

of

Printed Circuit Board Type Rogowski Coil.

D. SU MU, and Process Bus

The analogue voltage signals from the Rogowski coil and

he divided vo ltage signals are con verted into digital signals at

Processus

- -

-

each

SU,

synchronized by a time synchro nization signal from

the MU, and transmitted to the MU. The MU adds time stamps

to the sampled digital signals from each SU, and merges them

Fig. 1The System Configuration of Electronic CTs and VTs.

B.

Rogowski Coil

A known p roblem regarding Rogowski coils without an iron

core is the large ratio error that results from manufacturing

difficulties, such as lack of uniformity for coil pitch or coil

cross section, and changes in the operating temperature

conditions. In order to solve this problem, the authors

developed the Rogowski coil by making coils in the form of

patterns on printed circuit board. By applying the

manufacturing technology of the printed circuit board it

became possible

to

manufacture the Rogowski

coil

with

a

uniform and highly prec ise winding pitch.

As

a result, a very

small and high accuracy Rogowski co il is achieved, suc h as the

printed circuit board type Rogowski coil shown in Fig. 2. As

the energized part of ECTs utilizing Rogowski coils are very

small, it is possible to integrate them directly not only on a

dead tank type circuit breaker

or

gas insulated switchgear

(CIS) but also on a live tank type circuit breaker or air

insulated switchgea r (AIS). By do ing this it is possible to limit

the number of insulators and the architecture of the substation.

C. Capacitive Voltage Divider

The high-voltage side capacitor of the capacitive voltage

divider is formed with the primary electrode at the high

voltage conductor and the middle electrode floating. The

dielectric is the gas used in switchgear: pure SF6. Using a

capacitive voltage divider, the risk of the ferroresonance

phenomena can be restricted. CIS size can be reduced

drastically by adopting the developed Rogowsk i coil and

capacitive voltage divider instead of conventional

CTs

and

VTs.

to comb ined serial current and voltage data, an d transmits this

data to a protection relay unit and bay control unit via the

process bus.

The time-synchronization function of the MU utilizes the

timing signal from a sampling master, for instance it may

generate the sampling signal based o n the standard signal of

the Global Positioning System (GPS). The time signal is

shared within the substation.

The process bus connects the MU for ECTs and EVTs,

protection relay units, BCU s and CMUs. T he process bus uses

the standard communication protocol of IEC 61850-9 for

interoperability.

In

the digitized integrated su bstatio n, primary

equipment and substation system are connected by process

level LAN, for almost all the information in the substation,

such as sampled digital values o f the currents and the voltages,

operating commands, state condition of primary equipment.

Th e digital interface of the MU and the transmitted data frame

is designed based

on

IEC 61850-9,

so it

is suitable to apply

ECTs and EVTs to the digitized integrated sub station.

111. I-AIS

w m

LECTRONICTs

I-AIS

[41 is Toshiba’s new concept high voltage switchgear.

The switchgear is an integration

of

live tank type gas circuit

breaker, live tank type disconnector, earthing switch and

electronic CT,

so

called Integrated Air Insulated switchgear (1-

AIS). The

I-AIS

ith

ECT

is described here.

A. Configurationof I-AIS with Electronic CT s

Fig. 3 shows the system configuration of 245kV I-AIS with

Electronic CT. he Rogowski coil and

SU

are mounted at top

of the circuit breaker charged to a high-voltage. Power to

supply the SU with a high-voltage potential is transmitted as

laser light from a Laser D iode Unit (LDU) at ground potential.

The SU at high-voltage potential and the MU at ground

460


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potential are connected by high-voltage optical sens or link that

is optical fiber cable with insulator, so the Rogowski coil and

the

S U

is insulated completely against the

M U

at ground

potential. The analogue signal from the Rogowski coil is

converted into 16bit optic digital signal at the SU, and is

transmitted

to MU

through the optical fiber insulator.

The specification of Electronic

CT

for 245kV

I-AIS

is

shown in Table 1

For Protection :OlCF H

B.

Experimental Results

1 Linearity

of

Current M easurements

The linearity of current measurements of the E CT applying

a printed circuit board type Rogowski coil with SU is shown in

Fig. 4. The ratio error at 200

% In

and

1 % In (In =

3150

A)

are

0.02

%

and 0.68

%

respectively. The EC T satisfies fully

the accuracy lim it of IEC C lass 0.5.

The ratio error of the printed circuit board type Rogowski

coil alone is less than 2 0.1

%

under the primary current

between

1%

In

and 200

% In

(not shown).

1.5

1

-

0.5

B

0

.-

2

0.5

-1

1.5

0 1000 2000 3000 4000

5000

6000 7000

Primary

Current [A]

0 1000 2000 3000

4000 5000 6000

7000

Primary

Cumnt

[A]

F O ~

rotection :

EC

Class 5~

Standard IEC60044-8

100

80

60

B 40

-

-

g 20

- 0

g

-20

-40

e

-60

80

100

(a) I-AIS ith ElectronicCT.

Fig. 4 The Linearity

of

Current Measurem entsof Electronic

CT.

2 Temperature Characteristics

The temperature characteristic of the ECT applying the

printed circuit board type Rogowski coil with SU is show n in

Fig. 5 . Under an operating temperature range between -40

C

and +60

C,

the ratio error drift of the ECT

is

less than +0.1 %

and the drift of phase displacement is less than d 0 min

without temperature compensation.

The temperature characteristic of the printed circuit board

type Rogowski coil alone is less than

2 0.05 %

of the ratio

error and less than 2 min of the phase displacement under an

operating temperature range between

-40

C and

+60

C (not

shown) when the burden (pure resistance), normally mean

of

the input impedance

of

SU, is suitably chosen.

In

the case of

I

AIS

the input impedance of the

S U

was set to 1.25

kQ.

@) Merging U nit (Left) and Laser Diode U nit (Right) at ground potential.

Fig.

3

The System C onfigurationof 245kV I-AISwith ElectronicCT

46

1


4/6

60 40

-20

0

20 40

60 80

Temperature [“c]

30

I I I

I I I

60 40 -20 0 20 40 60 80

Temperature

[“c]

Fig. 5 The Temperature Char acteristicof Electronic

m.

3 Transient Response

For protection purposes the transient response of the ECT t

the time of fault current is important. Fig.

6

shows the

ECT

secondary output waveform (digital signal waveform) (lower)

and primary current waveform measured with a shunt (upper)

which were recorded in a 50 kA short circuit current breaking

test with 52 % DC component. The Rogowski coil is linear, so

that no saturation occurs even when

a

large current

of

several

lOkA with DC component is measured.

Another problem concerning conventional C T s is the low

frequency characteristic, which can be defined as a

transmission time constant. In contrast to conventional C T s

where the DC transmission performance is a characteristic

which can not be adjusted, the ECT allows the time constant to

be adjusted according to the specifications of the customer.

This is done in the digital processing

of

the MU.

IV. ELECI’RONICVTS M)R AIS

A .

Configuration of Electronic VTsfor

AIS

Fig. 7 shows Electronic VT or 245kV AIS The reduced

size and weight compared to a conventional oil-filled

VT

allows placement in a compact substation.

A

capacitive

voltage divider with an SF 6 gas capacitor as the high-voltage

side capacitor and a mica capacitor as the voltage divider

capacitor is constructed in the lower tank on ground potential.

The

SU

is arranged near the lower tank and the power to

supply the SU is

DC

l lOV. The S U is connected to the

MU

by

optical fiber.

60

40

20

3 0

c

= -20

f -40

-60

E 80

120

-1

40

a 100

60

40

3

20

g

20

4 0

-40

-60

80

100

120

-140

I

t

\ I

v

I

0 20 40 60

EO

100

Time

[ms]

+

+

+ +

+ +

+ ++

0

20 40 60 80 100

Time [ms]

Fig.

6

The ECT econdary Ou tput Waveform (Lower) and Primary Current

Waveform measured with a Shunt (Upper) which were R ecordedin a

50

kA

Short Circuit Current Breaking T est.

The analogue signal from the capacitive voltage divider is

converted into 16bit digital signal at the SU, nd is transmitted

to the MU that is the com mon unit with the ECT which merges

the sampled signals of ECTs and

EVTs

to combined serial

data.

The specification

of

the Electronic

VT

or

245kV

AIS

is

shown in Table 2.

Fig.

7

The Electronic

V T

or245kV AIS

462


5/6

Rated Primarv Voltaee I

245

/

\13

kV

Rated Frequency

Rated Secondar y Output

(16bit Digital Output)

Sampling Rate

Accuracy Class

Standard

5 O H z l 6 o H z

For measuring

:

2D41 H

For Protection

:

2D41

H

2.4

lrHz

or50Hz

2.88 kHz for 60Hz

For measuring

:

EC Class 0.5

For Protection : EC Class 3P

IE C6 0 0 4 4 - 7

(Decimal : 1585)

(Decimal : 11585)

B. Experimental Results

1 Linearity of Voltage Measurements

The linearity of Voltage Measurements of the capacitive

voltage divider for EVT is shown in Fig. 8. The ratio error of

the capacitive voltage divider is less than 0.1

%

under the

primary voltage between 2

Vn

and 150%

Vn

(Vn

=

245h/3

kV). It is suggested that the EVT with the SU and the

capacitive voltage divider satisfy fully the accuracy limit of

IEC C lass 0.5.

-4

...........

J . . . . . . . . . . . . .

L..........

,

U

0

20

40 60

80 100 120 140 160

Primary Voltage [%Vn]

:

00 Vn

= 245 /

$3

3An

zoo

160

1

80

8

-

0

9 40

6

$ -80

-

g 120

40

g -120

-160

-200

I

I I

I I I

I

I I

.

-__

0

20

40

60

80 1 0 0

120

140

160

Primary Voltage [%Vn] : 100%Vn

=

245 / 3

Fig. 8 The finearity of Voltage Measurementsof Capacitive Voltage Divider

for

Electronic

VT.

2 Temperature Characteristics

The temperature characteristic of Voltage Measurements of

the capacitive voltage divider for EVT is shown in Fig. 9.

Under the operating temperature range between

-20 C

and

+60

C, the error drift of the capacitive voltage divider is less

than 0.1 % without temperature com pensation.

0.5

0.4

0.3

0.2

0.1

-

g o

;0.1

w

a

.-

-0.2

-0.3

0.4

-0.5

I

-20

-10

0

10

20 30 40 50 60

Temperature [ c]

Fig. 9 The Temperature Characteristicof Capacitive Voltage Divider for

ElectronicVT.

V INTEGRATED GIS

m

L E ~ O N I C

Ts

AND VTs

Fig.

10

shows the system configuration of the GIS with

electronic C T s and VTs

for

the digitized integrated substation.

The SUS are attached close to the printed circuit board type

Rogowski

coils and the capacitive voltage dividers

respectively. The M U is mounted on the primary apparatus in

the

GIS

application as part of the Process Control Unit (PCU)

which is an integrated unit of protection relay unit (PU),

control unit (CU) and MU. The PU, CU, MU, and CMU

(instead of local control cubicle) are interfaced with each other

via the process bus, and the station bus links these components

to

the station control unit (SCU). Information

on

the station

bus

is

transmitted to the remote office through the remote

terminal unit (RTU) r the gateway (GW).

Control

Room

Equipment

Yard

PC U Process Control Una

CU: Contro l unit

PU: Protectionunit

MU: Merging unit

SU: Sensing un il

G W

Gateway

ECT: Electronics Current ransformer

EVT: ElectronicsVoltage ransfo rmer Bui -n

CMU: Controland monilor ingunit

BP:Bus protectionunit

SCU: S ta l in umt ro l un i t

HMI: Human interface

RTU: Remote erminal unit

Fig. 10 The System Configuration of the GIS with Electronic C T s and

VTs

for the Digitized Integrated Substation.

463


6/6

Almost all the information in the digitized integrated

substation, such as current and voltage information, is

transmitted as digitized data via the process bus and station

bus, so that easy data acquisition of such digitized data is

possible not only for operational, engineering, maintenance

staff in operation center but also for sales, marketing, quality

engineering, and management people at remote places.

VI. CONCLUSIONS

Electronic instrument transformers, which are applied to

digitized substation systems integrated w ith primary equipment,

were developed. The system has following features.

(1)

The EC T is based

on

the principle of a Rogowski coil of

printed circuit board type, and the

EVT

applies a capacitor

voltage divider principle.

(2) The analogue voltage signals from the Rogowski coil

and the divided voltage signals are converted into digital

signals at each SU, and the MU merges sampled digital

signals to combined serial data, and transmits it to a

protection and control unit via the process bus.

(3)

Almost all the information in the digitized integrated

substation, such as current and voltage information, is

transmitted as digitized data, so that people from various

places should be able to access the required information.

(4)

The configuration and the experimental results of

ECTs

and EVTs, which are applied for I-AIS, AIS, GIS in

digitized integrated substation, were presented. The linearity

of current and voltage measurement, temperature

characteristic, transient response show ed good performance.

(5) The electronic CTs and VTs on primary equipment can

be connected with protection and control unit via process

bus using standardized protocol instead of a huge number of

wire cables. Therefore civil work for the cable pit, and wire

connection and check work w ill be greatly reduced.

VII.

REFERENCES

(11

A. Kaczkowski

et

al, “Combined sensors for current and voltage are ready

for applications in GIS”, CIGRE 1998 session 12-106

(21

J.

P. Dupraz et al, “The integration of electronic a s nd VTs in power

switchgear : challenges and choices”, CIGRE 2000 session 12/23/34/-01

(31 R. Gross, et ai, “Substation control and protection system for novel

sensors”, CIGRE 2000 session 12/23/34/-03

[4] A.

Kobayashi,

et

al,

“252kV

New-Concept Integrated Air-Insulated-

Switchgear”, The Beijing International Conference Power Transmission

and Distribution Technology 2001, p.743

VIII. BIOGRAPHIES

Minoru Saitoh received his

B.S.

nd M.S. degree in electrical engineering

from Science University of Tokyo in 1992 and 1994 respectively. In 1994, he

joined Toshiba Corporation. Since then, he has been engaged in the

development and design of Non-conventional

CTs

and VTs, and control,

monitoring and diagnostic system of gas-insulated switchgear. MI. Saito is a

member of IEE of Japan and a member of the Japan Society of Applied

Physics.

Tatsuya Kimura received his B.S. nd M.S. degree in electrical engineering

from Doshisha University in 1990 and 1992 respectively. In 1992, he joined

Toshiba Corporation. Since then, he has been engaged in the research and

development of communication system and sensing system. MI. Kimura is a

member of IEICE of Japan.

Yyii Minami

received his B.S degree in control engineering from Kyushu

Institute of Technology in 1991. In 1991, he joined Toshiba Corporation.

Since then, he has been engaged in the development of diagnostic technology

of electronic device, the development and design of power protection relay.

Mr. Minam i is a member of

IEE

of Japan.

Naoyoshi Yamanaka received his B.S degree in electrical engineering from

Hiroshima Institute of Technology in

1990.

In

1990,

he joined Toshiba

Corporation. Since then, he has been engaged in the development and design

of power protection relay.

Shiro Maruyama received his

B.S.

and M.S. degree in electrical and

electronics engineering from Nagoya University in 1980 and 1982

respectively. In

1982,

he joined Toshiba C orporation. Since then, he h as been

engaged in the development and design of high-voltage gas-insulated

substations and their monitoring and diagnostic system. MI. Maruyama is a

member of DEE of Japan.

Takashi Nakajima

received his

B S

and M.S. degree in electrical

engineering from Yamagata University in

1976

and

1978

respectively.

In

1978, he joined Toshiba Corporation. Since then, he has been engaged in the

development and design of high-voltage gas-insulated substations (GIS) and

their monitoring and diagnostic systems. Mr. Nakajima is a member of E E of

Japan.

Masayuki Kosakada (M’1991) received his

B.S.

degree in electrical

engineering from the University

of

Tokyo in 1986. In 1986, he joined To shiba

Corporation. Since then, he has been engaged in system engineering of

substation equipment such as gas-insulated switchgear, circuit breaker,

transformer and substation system. MI. Kosakada is a member of IEEE and

IEE of Japan.

464

electronic instrument transformer

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