application of electronic inst transformer

8/18/2019 Application of Electronic Inst Transformer

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Abstract --Embarking from the sensing principle of electronic

transformer, the paper introduced the type and the constitution

of electronic current transformer and electronic voltage

transformer. By comparing the active and passive optical

transformer in our country, we pointed out that the passive

optical transformer have excellent measurement quality, it also

have the same practical conditions as the active optical

transformer. The paper elaborated the application project of

electronic transformer in digital substation, and pointed out that

the using of electronic transformer would accelerate the

application of digital substation from the experiment site to the

popularization.

Index Terms--Adaptive optical current transducer (AOCT);

Adaptive optical voltage transformer (AOVT); Digital substation;

Electronic current transformer; Electronic voltage transformer

I. I NTRODUCTION

ITH the development of digital technology, digital

substation [1] will become the inevitable trend of

substation construction after the synthesis automation

technology. As an important part of digital substation,

electronic transformer signal measurement quality and

running stability are the important guarantee of substation andelectric network steady operation. After several decades of

research and development, electronic transformer with

different principle now has been widely used in different

voltage class’s substation. This paper mainly introduced

electronic transformer and its application in the substation

combining with many years’ research results of electronic

transformer in the author’s team.

Hongxing Wang is with School of Electrical Engineering and Automation,Harhin Institute of Technology, Haerbin, China (e-mail:[email protected]).

Guoqing Zhang is with School of Electrical Engineering and Automation,Harbin Institute of Technology, Haerbin, China. (e-mail:[email protected]).

Zhizhong Guo is with School of Electrical Engineering and Automation,Harbin Institute of Technology, Haerbin, China. (e-mail: [email protected]).

Jiaying Wang is with School of Electrical Engineering and AutomationHarhin Institute of Technology, Haerbin, China (e-mail:[email protected]).

Xingguo Cai is with School of Electrical Engineering and Automation,Harbin Institute of Technology, Haerbin, China. (e-mail:[email protected]).

978-1-4244-1762-9/08/$25.00 ©2008 IEEE

II. THE PRINCIPLE AND PRACTICAL PROGRESS OF ELECTRONIC

TRANSFORMER

Electronic transformers which have analog quantity voltage

output or digital output are used for frequency of 15~100 Hz

electrical metering equipment and relay protection device [1-

2]. It includes all kinds of power system transformer with

electronic measurement output, covers a variety of

measurement principles, methods and measuring transmission

[3]. According to the sensing part whether needs to provide

source, the electronic transformer can be divided into activetransformer and passive transformer, the main principle of two

kinds of transformer is shown in TABLE I.

TABLE ITHE MAIN ACHIEVE PRINCIPLE OF ELECTRONIC TRANSFORMER

Current Transformer Voltage Transformer

ActiveFaraday’s law of

electromagnetic inductionVoltage divider

PassiveFaraday magneto-optic

effectPockels effect

Converse piezoelectric effect

Compared with the traditional transformers, the electronic

transformers have some advantages, such as simple insulation,

wide dynamic range, wide measuring frequency bandwidth,

small volume, light weight, anti-electromagnetic interference,and easy digital signal transmission, which are receiving the

universal attention and applying gradually in the project [2].

A. Electronic Current Transformer

1) Active Electronic Current Transformer:

The active electronic current transformer is mainly divided

into two kinds, the Rogowski coil transformer and the low

power loss iron core coil transformer. The basic principle of

low power loss iron core coil transformer is the same as

traditional electromagnetic transformer. The low power loss

iron core coil transformer is mainly used in measuring the

metering signal. The Rogowski coil is the air coil winded onthe non-ferromagnetism skeleton, so it avoid the problem of

magnetic saturation and magnetic hysteresis et al.

The operating principle of Rogowski coil current transformer

is shown in Fig.1.The current-carrying conductor passes

through the centre of coil. When the current is passing through

the conductor, there will be an induced electromotive force e

in the both ends of the coil. The relationship between e and

primary current is shown in (1).

0( )2

NS Mdi die t

dt R dt

µ

π = − = − × (1)

Application of Electronic Transformers inDigital Substation

Hongxing Wang, Guoqing Zhang, Zhizhong Guo, Jiaying Wang, and Xingguo Cai

W



Where μ0 is the vacuum magnetic permeability; N is the turn

number of coil; S is the cross-sectional area of per turn coil; R

is the distance between coil center and conduction bar center.

As can be seen from (1), the output voltage of Rogowski coil

are proportional to current slew rate, if acquiring the integral

of output voltage, the value of primary current is gained.

LED (light-emitting diode) is light source of LEDFig. 1. The structure diagram of Rogowski coil current transformer.

The Rogowski current transformer based on Faraday’s law of

electromagnetic induction solves the problem of

electromagnetic saturation, but it cannot be used to measure

steady direct current according to its basic principle. It also

can not assure the accuracy in measuring the slow change non-

periodic component. The Rogowski current transformer can

not reconstruct the change of dynamic current completely [3]

because the measured frequency bandwidth is limited by the

principle of measurement.

2) Passive Electronic Current Transformer:

The passive electronic current transformer is also called

optical current transformer (OCT) which realize the primary

current measurement by using of optical principle, and at

present more researches are mainly based on the principle of

Faraday magneto-optic effect. As shown in Fig. 2, after thelinear polarized light pass through Faraday magneto-optical

material in magnetic field, the polarization plane will be

deflected. The relationship between deflection angle θ and

magnetic intensity is:

∫= L Hdl V µ θ (2)

Where μ is the magnetic permeability of magneto-optical

material, V is verdet constant of magneto-optical material, L is

the polarized light optical path length in the magneto-optical

material, H is the magnetic intensity.

Fig. 2. The principle of Faraday magneto-optic effect.

As shown in (2), the deflection angle is only proportional to

magnetic intensity; therefore, the principle of Faraday

magneto-optic effect has good measurement linearity, not only

can measure the changing current, but also can measure the

steady continuous current [3-8]. The optical current

transformer based on the principle of Faraday magneto-optic

effect avoids the question of measuring frequency band in

measuring principle [3-8]. However, temperature drift of

measurement accuracy and long-term operation stability arethe two major technical problems impeding the application of

optical current transformer practical. The subject term

composed by Harbin Institute of Technology and North China

Electric Power University proposed achieve principle of

adaptive optical current transducer (AOCT) [4]. The AOCT

obtained the high accuracy stable state measurement result by

using adaptive method to solve the temperature drift of

measurement accuracy. The AOCT has ideal dynamic

response capability under trouble circumstance, and it also

solved the instability of optical material in long-term running

by using solenoid collecting magnetic field optical structure,

which enabled OCT to achieve the practical degree. The OCT

is operating well in Baoding electrical network for 25 months.The test result [3-4] indicated that the stable state measuring

accuracy grade of AOCT can reach to 0.2 and maximum peak

instantaneous error of non-periodic component electric is less

than 士 1%. Fig. 3 is the 110kv OCT developed by our

research term. It has a good running state since it is installed

in the XGZ substation in Heihe city in Heilongjiang province

in November 2007.

Fig. 3. The 110kV optical current transformer running in the XGZ substationin Heihe city.

Both Rogowski coil current transformer and optical current

transformer have no saturated characteristic, the former can’t

effectively deliver changing direct component-current and low

frequency component current, but the latter doesn’t have

survey band limiting and can obtain entire fidelity current

waveform of primary current. So the latter’s dynamic

measurement quality is better than the former.

Polarization Plane RotationAngle of Polarized Light θ

Magnetooptic Material

Incident Light

PolarizeEmergent Light

Polarized Light

Magnetic Field Comingfrom Measured Current B Detector

PIN TypePhotodetector

Metering

A/DConvertor LED

Optical Fiber

Protection

SignalProcess

IntegralTransformation

Coil

Bus Bar

i



B. Electronic Voltage Transformer

1) Active Electronic Voltage Transformer:

The realize form of active electronic voltage transformer

mainly have resistor divider, capacitive divider and series

induction voltage divider. The structure diagram of active

voltage transformer is shown in Fig. 4. After going through

the divider, pretreatment, A/D convertor, and LED

transformation, the measured high voltage was delivered to

control room as the form of digital optical signal. the

measured high voltage will undergo electro-optical

transformation and the corresponding signal processing which

processed by PIN control room and the signal processing

circuit, then the electronic signal which applied to

microprocessor protection and metering will be exported. The

key technology of active electronic voltage transformer is the

stability of the sensor measurement accuracy, source supply

technology, long-distance electronic module’s reliability and

maintainability.

Fig. 4. The structure diagram of active electronic voltage transformer.

At present, the highest level of voltage transformer based on

resistor divider is only 132 kV. It nearly can not used in

practice because of the limitations of the resistance power and

accuracy in UHP net work [9]. The advantage of high-voltage

measurement system based on capacitance divider is

obviously analyzed from the measurement principle, but this

kind of transformers have more serious flaw in primary

sensing structure and the electromagnetic shielding. So its

application still needed to gain more project experience and

there is no successful project application report at present. In

recent years, some researchers have developed a series of

induction divider measurement system by using of non-

saturable reactor to divide voltage [9]. It has been applied in

the project. But this principle is still used sentimental iron

coil. Compared with the traditional voltage transformer,

ferroresonance still exists.

2) Passive Electronic Voltage Transformer:

The Passive electronic voltage transformer is usually named

as optical voltage transformer (OVT), the measure principle of

OVT is divided into two kinds: one is based on Pockels effect

and the other is based on converse piezoelectric effect. The

present study and application is focused on the OVT based on

the Pockels effect, and the product has been on sale. The OVT

based on converse piezoelectric effect has the advantages of

simple optical system and low cost, but its application is

limited by the need of special fiber and the complicated

adjusting of signals [10].

The Pockels effect suggest that the refraction index of some

crystal will be changed under the effect of externally electric

field, the change of refraction index will induce obviously

optical effects. Under the effect of externally electric field, alinearly polarized light will be separated into two beam with

the polarization direction vertical to each other when it pass

through the electro-optic crystal, the phase difference δ is in

direct proportion to the voltage, which is expressed as (3).

π

π δ

U

U kE == (3)

Where E is the externally electric field in crystal, k is a

constant related to the crystal properties and the incidence

wavelength. U is the externally voltage added in crystal. Uπ is

the half-wave voltage of the crystal, half-wave voltage is the

externally voltage added in crystal when the phase difference

of two birefringence beam induced by Pockets effect reachto 180°. If we transfer the changing of phase difference to the

changing of output light intensity, we can get the voltage after

the optic-electronic transform and the corresponding signal

processing. Fig. 5 is the principle picture of the optical voltage

transformer.

Fig. 5. The principle diagram of optical voltage transformer.

The method of measuring voltage based on the Pockels effect

is same with the method of measuring current based on the

Faraday magneto-optic effect, so is the advantages and

disadvantages. So far the stability in long-running of theoptical voltage transformer is a technique difficult in the

process of practicality and productivity [10-12]. The author’s

research team have dedicate to the study of the adaptive

optical voltage transformer (AOVT). Benefiting from the

successful experience of adapting optical current transformer,

we studied the adapting optical voltage transformer with

closed loop system properties. We do believe that the adaptive

optical current transformer will realize practicality quickly.

Comparing the active electronic voltage transformer based on

the principle of voltage divider to the passive electronic

Optical FiberOptical Fiber

Collimating

Lens

Polarizer

X1 λ/4

Waveplate

Collimating

Lens

X3 X2

Detector

Electro-optic Crystal

LEDSignal

Process

V

PIN Type

Photodetector

High-voltage Bus Bar

Metering

Z1

A/D

ConvertorSignal

Pre-process LED

Z2 Optical Fiber

Protection

PIN TypePhotodetector

SignalProcess

Voltage

Divider



voltage transformer based on the principles of optics, both of

them can solve the problem of ferromagnetic resonance. But

the sensor of the former is affected by the capacitance, so the

measurement accuracy is bad. However, the latter have

excellent linearity and measurement precision; moreover, it is

passive and not effected by the electromagnetic interference.

All of the advantages of the passive electronic voltage

transformer made it become an ideal project of independent

installed voltage transformer. It will be realized practicalityafter avoiding the effects of temperature and the vibration

completely.

III. APPLICATION OF ELECTRONIC TRANSFORMERS IN DIGITAL

SUBSTATION

Digital substation is a modernization substation which can

realize the information sharing and interoperability between

the intelligent devices. It is layer-by-layer constructed by the

electronic transformers, the primary intelligent devices, and

the secondary networking equipment on the bases of the

IEC61850 protocol [13-15]. The system of digital substation is

compartmentalized to process level, bay level and station level

according to IEC61850. The functions of the process level are

achieved by the devices of the bay level in the existing

system. With the application of the electronic transformers

and intelligent switching technology, the separation of the

process level functions separated from the bay level device

has become an inevitable trend in the future Digital substation.

The primary requirement of the digital substation is to realize

digital measurement output in process level, this is the final

demand to the secondary output of the new transformer.

Electronic transformer can transmit digital signal of samples,

which is most compatible to be used in digital substation.

Nowadays, transforms based on different principles are being

applied in engineering. However, optical transformers haveexcellent quality of dynamic measurement. A set of optical

transformer can realize measurement, metering, control,

protection and fault recorder in the same time, so it has a

greater potential in the application of digital substation. As is

shown in Fig. 6, the optical measurement system (OMS)

which face to the bay lever is composed of optical voltage

transformers, current transformers and merging unit (MU), a

merging unit is the digital interface between electronic

transformers, intelligentzed primary facility and the secondary

facility. In this system, optical voltage transformers, current

transformers and merging unit are the facilities of process

level, and microcomputer protecting equipment and interval

control device belong to the facilities of bay level. The outputsof optical voltage and current transformers are digital signals

and communicate with MU on 10M Ethernet following IEC

61850-9-1 point-to-point one-way communication protocol.

MU communicates with microcomputer protecting equipment

of 100MB Ethernet following IEC 61850-9-2 one-to-many

one-way communication protocol. This can insure the

rapidity, reliability and anti-interference capability of

sampling data transmission. The OMS is the basic measuring

unit of constructing digital substation. With the development

and practicality of electronic transformer, OMS will be widely

applied in process level.

Fig. 6. The block diagram of Bay-oriented optical measurement system.

Electronic transformer as the decisive equipment for building

the digital substation, the applied situation at the site is stillneed accumulate experience. There also exist the problems of

communication reliability and network organizing in the

process level. Therefore, the process level of digital substation

should be realize gradually according to the first system

requirements, it should be first pilot operate in a single

interval, then promote to the whole substation after

accumulating enough operating experience, and then realize

the digital for the whole substation.

IV. CONCLUSION

The electronic transformer is the basic equipment to

construct digital power system. The electronic transformerwill operate on basic measure in modern power system.

Compared with tradition transformer, the electronic

transformer is superior in insulation, dynamic range,

saturation capability, bulk, price et al. These advantages will

be more obvious with the enhancement of voltage grade. At

present, Many electronic transformers have run into operation,

for example, the six adaptive optics current transformers

(AOCT) developed by Harbin Institute of Technology and

North China Electric Power University cooperating with two

sets of WXH-823 computer-line protection form the fiber-

optical current differential protections, this device has been put

into test operation in an 35kv power plant grid connection tie-

line between power grids in Baoding SCY substation andKGZ substation, and has been operating well yet. As an

important component of digital substations, the electronic

transformer will be generalizing application in power system

after accumulating of operating experience. It also will speed

up the development of digital substations from the pilot to

wider application. It made the realization of the power system

protection, control, measurement, data communications

integration become possible.

OMS=OCT+OVT+MU

To Station Level

Process Level

OCT

OVT

Ethernet

Merging Unit

MicrocomputerProtective Device

BayControll

Bay Level



V. R EFERENCES

[1] D. K. Xu, H. S. Tang, and Z. J. Sun, “Application of ElectronicInstrument Transformer in Digital Substation,” Electrical Equipment,Vol. 9, No. 3, pp. 12-16, Mar. 2008.

[2] C. M. Luo, G. X. Zhang, and P. Wang, “Electronic Type InstrumentTransformer and Its Present Technical Development Manner,” ElectricalEquipment, Vol. 8, No.1, pp.20-23, Jan. 2007.

[3]

Z. Z. Guo, “Comment on the Research of Electronic CurrentTransformers,” Relay, Vol. 33, No. 14, pp. 11-14, Jul. 2005.

[4] Y. S. Li, Z. Z. Guo, Y. H. Yang, W. B. Yu, G. Q. Zhang, and H. Gao,

“ Research on the Basic Theory of Adaptive Optical CurrentTransducer,” Proceedings of the CSEE, Vol. 25, No. 22, pp. 21-26, Nov.2005.

[5]

Q. F. Shang, “Practicability Research on Optical Current Transformer,”Ph.D. dissertation, Univ. North China Electricity Power, School ofElectrical and Electronic Eng., 2005.

[6] W. B. Yu, “Temperature Characteristic Research on Irradiance ofOptical Current Transformer,” Ph.D. dissertation, Haerbin Institute ofTechnology, School of Electrical Engineering and Automation, 2005.

[7] Y. S. Li, “High-precision Self-adaptive Optical CT and Its StabilityResearch,” Ph.D. dissertation, Univ. North China Electricity Power,School of Electrical and Electronic Eng., 2004.

[8]

G. Q. Zhang, “Theory and Practicability Research on Optical CurrentTransformer,” Ph.D. dissertation, Haerbin Institute of Technology,School of Electrical Engineering and Automation, 2005.

[9] D. X. Huang, Z. J. Sun, and Y. L. Chen, “An inductive High VoltageDivider with Digital Output using Optoelectronic Modules,” High

Voltage Apparatus, Vol. 41, No. 2, pp. 143-145, Apr. 2005.[10]

S. N. Luo, “Theoretical and experimental study on Electronic CurrentTransducers and Voltage Transformers,” Ph.D. dissertation, HuazhongUniversity of Science and Tech., College of Electrical & ElectronicEng., 2001.

[11] Y. G. Cheng, H. J. Liu, Y. X. Li, X. F. Meng, and M. J. Zhang, “BasicPrinciple and Current Development of Optical Voltage Transformer,”Electric Power Automation Equipment, Vol. 24, No. 5, pp. 87-90, May.2004.

[12]

X. Xiao, “Theoretical and experimental study on Electronic CurrentTransducers and Voltage Transformers,” Ph.D. dissertation, HuazhongUniversity of Science and Tech., College of Electrical & ElectronicEng., 2003.

[13] Y. W. Chen, “Practical Research on digital substation,” M.D.dissertation, Univ. Zhejiang, College of Electrical Eng., 2007.

[14]

X. Gao, and P. C. Zhang, “Main Features and Key Technologies of

Digital Substation,” Power System Technology, Vol. 30, No. 23, pp. 67-71, Dec. 2006.[15] L. X. Li, P. Q. Miao, and J. F. Wang, “Analyze and Implementation of

Substation Automation System Based on IEC 61850 Standard,” PowerSystem Technology, Vol. 30, Supplement, pp. 321-324, Oct. 2006.

VI. BIOGRAPHIES

Hongxing Wang was born in Hebei province

in China, 1977. He is now a Ph.D. candidate of

Harbin Institute of Technology. His main

research areas are optical measurement technique

and its application in power system.

Guoqing Zhang was born in 1969, china. He

is now an assistant professor of Harbin Institute

of Technology. His main research areas are

optical measurement technique and its

application in power system.

Zhizhong Guo was born in 1961, China. He

has been a professor of Harbin Institute of

Technology from 1994. From 1999, he worked at

Beijing XJ Electric CO., LTD, China. His main

research areas are informatization, automation

and optimization of power system, stability

analysis and control for power system and

optical measurement technique.

Jiaying Wang was born in 1981, china. She

is now a Ph.D. candidate of Harbin Institute of

Technology. Her main research areas are optical

measurement technique and its application in

power system.

Xingguo Cai was born in 1945, china. He isnow a professor of Harbin Institute of

Technology. His main research areas are

informatization, automation and optimization of

power system, stability analysis and control for

power system.

application of electronic inst transformer

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