Transformer Model for TRV.pdf

The International Conference on Electrical Engineering 2009

1

Transformer Model for TRV Calculation at the Transformer Limited Fault Condition by EMTP MYOMIN Thein, Non-member, IKEDA Hisatoshi, Fellow, IEEE , , HARADA Katsuhiko, Nonmember, OHTSUKA Shinya, Member, IEEE, HIKITA Masayuki, Senior Member, IEEE, HAGINOMORI Eiichi , Non-member, and KOSHIDUKA Tadashi, Member, IEEE,  Abstract-- The transient recovery voltage (TRV) of the transformer limited fault (TLF) current interrupting condition was investigated with several transformers by using current injection (CIJ) method. A transformer model for the TLF condition is treated as leakage impedance and a stray capacitance with an ideal transformer in a computation by EMTP. By using the frequency response analysis (FRA) measurement, the transformer constants were evaluated at high frequency regions. FRA measurement graphs showed that the leakage inductance value of the test transformers gradually decreases along with the frequency. The TRV which is obtained by experiment and EMTP simulation gave the reasonable agreement. Index Terms-- Accurate impedance value, EMTP, frequency response analysis, transformer equivalent circuit, transformer limited fault, transient recovery voltage.

I. INTRODUCTION

N

OWADAYS the power consumption of the electric power system is being increase due to the development of industrial usage, population increment and perfection of living standard. To fulfill the electricity requirement, it is needed to expand the electric power system. The dealing of a large capacity power transformer became one major role in the electric power system expansion especially above 200 kV. Since large power transformers possess small leakage impedance, when a fault occurs in a power system, the transformer limited fault (TLF) current became to exceed an interrupting current of the condition defined in the relevant IEC standard. In this circumstance, the transient recovery voltage (TRV) at the TLF condition became one of the biggest issues. The TRV should be investigated carefully at the TLF condition in order to present a suitable TRV value standards. Over the past decades, for drafting the standards of TRV parameters associated with the TLF current interrupting has MYOMIN Thein, IKEDA Hisatoshi, HARADA Katsuhiko, OHTSUKA Shinya and HIKITA Masayuki are with the High Voltage Engineering, Kyushu Institute of Technology, 1-1, Sensuicho, Tobata-ku, Kita-kyushu, Fukuoka 804-8550, Japan ( e-mail: [email protected], ikeda@ele. kyutech. ac.jp; [email protected]; [email protected]; [email protected]. jp ). HAGINOMORI Eiichi is with Chuo University, 13-27, Kasuga-1, Bunkyo-ku, Tokyo 112-8551, Japan (e-mail: [email protected]) KOSHIDUKA Tadashi is with Toshiba Corporation, 2-1, Ukichimacho, Kawasaki-ku, Kawasaki, Kanagawa 210-0862, Japan (e-mail: tadashi. [email protected])

been conducted by several studies. Several groups have proposed norms and standards related to TRV parameters for the highest levels of fault currents encountered [1], [2]. On the other hand, a valuable review can be published on the subject of transformer TRV [3]. The most cases used the value of a leakage inductance of 50/60Hz and a stray capacitance to analyze TRVs. A phenomenon has been known about magnetic flux which will not be able to enter an iron core of a transformer winding at high frequency regions. Therefore the leakage inductance will change along with the frequency. A leakage inductance of 50/60Hz may give wrong TRV. A transformer consists of very complex components composing a network of resistances, capacitances and self or mutual inductances. For the purpose of calculating TRV accurately at TLF conditions, with equivalent circuit elements at the TRV frequency range around 10 ~ 100 kHz, we studied TRV at TLF interrupting condition by current injection (CIJ) method with three different kinds of transformer. The EMTP transformer model for each experiment was constructed with the leakage inductance, stray capacitance, winding resistance and damping resistor which are determined from FRA measurement graphs. The experiment and simulation results gave reasonable results and it is presented in this paper. II. TRANSFORMER LIMITED FAULT IN POWER SYSTEM The TRV of the TLF interrupting condition are often the most severe kind of fault to be encountered in the electric power system [3], [4]. The TLF interrupting is defined as a fault where all fault currents are supplied through a transformer. Since the transformer’s impedance is the most dominant feature on the TRV of TLF conditions, it is clear that the selection of the transformer equivalent circuit is an important matter [5].The fault clearing case in an actual power system is shown in Fig. 1. III. EXPERIMENT The TLF interrupting condition in power system is presented with the CIJ measurement method in our study. The schematic diagram of experiment circuit is shown in Fig. 2. The TRV can be investigated by both current interrupting and current injection (CIJ) methods. The former one includes various factors affecting on a TRV shape such as current chopping and the arcing voltage of interrupting equipments [1],

2

Source impedance

TRANS;

CB

F A U L T

G

P

3300/415V Short-circuit impedance Capacitor charging circuit

Fig. 2. Schematic diagram of experiment circuit

Experiment FRA measurement Leakage inductance (Lt) Stray capacitance (Ct)

Time varying voltage and current wave

EMTP model 1

Leakage inductance (Lt*) Stray capacitance (Ct*) Damping resistor

Main voltage oscillation and TRV oscillation

EMTP model 2

EMTP model 3

10 1 0.1

10

0

10

1

10

2

10

3

10

4

10

5

10

6

Fig. 5. FRA measurement graph of test transformer

Fig. 1. TLF equivalent circuit in power system

Current injection

100

Frequency(Hz)

S

Current Injection circuit

Fig. 4. Schematic diagram of impedance measurement circuit

Impedance()

[6]. To investigate TRV the latter is preferable. The TLF condition of actual power system is replaced as CIJ circuit in experiment. To energize capacitor C, capacitor charging source was used. Power source G and source impedance are replaced as short-circuit impedance in experiment. Three different kinds of transformer have been investigated in our experiment to study TRV at TLF interrupting condition. The flow chart of our experiment is shown in Fig. 3. We have reported the transformer model for 4 kVA two windings low voltage and 5 kVA three windings pole transformers by this research flow [5], [7], [8]. In this paper the experiment and simulation results of 300 kVA two windings transformer are presented.

Leakage inductance (Lt**) Stray capacitance (Ct**) Calculated from resonance values

Compare

Fig. 3. Experiment flow chart

Lt (1) 1   2 LtCt Where, Lt* = leakage inductance that is calculated from equation(1) Lt = leakage inductance that is calculated from FRA graph Ct = stray capacitance that is calculated from FRA graph Rp (2) R 1  (RpCt  ) 2 Where, Rp = resistance of test transformer at resonance point that is obtained from FRA graph. Ct* = capacitance of test transformer at resonance point R = damping resistor Lt * 

The transformer constant (Lt and Ct) for model 1 is directly calculated from FRA measurement graph [5], [7], [8]. Precise transformer constant (Lt* and Ct*) is calculated by (1) and damping resistor is calculated by (2). These values are used in EMTP transformer model 2 [8]. The transformer constant for model 3 (Lt** and Ct**) is calculated at resonance point of the FRA graph. The calculated values are expressed in Table II. A. Impedance Measurement The frequency response analysis (FRA) measurement method is a powerful diagnostic test technique and became popular for measuring transformer impedance [9]. FRA measurement was used to obtain the impedance of the test transformer. The impedance was measured by FRA device (NF FRA5059). The measureable frequency range is between 0.1 mHz to 2.2 MHz. The experimental setup is shown in Fig. 4. The FRA measurement was conducted at the secondary side while the primary side is short-circuited the measurement result is expressed in Fig. 5

3 TABLE I TEST TRANSFORMER SPECIFICATION 300 kVA

No. of phase

single

Rated frequency

50 Hz

Rated voltage (HV)

3300 V

Rated current (HV)

90.9 A

Rated voltage (LV)

415 V

Rated current (LV)

723 A

Type

0.3

Voltage(V)

Rated power

-0.1 0

10

15

Fig. 7(a). Main oscillation of experiments

3.69%

1.5 1.0

0.16 0.00016

Voltage(V)

Lt Lt*

Inductance(mH)

Inductance(mH)

5

Time(ms)

0.00018 0.18

0.00014 0.14

285Hz

0.1 0.0

Top runner oilimmersed

Short-circuited impedance at 75 ° C

0.2

0.12 0.00012 0.10 0.0001

0.08 0.00008 0.06 0.00006

540 kHz

0.5 0.0 -0.5

0.04 0.00004

-1.0

0.02 0.00002

0

0

2 2 4 6 2 6 .1 2 7 4 5 6 4 5 1 5 6 6 4 9 7 .50 58 75 25 31 .01 02 68 52 53 72 59 .19 .00 .86 .05 0.4 6.6 0.3 7.2 3.3 92 43.3 22.1 44.3 33.6 827 81.7 86.3 78.4 70.9 93.9 114 759 523 654 106 245 877 607 135 102 1 2 3 5 12 19 30 47 73 17 27 42 66 10 15 24 38 59

D. Experiment 2 and results In this experiment we used short-circuit impedance values of 10 H (L3) at the primary side of the test transformer. Current injection was done at the secondary side. Experiment result is shown in Fig. 7(c), which is the TRV oscillation. The main oscillation of the experiment 2 is same as the experiment 1.

15

20

Fig. 7(b). TRV oscillation of experiment 1 1.5

Fig. 6. Inductance of FRA measurement (Lt) and inductance of precise calculation (Lt*)

C. Experiment 1and results In this experiment the CIJ was done at the secondary side of the test transformer and short-circuit impedance of 1.87 mH (L3) and 0.7 ohms are connected at the primary side. Experiment results are shown in Figs. 7 (a) and (b). Fig. 7(a) is the main oscillation and Fig. 7(b) is the TRV oscillation.

10 Time(s)

Frequency(Hz)

1.0 Voltage(V)

B. Test Transformer To investigate TRV at TLF condition, 300 kVA two windings transformer was used since it has obviously large capacity compared to the previous tested transformers (4 kVA and 5 kVA). The transformer specifications are expressed in Table I. The inductances graph is shown in Fig. 6, which was calculated from FRA measurement data. When it is considered at the point of frequency 45 kHz, the left portion of inductance values might be the leakage inductance and the resistance. The right portion includes the capacitance effect since 1/jCt becomes equivalent to jLt at the high frequency range. The inductance value which was sudden changes at around 183 kHz and 212 kHz in Fig. 6. This phenomenon cannot be understood at the moment.

5

0.5

540 kHz

0.0 -0.5 -1.0 0

5

10

15

20

Time(s)

Fig. 7(c). TRV oscillation of experiment 2

IV. EMTP MODEL FOR TRV CALCULATION Fig. 8 corresponds to the EMTP model circuit for the experiment 1. By changing the transformer constants which are expressed in Table II, the simulation results of main and TRV oscillation were obtained for the experiment 1. Simulation with three transformer constants gave same result in main oscillation with the experiment. Fig. 10 is the main oscillation result for both EMTP simulations for experiment 1 and 2. For TRV oscillation the different oscillation results were obtained. Fig. 7(b) is the TRV oscillation for the experiment 1 and it is 540 kHz. TRV oscillation of EMTP transformer constants 1 and 2 is 440 kHz and it is shown in Fig. 11(a) and (b). Fig. 11(c) is TRV oscillation of EMTP transformer constant 3, it is 420 kHz. Fig. 9 corresponds to EMTP model for the experiment 2. The simulation gave 285 Hz of main oscillation for this model which is same result with the experiment. The simulation result of TRV oscillation with this model gave 540 kHz and it is expressed in Fig.12.

4 1.5 [V]

V. DISCUSSION This study was conducted with two different values of short-circuited impedance at the primary side while the same CIJ circuit was applied at the secondary side. In actual power system, transformer impedance is significantly larger than short-circuit impedance, so that majority of voltage is shared by the transformer impedance during the TLF condition. In the experiment 1 leakage inductance (Lt) is two times greater than short-circuit impedance (L3). The results showed, -TRV exists by leakage inductance and stray capacitance in experiment Fig. 7(b).

with Lt and Ct 0.5 0.0

440 kHz

-0.5 -1.0

0

4

(file 300kVA_Send_Cij_2_ICEE09.pl4; x-var t) v:SW

(a)

8

12

16

[us] 20

TRV oscillation of EMTP simulation with Lt and Ct

1.5 [V]

TABLE II TRANSFORMER CONSTANTS Transformer Transformer constant 1 constant 2 Secondary

1.0

1.0

Transformer constant 3

Lt

Ct

Lt*

Ct*

Lt**

Ct**

57.846 H

1.502 nF

57.7 H

1.506 nF

45.97 H

1.89 nF

with Lt* and Ct* 0.5 0.0

440 kHz

-0.5 -1.0

0

4

(file 300kVA_Send_Cij_2_ICEE09.pl4; x-var t) v:SW

(b)

8

12

16

[us] 20

TRV oscillation of EMTP simulation with Lt* and Ct*

1.5 [V] 1.0

with Lt** and Ct** 0.5

Fig. 8. EMTP model circuit for experiment 1 0.0

420 kHz

-0.5 -1.0

0

4

(file 300kVA_Send_Cij_2_ICEE09.pl4; x-var t) v:SW

(c)

8

12

16

[us] 20

TRV oscillation of EMTP simulation with Lt** and Ct**

Fig. 11. TRV oscillation of EMTP simulation for experiment 1 1.5 [V]

Fig. 9. EMTP model circuit for experiment 2

1.0 0.35 [V]

0.5

0.26

0.0 0.17

540 kHz

-0.5

285Hz

0.08

-1.0

0

4

(file 300kVA_Send_Cij_try5.pl4; x-var t) v:SW

-0.01

8

12

16

[us] 20

Fig. 12. TRV oscillation of EMTP simulation for experiment 2 -0.10 0

4

8

12

16

[ms]

20

(f ile 300kVA_Send_Cij_2.pl4; x-var t) v:SW

Fig. 10. Main oscillation of EMTP simulations

-TRV exists by leakage inductance, short-circuit impedance and stray capacitance in EMTP Fig. 11(a), (b) and (c). From this study it was considered that to get satisfactory result in TRV frequency;

5

- to study the influence of short-circuited inductance (L3). The reason is the stray capacitance of the primary winding is very large while it was seen from the secondary side. It was studied with the experiment 2. We used 10 H inductor for short-circuit impedance in this experiment. It is several times smaller than the leakage inductance of the transformer. The experiment and simulation gave agreeable results in experiment 2. For the future it is desirable to identify the relation between the transformer stray capacitance and shortcircuit impedance. VI. CONCLUSIONS We obtained the following conclusions for the accurate TRV calculation by EMTP at the TLF condition. For the transformer model:(1). Leakage impedance can be obtained from FRA graph by calculation which is expressed in the flow chart of Fig. 3. (2). A stray capacitance can be obtained from the resonance frequency and calculated leakage impedance. (3). A damping resistor can be obtained from impedance at the resonance frequency. (4). Frequency dependent effect of leakage inductance used in EMTP transformer model should be considered. For current injection method:(1). By using the transformer model the EMTP calculation and the experiment give an agreeable results. (2). Current injection is not suffered from current chopping and arcing voltage which are main difficulities in an interrupting method.

VII. REFERENCES [1]

[2]

[3] [4]

[5]

[6]

[7]

[8]

Robert H. Harner, “Distribution System Recovery Voltage Characteristics: I- Transformer Secondary-Fault Recovery Voltage Investigation,” IEEE Trans. Power Apparatus and Systems, Vol. PAS87, No.2, pp 463-487, Feb 1968. Robert H. Harner, J. Rodriguez, “Transient Recovery Voltages Associated with Power-System, Three-Phase Transformer Secondary Faults,” IEEE Trans. Power App. Syst., vol. PAS-91, pp. 1887-1896, Sept./Oct. 1972 P.G. Parrott, “A Review of Transformer TRV Conditions,” CIGRE WG 13.05, ELECTRA No. 102 pp 87-118. “Transient Recovery Voltage Conditions to be Expected when Interrupting Short-circuit Currents limited by Transformers,” CIGRE Report 13-07, 1970. E. Haginomori ,M. Thein, H. Ikeda, S. Ohtsuka, M. Hikita, and T.Koshiduka, “ Investigation of transformer model for TRV calculation after fault current interrupting,” ICEE 2008, Panel discussion, Part 2, PN2-08,. A.Ametani, N.Kuroda, T.Tanimizu, H. Hasegawa and H.Inaba, “Field test and EMTP simulation of transient voltages when cleaning a transformer secondary fault”, Denki Gakkai Ronbunshi, Vol. 118B,No.4, April 1998, pp.381-388 M. Thein, M. Hikita, S. Ohtsuka, H. Ikeda, K. Harada, E.Haginomori and T. Koshiduka, “Investigation of transformer model for TRV calculation after fault current interrupting with pole transformer,” Annual Conference of Power & Energy Society, IEE of Japan, September 24-26, 2008, Hiroshima University, paper 38-311, pp.17-18 M. Thein, H. Ikeda, K. Harada, S. Ohtsuka, M. Hikita, E.Haginomori and T. Koshiduka, “Investigation of Transformer Model for TRV Calculation by EMTP,” The Sixth International Workshop on High Voltage Engineering IWHV 2008/Kyoto, ED-08-117, SP-08-32, HV08-46,pp 49-52, Oct. 24-25, 2008.

[9]

S. A. Ryder, “Transformer Diagnosis Using Frequency Response Analysis: Results from Fault Simulations,” IEEE PES Summer Meeting, Volume 1, Issue, 25-25, vol.1, pp 399-404 July 2002.

VIII. BIOGRAPHIES MYOMIN Thein (Non-member) was born in Meikhtila, Myanmar, June 6, 1974. He received the B.E degree in Electrical Power Engineering from Yangon Institute of Technology, Myanmar in 2001. From 2001 to 2003 he worked at Planning Department, from 2003 to 2006 he worked at Power Station as an Sub- station operation engineer, Myanma Electric Power Enterprise, Myanmar. Since 2007, he is a master student in Kyushu Institute of Technology, Japan. Hisatoshi IKEDA (Fellow) entered Toshiba in 1974, after graduated Tokyo University. In Toshiba he worked as a research engineer of substation equipment. He received his doctor degree form Tokyo University in 1990. From 2007, he is a visiting professor of the funded research lab. by Kyushu Electric Power Co. at the Kyushu Institute of Technology. He is Fellow of IEEE, a chairman of IEC/SB1 and JICCG and Senior member of IEEJ.

Katsuhiko HARADA (Non-member) received the B.S. degree in 1994 and the M.S. degree in 1996 from Kinki University. Since 1996, he has been associated with the Department of Electrical and Communication Engineering, Kinki University, where he was a Researcher from 1996 to 1998, a Part-time Lecturer from 1999 to 2007. Since 2007 he has been working as an Assistant Professor at the Kyushu Institute of Technology. He received an IEEJ Excellent Presentation Award in 2005. He is engaged in research on power electronics and photovoltaic power generation system. Shinya OHTSUKA (Member) was born on 16 January 1971. He received the B.S., M.S. and Dr. degrees in Electrical Engineering from Kyushu University, Japan, in 1994, 1996 and 1998, respectively. He was a Research Fellow of the Japan Society for the Promotion of Science (JSPS) from 1996 to 1998 and an Assistant Professor of the Faculty of Engineering at Kyushu Institute of Technology, Japan from 1999. Since 2006, he has been an Associate Professor in Kyushu Institute of Technology. He has been engaged in researches on the insulation properties of SF6 gas and environmentally benign gas, partial discharge detection technique for insulation diagnosis of power apparatus and high electric field phenomena. Dr. Ohtsuka is a member of the Institute of Electrical Engineers of Japan (IEEJ), the Institute of Engineers on Electrical Discharges in Japan (IEEDJ), the Cryogenic Association of Japan, CIGRE D1.33 and IEEE. Masayuki HIKITA (Senior member) was born in 1953. He received B.Sc. and Dr. degrees in electrical engineering from Nagoya University of Japan, in 1977, 1979, and 1982, respectively. He was an Assistant, a Lecturer, and Associate Professor at Nagoya University in 1982, 1989, and 1992, respectively. Since 1996, he has been a professor of the Department of Electrical Engineering, Kyushu Institute of Technology. He was Visiting Scientist at the High Voltage Laboratory in MIT, USA, from August 1985 to July 1987. Dr. Hikita has recently been interested in research on development of diagnostic technique of power equipment. He is a member of the Japan Society of Applied Physics, IEE Japan and Senior member of IEEE.

6 Eiichi HAGINOMORI (Non-member) received BS degree in 1962 and Dr. Eng in 1986 from Tokyo Institute of Technology, since 1962 engaged in designing ABB & GCB. From 1991, he was (visiting) professor in the above Institute and in Kyushu Institute of Technology. He has joined to WG1, WG10, WG21 and MT36 in IEC-SC17A over 30 years, and also CIGRE WG-A3.11. In 2005, he received IEC 1906 AWARD.

Tadashi KOSHIDUKA (Member) was born in Saitama, Japan on June 29, 1965. He received his B.S. degree in 1989 and M.S. degree in 1992, both in electrical engineering from Tokyo Denki University, Japan. In 1992, he joined Heavy Apparatus Engineering Laboratory of Toshiba Corporation, Kawasaki, Japan. He received 2008 IEEJ Technical Development Award and 2001 IEEJ Distinguished Paper Award. Mr. Koshiduka is a member of IEEE.