A Synthetic Test Circuit for Current Switching Tests of ...

[Pages:4]Paper presented at the IEEE PES T&D conference in Chicago, USA, April 21-24, 2008

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A Synthetic Test Circuit for Current Switching Tests of HVDC Circuit Breakers

Baoliang Sheng, Senior Member, IEEE

Abstract -- High voltage direct current (HVDC) circuit breaker current switching test in a test laboratory is difficult due to the limited test power installation. Reproduction of test stresses by means of direct testing confronts huge investment. Synthetic testing, as an alternative method, could amplify the test power more than ten times with a relative low cost. A synthetic test circuit based on the most used parallel current injection method was developed for the current switching test of HVDC circuit breakers. This synthetic test circuit could reproduce the current and voltage stresses equal to or greater than those could meet in service.

Index terms -- HVDC circuit breakers, load current switching, synthetic test circuit, testing

I. INTRODUCTION

HVDC circuit breakers are used in the HVDC transmission lines to reroute the direct current (DC) current during reconfiguration of the main circuit and to help extinguish fault current while system fault occurs. In multi-terminal systems the HVDC circuit breakers give the operational circuit changes with an uninterrupted power flow or rapid restoration of the power flow following a fault.

Typical switching current and voltage for a metallic return transfer breaker, which normally has a high request than other breakers such as ground return transfer switch, neutral bus switch and neutral bus grounding switch, are around 4kA and 70kV for 500kV DC transmission system [5].

To verify the switching performance of a DC circuit breaker it could be ideally using a practical power supply or similar system in the test laboratory when a type test is conducted.

Theoretically it is possible for a laboratory to build up a test circuit representative of the grid with all station equipment installed. This test method is defined as direct test. This method is preferred when both the test current and voltage are low. At high current and high voltage ratings, this method, however, is not feasible due to the huge power installation needed in the test laboratory. For testing of a HVDC circuit breaker this method is neither an economical nor a very practical solution.

To test the HV DC circuit breakers a synthetic testing method has to be developed. In a synthetic test circuit, the test

B.L. Sheng is with ABB AB, HVDC, 77180 Ludvika, Sweden (e-mails: baoliang.sheng@se.)

current and voltage are supplied from two or more power sources. Due to the fact that current and voltage stress the circuit breakers at different time intervals, each source supplies either a high current or a high voltage only.

Several methods have been investigated in the way to connect the two or more sources together in the synthetic testing. To minimize the influence caused by transit from one source to another, especially from the current source to the voltage source, an overlap of these two sources is preferable.

A synthetic test circuit based on the parallel current injection method has been successfully developed for test of HVDC circuit breakers. This paper reports this synthetic test circuit and the result of full-scale test of a HVDC breaker used in a r500kV 3000MW HVDC transmission system.

II. HVDC CURRENT SWITCHING AND HVDC CIRCUIT BREAKER

Absence of cyclic moments of current zero in a DC system makes the DC current switching difficult for arc distinguishes only at current zero. To create current zeros for a HVDC breaker is un-separated part in DC current switching [1][2][3].

To use auxiliary circuits, together with a breaker, is the most used method in direct current switching in HVDC application. Figure 1 in below illustrates this combination method of SF6 circuit breaker (CB) and auxiliary circuits in practical.

The auxiliary circuit consists of either a passive circuit or an active circuit depending on the DC current range [4]. In an active auxiliary circuit the capacitor C in Figure 1 is precharged prior to the current switching and one circuit breaker is inserted between capacitor C and inductor L.

A

L

C

CB

Id

Fig. 1 A HVDC circuit breaker with a passive auxiliary circuit

978-1-4244-1904-3/08/$25.00 ?2008 IEEE

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III. CURRENT AND VOLTAGE ACROSS THE HVDC CIRCUIT BREAKERS

After the contacts separation an arc voltage is established inside the circuit breaker arc-quenching chamber. The arc voltage increases with the travel of moving contact and, starts a current oscillation if a parallel capacitor is fast used such as the HVDC circuit breaker with an auxiliary circuit. This oscillation current can lead to, depending on the arc chamber design and capacitance in parallel, an instable arc with oscillation current zeros or a stable arc without oscillation current zeros. For the circuit breaker design without oscillation current zeros an active auxiliary circuit has to be employed to create current zero crossing for breaker current extinguishing.

In spite of different type of auxiliary circuits in use, the capacitor and reactor combination of the auxiliary circuit, together with the arc voltage or pre-charged voltage, determines the current derivative at zero crossing and rate of rise of recovery voltage after current zero. These values are predictable.

circuit is used to supply the recovery voltage after current switching. An auxiliary circuit breaker and a spark gap are implemented in the circuit to connect these two sources to the test object at specific time interval. The operation principle of this synthetic test circuit is illustrated in Figure 3 and further described as follows:

Test current Id

Injected current

Trip TB & AB1 AB2 closes AB1 clears TB clears

TB arcing time

Recovery voltage across the TB

IV. A SYNTHETIC TEST CIRCUIT FOR TESTING OF HVDC CIRCUIT BREAKERS

A. Principle

A synthetic test circuit, based on the parallel current injection method, was developed in ABB at Ludvika, Sweden, to test x the HVDC circuit breakers used in the Three-Gorges Changzhou HVDC Transmission Project.

A conventional 12-pulse rectifier is used as the current source to supply the DC test current and a voltage oscillation x

Fig. 3 Illustration of test circuit timing sequence

The 12-pulse rectifier is controlled to generate a DC test current to the test breaker (TB) through smoothing reactor (Ls) and auxiliary breaker (AB1) at a relative low generator driving voltage AB1 and TB open simultaneously and DC current arcs are established inside the interrupting chambers of these

Conv. 1

T1

LS

AB1

G

Arr

AB2 Arr

TB

Conv. 2

T2

LS

Lh

Gap

Re

+

Ce

Ch

-

Fig. 2 Synthetic test circuit for the current switching test of HVDC circuit breakers

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breakers

x Spark gap in the voltage circuit is ignited at the instant that the arcing time of TB will be equal to the prospected value

x AB2 closes and bypasses the DC current

x AB1 clears as the DC current transfer from AB1 ? TB branch to AB2 bypass branch

x TB is stressed by the injection current alone from the voltage circuit after AB1 clears.

x TB clears at injection current zero crossing and withstands a transient recovery voltage and subsequent DC voltage afterwards

x DC source rectifier's is blocked by stopping firing signal sending

B. Determination of circuit parameters

DC current source shall provide a DC current equal to the current in service. This current source could be with a low driving voltage. This driving voltage, however, shall be higher than the sum up of arc voltages in AB1 and TB. A back-to-back HVDC bridge, Figure 4, is operated as a rectifier to supply the DC current.

A voltage oscillation circuit is used to represent the DC current change prior to the current zero crossing and the transient recovery voltage after switching. This circuit, Figure 5, consists of a DC charger, two capacitor banks, one reactor bank and one resistor bank. The circuit parameters shall give close representation of the service current before the current zero crossing and representation of a recovery voltage (both transient and DC voltage) after the current zero crossing. To meet these, better understanding to auxiliary circuit parameter and arc behavior of the circuit breaker is necessary.

Fig. 5 Section of the voltage circuit

V.TEST AND TEST DESCRIPTION The HVDC circuit breaker for Three Gorges Changzhou HVDC transmission project [4] has been tested in this synthetic test circuit. One typical test oscillogram is given in Figure 6.

As described in section IV of this paper a 12-pulse HVDC thyristor valve provides the prospective DC current. This DC current is adjustable from a few hundreds of amperes up to 4300A depending on the test requirements.

A main capacitor bank, Ch, is pre-charged to the level slightly higher than the voltage that circuit breaker should withstand in service after current switching. The spark gap, Gap in Figure 2, is triggered at the instant that can lead the total arc time equal to the prospected arc time. The transient recovery voltage (TRV) control branch, Lh ? Re ? Ce, together with the charge voltage on capacitor bank Ch, is chosen to produce a TRV similar to the one that will meet in service.

Several tests were made with voltage circuit spark gap triggered at various instants to acquire the minimum arc time of circuit breaker for a successful current switching.

Fig. 4 A 12-pulse HVDC thyristor valve in the current section supplies a DC current up to 4300A

Figure 6 is a typical test osillogram to show that DC breaker successfully switched off the load current and withstand the subsequent recovery voltage. When the arc time is too short the injection current will flow more than one halfloop until the breaker arc chamber can create sufficient pressure to extinguish the arc.

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8 kA

6

It 2 k/div

2

0

-2 40 kVolt

0

Ut 40 k/div

-80

-120

-160 100 10 ms/div

110

120

130

Fig. 6 Test oscillogram

VIII.BIOGRAPHIES

Baoliang Sheng obtained his B.Sc degree from

Xi'an Jiaotong University, China, and his Ph.D.

from Delft University of Technology, the

Netherlands, both in Electrical Engineering. From

1982 to 1992 he was a test and research engineer at

XIHARI, China. He was a research engineer at

KEMA B.V., the Netherlands, and pursued his

Ph.D. at Delft University of Technology from 1992

to 1996. He joined ABB Ludvika, Sweden in May

1996. He is Company Specialist in High Power

Testing of Electrical Power Equipment and Senior

Specialist in Testing of HVDC Converter Valves and SVC Valves. He is

convenor of IEC SC22F WG15 and member of several working groups in IEC

140

TC33 and IEC SC22F. He is Senior Member of IEEE.

ms

VI. CONCLUSIONS

To use a direct test circuit to verify the current switching performance of an HVDC circuit breaker is infeasible and unappreciable due to the need of huge test power installation in the test laboratory. Synthetic testing, as an alternative, is a favorable economical and technical solution. Synthetic testing can make equivalent test if the synthetic test circuit is properly designed.

A synthetic test circuit based on the well-known parallel current injection method was successfully developed. The use of current injection method to couple the voltage circuit into the current circuit exposes the test breaker to the same circuit parameters in the switching interval of circuit breaker. This method is superior to others in test equivalence.

Laboratory test for the HVDC circuit breakers used in the Three-Gorges HVDC transmission projects reveals this circuit is of high flexibility on the circuit parameter adjustment and close representation of current and voltage stresses. The DC current switching characteristics of HVDC circuit breakers used in Three-Gorges have been investigated in this test circuit. The circuit breakers passed the test successfully.

VII. REFERENCES

[1] W. Pucher, B. Koetzold and P. Joss, "Fundamentals of HVDC interruption," ELECTRA, No. 5, June 1968, pp. 24-38

[2] Cigr? WG 13-03: "Introduction to the Testing of High Voltage Direct Current Circuit Breakers"; Electra, No.56, pp. 29-59, 1978

[3] ?. Ekstr?m, H.H?rtel, H.P.Lips, W.Schultz, P.Joss, H.Holfeld and D.Kind: "Design and testing of an HVDC circuit-breaker"; in Cigr? 1976 Session 13-06

[4] Dag Andersson and Anders Henriksson: "Passive and Active DC Breakers in the Three Gorges Changzhou HVDC Project"; in proceeding of 2001 International Conference on Power Systems (ICPS2001), pp. 391-395

[5] S. Tokuyama, K. Arimaysu, Y. Yoshioka, Y. Kato and K. Hirata: "Development and Interrupting Tests on 250kV 8kA HVDC Circuit Breaker"; IEEE Trans. On Power Apparatus and Systems, Vol. PAS-104, No.9, Sep. 1985, pp. 2453 ? 2459

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