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

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Paper presented at IEEE PES 2008 T&D Chicago meeting, Apr. 21 – 24, 2008

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A Synthetic Test Circuit for Current SwitchingTests of HVDC Circuit Breakers

Baoliang Sheng, Senior Member, IEEE

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

meet in service.

Index terms — HVDC circuit breakers, load currentswitching, synthetic test circuit, testing

I. I NTRODUCTION

HVDC circuit breakers are used in the HVDC transmissionlines to reroute the direct current (DC) current duringreconfiguration of the main circuit and to help extinguish faultcurrent while system fault occurs. In multi-terminal systemsthe HVDC circuit breakers give the operational circuitchanges with an uninterrupted power flow or rapid restorationof the power flow following a fault.

Typical switching current and voltage for a metallic returntransfer breaker, which normally has a high request than other breakers such as ground return transfer switch, neutral busswitch and neutral bus grounding switch, are around 4kA and70kV 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 orsimilar system in the test laboratory when a type test isconducted.

Theoretically it is possible for a laboratory to build up a testcircuit representative of the grid with all station equipmentinstalled. This test method is defined as direct test. Thismethod is preferred when both the test current and voltage arelow. At high current and high voltage ratings, this method,however, is not feasible due to the huge power installationneeded 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 testingmethod has to be developed. In a synthetic test circuit, the test

B.L. Sheng is with ABB AB, HVDC, 77180 Ludvika, Sweden (e-mails: [email protected])

current and voltage are supplied from two or more powesources. Due to the fact that current and voltage stress thcircuit breakers at different time intervals, each sourcesupplies either a high current or a high voltage only.

Several methods have been investigated in the way toconnect the two or more sources together in the synthetictesting. To minimize the influence caused by transit from onsource to another, especially from the current source to thvoltage source, an overlap of these two sources is preferable.

A synthetic test circuit based on the parallel curreninjection method has been successfully developed for test oHVDC circuit breakers. This paper reports this synthetic tescircuit and the result of full-scale test of a HVDC breaker usein a 500kV 3000MW HVDC transmission system.

II.HVDC CURRENTSWITCHING ANDHVDC CIRCUITBREAKER

Absence of cyclic moments of current zero in a DC systemmakes the DC current switching difficult for arc distinguisheonly 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 themost used method in direct current switching in HVDCapplication. Figure 1 in below illustrates this combinatiomethod of SF6 circuit breaker (CB) and auxiliary circuits in practical.

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

CB

CL

A

Id

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

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



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III. CURRENT ANDVOLTAGE ACROSS THEHVDC CIRCUITBREAKERS

After the contacts separation an arc voltage is establishedinside the circuit breaker arc-quenching chamber. The arcvoltage increases with the travel of moving contact and, startsa current oscillation if a parallel capacitor is fast used such asthe HVDC circuit breaker with an auxiliary circuit. Thisoscillation current can lead to, depending on the arc chamberdesign and capacitance in parallel, an instable arc withoscillation current zeros or a stable arc without oscillationcurrent zeros. For the circuit breaker design withoutoscillation current zeros an active auxiliary circuit has to beemployed to create current zero crossing for breaker currentextinguishing.

In spite of different type of auxiliary circuits in use, thecapacitor 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 ofrise of recovery voltage after current zero. These values are predictable.

IV. A SYNTHETICTEST CIRCUIT FORTESTING OFHVDCCIRCUITBREAKERS

A. Principle

A synthetic test circuit, based on the parallel current injectionmethod, was developed in ABB at Ludvika, Sweden, to testthe HVDC circuit breakers used in the Three-Gorges

Changzhou HVDC Transmission Project.

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

circuit is used to supply the recovery voltage after currenswitching. An auxiliary circuit breaker and a spark gap areimplemented in the circuit to connect these two sources to thtest object at specific time interval. The operation principle othis synthetic test circuit is illustrated in Figure 3 and furthedescribed as follows:

Test current Id

TB arcing timeTrip TB & AB1

TB clears

AB2 closes

AB1 clears

Injected current

Recovery voltage across the TB

Fig. 3 Illustration of test circuit timing sequence

The 12-pulse rectifier is controlled to generate a DC tescurrent to the test breaker (TB) through smoothing reacto(Ls) and auxiliary breaker (AB1) at a relative lowgenerator driving voltage

AB1 and TB open simultaneously and DC current arcare established inside the interrupting chambers of these

TB +

-

Gap

T1

T2

G

C e

AB1

R e

Ch

Lh

Arr

Conv. 1

Conv. 2LS

LS

Arr AB2

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



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breakers

Spark gap in the voltage circuit is ignited at the instantthat the arcing time of TB will be equal to the prospectedvalue

AB2 closes and bypasses the DC current

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

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

TB clears at injection current zero crossing andwithstands a transient recovery voltage and subsequentDC voltage afterwards

DC source rectifier’s is blocked by stopping firing signalsending

B. Determination of circuit parameters

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

A voltage oscillation circuit is used to represent the DCcurrent change prior to the current zero crossing and thetransient recovery voltage after switching. This circuit, Figure5, consists of a DC charger, two capacitor banks, one reactor bank and one resistor bank. The circuit parameters shall giveclose representation of the service current before the currentzero crossing and representation of a recovery voltage (bothtransient and DC voltage) after the current zero crossing. To

meet these, better understanding to auxiliary circuit parameterand arc behavior of the circuit breaker is necessary.

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

Fig. 5 Section of the voltage circuit

V.TEST ANDTEST DESCRIPTION

The HVDC circuit breaker for Three Gorges ChangzhouHVDC transmission project [4] has been tested in thisynthetic test circuit. One typical test oscillogram is given iFigure 6.

As described in section IV of this paper a 12-pulse HVDCthyristor valve provides the prospective DC current. This DCcurrent is adjustable from a few hundreds of amperes up t4300A depending on the test requirements.

A main capacitor bank, Ch, is pre-charged to the levelslightly higher than the voltage that circuit breaker shoulwithstand in service after current switching. The spark gapGap in Figure 2, is triggered at the instant that can lead thetotal arc time equal to the prospected arc time. The transienrecovery voltage (TRV) control branch, Lh – R e – Ce, togetherwith 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 gaptriggered at various instants to acquire the minimum arc timof circuit breaker for a successful current switching.

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



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100 140110 120 130ms10 ms/div

8

-2

kA

It2 k/div

0

2

6

40

-160

kVolt

Ut40 k/div

-120

-80

0

Fig. 6 Test oscillogram

VI. CONCLUSIONS

To use a direct test circuit to verify the current switching performance of an HVDC circuit breaker is infeasible andunappreciable due to the need of huge test power installationin the test laboratory. Synthetic testing, as an alternative, is afavorable economical and technical solution. Synthetic testingcan make equivalent test if the synthetic test circuit is properlydesigned.

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

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

VII. R EFERENCES

[1] W. Pucher, B. Koetzold and P. Joss, “Fundamentals of HVDCinterruption,” ELECTRA, No. 5, June 1968, pp. 24-38

[2] Cigré WG 13-03: “Introduction to the Testing of High Voltage DirectCurrent Circuit Breakers”; Electra, No.56, pp. 29-59, 1978

[3] Å. Ekström, H.Härtel, H.P.Lips, W.Schultz, P.Joss, H.Holfeld andD.Kind: “Design and testing of an HVDC circuit-breaker”; inCigré1976 Session 13-06

[4] Dag Andersson and Anders Henriksson: “Passive and Active DCBreakers 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 CircuitBreaker”; IEEE Trans. On Power Apparatus and Systems, Vol. PAS-104,

No.9, Sep. 1985, pp. 2453 – 2459

VIII.BIOGRAPHIES

Baoliang Sheng obtained his B.Sc degree fromXi’an Jiaotong University, China, and his Ph.D.from Delft University of Technology, the Netherlands, both in Electrical Engineering. From1982 to 1992 he was a test and research engineer atXIHARI, China. He was a research engineer atKEMA B.V., the Netherlands, and pursued hisPh.D. at Delft University of Technology from 1992

to 1996. He joined ABB Ludvika, Sweden in May1996. He is Company Specialist in High PowerTesting of Electrical Power Equipment and Senior

Specialist in Testing of HVDC Converter Valves and SVC Valves. He iconvenor of IEC SC22F WG15 and member of several working groups in IECTC33 and IEC SC22F. He is Senior Member of IEEE.

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