international journal of scientific & engineering research ......the recent time the design...

International Journal of Scientific & Engineering Research Volume 4, Issue3, March-2013 1 ISSN 2229-5518

IJSER © 2013 http://www.ijser.org

Optimization of High Voltage Arc Assist Interrupters

Himanshu Joshi, Anjani Pandharkar, Ghanashyam Patil

Abstract -- The circuit breaker is one of the most important unit in the electrical power system. The protection, stability and continuity of the

system depend on the circuit breaker's ability to switch line, load and exciting currents and to interrupt fault currents. High voltage circuit

breakers, have to operate with extremely high reliability in the power system to ensure the economical and reliable power distribution. It is

observed over the years that most of the failures in circuit breakers are of mechanical nature. Consequently the development efforts over

the last decade has been focused towards thedevelopment of high efficiency interrupters which requires low energy mechanism. The first step

towards the high efficiency interrupter is the development of Arc Assist Interrupters. In the conventional Puffer type interrupters of a high

voltage SF6 circuit breakers, a considerable amount of mechanical energy is used to compress the gas in order to create a gas flow to remove

the arc energy. In arc assist Interrupters, arc energy is used to increase the gas pressure required for interruption. This paper discusses the

results of detailed flow field and electric field computations. Effect of nozzle shape and thermal chamber volume on the pressure rise is ex-

plained. Also capacitive current interrupting performance is estimated based on electric field and gas flow analysis. This paper helps to con-

clude simulation study using ga flow calculation program which is very useful to understand the mechanism of pressure generation, and it is

also very useful to find the data of the optimum design of the interrupter.

Index Terms— Arc Assist Interrupters, Thermal Puffer, Nozzle, Gas Circuit Breaker (GCB), Capacitive Current Switching, Gas

Density, Electrostatic Stress, Breakdown Voltage (BDV)

—————————— ——————————

1 INTRODUCTION The development of SF6 gas circuit breaker started around 1950's,

since then it has undergone many technological changes. Several

types of SF6 circuit breakers have been developed by various manu-

facturers in the world during last twenty years, for rated voltages

from 6.6kV to 1100kV. During every development phase the aim was

to design a new compact, highly reliable and low energy circuit

breaker. Figure 1 shows the cross section of typical puffer type gas

circuit breaker. When breaker is fully closed, the pressure in the

puffer cylinder is equal to that outside the cylinder. During opening

stroke puffer-cylinder and moving contact tube start moving against

the fixed piston, and there is relative movement, as a result gas gets

compresses in the cavity between puffer cylinder and piston. After

certain travel contact separates and arc is drawn between the arcing

contacts. During the arcing period, compressed SF6 gas is blown

axially along the arc through a convergent divergent nozzle. As a

result the arc gets extinguished. The above principle utilizes mechan-

ical energy to compress the gas required for quenching the arc.

The development of SF6 gas circuit breaker started around 1950's,

since then it has undergone many technological changes. Several

types of SF6 circuit breakers have been developed by various manu-

facturers in the world during last twenty years, for rated voltages

from 6.6kV to 1100kV. During every development phase the aim

was to design a new compact, highly reliable and low energy circuit

breaker. Figure 1 shows the cross section of typical puffer type gas

circuit breaker. When breaker is fully closed, the pressure in the

puffer cylinder is equal to that outside the cylinder. During opening

stroke puffer-cylinder and moving contact tube start moving against

the fixed piston, and there is relative movement, as a result gas gets

compresses in the cavity between puffer cylinder and piston. After

certain travel contact separates and arc is drawn between the arcing

Himanshu Joshi is currently pursuing masters degree program in electric power systems in Pune University, India. He is working with Crompton Greaves Limited since 2002. He is having an experience in the field of Type Testing of Gas Circuit Breakers, Dielectric Design and Gas Flow Design of Interrupters PH-+919881707734. E-mail: [email protected]

Anjani Pandharkar and Ghanashyam Patil is currently pursuing masters degree program in electric power systems in Pune University, India. Both have them have an experience with R & D-Gas circuit Breakers with Crompton Greaves Limited, Nasik E-mail: [email protected] and [email protected]



contacts. During the arcing period, compressed SF6 gas is blown

axially along the arc through a convergent divergent nozzle. As a

result the arc gets extinguished. The above principle utilizes mechan-

ical energy to compress the gas required for quenching the arc.

Figure 1 Puffer Type Interrupter

The recent time the design efforts has been shifted to develop the arc

assist type gas circuit breakers. wherein the arc energy is used to

increase the gas pressure required for quenching the arc. But during

the low current interruption the arc energy is not sufficient to in-

crease the gas pressure, an additional gas flow required by the me-

chanical compression. Figure 2 shows the typical cross section of arc

assist interrupter.

Figure 2 Arc Assist Interrupter One of the major limitations of the arc assist interrupters is that the

higher gas pressure is associated with higher gas temperature, which

reduces the dynamic voltage withstand capability between contact

space. Also breaking of low currents wherein arc energy is not suffi-

cient is a major challenge to the designers. There are many parame-

ters which influence interrupting performance such as volume ratio

of two chambers, nozzle structure, breaking current, moving speed

etc. Therefore design work is very complicated and development of

this type of GCB need very long time. But optimization is possible

through the detailed computations of flow field and the electric field

distribution in various phases of interrupting process and under dif-

ferent stress conditions.

2 THE FLOW SOLVER The Kernel of the solver is based on the solution of the unsteady

Euler equations of gas dynamics. The solver computes the solution

by integration of the Euler equations on a moving and deforming

unstructured triangular grid using a finite volume method. Two

modes of operation of the circuit breaker can be simulated viz. Cold

mode and Arc mode. In Cold mode, simulation of operation of cir-

cuit breaker is done without electric arc. This allows the simulation

of the transient flow field occurring during the operation. In addition,

a solution of electric field can be obtained inside the chamber, allow-

ing the computation of the ratio (E/N) which governs the dielectric

strength of the chamber. The emporal variation of the dielectric

strength which depends on both the inter electrode spacing and the

fluid density distribution resulting from the flow can thus be ob-

tained. In the Arc mode i.e analysis with the real current, an arc

model is added to the Cold mode which includes the computation of

Ohmic heating, the Lorentz forces and the radiation transfer. Nozzle

ablation can also be simulated based on the incident radiative flux.

[5], [8]

3 RESULTS AND DISCUSSION

Many computer simulations done to see the effect of various parame-

ter on the pressure rise in thermal chamber. Figure 3 below shows

gas pressure in thermal and compression chamber during current

interruption. The pressure in the thermal chamber increases by tem-

perature rise of gas and the temperature increase occurs by a hot gas

flow from arcing zone. [2]

Figure 3 Pressure rise during current interruption Firstly the effect of current magnitude is analyzed Figure 4 shows the

influence of magnitude of interrupting current on the pressure rise in

thermal chamber. The interrupting current varied from 0.5 kA to 40

kA. The result shows that pressure in thermal chamber increases with



increasing interrupting current.

Figure 4 Effect of interrupting current on pressure rise in

thermal chamber

Figure 5 shows the influence of arcing time on the pressure rise in

thermal chamber. The arcing time is varied from 10ms to 22ms. The

result shows that pressure rise in thermal chamber changes by arcing

time.

Figure 5 Effect of arcing time on pressure rise inthermal

chamber

Figure 6 shows the influence of nozzle throat length on the pressure

rise in thermal chamber. Three different throat lengths are considered

for analysis viz. 1pu =10mm, 2pu=20mm and 3pu=30mm. The result

clearly shows that long throat nozzle increases the pressure in the

thermal chamber considerably. [3]

Figure 6 Effect of nozzle throat length on pressure rise in thermal

chamber

Figure 7 shows the influence of nozzle throat diameter on the pres-

sure rise in thermal chamber. Three different throat diameters are

considered for analysis viz. 1pu, 2pu and 3pu. The result shows that

smaller the throat diameter higher the pressure rise in the thermal

chamber. [3]

Figure 7 Effect of nozzle throat diameter on pressure rise in thermal

chamber

Figure 8 shows the influence of volumes of thermal and compression

chamber on pressure rise in thermal chamber. Three cases are ana-

lyzed here, wherein the volume ratios of thermal to compression

chamber are considered as 1:1, 1:0.5 and 0.5:1. The result shows that

the effect of volume of thermal chamber is bigger than that of the

compression chamber. [1]



Figure 8 Effect of thermal and compression chamber volume

on pressure rise in thermal chamber

4 CAPACITIVE CURRENT SWITCHING

Many researches have shown that the dielectric withstand voltage

calculated by electric field and static gas pressure is not so accurate

because of the formation of shock wave at the tip of arcing contact.

The tip of the fixed arcing contact is investigated to get the dielectric

recovery strength, as the maximum electric field strength and varia-

tion in the gas density occurs due to the formation of shock waves.

Here four points are considered on the tip of arcing contact. Figure 9

shows the points of calculation.

Figure 9 Points of calculation on arcing contact tip

Gas flow analysis and electrostatic analysis is carried out during

opening operation of breaker. Figure 10 and 11 shows the electrostat-

ic stress and gas density variation on four points.

Figure 10 Electric stress on arcing contact tip

Figure 11 Gas density variation on arcing contact tip

Finally the dynamic BDV is calculated for all four points based on

the streamer criterion. Figure 12 shows the dynamic BDV and ap-

plied voltage Vs time. From BDV curve, it is clear that in dynamic

condition max BDV always shifts on tip of arcing contact.

Figure 12 Transient BDV on arcing contact tip Hence this method is more accurate to evaluate the capacitive

switching performance. [4], [6], [7]



5 CONCLUSION

- Simulation study using calculation program is very useful to

understand the mechanism of pressure generation, and it is also

very useful to find the data of the optimum design.

- The nozzle throat diameter and the length of nozzle throat in-

fluence the pressure rise in the thermal chamber considerably.

The influence is as large as the influence of interrupting current.

- The thermal effect of pressure rise in the thermal chamber is

big in relatively earlier interrupting phase.

- The volume of the thermal chamber influences the pressure

rise in the thermal chamber very much. The gas in the smaller

thermal chamber is easily heated by the back flow of hot gas,

and higher temperature in thermal chamber increases the pres-

sure there.

- The volume of compression chamber influences the pressure in

the thermal chamber also. The larger volume increases the pres-

sure in compression chamber, and it influences the pressure in

thermal chamber at the longer arcing time.

- To improve the dielectric performance of circuit breaker, it is

effective to reduce the maximum electric field strength and the

formation of the shock wave near the arcing contact.

ACKNOWLEDGMENT The authors wish to thank Crompton Greaves Limited for providing continual guidance to work on Gas Flow Design of Arc-Assist Interrupters.

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[2] Jan Sedlacek et al. “Optimization of high Voltage self blast inter

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[3] J-C Lee et al. “Effects of nozzle shape on the interruption per

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[4] F.Endo et al. “Analytical prediction of Transient breakdown

characteristics of SF6 gas circuit breakers”. IEEE Trans. Power

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[5] J.Y.Trepanier, M.Reggio, et al, “Analysis of The Dielectric

strength of an SF6 circuit breaker”, IEEE Trans. Power Delivery,

Vol.6, No 2, Apr 1991.

[6] A. Pedersen, “Criteria for Spark Breakdown in Sulfur Hexafluo

ride”, IEEE Trans. Power Apparatus and Systems, PAS-89(8),

pp.2043~2048, Nov. 1970.

[7] H.K.Kim et al. “Optimal Design of Gas Circuit Breaker for In

creasing the Small Current Interruption Capacity”. IEEE Trans.

On Magnetics, Vol. 39, No.3, May 2003.

[8] Lin Xin, Li Junmin, et al. “Numerical Calculation of Interrup

tion properties of the Self Extinguishing type SF6 circuit breaker

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BIOGRAPHY

[1]

Himanshu Joshi was born in 1978 in India. He received the

Bachelor degree in Electrical Engineering from Pune University

in 2002. Currently he is doing Masters Degree in Power Systems

from Pune University.

Currently, he is working with Crompton Greaves Limited,

Nashik, India. Engaged in R & D works on Gas Circuit Breakers.

Actively involved in development of SF6 Gas Circuit Breakers

and Type Testing of SF6 Gas Circuit Breakers.

Research Interest is in Dielectric Design of High Voltage Gas

Circuit Breakers, Gas Flow Analysis.

Authored 2 Technical Research Papers in Different

National and International Conference. He has contributed for

Filing 9 Patents and 2 Design Registrations.

international journal of scientific & engineering research ......the recent time the design...

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