analysis of electric eld for solid-state isolated multi

Analysis of electric field for solid-stateisolated multi-circuit breaker according

to switching mode

Young Sun Kim*Department of Electrical and Electronic Engineering,

Joongbu University,Goyang, 10279, South Korea

[email protected],

Corresponding author*

Phone:+82-31-750-1631

February 4, 2018

AbstractBackground/Objectives: The solid-state isolated multi-

circuit breaker (SIMCB) is an eco-friendly power device thatdoes not use SF6, which is used as an insulating mate-rial, and substitutes epoxy mold method to eliminate globalwarming gas.

Methods/Statistical analysis: In order to improvethe insulation performance of the circuit breaker, the per-formance of the electrode part enclosure design and epoxymaterial is very important. In this paper, electric field anal-ysis algorithm of circuit breaker is presented and modelingof shape and material properties are made. An electrostaticfield finite element analysis was applied to the electric fieldanalysis of the circuit breaker.

Findings: In addition, the electrostatic field analysis ofthe SIMCB was performed according to the ON and OFFmodes of the main switch and the earth switch. We ana-lyzed the field distribution, potential distribution, and elec-tric field strength in a specific path.

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International Journal of Pure and Applied MathematicsVolume 118 No. 19 2018, 1573-1586ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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Improvements/Applications: The results of this anal-ysis can help to alleviate the electric field concentration ata specific site in the design of the circuit breaker.

Key Words: Epoxy material, Finite element analysis,Multi-circuit breaker, Solid-state, Switching mode.

1 Introduction

Switches and breakers are commonly used as devices for inputtingor disconnecting energy into an electric circuit.The switch can nor-mally turn the load current on and off, but cannot control the largeshort-circuit current that flows when the wire is short-circuited dueto a fault or other reason.It is a circuit breaker to block such a largecurrent, and the breaker has a powerful contact opening / closingmechanism and an arc extinguishing device for quickly absorbingthe arc energy generated when breaking1,2.

Solid-state isolated multi-circuit breakers (SIMCB) are com-posed of five main components. These are solid-state frame, open-ing/closing part, arc extinguishers, contacts and trip units.

The frame, also called as the molded case, provides an insulatedouter housing to install all of the multi-circuit breaker components.It is often made of glass polyester material or thermosetting syn-thetic resin with durability and high dielectric strength in a com-pact design.

The operating mechanism adjusts the opening and closing ofthe contact electrode. How fast the electrodes move is determinedby opening and closing the contacts. Also, There is an arc ex-tinguisher that extinguishes the arc.An arc is created whenever acircuit breaker interrupts a current flow. The task of the arc ex-tinguisher is to limit and then crush and destroy the arc. Finally,the trip unit is the brain of the circuit breaker. The function ofthe trip device is to trip the actuating mechanism in the event of ashort circuit or long-term overload of the current.Currently, the de-velopment of alternative insulation materials for SF6 gas has beendivided into two types at home and abroad. Dry air or N2 gas isbeing developed as an alternative insulator. Hitachi is leading theresearch in Japan, and in Korea, development is under way throughtechnology introduction3,4.

The insulation properties of solid insulation materials must have

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consistency over the life span from air to solid insulation medium.Thisproperty is considered as an evaluation item to be provided atleast.Especially, when the surface is damaged by 60Hz or shockwavewithstand voltage installed outside, it is characterized by a failuredue to various insulation characteristics such as flashover, electricbreakdown and puncture caused by creeping discharge.The insulat-ing material is selectively recoverable, but in the case of puncture itmeans perpetual damage to the article or the entire product, thusre-recognizing its importance in the molding process. Generally, inthe case of epoxy, the insulated layer, which is the boundary el-ement between the filling part and the outer atmosphere layer, isdesigned to have a minimum design value of at least about 20 mm5.

In this study, external frame and shield design and fabricationare performed. In addition, alternatives are required to maintain in-sulation performance against surface condensation due to tempera-ture changes in common ducts or underground manholes.Therefore,a shield structure was constructed to mitigate the non-uniform elec-tric field, which is the cause of local dielectric breakdown of theepoxy. In the future, it will be improved or supplemented to opti-mize the shield structure to reduce the internal local electric fieldconcentration, to suppress the deterioration of the epoxy, and tomaintain the permanent insulation property.

And the numerical analysis of the solid insulation part, whichis core technology in the circuit breaker design, is to select the finalmodel as a way to improve the design. The consideration of themodel design is to construct an electrostatic shield on the surfaceof the insulator, thereby reducing the incidence of phase-to-phaseaccidents and greatly improving operator safety.In the insulationdesign of the product, the design should be designed to minimizethe localized field part and to reduce the maximum electric field dueto the diversity of the potential distribution between the internalcomponents and external shapes.The inner structure is composed ofthe Vacuum Interrupter for the opening part and the grounding partin parallel, and the drawing direction of the lower bushing (Outer-cone) is different for the connection with the bus-bar.Through theelectric field analysis of the solid insulated type circuit breaker,the analysis algorithm was derived, the main design parameterswere derived, and the objective function was selected for the designpurpose.

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2 Finite Element Analysis for Numeri-

cal Analysis

For the electric field analysis of SIMCB, two dimensional finite el-ement analysis is required. In this chapter, we derive the gov-erning equations of electrostatic systems derived from Maxwell’sequations5,6.In the case of electrostatic field, since the phenomenaof the system do not change with time, the field analysis is car-ried out by adopting the following from Maxwell’s equations andauxiliary equations7,8,9,10.

∆×−→E = 0 (1)

∆ · −→D = ρv (2)

−→D = ε

−→E (3)

Where E is the electric fieldintensity,D is the electric flux densityand v is the space charge density. The relation between electric fieldintensity and electric scalar potential is as follows.

−→E = −∆ϕ (4)

The electrostatic field governing equation of the form of the Poissonequation can be obtained by substituting equation (3) into equation(2).

−∆ · (ε∆ϕ) = ρv (5)

In order to apply the finite element method, the governing equationsare expressed in the two-dimensional space as follows.

∂

∂x(ε∂ϕ

∂x) +

∂

∂y(ε∂ϕ

∂y) = −ρv (6)

In the two-dimensional electrostatic field analysis, since the phe-nomenon of the system does not change with respect to the timeand the z-axis, the electric potential and the electric field intensityare as follows.

ϕ = ϕ(x, y) (7)

−→E = Ex(x, y)ax + Ey(x, y)ay (8)

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3 Solid-State Isolated Multi - Circuit

Breaker

SIMCB is electric power equipment that is replaced by epoxy moldmethod without using SF6 which is used as insulation material.Itis an eco-friendly device because there is no global warming gasemission after the end of use period of the device.The design of thehousing portion containing the electrode portion in the design ofthe circuit breaker becomes very important.The housing materialis solid insulation type using Epoxy material which has excellentinsulation performance and can design the structure of the blockingpart compactly.

3.1 Structure and material characteristics

Figure 1a) shows the outer shape of the housing of the SIMCBwith electrodes inside and the side cut-out of the housing in orderto understand the internal structure is shown in Figure 1b).

Fig. 1.a) Housing and b) Its Side-cut View of Solid-stateIsolatedMulti-Circuit Breaker

The SIMCB consists of a main switch (MS) and a earthswitch(ES). The remaining parts are filled with solid insulation materials.In order to analyze the electric field of the SIMCB housing, theshape is modeled as shown in Figure2, and the structure and nameof each part are shown next to it.

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Fig. 2.Structure and Name of the Housing for SIMCB

As the input condition for the electromagnetic field analysis,the relative permittivity, which is the material properties of theinsulator, were 4.2 and 12 for epoxy and silicone. The rest of thearea, copper, air, iron, and graphite, were processed with a relativepermittivity of 1. Figure 3 shows the material composition of thebreaker housing using color.

The epoxy used in this study has already been manufacturedfor the first time around 1930, and now it is expanding its cover-age area with market power surpassing silicone due to the follow-ing advantages.The advantages are listed below. Excellent electri-cal insulation, excellent adhesive property, excellent chemical re-sistance, excellent water resistance, excellent mechanical strength,low shrinkage in the curing step, low residual stress, curing at lowtemperature, low viscosity, moldable regardless of shape and excel-lent self-extinguishing property, excellent environmental resistanceand excellent weather resistance.

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Fig. 3.Material Configuration of the Housing for SIMCB

3.2 Electric field analysis of SIMCB accordingto switching mode

In the use of electric power equipment, concentration of an electricfield in a specific area promotes insulation breakdown and dete-rioration of the product, and therefore has a direct relation withthe performance and life of the product. Therefore, this problemis solved through electromagnetic field analysis at design and man-ufacturing stage. The analysis method was finite element analysis(FEA), which is one of the representative methods of numericalanalysis of electromagnetic fields. The configuration of the elec-trode part of the SIMCB consists of the main switch at the lowerend and the earth switch at the upper end. The mode was de-termined by opening and closing these switches, and electric fieldanalysis was performed for each mode like Table 1.

Table 1. Operation Switching Mode of SIMCB

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3.2.1 In case of mode I (Main SW: OFF, Earth SW: ON)

When the switching mode is I, the shape and boundary conditionsof the analysis model are shown in Figure 4.The boundary condi-tions (1) are 100 [V] for the field shield, current transformer, upperbushing electrode, ES movable electrode, fixed electrode, movablefixed frame, MS movable electrode, ant the fixed boundary condi-tion (Dirichlet BC, (2)) of 0 [V] was entered and analyzed in thelower bushing electrode, the MS fixed electrode, the shield layer,the voltage detector, and the voltage detector fixed rod. Naturalboundary condition (Neumann BC, (3)) was applied to the otherboundary surface.

Fig. 4.Analysis Model and Boundary Condition (Main SW: OFF,Earth SW: ON)

Figure 5 shows the Distributions of equi-potential Line andelectric field intensity of solid-stateisolated multi-circuit breakerinmode I (Main SWITCH OFF, Earth SWITCH ON). Potential ishigher in the red color and lower in the blue color.

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Fig. 5.a) Distributions of Equi-potential Line and b) ElectricField Intensity of Solid-stateIsolated Multi-Circuit Breaker (Main

SW: OFF, Earth SW: ON)

3.2.2 In case of mode II (Main SW: OFF, Earth SW:OFF)

Figure 6a) shows the boundary conditions for switching mode II.In this case, 100 [V] was applied to the field shield, the currenttransformer, the upper bushing electrode, the ES fixed electrodeand the MS movable electrode, and the lower bushing electrode, theMS fixed electrode, the ES movable electrode shield layer, In thevoltage detecting section fixed bar, 0 [V] was applied to give a fixedboundary condition (Dirichlet BC). Natural boundary conditions(Neumann BC) were applied to other boundary surfaces.Figure 6b)shows the equi-potential distribution when the main switch is OFFand the earth switch is OFF. The more positive the color is, thehigher the potential. The colder the color is, the lower the potential.

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Fig. 6.a) Boundary Condition and b) Distribution ofEqui-potential Line for Solid-stateIsolated Multi-Circuit Breaker

(Main SW: OFF, Earth SW: OFF)

Figure 7a) shows the electric field distribution in the switchingmode II by color. Figure 7b) shows the field strength in a specificpath from the voltage detector to the upper bushing. The distancefrom the upper electrode is inversely proportional to the distance,and the electric field is rapidly decreased.

Fig. 7.a) Distribution of Electric Field Intensity with Check Pathand b) Extracted Electric Field Intensity along the Check Path

(Main SW: OFF, Earth SW: OFF)

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3.2.3 In case of mode III (Main SW: ON, Earth SW:OFF)

Figure 8 shows the boundary conditions and distribution of theequipotential and electric field in the switching mode III. This caseis similar to the case of modes I and II, but the voltage applicationarea is expanded due to conduction of the main switch. In addi-tion, the concentration of the electric field is shown to be relaxedcompared to other cases. By performing SIMCB electric field anal-ysis according to switching mode, shape and material, it is possibleto prevent the localization of electric field locally, thus preventingheat breakage in advance.

Fig. 8.a) Boundary Condition for Numerical Analysis whenSwitching Mode III and Distribution of Equi-potential Line and

Electric Field Intensity (Main SW: ON, Earth SW: OFF)

4 Conclusion

In this paper, electric field analysis is performed on SIMCB usingsolid-isolated material instead of SF6 gas as insulation material.The structure and material of SIMCB were set and used for electricfield analysis, and the intensity profile of the electric field at theelectrode site was examined. In addition, electric field analysiswas performed for each switching mode according to the operationof main switch(MS) and earth switch(ES). This paper will helpto design variables and materials to prevent local concentration ofelectric field in initial design of multi-circuit breaker.

AcknowledgmentThis paper was supported by Joongbu University Research &

Development Fund, in 2018.

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analysis of electric eld for solid-state isolated multi

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