Controlled switching of high-voltage circuit breakers - ABB

Release instant of circuit

breaker

Breaker operating time

Calculated time delay

signal analysissignal prediction

HIGH VOLTAGE PRODUCTS

Controlled switching of high-voltage circuitbreakers

1. Introduction

Controlled switching (also known as point-on-wave switching orsynchronous switching) is the technique of controlling circuitbreaker (CB) switching operations to occur at an optimum instantin each phase: For CB closing, current inception (making) is tar-geted at a specific phase angle of the gap voltage across the CBcontacts. For opening, contact separation is targeted at a specificphase angle of the current through the CB. The optimum target in-stants depend on load type and configuration, CB characteristics,and power system properties.

The purpose of controlled switching is minimizing harmful electricaltransients upon planned switching of loads such as shunt capaci-tor banks, shunt reactors, no-load power transformers, and un-loaded power cables. The method is also gaining acceptance forre-energizing of Extra High Voltage (EHV) transmission lines, re-placing traditional pre-insertion resistors. For each applicable typeof equipment and its design and connection configuration, CIGREhas recommended suitable controlled switching strategies andcommissioning procedures [1][2][3] which are summarized below.

Controlled switching of a circuit breaker is achieved by a controlledswitching device (CSD, also called point-on-wave controller). TheCSD analyzes the primary voltage and current signals from sub-station VTs and CTs to identify suitable switching targets. Upon re-ceiving a CB closing or opening command, it issues a delayedcommand to each CB pole according to the intended controlledswitching strategy. Note that, except for reclosing on transmission

Controlled switching can minimize harmfulelectrical transients upon planned switchingof loads such as shunt capacitor banks,shunt reactors, no-load power transformers,and unloaded power cables.

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lines, controlled switching is to be employed only for intentionalswitching operations; protection trips must be hardwired to the CBdrive directly, bypassing the CSD.

As a prerequisite for successful controlled switching, the CSDneeds to know the mechanical and electrical properties of the con-trolled CB, which are ideally obtained from type testing according to[3][4]. The CSD uses the information on these properties to predictthe electrical and mechanical operating times of each CB pole so asto issue the output command in time for hitting the controlled switch-ing targets.

The functional principle is demonstrated in Figure 1. The CSD con-tinuously extracts the zero crossings of the reference voltage. Uponreceipt of a switching command, it calculates the delay time neces-sary for switching at the configured target angle, given the pre-de-termined CB operating time. Depending on the mechanical andelectrical properties of the CB, it also adjusts the targets for optimalreduction of switching transients.

Release instant of circuit breaker

Breaker operating time

Calculated time delay

Signal analysis signal prediction

Random instant of

switching commandRandom switching instant

optimal switching instant

Fig. 1: Principle of Controlled Switching

In most CB designs, the operating times may vary with external pa-rameters such as control voltage, temperature, idle time, or storedenergy in the drive [4]. If it is not possible to keep these parameters

constant (e.g. by using a stable power supply or by installing the CBin a temperature-controlled environment), the CSD can reduce theirimpact by applying a compensation curve. Moreover, for the sameCB type, parameters that need to be compensated will vary basedon specific site conditions. Furthermore, the CB’s operating charac-teristics may change over the years or with the number of opera-tions due to aging. The CSD can track this effect by a feature calledadaptive correction: After each operation, it compares the actualswitching instant to the target instant and applies a fraction of thedifference as a correction value to the next CB operation. The actualswitching instants are obtained from either CB current, load sidevoltage, or a mechanical position sensor; the choice depends uponthe availability and suitability of the measurement devices.

2. Common load types

2.1 Shunt capacitor bank and uncompensated powercable

Uncontrolled energization of a capacitor bank or uncompensatedpower cable often causes high transient inrush currents and result-ing switching overvoltages of several pu [1]. These may lead to in-crease in circuit breaker wear and may damage the insulation andjoints of the cable. To minimize inrush currents, energization is ide-ally performed near gap voltage zero of each CB pole. In a three-phase system, the connection configuration (YN, Y, or D) of the ca-pacitor bank determines the optimal energizing targets in eachphase.

Figure 2 demonstrates controlled energization of an ungrounded ca-pacitor bank to mitigate inrush currents. In this example, the inrushcurrents in the second graph are well managed in the range of 2 pufor all three phases.

HITACHI ENERGY | GENERAL TECHNICAL INFORMATION | CONTROLLED SWITCHING OF HIGH-VOLTAGE CIRCUIT BREAKERS 3 / 16


System voltage L1

System voltage L2

System voltage L3

Inrush current L1

Inrush current L2

Inrush current L3

High Inrush first peaks

System voltage L1

System voltage L2

System voltage L3

Inrush current L1

Inrush current L2

Inrush current L3

Reduced inrush current first peaks

Fig. 2: Inrush current mitigation by controlled energization of an ungrounded capacitor bank

Controlled de-energization of a capacitor bank or power cable is typ-ically not needed, as most modern CBs show a very low probabilityof re-strikes (C2 class). However, in some cases, an increasedsafety margin against re-strikes may be preferred. If controlledopening is applied, the contact separation targets are set to ensuresufficiently wide contact gap at the time of arc extinction.

2.2 Shunt reactor

When de-energizing a shunt reactor, interaction between the reac-tor's inductance and stray capacitances causes oscillating voltagetransients with frequency in the range of kHz. Generally, in modernalternating current (AC) CBs with SF6 as dielectric medium, the cur-rent is interrupted in the vicinity of a natural current zero with verylow value of chopping currents. Consequently, the voltage transientacross the breaker (TRV) may not always have too high magnitude

but will have a very short rise time in range of a millisecond. Thiscan lead to breakdown of the dielectric withstand of the contact gapand, hence, re-appearance of the current through arcing. This phe-nomenon is known as re-ignition. Although CBs can withstand re-ig-nitions, some re-ignitions may be harmful to both shunt reactor andcircuit breaker depending on CB design, reactor specification, andpower system configuration, and should be avoided [2][3][5].

IEC standard [5] defines the type testing procedures for circuitbreakers intended for reactor switching duty. This test is mainly toobtain the corresponding circuit breaker characteristic parameterssuch as chopping current and voltage withstand capability. With thetest circuit used, the results are most relevant for the specific nomi-nal current magnitude and transient recovery voltage (TRV) shapeapplied to the circuit breaker. For every installation, the TRV shapeas well as the chopping current will differ based on the design, con-nection configuration and specification of the reactor. It will also be



impacted by the stray capacitances at site. Consequently, thestresses on the circuit breaker and the reactor will be different fromthat imposed during the type testing. Therefore, it is challenging toanticipate the impact of these variations on expected life cycle dura-tion of the breaker or the reactor. To minimize this impact, IEC,IEEE and CIGRE study committees recommend application ofpoint-on-wave (PoW) or controlled switching [3]…[7].

Controlled opening is used to reduce the probability of re-ignitionsby ensuring adequate gap between arcing contacts at the time ofthe natural current zero where the arc is expected to be quenched.

The required arcing time* for each CB pole shall be determined con-sidering the last half-cycle length (which may be extended or short-ened due to interaction between phases) and probable overvoltageacross the contact gap post interruption.

*Arcing time is defined as the time from contact separation in the CB until current interruption.During that time, current flow continues through an electrical arc inside the interrupter.

Figure 3 shows controlled de-energization of a YN connected shuntreactor with 3-limb core. Due to the magnetic coupling betweenphases, the last half cycle (current loop) in the second phase toopen (L3) is shortened whereas it is elongated in the last phase toopen (L2).

Reactor current L1 (last loop unaltered)

Reactor current L2(last loop elongated)

Reactor current L3(last loop shortened)

Output command L1

Output command L2Output command L3

Arcing time L1

Arcing time L2

Arcing time L3

Reference voltage (L2)

Fig. 3: Controlled de-energization of a 3-limb reactor using single-phase reference voltage

Other methods such as surge arresters can also be used to sup-press the TRV peak [8]. Nevertheless, the preferred solution needsto be evaluated for each installation [9]. Utmost care shall be takenif the reactor currents are below the range defined in IEC62271-110[5], as this may result in more severe transient recovery and chop-ping overvoltages.

For further information, refer to the GTI on shunt reactor switching[10].

Energization of a shunt reactor at undesirable instant may lead todissimilar DC component in current of the three phases and result inhigher level of neutral/zero-sequence current continuing for longtime. This may increase the probability of nuisance tripping duringenergization in case of sensitive protection settings. Such trippingmay further lead to unintentional re-ignition in at least one of the CB

poles, as protection trips will be executed without PoW control. Con-trolled energization is often implemented to minimize the DC com-ponent in charging currents and, thereby, the probability of said nui-sance tripping. It is worth noting that reactor cores typically do notsaturate and hence, the charging current will have sinusoidal wave-shape (power frequency only) with exponentially decaying DC com-ponent. The ideal energization target is gap voltage peak for eachpole of the CB.

Figure 4 presents energization of a star grounded reactor. In firstgraph, due to switching happened at undesirable instance, there ex-ists large asymmetry in three phase currents and high zero se-quence current lasting for long time. Whereas, in second graph, withcontrolled switching having negligible deviation in pole-wise switch-ing targets, the asymmetry in phase currents and zero sequencecurrent are minimized, which reduces probability of protection mal-operation.




Neutral current

Current L1

Current L2

Current L3

Asymmetric DC component in all three phase currents,high neutral current


Neutral current

Current L1

Current L2

Current L3

Minimized asymmetry in three phase currents, very low neutral current

Fig. 4: Minimization of asymmetric DC currents on reactor energization

2.3 Power transformer

During no-load energization of a transformer, controlled switching isused for reducing inrush currents and, consequently, voltage distor-tion in the power system. In a weak grid, this distortion may other-wise lead to considerable voltage dip. If the transformer is directlyconnected to a long transmission line, it may create temporary over-voltage due to resonance of the line capacitance with the trans-former inductance, which can even lead to nuisance tripping of otherequipment connected to the same grid.

The magnetizing curves of modern power transformers are often de-signed for high operating flux densities, placing the saturation pointjust above the rated voltage of the transformer. This tight design

may lead to very steep rise in magnetizing inrush current for evenslightly asymmetric operating flux. Therefore, achieving symmetricalflux on energization requires consideration of residual fluxes in thecore from the previous de-energization and of dynamic fluxes due tointer-phase coupling effects – either electrical coupling through adelta connected winding or magnetic coupling through a three-limbcore. To mitigate inrush currents, no-load energization of a trans-



former is ideally performed at a phase angle where prospectivesource-side flux (integral of source voltage) is equal to transformer-side (residual and dynamic) flux in each phase.

The information on residual fluxes can be obtained in two ways:

1. Controlled opening of the CB to set a repeatable pattern ofresidual fluxes in the core. The associated controlled closingstrategy is manually fine-tuned during commissioning. This ap-proach is possible in all installations but is less efficient afteruncontrolled tripping of the CB.

2. Residual flux estimation by integrating the transformer voltageduring CB tripping. The CSD automatically adapts the con-trolled closing strategy to the calculated fluxes, which may varybetween operations. This approach requires a three-phase volt-

age transformer directly connected to one of the windings of thepower transformer; its efficiency may be limited in installationswhere the residual flux may change after de-energization by CBgrading capacitors or other equipment.

Controlled de-energization of a power transformer is usually notnecessary in itself, only to aid controlled energization as explainedabove, as a modern circuit breaker will immediately chop the smallmagnetizing current with negligible risk of re-ignition [2].

Figure 5 shows no-load energization of a power transformer con-nected to a weak grid. It can be observed that mitigation of inrushcurrent assists in minimizing voltage distortion on the grid and re-duces the probability of nuisance tripping of other connected equip-ment.

Grid voltage L1

Grid voltage L2

Grid voltage L3

Inrush current L1

Inrush current L2

Inrush current L3

Distorted grid and transformer winding voltages due to uncontrolled switching and high inrush currents on weak grid

Transformer windingvoltage L1

Transformer winding voltage L2


Voltage dip due to high inrush current

Grid voltage L1

Grid voltage L2

Grid voltage L3

Inrush current L1

Inrush current L2

Inrush current L3

Minimized distortion in grid and transformer winding voltages due to controlled switching with reduced inrush currents on weak grid

Transformer windingvoltage L1



Fig. 5: Minimizing inrush currents and voltage distortion during transformer energization on a weak grid



2.4 Unloaded transmission line

For unloaded transmission lines, controlled energization is used tominimize the switching overvoltage on the line during dead-linecharging as well as during re-energization as part of auto-reclosuresequence. To achieve this, each phase is ideally energized at gapvoltage zero of the corresponding CB pole. For controlled auto-re-closing, the CSD needs to consider any trapped charge remainingon the line from the preceding trip.

The trapped charge voltage may be a decaying DC for an uncom-pensated line. The CSD must be able to detect these conditions andaccurately predict the CB gap voltage, which also depends on the

properties of the line VT. Figure 6 shows successful controlled re-energization of an uncompensated transmission line. The scenariois single-phase auto-reclosure following a temporary phase-toground fault in L1. Upon isolation of the line from both ends, the faultarc may still persist by energy being fed from the healthy phasesdue to inter-phase coupling. This phenomenon, which is also shownin the figure, is known as “secondary arc”. Successful auto-reclosureis only possible when the secondary arc has been quenched. In theexample shown in Figure 6, the secondary arc gets quenched andhence, the auto-reclosure is successful. It can also be observed thatthe switching overvoltage post re-energization is effectively miti-gated using controlled switching.

Fault persisting due to secondary arc

Line side voltage in the healthy phase L2


Current in the faulted phase L1

Current in the healthy phase L2


line voltage post quenching of secondary arc

Mitigated overvoltage post successful auto-reclosure

L1-g fault

Secondary arc quenched

Line side voltage in the faulty phase L1Fault isolated at opposite end of the lineFault isolated at local end of the line

Asymmetry in healthy phase currents till isolation of fault from remote end

Fig. 6: Successful controlled auto-reclosing on uncompensated transmission line

For a shunt compensated line, an oscillating AC voltage with typi-cally more than one frequency component is observed post de-ener-gization of the line. The resulting waveform of the gap voltageacross the CB is a beat signal, the properties of which depend uponthe electrical parameters of the transmission line, on the instant atwhich the temporary fault is cleared, and on the level of shunt com-pensation. Thus, the CSD shall be able to detect the instants of linede-energization and of fault isolation in addition to accurate predic-tion of the zero crossings on the beat pattern of the gap voltage

waveform. Here also, successful auto-reclosure is only possiblewhen the secondary arc has been quenched. Often this is facilitatedby an impedance in the neutral current path, such as a neutralgrounding reactor (NGR). Figure 7 shows successful re-energizationof a shunt reactor compensated line with compensation level lessthan 50%. It can also be observed that the switching overvoltagepost re-energization is effectively mitigated using controlled switch-ing.



Voltage pattern during secondary arc



Current in the faulty phase L1



Beat pattern post quenching of secondary arcMitigated overvoltage post successful auto-reclosure

L1-g fault

Secondary arc quenched

Line side voltage in the faulty phase L1Fault isolated at opposite end of the line

Fault isolated at local end of the line

Asymmetry in healthy phase currentstill isolation of fault from remote end

Fig. 7: Successful controlled auto-reclosing on shunt compensated transmission line

Like for capacitor banks, controlled de-energization is typically notneeded for transmission lines. Nevertheless, it can be optionallyemployed for ensuring re-strike free operation of the circuit breaker.

3. Special applications

3.1 Generator circuit breaker in pump storage power plant

Generator circuit breakers (GCBs) in pump storage power plantsare operated frequently, often several times per day. Whereas ingeneration mode, the plant operator can reduce the generatedpower to near-zero prior to de-energization, in pump mode the GCBwill interrupt the full motor current of several kA. The arc drawn by

this high load current will rapidly erode the arcing contacts within theinterrupter, which necessitates rather short overhaul intervals of justa few years.

Controlled opening can be applied for separating the contactsshortly before natural current zero. As the arc energy is proportionalthe arcing time, keeping this time short will minimize contact erosionand thereby extend the electrical life of the GCB.

Ideally, each GCB pole can be opened individually for optimizedarcing time. For GCBs that allow only simultaneous operation of thethree poles by design, the arcing time can be minimized in onephase, and this optimized phase is rotated randomly or systemati-cally. This balanced approach will statistically reduce interrupterwear over uncontrolled switching. Figure 8 shows controlled de-en-ergization of a GCB to reduce the electrical wear of the interrupter.Being SPO GCB, arcing time is equally optimized for all three polesof the CB.



Current L1

Current interruption L2


Output command

L1Output

commandL2

Output command

L3

Arcing time L1

Arcing timeL2

Arcing time L3



Current L2

Current L3

Fig. 8: Controlled opening of a GCB connected to a pump motor of approximately 4.2 kA

3.2 Shunt compensated cable

Renewable plants and oil platforms are often fed by long underseaHV cables, which may pull high capacitive inrush currents duringtheir no-load energization. The capacitance of a long power cable isoften compensated by shunt reactors at one or both ends, to mini-mize this reactive power pull. Many times, controlled energization isrecommended to minimize these capacitive charging inrush currents

and thereby the overvoltages on the cable, which otherwise may in-crease the risk of failure of the cable insulation. In such cases, ener-gization at voltage zero may cause missing current zeros, whichposes a risk of circuit breaker failure in case of protection trip shortlyafter energization. This can be prevented by applying a non-zero en-ergization target in each phase [3]. Figure 9 demonstrates controlledenergization of a 100% shunt reactor compensated cable for bothzero and non-zero energization targets



Cable current L1

Cable current L2

Cable current L3

Cable voltage L1

Cable voltage L2

Cable voltage L3

Initial peak close to 1 pu



Cable current with missing zeroes for more than 350 ms



Energization at voltage zero target leading to missing zeroes phenomenon

Cable current L1

Cable current L2

Cable current L3

Cable voltage L1

Cable voltage L2

Cable voltage L3

Initial peak1.65 pu

Initial peak1.70 pu

Initial peak1.65 pu

1240 A peak (Steady state 50 A peak)



Energization away from voltage zero target eliminating missing zeroes phenomenon

Fig. 9: Minimizing switching overvoltages and avoiding missing zeroes during cable energization

It can be observed that applying switching targets after gap voltagezero effectively mitigates the missing current zero phenomenon is.However, this targeting strategy may lead to somewhat higherswitching overvoltages. Accordingly, the capability of the cable insu-lation to withstand this overvoltage and consequences on grid sta-bility need to be verified prior to implementing this solution.



3.3 Reactor with very low current rating or non-solidlygrounded neutral

For reactors having low current ratings or non-solidly grounded neu-tral, the peak of the transient recovery voltage and its rate of risepost current interruption may be more severe due to the possibilityof higher chopping currents. For reactors having effectively or non-effectively grounded neutral, the first pole to de-energize will experi-ence higher overvoltages. In such cases, to achieve successful in-terruption using controlled de-energization, larger gap between arc-

ing contacts may be required. Consequently, the required arcingtimes may exceed the nominal half cycle length, leading to inten-tional re-ignition. The needed arcing times* shall need to be evalu-ated considering the reactor design and circuit breaker electricalcharacteristics [5].

*Consult the CB manufacturer to get the arcing time settings of the CSD.

Figure 10 shows one such case where arcing time larger than half-cycle length is used to achieve successful current interruption for re-actor with low current rating and grounded through neutral ground-ing reactor (NGR).

Current L1



Output command L1Output command L2

Output command L3

Arcing time L1 *

Arcing time L2 **

Arcing time L3 ***

Reference voltage L1Current interruption L1

Current L2

Current L3

Contact separation L1



* Greater than ½ cycle – intentional re-ignition** Greater than ½ cycle – intentional re-ignition*** Less than ½ cycle – no re-ignition

Fig. 10: : Controlled de-energization of shunt reactor with low current rating and grounded through NGR, showing arcing times exceeding the nominal half cycle length

3.4 Transformer with large capacitive load –Ferroresonance

In case of no-load energization of a power transformer together witha large capacitive element like a transmission line, ferro-resonancewill occur. If controlled switching is targeted to minimize inrush cur-rents, voltage sag may be observed due to the high inductance ofthe transformer. Here, the effect of the capacitance element will benegligible. On the other hand, energization with high inrush currentsmay lead to overvoltage. In this case, the capacitance will dominateover the low inductance of the transformer. The same can be ob-

served in Figure 10. The amount of overvoltage or voltage sag de-pends on the configuration and design parameters of the trans-former and the capacitance. The switching angles and surroundingsystem parameters will also impact. In such cases, the controlledswitching strategy shall be chosen for the desired transient mitiga-tion (voltage distortion, inrush currents):

● High inrush currents resulting in overvoltage due to ferroreso-nance dominated by the line capacitance

● Low inrush currents resulting in undervoltage due to ferroreso-nance dominated by the transformer inductance



Grid voltage L1 after switching showing ferro-resonance overvoltage

Magnetizing inrush current L1Magnetizing inrush current L2Magnetizing inrush current L3

Grid voltage L1 before switching

High inrush currents, Lower inductance offered by transformer

Magnetizing inrush current L1Magnetizing inrush current L2Magnetizing inrush current L3

Grid voltage L1 after switching showing voltage dipGrid voltage L1 before switching

Low inrush currents, Higher inductance

offered by transformer

Fig. 11: Controlled energization of a power transformer connected to transmission line: (a) high inrush currents resulting in overvoltage due to ferroresonance dominatedby the line capacitance (b) low inrush currents resulting in undervoltage due to ferroresonance dominated by the transformer inductance



3.5 Variable loads

In some controlled switching applications, the CB may not alwaysswitch the same load, or the relevant properties of the load maychange in service. Some examples include,

● The middle CB in a 1½-breakers or similar arrangement

● Transmission line or power cable having shunt reactors that canbe connected or disconnected

● Switchable grounding of the neutral point of a power transformer

Each of these cases requires the CSD to detect the currently activesystem condition and dynamically adjust its operation accordingly.

For example, consider CB2 in the 1½-CB arrangement shown inFigure 11. On the upper end, it is connected to a capacitor bank,which requires energization near voltage zero; the reference signalfor energizing the capacitor would be taken from VTr or V2. On thelower end, it is connected to a power transformer, which should beenergized near voltage peak; the reference signal would be takenfrom VC or V1. Through suitable internal and external logic, theCSD will receive and consider the appropriate reference signal, con-trolled switching strategy, and feedback signal in each of these sce-narios.

CB1

CB2

CB3

V1

V2

VC

VTr

Fig. 12: Variable controlled switching duty on the middle breaker in a 1½-CB diameter

4. Equipment properties

4.1 Circuit breaker characteristics

Controlled switching can be effectively used for different types of CBtechnologies viz. live tank, dead tank, gas insulated, and mixedtechnology. Moreover, the repeatability in mitigation performance

needs stable CB characteristics. Mechanical parameters include op-erating time variation at rated operating conditions, mechanical ag-ing, and the impact of external parameters like temperature, DCvoltage, idle time etc., on the operating times. The same is governedby type of operating mechanism used, e.g. spring drive, hydraulicdrive, hydraulic-spring (hybrid) drive, or motor drive. The electricalparameters include rate of decrease of dielectric strength (RDDS),electrical aging etc. These parameters are governed by the type ofinterrupter design – puffer type, self-blast type etc., whether singleunit or multi-unit per phase, with or without grading capacitors formulti-unit designs etc. To achieve long term reliability in mitigationperformance, the CSD needs to accurately monitor the variation inthe mechanical and electrical characteristics due to aging effect, andit needs to adapt for the same over its entire service period. This isdone by adaptivity function of the CSD.

4.2 CB suitability for controlled switching

The assessment of CB suitability shall be performed for both con-trolled closing and controlled opening operations. The opening oper-ations shall be assessed based on successful reactor switching typetest duty performed for the individual CB type. For closing opera-tions, the suitability shall be assessed based on the gap voltage tar-geting requirement for individual poles of the CB, which depends onthe type, design and connection configuration of the power equip-ment to be switched. The assessment should be performed specifi-cally for the intended system frequency, as the time period of thegap voltage wave significantly affects the performance of controlledclosing operation. Two extremes of targets, viz. gap voltage zeroand gap voltage peak energization, need to be assessed, as thesame will cover most of the power system equipment with diversedesign and connection configurations.

The assessment of a circuit breaker’s suitability for targeting ener-gization at gap voltage zero and peak at 50 Hz is shown in Figure12. As explained in CIGRE TB-757 [3], the worst-case pre-strikevoltage for optimal energization is determined and categorized. Sim-ilar assessment shall be done for different gap voltages based onequipment design and connection configurations.



Optimized peak target for inductive loads (transformers, reactors)

Optimized zero target for capacitive loads(capacitor banks, cables)

Fig. 13: CB suitability assessment for gap voltage zero and peak targets at 1 p.u. gap voltage, 50Hz

Consequently, the suitability for gap voltage zero and gap voltagepeak targets for various load configurations can be determinedbased on the maximum deviation in making targets. The suitabilitycan be categorized in four levels 1…4, with 1 being not suitable and4 being well suitable [3]. An example of the deviation limits for gapvoltage peak and gap voltage zero targets for levels 1 to 4 are givenin Table 1

Table 1 Categories of worst-case pre-strike voltage for assessmentof CB suitability, based on [3]

*Values are indicative and are used to demonstrate the proposed assessment procedure. Themitigation performance also depends upon equipment design, CB characteristics and systemtopology.

Target Criteria Minimum pre-strike voltage when energizing near gap

voltage peak (%)*

Maximum pre-strike voltage when energizing near gap voltage zero

(%)* Rank

Nicely suitable 100 to 80 0 to 30 4

Moderately suitable 80 to 70 30 to 40 3

Suitable at risk 70 to 60 40 to 50 2

Not suitable < 60 > 50 1

Hitachi ABB Power Grids’ high-voltage circuit breakers fulfill the requirements listed above andare thus well suitable for controlled switching application.

4.3 Voltage transformers

Every CSD requires a targeting reference signal, which is usuallythe voltage on the source side of the CB e.g. from a busbar VT. Foroptimal accuracy of controlled switching operations, the phase dis-placement of the VT signal should not exceed ±1 electrical degreeat steady-state nominal voltage.

In some applications, most notably with power transformers, the ac-tual switching instants can be determined from the three-phase volt-age signal on the load side of the CB. Here, inductive VTs are rec-ommended as they usually have better accuracy than capacitiveVTs in rendering the switching transients. See Figure 14

Capacitive VT measurement (higher harmonic noise)

Inductive VT measurement (minimum noise)

Fig. 14: CVT response vs. inductive VT response



4.4 Current transformers

The current through the CB is most often used as feedback signal tothe CSD for determining CB status and actual switching instants.For controlled switching, protection cores should be used to preventsaturation. CTs of accuracy class 5P (IEC) / C (ANSI) or better arerecommended.

Protection CT core (minimum distortion)

Metering CT core (large distortion in waveform due to saturation)

Fig. 15: Transient current rendering by metering core vs. protection core

4.5 Controlled switching devices

Smooth implementation of controlled switching is best assured byinstalling CB and CSD from the same manufacturer. Power Grids of-fers CSDs for all applications described in this document and formany more, to go with its circuit breakers of all technologies.

In addition to the basic controlled switching and optimization func-tionality, state-of-the-art CSDs feature additional functions to addvalue for the user. This may include,

● Monitoring of CB switching operations, utilizing the signals al-ready used for controlled switching (i.e. not requiring additionalsensors on the CB)

● Guided entry of application parameters for easy setup in the in-stallation

● Embedded web server for graphical access to recorded data

● Communication interfaces according to IEC 61850 for seamlessintegration into a digital substation

5. Conclusion

For every circuit breaker that will switch one or more of the loadtypes listed above, controlled switching is beneficial to the CB itself,to the switched load, to equipment insulation, and/or to the powersystem. The reduction of switching transients will result in extendedequipment lifetime, improved power quality, and, ultimately, costsavings. To get best mitigation performance, controlled switchingshould be applied as an overall solution considering CSD, CB andpower system aspects

6. References

[1] CIGRE WG 13.07: “Controlled Switching of HVAC Circuit Break-ers: Guide for Application – Lines, Reactors, Capacitors, Transform-ers, 1st part.” ÉLECTRA, No. 183, April 1999, pp. 43-73.

[2] CIGRE WG 13.07: “Controlled Switching of HVAC Circuit Break-ers: Guide for Application – Lines, Reactors, Capacitors, Transform-ers, 2nd part.” ÉLECTRA, No. 185, August 1999, pp. 37-57.

[3] CIGRE WG A3.35: Guidelines and best practices for the commis-sioning and operation of controlled switching projects. CIGRE Tech-nical Brochure No. 757, 2019.

[4] IEC/TR 62271-302: High-voltage switchgear and controlgear –Part 302: Alternating current circuit-breakers with intentionally non-simultaneous pole operation. Edition 1.0, 2010.

[5] IEC 62271-110: High-voltage switchgear and controlgear – Part110: Inductive load switching. Edition 4.0, 2017.

[6] IEC/TR 62271-306: High-voltage switchgear and controlgear –Part 306: Guide to IEC 62271-100, IEC 62271-1 and other IEC stan-dards related to alternating current circuit-breakers. Edition 1.1,2018.

[7] IEEE Std C37.015-2017: IEEE Guide for the Application of ShuntReactor Switching.

[8] CIGRE WG B5.37: Protection, Monitoring and Control of ShuntReactors. CIGRE Technical Brochure No. 546, 2013.

[9] CIGRE Green Book: Switching Equipment. Springer, 2019.

[10] General Technical Information: Shunt reactor switching – Highvoltage circuit-breakers.High Voltage Products, 2020.

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Controlled switching of high-voltage circuit breakers - ABB

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