IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 50, NO. 5, SEPTEMBER/OCTOBER 2014 2989

Circuit Breaker Transient Recovery VoltageRequirements for Medium-Voltage

Systems With NRGRasheek Rifaat, Senior Member, IEEE, Tarjit Singh Lally, and James Hong

Abstract—The industrial distribution power systems inNorthern Alberta supplies electrical energy to satellite locationsand mining areas. In some aspects, these systems differ from theircounterparts in regular utility distribution cases. Accordingly,they require special attention when performing transientrecovery voltage (TRV) studies and identifying ratings fornew breakers to be added to the system. Meanwhile, NorthAmerican (IEEE) and European (IEC) Standards are embarkingon significant efforts to harmonize breaker specifications andtesting requirements, including TRV tests. An electromagnetictransient program (EMTP) study has been performed toverify system TRV requirements under different conditionsagainst Standard requirements and supplier’s provided testdata. Concerns, lessons learned, and some other findingsassociated with the study are documented in this paper forfuture references and for advancing robust usage of EMTP(alternative transient program) for the performance ofsuch studies for subtransmission and distribution systems indifferent electrical systems.

Index Terms—Breaker ratings, electromagnetic transientprogram (EMTP), high-voltage (HV) circuit breakers, medium-voltage circuit breaker, transient recovery voltage (TRV).

I. INTRODUCTION

THE deregulation of electrical generation in Alberta al-lowed large industrial system identities to own and/or

operate their electrical generation, transmission and distributionequipment, lines, and systems within and in-between theirfacilities. Upon getting the required permits and after beinggranted the status of Industrial System Designate, industrialfacilities could generate, transmit, and distribute their electricalenergy within the designated area. As long as they adheredto the applicable requirements, real-time connections to theAlberta Integrated System are permitted at specific points ofcommon coupling where they may export excess energy orimport shortfall energy as the case may be. Other transmissionor distribution facilities and systems are owned and operated by

Manuscript received June 29, 2013; accepted November 5, 2013. Date ofpublication February 28, 2014; date of current version September 16, 2014.Paper 2013-PSPC-401, presented at the 2013 IEEE Industry ApplicationsSociety Annual Meeting, Orlando, FL, USA, October 6–11, and approved forpublication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS bythe Power Systems Protection Committee of the IEEE Industry ApplicationsSociety.

The authors are with Jacobs Canada Inc., Calgary, AB T2C 3E7, Canada(e-mail:rasheek.rifaat@jacobs.com; tarjitsingh.lally@jacobs.com; james.hong@jacobs.com).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TIA.2014.2309175

an area designated utility as listed in the Electric Utility Act, theAlberta Utilities Commission, and the Alberta Electric SystemOperator.

When initially developed, the subject area was remote with asparse population, little generating capacity, and scarce voltagesupport. Since then, the oil recovery in Fort MacMurray con-siderably changed every aspect of the area’s electrical system.Now, there are several generation and cogeneration facilities,a number of interconnecting lines, and far more complex sys-tem configurations. The system voltages in that area run with+ 5%–+ 10% voltage above their midclass point. The area’s69-kV system is running at 72- to 74-kV continuous operatingvoltage with some areas having a maximum continuous operat-ing voltage as high as 75.9 kV.

Another aspect of the subject systems is associated with howthe system neutral is connected to ground. The 69-kV systemsin most North American utilities have solidly grounded neutralsystems. In the subject case, the main source transformers areequipped with 200-A neutral resistance grounding arrange-ments to suit mining applications for the area. The MiningCodes and Standards require that ground potential rise be lim-ited to 100 V. Such limitations would have been difficult withsolidly neutral grounded systems, due to high-line to ground-fault currents. The case in this paper is selected to highlightfactors associated with transient recovery voltage (TRV) studiesin industrial and mining areas where system voltages, neutralconnections, and overall operating conditions may differ fromtypical distribution utility cases.

It is assumed that the facility substation is an existing sub-station that, over two decades, encountered several changes. Anew breaker was to be added to the existing substation in orderto provide a looped circuit supplying satellite and mining areas.Inherited operating practices require the system to operate witha minimum bus voltage of 72.5 kV with a potential to increasemaximum continuous operating voltage unless restricted byidentified system needs. The breaker shall be specified to NorthAmerican Standards which have been recently updated to har-monize with IEC Standards. Fig. 1 shows an overall single-linediagram for the case study.

II. BREAKER TRVs

A. What Is TRV?

When a breaker trips, its three-phase poles mechanicallytravel apart introducing gaps between their stationary and mov-ing parts. In simple arrangements, each side of the pole could

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2990 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 50, NO. 5, SEPTEMBER/OCTOBER 2014

Fig. 1. 72.5-kV distribution system in Industrial Northern Alberta.

be a supply side and/or a load side of the breaker. The currentcontinues to flow in ionized newly created air or a gas gap untilit reaches a value of zero (zero crossing). In a typical ac system,the current will cross zero within 1/2 cycle (i.e., 8.3 ms in an60-Hz system and 10 ms in an 50-Hz system) after contactdeparting. The zero crossing will occur at a different time foreach phase of the three phases in the system.

During interruption of ac current, the arc loses conductivityas the instantaneous current reaches zero. Within a few mi-croseconds after current zero, the current stops flowing in thecircuit. The electrical system’s response to the sudden changein current differs on the two sides of the breaker. The differencein voltage between the two sides during the interruption processgenerates TRV. TRVs could be exponential (overdamped) oroscillatory (underdamped). The TRV is dependent on the elec-tric circuit on the two sides of the breaker. Interruption will befully successful if arcing does not reoccur due to TRV. The fulldefinition of the circuit breaker ability to withstand the TRVand the power frequency recovery voltage is given in [3].

TRV is also affected by other system and breaker parameterssuch as prefault voltage, fault current, and system neutralgrounding arrangement.

Standards identified two categories of breakers those that arerated above 100 kV and those that rated below 100 kV. Circuitbreakers with rated voltage less than 100 kV are classifiedinto two classes, i.e., S1 and S2. A circuit breaker class S1 isintended to be used in a cable system. A circuit breaker classS2 is intended to be used in an overhead line system [6].

To simplify the required calculations needed to establishthe Standards requirements, factors were used. Two importantfactors are used in IEEE Standards [3] and [5]; the first pole toclear factor “Kpp” and the amplitude factor “Kaf.” The defini-tions are in the relevant standards [3] and [5]. The first factor“Kpp” is due to each pole of the breaker having a zero-crossing

point that is different from other poles. Hence, one of the poleswill be “the first to clear.” With basic symmetrical componentsanalysis, Kpp = 3X0/(X1 + 2X0). Accordingly, it will be afunction of the system neutral grounding arrangement. Withsome assumption of that ratio, for effectively grounded systems,X0/X1 is ≤3, and the first pole to clear factor is 1.3. For a non-effectively grounded system or an ungrounded system is 1.5.

The amplitude factor reflects the damping in the system. Itwill be affected by the lines connected at the subject breaker(overhead, cables, long lines, short lines). The Standards es-tablish values for this factor based on worst case scenario fortypical systems.

If the system has a standard operating voltage and standardconfigurations, then a breaker that is designed and tested inaccordance with the standards might be able to withstand theTRV. If the system operating voltage is nontypical and its con-figuration is special, then a TRV study might help in verifyingif a selected breaker is capable to withstand the TRV.

B. Breaker Standards

North American Standards (ANSI/IEEE) for high-voltage(HV) breakers have continuously been revised and updated.ANSI breaker standards are part of the IEEE C37 Series [3]–[6].IEEE Standard C37.011-2005 [3] is the Application Guidefor breaker TRV, and C37.06-2009 [4] is the overall ratingstandard, which also include reference to TRV (main part andinformative appendix). Recent changes in these standards havefocused on the harmonization between IEC and ANSI/IEEE.In recent years, Standards [3]–[5] were revised in the directionof harmonization. One key aspect of the harmonization is thesupplier’s ability to perform a single set of tests per breakertype that will address both North American and Internationalmarkets. IEC also adopted harmonization policies as demon-strated in adding amendments such that Amendment 1 to IEC62271-100.

C. Applications of Standards to Case Study

From Standard IEEE-C37.06, the following factors are ad-dressed [4, Table 6].

• Breaker class is S2; circuit breaker is rated below 100 kVfor overhead lines.

• System is noneffectively grounded.• Breaker rated maximum voltage is 72.5 kV.

The rated maximum operating voltage for breakers was alsodefined in [5]. The definition stipulates that such rating is “theupper limit for operation.” Hence, for a typical 69-kV systemwith 5% margin, 72.5 kV is the proper rated maximum voltage.As explained in earlier sections of this paper, the 69-kV systemin Northern Alberta is labeled as a 72.5-kV system. For thissystem, the rated maximum voltage is 72.5 kV +5% (76 kV),which is a nonstandard maximum voltage for breakers under theupdated Standards. Nevertheless, selecting a suitable breakerfor the subject system would be another part of the breakerselection exercise. The verifications for the TRV part mightbe done utilizing the updated Standards, supplier’s data sheet,

RIFAAT et al.: CIRCUIT BREAKER TRV REQUIREMENTS FOR MEDIUM-VOLTAGE SYSTEMS WITH NRG 2991

TABLE IT-VALUE VERSUS TRV PEAK FOR 72.5-kV BREAKERS

breaker type tests, and the electromagnetic transient program(EMTP) model of the subject system.

Breaker suppliers have been offering international breakerswith higher voltage classes (i.e., 100 kV, 115 kV, etc.) andreadjusting them for the area’s specifications. Most of suchvoltages are not typical in North America. Hence, the supplier’sapproach would be to readapt the original breaker type testsas much as possible and supplement them if necessary byIEEE tests. Such readjustment will mean that TRV type testscould differ from breakers made entirely to North AmericanStandards. In the case study, information was requested fromthe suppliers, and test results were received and used in the TRVStudy.

D. Breaker TRV and Test Requirements

The Standards show what TRV parameters are to be expectedfrom the supplier for each breaker class. The following showsthe ratings for TRV in breakers less than 100-kV rating andclass S2 [4, Table 7]. It might be observed that the Standardvalues are preferred values and not mandatory. It might be alsoobserved that TRV parameters are shown at different values ofcircuit breaker short-circuit data, namely, T100 (100%), T60(60%), T30 (30%), and T10 (10%). For 72.5-kV breakers,Table I of this paper shows a summary of TRV peak voltage val-ues as extracted from Table 7 of the Standards to demonstratehow calculations are conducted on selected breaker ratings andfor reference purposes. As an example, If the system’s ultimateshort-circuit current is between 24 and 40 kA, then the breakerT100 values shall be used. If the system’s ultimate short-circuitcurrent is between 12 and 24 kA, then T60 values of 146 kAcan be used. Similar derivations could be used for T30 and T10conditions.

III. TRV STUDY USING EMTP

The calculations to obtain the peak value at T10 for 72 kVbreaker is given as an example in C37.011 [3]. StandardC37.04b [5] shows how to combine the envelope and the testvalues for a circuit breaker in order to devise testing procedurefor breaker TRV capability. Standard C37.011 suggested forTRV studies to utilize an approach similar to the approachverifying that a breaker is tested for certain TRV requirements.TRV requirements shall be verified for peak value (TRV peakvalue) and the rate of rise of recovery voltage value (RRRV)(see Fig. 2).

Some years ago, calculations of transient voltage weredone using system equivalent circuits, initial conditions, andmathematical equations with some approximations and hand-

Fig. 2. Simplified superimposition of TRV envelope over system TRV.

held calculators. Similar exercises can be performed usingEMTP alternative transient program (ATP) (see Fig. 3), bymodeling the system fault condition on one side of thebreaker, allowing fault clearing time, then switching the breakeroff (switch circuit interruption at the zero crossing of eachphase). In order to establish most representative modeling, caremust be given to the following factors that affect the TRVcalculations.

• Modeling of each side shall include the source withits most representative short-circuit characteristics (worstcase scenario).

• Modeling shall include capacitances and reactances as-sociated with the connected system. That shall includeequipment and bus capacitances.

• Equipment may be lumped at each side; however, lumpingof equipment must not affect the transient performance ofeach side.

• If the system includes a back-feed through a parallel path,it is recommended to isolate the parallel path as it couldskew the results.

• The model configuration shall allow calculations to bedone separately for:

• terminal TRV (TRV with a fault near breakerterminal);

• short-line TRV (Fault at the remote end of a shortline);

• if required out-of-phase TRV shall be also calculated.• If calculations are required for different source circuit

ratings, the source modeling and configuration shall allowcalculations to be done separately for:

• T100;• T60;• T30;• T10.

• If calculations are required for different system maximumcontinuous operating voltages, as shown in the subsequentexample.

Consider the system shown in Fig. 1 as an example. Twobreakers were to be examined for TRV, i.e., Breaker A andBreaker C. Breaker B shall be left open for the TRV calculationpurposes.

2992 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 50, NO. 5, SEPTEMBER/OCTOBER 2014

Fig. 3. EMTP model for the example shown in Fig. 1.

The following comments address the results of several runsand are shown in Figs. 4–6.

• Fig. 4(a): While source system voltage is at 79 kV, abreaker terminal fault occurs. TRV peak values are accept-able for T10 and T30, marginal for T60, and unacceptablefor T100. This means that if the system ultimate shortcircuit would be 12 kA or less, the proposed breaker willbe acceptable; otherwise, an alternative breaker shall beconsidered. RRRV, which is the initial slope of the voltagecurve, meets the requirements for all test ratings.

• Fig. 4(b): While system voltage is at 76.125 kV, a breakerterminal fault occurs. TRV peak values are acceptable forT10, T30, and T60 and unacceptable for T100. This meansthat if the system’s ultimate short circuit is equal to 24 kAor less, the proposed breaker will be acceptable; otherwise,an alternative breaker shall be considered. RRRV, which isthe initial slope of the voltage curve, meets the require-ments for all test ratings.

• Fig. 4(c): While system voltage is at 74.16 kV, a breakerterminal fault occurs. TRV peak values are acceptable for

T10 and T30, and T60 and marginal for T100. This meansthat if the system’s ultimate short circuit would be less than40 kA, the proposed breaker will be acceptable. RRRV,which is the initial slope of the voltage curve, meets therequirements for all test ratings.

• Fig. 4(d): While system voltage is at 72.5 kV, a breaker ter-minal fault occurs. TRV peak values are acceptable for allT classes: T10, T30, T60, and T100. RRRV, which is theinitial slope of the voltage curve, meets the requirementsfor all test ratings.

To demonstrate the sensitivity of TRV to effective neu-tral grounding, additional model runs were performed. Fig. 5shows the reduction in system TRV requirements when solidlygrounded system.

Short-line TRV analysis was also required. Since the lineconnected to the breaker is a short line, a fault was simulatedat remote end of the line. Results show TRVs are within thebreaker capability.

Breaker C is in a remote substation, and it was requestedto verify its capability. To simulate the case for Breaker C,

RIFAAT et al.: CIRCUIT BREAKER TRV REQUIREMENTS FOR MEDIUM-VOLTAGE SYSTEMS WITH NRG 2993

Fig. 4. (a) (Top) Breaker A, terminal fault, system voltage 79 kV. (b) Breaker A, terminal fault, system voltage 76.125 kV. (c) Breaker A, terminal fault, systemvoltage 74 kV. (d) (Bottom) Breaker A, terminal fault, system voltage 72 kV.

2994 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 50, NO. 5, SEPTEMBER/OCTOBER 2014

Fig. 5. Hypothetical system with solidly grounded neutral, i.e., TRV at twodifferent voltages.

Fig. 6. Short-line TRV results are within the envelope.

Breaker A was closed. The fault branch in the EMTP model wasrelocated to the load side of Breaker C. The fault was simulatedand breaker C was similarly tripped as breaker A did in earliercases. The TRV peak value is less than all test ratings of circuitbreakers. Additionally, the RRRV is inside of the initial slopefor all test ratings (see Fig. 6). Hence, the worst case scenariowas confirmed to be at the source substation as anticipated.

IV. CONCLUSION

If industrial system operating voltages are out of typicalrange, TRV analysis is critical for breakers performance ver-ifications. In industrial and mining supply systems, wheresupply transformer neutral might not be solidly grounded suchverification become more critical. Use of the updated IEEEStandards in combination with the appropriate EMTP (ATP)system models and runs will allow completion of the analysisand appropriate selection of breaker. An example of a 72.5-kVdistribution system was discussed and demonstrated to assistpreparation of TRV study cases for similar systems.

REFERENCES

[1] C. L. Wagner, D. Dufournet, and G. F. Montilllet, “Revision of the ap-plication guide for transient recovery voltage for AC high-voltage circuitbreakers of IEEE C37.011: A working group paper of the high voltagecircuit breaker subcommittee,” IEEE Trans. Power Del., vol. 22, no. 1,pp. 161–166, Jan. 2007.

[2] R. W. Alexander and D. Dufournet, Transient Recovery Voltage (TRV) forHigh-Voltage Circuit Breakers. St. Pete Beach, FL, USA: Tutorial IEEESwitchgear Committee, May 2003, ch. 7, Alstom T&D Tutorial.

[3] Application Guide for Transient Recovery Voltage for AC High-VoltageCircuit Breakers, IEEE Std. C37.011-2005, 2005.

[4] IEEE Standard for AC High-Voltage Circuit Breakers Rated on aSymmetrical Current Basis—Preferred Ratings and Related RequiredCapabilities for Voltages above 1000 V, IEEE Std. C37.06-2009, 2009.

[5] IEEE Standard Rating Structure for AC High-Voltage Circuit Breakers,IEEE Std. C37.04-1999 (R2006), 2006.

[6] IEEE Standard Rating Structure for AC High Voltage Circuit BreakersRated on Symmetrical Current Basis, Amendment 2: To Change theDescription of Transient Recovery Voltage for Harmonization with IEC62271-100, IEEE Std. C37.04, 1999.

[7] High-Voltage Alternating Current Circuit Breakers, IEC Pub. 60056 (Ed4.0b), IEC, Geneva, Switzerland, 1987.

[8] High Voltage Switchgear and Control Gear––Part 100, AlternatingCurrent Circuit Breakers, IEC Pub. 62271-100 (Ed. 2), IEC, Geneva,Switzerland, 2008.

[9] ATP Rule Book, Alternative Transient Program Rule Book,Canadian/American EMTP User Group, West Linn, OR, USA, 1993.

[10] R. Rudenberg and G. McKay, Transient Performance of Electric PowerSystems–Phenomena in Lumped Networks, 1st ed. New York, NY, USA:McGraw-Hill, 1950.

[11] J. A. Martinez-Velasco, Ed., Power System Transients ParameterDetermination—Chapter 7. Boca Raton, FL, USA: CRC Press, 2010.

Rasheek Rifaat (M’76–SM’93) received the B.Sc.degree from Cairo University, Giza, Egypt, in 1972and the M.Eng. degree from McGill University,Montreal, QC, Canada, in 1979, both in electricalengineering.

Between 1975 and 1981, he was with UnionCarbide Canada Ltd., Beauharnois, QC. In 1981, hejoined Monenco Consultants, Calgary, AB, Canada,and Saskmont Engineering, Regina, SK, Canada,where he was involved in thermal power generatingplant projects. Since 1991, he has been with Jacobs

Canada Inc., Calgary, working on large- and medium-size power cogenerationprojects, and oil and gas projects. He has published a number of paperson power system protection and industrial and cogeneration power systemmodeling and analysis.

Mr. Rifaat is a Registered Professional Engineer in three Canadian Provinces:Alberta, Saskatchewan, and Ontario.

RIFAAT et al.: CIRCUIT BREAKER TRV REQUIREMENTS FOR MEDIUM-VOLTAGE SYSTEMS WITH NRG 2995

Tarjit Singh Lally received the B.Sc. degree in elec-trical engineering from Panjab University, Chandi-garh, India, in 1974.

He was with the Department of Atomic Energy,Mumbai, India, and then the State Electric UtilityCompany Board, Punjab, India. In 1995, he movedto Canada where he worked as an Electrical En-gineer with Magna Projects, Calgary, AB, Canada,until 2002. Since 2002, he has been an ElectricalEngineer with Jacobs Canada Inc., Calgary. His tech-nical interest area includes system studies, protection

coordination, and high-voltage substations equipment and systems. He enjoyscoaching and providing technical support to future electrical system and high-voltage engineers.

Mr. Lally is a Registered Professional Engineer in in two CanadianProvinces: Alberta and British Columbia and two US States: Georgia andVermont.

James (Jinsoo) Hong received the B.Sc. degree inelectrical engineering from the University of Alberta,Edmonton, AB, Canada, in 2012.

Since May 2012, he has been an Electrical En-gineer (in Training EIT) with Jacobs Canada Inc.,Calgary, AB. While working at Jacobs, his workhas included electrical power systems modeling andanalysis. He has prepared various industrial systemmodels utilizing several commercial software pack-ages, as well as the publicly available electromag-netic transient program (EMTP), and the alternative

transient version (EMTP/alternative transient program). He has been alsoinvolved in studies associated with system modeling, including power systemanalysis, power system transients, harmonics, and protection studies.