Setting-Specific Representation of Tripping ... · PDF fileTripping time Overload relay MCB MCB Miniature circuit-breaker ... C and D), the overload relay ... lable using a 3-pole

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Setting-Specific Representation

of Tripping Characteristics and

Competent Assessment of their Interaction

Technical PaperDipl.-Ing. Wolfgang EsserDipl.-Ing. Dirk Meyer

2nd Revised Edition, 2007

Circuit-breakersNZM

Circuit-breakersIZM

Switchboard systems

Reliably and safely controlling,switching and managing power. In industry, in buildingsand in machine construction.Innovative protection concepts.With built-in diagnostics andcommunication functions.Housed in modern switchboardsystems.

Tripping diagram

Tripping diagram

Tripping current [A]

Trip

pin

g t

ime

Overload relay MCB MCB

Miniature circuit-breaker

Fuse

Freely configurablecharacteristic

Motor-protectivecircuit-breaker

Freely configurablemotor characteristic

General specifications:Company: Moeller GmbH Bonn

Installation: NSV SelektivEditor: Max Mustermann

Date: 13.11.2006Line: 415 V / 50 Hz

For Moeller Electric Sales and Support call KMparts.com (866) 595-9616

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Brief summary

If several protective devices are to inter-act effectively in a switchgear system,it is necessary to compare their trippingcharacteristics in order to evaluate theirselectivity for the demands of enhancedsystem availability. It is important to usecharacteristic curves which take theactual individual settings on the protec-tive devices into account for all tests.This is practically impossible withprinted characteristic representations incatalogues. In this technical paper thedevice-specific setting features of differ-ent protective devices are presentedand assigned to the various types ofelectrical equipment. The Moeller“CurveSelect” software tool enables asimple common representation of thecurves on multiple protective devices onthe same time and current scales forvery little effort.

This significantly simplifies the represen-tation of the curves. The tool enablesassessment of the Moeller circuit-breakers NZM and IZM, the motor-pro-tective circuit-breaker PKZM, the minia-ture circuit-breaker FAZ (tripping char-acteristic B, C and D), the overload relayZB and fuse types gL or gG. The charac-teristics of older switch generations arealso shown with circuit-breakers toenable planning of possible expansions. New in Version 1.071 is the freely defin-able representation of motor run-upcharacteristics, in order to determine ifthe selected motor protection deviceenables malfunction-free run-up of athree-phase asynchronous motor. As itmay be necessary to verify the interac-tion of non-Moeller products (e.g.medium-voltage protection devices orprotection devices from competitors),

the program now offers a feature whichallows the user to freely self-definecharacteristic curves. The additionalfeatures considerably add to the valuesoftware tool that can be used with 11user languages. The handling of the 11selectable languages can be found inthe program Read_Me file that allowsthe entry mask and the representationof the results to be displayed in the cho-sen language. Moeller provides thishelpful tool on the internet and on a CDfree of charge (Figure 1). The user isguided through the data entry phase bythe provision of permissible parameters.The handling involved with the Excel filebased tool is also briefly described inthis technical paper. The result, which allows for common representation of the curves as pro-tected engineering documentation with

Setting-specific representation of tripping characteristics and competent assessment of their interaction– Explanations regarding the Moeller “CurveSelect” V1.071 software tool –

Figure 1: Representation of the tripping characteristic of different protective devices on the same time and current scale. The device data and settings arestated at the upper end of the curves.

Tripping diagram


Trip

pin

g t

ime

Overload relay MCB MCB

Miniature circuit-breaker

Fuse

Freely configurablecharacteristic

Motor-protectivecircuit-breaker

Freely configurablemotor characteristic

General specifications:Company: Moeller GmbH Bonn

Installation: NSV SelektivEditor: Max Mustermann

Date: 13.11.2006Line: 415 V / 50 Hz


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individual project designations, canbe saved, printed or exported to otherdocuments. But also those who arefamiliar with the physical fundamentalprinciples and particularities of theequipment, should spare the time toread the section entitled “Handlingof the Moeller CurveSelect programV1.071 software tool” and considerthe advantages of the new tool.

In addition, the unique ARCON ® arc-fault protection system from Moelleris briefly presented. The system whichacts within a few milliseconds protectsagainst fatal injuries and ruinous dam-age to the system. All conventional pro-tective devices available on the marketare simply too slow to effectively pre-vent damage caused by an arc-fault.This additional protection is particularlyimportant when working under liveconditions in special circumstances.

Selection criteria for circuit-breakers- 4 main applications and personnelprotection -

Circuit-breakers provide the highestlevel of complexity with the setting oftheir tripping characteristics among theprotective devices in the low-voltageengineering field. The diverse settingpossibilities are explained using thenew NZM circuit-breaker as an example.The areas of application of the NZMcircuit-breakers, with releases for over-load and short-circuit currents andcomprehensive system accessories,are also extremely diverse.

NZM compact circuit-breakers (MCCB)are offered by Moeller with electronicreleases and with differing application-dependent variables for rated opera-tional currents between 15 and 1600 A.The smallest switch frame size, theNZM 1, and a simple standard variant ofthe NZM 2 and NZM 3 frame size, donot feature an electronic release as theyare exclusively equipped with electro-mechanical releases, intended as parti-cularly attractively priced circuit-brea-kers and as the lowest non-delayedstage in a selectivity (discrimination)chain. Three switch frame sizes with thedesignations NZM 2, NZM 3 and NZM 4contiguously cover the current range upto 2000 A and partly overlap in their ran-ges, with versatile electronic releases. The

IZM open circuit-breakers (ICCB) areadditionally offered in three frame sizesfor larger rated currents up to 6300 A(Figure 2). All switch frame sizes featureseveral variants with differing levels ofshort-circuit breaking capacity. The pri-ces of the switches reflect the short-circuit breaking capacity performanceas well as other features. As a result, theplanning engineer can economicallymatch the project-related switch ratingto the required short-circuit rating ofthe system. The selected switchingcapacity defines – corresponding toFigure 7 – the lower end of the trippingcharac-teristic which is presented later.Table 1 indicates the type variants avai-lable using a 3-pole switch in the IECversion. The range also includes swit-ches approved to the North AmericanUL and CSA standards and the regionalspecific 4-pole circuit-breaker versions.The application-specific variants of theswitch which are also indicated inTable 1 will also be described later.

The NZM circuit-breakers presented areused with differing protective tasks inpractically every type of low-voltagepower distribution system as outgoingcircuit-breakers. In small to mediumsized distribution systems, they alsoserve as incoming circuit-breakers upto 2000 A. In addition to pure power

distribution tasks, the switches areused for the protection of various typesof equipment against overload andshort-circuit as well as for protectionof the switchgear and the connectingcables and conductors and also inmachines and system controls. Theycomprehensively master the four mostimportant main application areas:

protection of systems motor protectiontransformer protection and generator protection (Figure 3).

Protection of systems is understood asthe protection of cables and conductorsas well as the protection of busbarsystems. It is highly significant inswitchgear systems for power distribu-tion (distribution board) – and not tobe neglected – for busbar trunkingsystems, the attractive alternative tocables. Protection of systems alsoincludes the protection of theswitchgear, protective devices andcontrol circuit devices as well as theautomation control systems installed inthe switchgear systems. The motor pro-tection, generator protection and trans-former protection fields of applicationserve the specific protection of statedequipment types [1]. For optimum pro-tection and economic use of this equip-ment, the tripping characteristics of the

1 MCCB = Molded Case Circuit Breaker2 ICCB = Insulated Case Circuit Breaker3 IEC = International Electrical Commission4 UL = Underwriter‘s Laboratories (http://www.ul.com)5 CSA = Canadian Standards Association (http://www.csa.ca)

Figure 2: The four frame sizes of the Moeller NZM compact circuit-breakers. Frame sizes NZM 1, NZM2 and NZM 3 feature a thermo mechanical and electromechanical release. The frame sizes NZM 2, NZM3 alternatively feature electronic releases as with the NZM 4 and the open circuit-breaker IZM asshown on the left.


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c)

b) ➜

➜

a) ➜d) ➜

protective devices must be matched asprecisely as possible, by the settingsdescribed later, to the individual per-formance of the equipment to be pro-tected. Economically viable operationalso means that the protective devicesdo not trip when not intended.

In addition to these functions whichare primarily intended to protect theequipment, the additional personnelprotection demands should not beneglected. Personnel protection isimplemented with all switch types asprotection against electrical shock, byfast automatic shutdown of dangeroustouch voltages. Sufficiently short trip-ping times must be ensured by theengineering and dimensioning of theswitch, e.g. by the observance of the“protective multiple earthing condi-tions” (IEC / EN 60 364-4-41, VDE 0100Part 410) [2]. The following additionalprotective functions do not influencethe necessary switch settings and trip-ping characteristic:

some switch frame sizes feature

optional, separately adjustablefault current or earth fault protectivefunctions,on all frame sizes personnelprotection is implemented by fastsafety disconnection of outgoersandequipment,an additional protective function,the undervoltage protection, canbe performed by the circuit-breakerif it is equipped with an undervoltagerelease,in this case they simultaneouslyguarantee the protection againstautomatic restart after an inter-ruption of the voltage supply, all NZM and IZM circuit-breakerspresented can provide main switchand isolating characteristics [3, 4].

In the power distribution field, switch-disconnnectors and circuit-breakers aregenerally the most important switchingand protective devices. At critical nodesin the electrical power supply whichareresponsible for the power supply toentire factories or town districts, fuseless

protection of the supply by circuit-breakers which are ready to restartquickly without the requirement forinstallation of spare parts are of primaryimportance. Selective or discriminativeprotection on various levels of the powernetwork ensures a high level of systemand process availability. This is under-stood to mean that only the protectivedevice in the vicinity of the short-circuitwill trip. The following are conventionalswitchgear combinations to implementselective (discriminative) networks:

fuse – fuse, fuse – circuit-breaker, circuit-breaker – fuse,circuit-breaker – circuit-breaker.

Figure 4 indicates an example for anetwork design with time selectivity(time-discriminating), which is achievedby using switches with differing short-time delays for the short-circuit release.Moeller helps the practically-mindedto find the optimum, selectiveengineering design – even includingdesigns considering fuses – with the

Figure 3: The four main applications of the NZM compact circuit-breakers, for which IZM circuit-breakers are partly used with higher currents:a) protection of systems / line protection b) transformer protection c) motor protection d) generator protection


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NetSelect or NetPlan planning software.The Moeller NZM and IZM circuit-breakers with electronic releases canalso be comfortably networked intomodern switchgear systems [5]. Dedicated software tools are also available for networking tasks.

Functional areas in the trippingcharacteristic and the thermalmemory of the release

Tripping characteristics indicate multiplefunction areas of the safety devices.Different releases installed in the samedevice are partly responsible for thediffering functional areas. The trippingcharacteristic expresses the behaviourof a protective device dependant on thedifferent levels of current flow and thetimes for which the currents are flo-

A

S1

S2

S3

S4

S5

S3S4S5

B

C

D

2h100

40

250A 1000A 2000A

10

10

40

4

1

1

4

400

10

50ms

50ms40

100

1

4

I[A]

CC

tv

100 200 400 1000 2000 4000 10000 20000

S3

S4

S5

Hochspannung

Niederspannung

Min

uten

M

illi-S

ekun

den

Seku

nden

Figure 4: Example of a cascade type network design. The switches on the various network levelsshould shutdown selectively. This can be implemented with time selectivity. The switch on the lowestlevel (S 5 in the example) features a non-delayed short-circuit release, all upstream switches have ashort-delay time of about 50 ms, 100 ms etc.

High voltage

Low voltage

Min

ute

sSe

con

ds

Mill

isec

on

ds

Frame sizes, applications, switching capacity, setting range of the NZM circuit breaker,

IEC-version, 3-pole switch

Type

Electromechanical release Electronic release

IEC switching capacity at 400 V IEC switching capacity at 400 V

B = 25 kA N = 50 kA H = 150 kA N = 50 kA H = 150 kA

Setting ranges in A Setting ranges in A

NZM..1 -A.. 15 - 160 15 - 160 15 - 160 *) - - -

NZM..1 -M.. 16 - 100 16 - 100 - - - -

NZM..1 -S.. 40 - 100 40 - 100 40 - 100 - - -

NZM..2 -A.. 100 - 250 100 - 250 15 - 250 - - -

NZM..2 -M.. 100 - 200 100 - 200 16 - 200 -ME.. 45 - 220 45 - 220

NZM..2 -S.. 125 - 200 125 - 200 40 - 200 - - -

NZM..2 - - - - -VE.. 50 - 250 50 - 250

NZM..3 - - - - -AE.. 125 - 630 125 - 630

NZM..3 - - - - -ME.. 110 - 450 110 - 450

NZM..3 - - - - -VE.. 125 - 630 125 - 630

NZM..4 - - - - -AE.. 315 - 1600 315 - 1600

NZM..4 - - - - -ME.. 275 - 1400 275 - 1400

NZM..4 - - - - -VE.. 315 - 1600 315 - 1600

-A.. Protection of systems and cables -M.. Motor protection -S.. Short-circuit protection (without overload protection)

-AE.. Protection of systems and cables-ME.. Motor protection -VE.. System and cable protection,

selective and generator protection

Table 1: Overview of the most important selection criteria for the NZM circuit-breakers and the solution with electromechanical or electronic releases.

*) H = 100 kA


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wing. The tripping characteristic indica-tes the behaviour of a circuit-breakerunder operational as well as underexceptional conditions. Constructivefeatures of the circuit-breaker can havean influence on the specific trippingcharacteristic. The tripping characteris-tic must correspond with the demandsof the equipment to be protected. Atrip will not occur underneath or leftof the tripping characteristic in thecontrolled admissible range. Thecurrent/time field underneath/left ofthe tripping characteristic can be usedoperationally (operational conditions).For example, in this range drives willalso operate intermittently resulting in ahigher current (in the overload range)for a short time. The equipment and theprotective devices can cool off in theintermittent pauses. The field above orright of the tripping characteristic indi-cates the range for exceptional condi-tions with the faults possible due to anoverload or short-circuit. The characte-ristic is generally represented as a log-log coordinate system. The characteris-tic covers three ranges as indicated inFigure 5:

a Non-trip range

In the first range, the switch will nottrip without reason when the equip-ment is not endangered. For this rea-son, the switch may not trip within2 hours (at I ≤ 63 A, within 1 hour)when started from the cold state, andat the reference temperature whenloaded on all poles with up to 1.05times the current setting Ir for thecurrent-dependant delayed overloadrelease (conventional non-trippingcurrent).

b Overload range

The second range is the overloadrange. In this range the current-dependant thermal (bimetallic)or current-dependant electronicdelayed overload release acts. WithNZM circuit-breakers, the overloadreleases are always adjustable withthe exception of special devicesdesigned for the North Americanmarket. The tripping time is longwith marginal overcurrents andbecomes shorter with larger cur-rents. This characteristic corresponds

with the load capability of the equip-ment to be protected. The permissi-ble overcurrents cannot be increasedas required, because the thermal anddynamic loading for the equipment,cabling, switchgear system andswitches increase with the square ofthe current (pay special attention tothis fact when engineering for high-inertia motors). The overload rangeextends up to the application rele-vant adjustable response range ofthe magnetic short-circuit instan-taneous release (comparable withan emergency brake). The rangebetween factor 1.05 and the factor1.2 to factor 1.3 current setting valueIr is defined as the current limitrange. This range is of particularimportance for standard-conformadjustment of the switch duringmanufacture. With electronic over-load releases on the circuit-breakers,e.g. for the motor protection, theposition of the curve on the time axis(tr) can also be offset to take heavystarting duty into consideration. Theset time tr applies for 6 times the cur-rent setting Ir. The designation “trip-ping class” (Class 5, 10, 20, etc.) isknow for a similar function with theelectronic motor-protective relay,and allows the max. tripping timeat 7.2 times the current setting Ir.On relays the standard setting is Class10 A with tr = 10 s.

The short-circuit circuit-breakerswithout overload release are a spe-cial type. This switch is combinedwith additional overcurrent protec-tive devices. These combinations areselected for the protection of motorswith extended start-up times orwhen the circuit-breaker is not sup-posed to trip with a self-correctingoverload. This type of switch is foundmore frequently in North Americathan in the IEC world.

c Short-circuit range

The permissible overload limit forthe equipment and the switch areexceeded here. This is where theshort-circuit range commenceswhere the non-permissible currentshould be shutdown as soon aspossible. The response value ofthe short-circuit release Ii (i = instan-

a b c

t Ir

tr

Irmv

tvIrm

I

Figure 5: The figure indicates a tripping characteristic with functional ranges1. Non-trip range / operating range to the left of or under the red tripping characteristic,2. Overload range, a brief overload is possible,3. Short-circuit range.The figure also indicates the variable parameters corresponding to Table 4, which enable application-specific design of the characteristic curve.


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taneous) is selected as a multipleof the rated current of the switch In(highest current setting). This multi-ple can be set to suit the application,i.e. the type of equipment to beprotected. If the rated current of theswitch is not fully exploited, themultiple setting at which the switchtrips is larger than the multiple set-ting which is set on the switch. If forexample motors are being protected,the response value of the short-cir-cuit release must be selected so thatit is not tripped by the inrush currentpeak (starting current). In this caseand with the protection of transfor-mers, it is often more useful whenthe circuit-breaker does not have tobe set to the highest level. This offersadditional security against prematuretripping, which can be particularlyimportant when the response valueof a short-circuit release is not adjus-table. Depending on the switch type,a differentiation is made betweennon-delayed (Ii) and short-timedelayed (Isd) short-circuit releases.A short-time delayed short-circuitrelease is always combined in thesame switch with a (higher setting)non-delayed short-circuit release.

With delayed releases, the currentand the additional delay time (tsd)must be set to suit the specificationsof the equipment to be protected.The delay time starts when the setcurrent of the delayed release isexceeded. Before a trip is initiated,the unit verifies if the set current stillexceeds the threshold value. Theset delay time is independent of thecurrent. The higher setting on thenon-delayed instantaneous short-circuit release (Ii) trips the switch ifits setting value is exceeded duringthe delay time. The non-delayedshort-circuit release is the emer-gency brake in this combination.

With a cascade-like selective (discri-minative) network design, the down-stream circuit-breaker in the vicinityof the fault must trip within thedelay time of the upstream circuit-breaker in order to reduce/interruptthe current in good time, otherwisethere is a danger that the upstreamdelayed circuit-breaker will also trip.Always when delayed releases forthe circuit-breaker or higher trip-ping times with overload relays(e.g. Class 40) are used, for exam-

ple with heavy starting duty oflarge motors, the design engineermust consider that all devices andcables in the entire circuit are sub-ject to a higher current load for anextended period of time. In suchcases, it is frequently the case thatthe switchgear and the cablesmust be overdimensioned accor-dingly.

An important feature for protection ofequipment and cables is the “thermalmemory” of the release. The thermalmemory simulates the heating effects ofthe equipment to be protected duringnormal operation and during the over-load phase. It permanently saves theheating factors to ensure that thethermal state of the equipment is still aknown factor after trip of a switch orafter a voltage loss. This provides thebasis for a further, optimum protectionfeature after an interruption in opera-tion or with an intermittent operationalcharacteristic. The thermal memorytakes the typical time constant for coo-ling of the load (cable or motor) intoconsideration when dissipating the sto-red heat which has thermally loaded thecable or motor.

Suitability for main and secondary applications,of the switch in the IEC version

Main applications Secondary application Type

Short-circuitprotection

(without over-load release)

Systemprotection

Cableprotection

Generatorprotection

Selectiveprotection

with delayedshort-circuitrelease

Motorprotection

Mainswitch

Emergencystop

yellow and “E” =electronic release

green = electro-mechan.release

X X N..-..

X (X) * X X NZM.. ..-S..

X X X X NZM.. ..(-4)-A..

X X X X NZM.. ..(-4)-AE..

X (X) ** (X) ** NZM.. ..-M..

X (X) ** (X) ** NZM.. ..-ME..

X X X X X X NZM.. ..(-4)-VE..

* Only in combination with suitable contactor and overload relay

** Only for single motor starter

(-4) Type suffix for 4-pole switch

Table 2: Application dependant main and secondary applications of the NZM circuit-breaker with electromechanical or electronic releases.


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The emulation of the cooling is imple-mented on the electronic releases usingthe same time constant with which theheating characteristic is determined.On bimetal releases this function resultsautomatically as the heated bimetalsmust cool down to return to their initialstates. During operation, the thermalmemory prevents the load, e.g. a motor,being subject to a thermal overloadafter an overload release caused by a

restart before it has cooled sufficiently.At the same time, the preheating of theequipment is taken into considerationby the thermal memory if an overloadoccurs. A restart is only possible whenthe electronic simulation or the reversebending process of the bimetals indi-cates that the motor is sufficiently cool.

If unfavourable cooling conditions areto be expected and the motor heats

up more quickly / cools down with a gre-ater delay than considered by the simu-lation, the motor will require additionalprotection using a thermistor tempera-ture detector and an EMT 6 evaluationunit.

Feature

Relevant standards

Current limit range

Ambient temperature

Conventional non-tripping current *)for the current dependant delayedtrip(May not trip within 2 h **), with load on allpoles, at reference temperature)

Conventional tripping current *)for the current dependant delayedtrip(Must be within 2 h **), according to loadwith the non-tripping current)

Single-phasing sensitivity

Definition:

May not trip within 2 h at:

Must trip within 2 h at:

Response range of the short-circuitrelease (Empirical values)Ir = setting of the overload release

Immunity to starting current

Selectivity

Overcurrent release

Tripping class

Thermal memory

Protection of systems

IEC / EN 60 947-1 [6] IEC / EN 60 947-2 [7]

Manufacture specified40 °C (at Moeller)

1.05 x current setting

**) 1 h at ≤ 63 A


**) 1 h at ≤ 63 A

Not intended

Not useful as the current loadingon the phase can be unbalancedand frequently is

approx. 6...10 x Ir

Conditional requirement

With multiple switches in seriesusually required

Must not be adjustable(Always adjustable with NZM and IZM)

Not intended

Useful

Motor protection

IEC / EN 60 947-1 [6] IEC / EN 60 947-4-1 [8]

Standard value 20 °C



Alternative permissible

Useful protective function, as thecurrent distribution of the phaseswith motors should be symmetric

2 pole 1.0 x current setting,1 pole 0.9 x current setting

2 pole 1.15 x current setting,1 pole 0 x current setting

approx. 8...14 x Ir

Required

Useful

Adjustable

Useful For matching to thestart-up behaviour of the motor

Essential requirement

Different demands placed on the circuit-breakerfor system and motor protection

Table 3: Different demands with both high sales applications of the circuit-breaker, the “protection of systems” conform to IEC / EN 60 947-2 [7] and the“motor protection” conform to IEC / EN 60 947-4-1 [8]

*) Definitions are informative but are only used in the IEC / EN 60 947-2 **) Refer to second column


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Necessity for variable trippingcharacteristics with modern circuit-breakers

The specific protective tasks and theapplication related operating conditions(utilization categories) of the statedequipment demand differing switchsettings. This relationship leads throughthe different, adjustable variables toapplication-specific switch variants,corresponding to those in Tables 1 and2. The demands placed on the spectrumof adjustment possibilities increasewhen multiple protective devices areconnected in series. This is always thecase especially when several main dis-tribution and sub-distribution boardsare arranged between the low-voltageincomer transformer and the equip-ment. In these cases, the switches andthe cables and conductors for the in-dividual segments of the circuit mustfrequently be dimensioned for differentcurrent levels. As a result, switches ofvarying frame size are often connectedin series in the current path.

The four listed fields of applicationplace different demands on the switchas indicated in the example for systemand motor protection in Table 3.The most important application-depen-dant parameters for the circuit-breakerselection are

occurrence of a symmetrical orunsymmetrical load, different, typical inrush peak currentsof the equipment to be protectedwith their differing current/dynamicresponse, normal operating currents, prospective overload currents withtheir differing current/dynamicresponse andfinally, the level of the short-circuitcurrents which are to be expected.

With the short-circuit currents, it is notonly the obvious question that is posedconcerning the maximum current levels,but also if the currents expected duringa malfunction exceed the overloadrange in the short-circuit range in orderto trip the switch with the necessaryspeed to prevent damage to the down-stream equipment and injury to person-nel. The question of adequate currentlevels is mainly an issue with low-power

generators or in circuits with long cablelengths, which result in a high lineimpedance and a high voltage drop. Forthis reason, a generator circuit-breakerwith a particularly low setting is avail-able. However, fast shutdown during amalfunction is a time-critical operationfor personnel protection with thedangerous touch voltages which result.However, during a short-circuit it ispossible that unintended high levelvoltage drops occur which can causeundefined switching states in thecontactor relays or on the voltagedependant releases in the system,and which also require a fast short-circuit trip. Undervoltage releasescan assist here.

The tool presented in this paper enablessimple representation of trippingcharacteristics, for known (selected)switches on a PC and the simple visualcomparison of the characteristic curvesof multiple switches and fuses, whichare connected in series in the currentpath at various levels in the network(Figure 4). The objective is to verify ifthe switches provide safe operation andif the selectivity exists between theprotective devices used in the overloadand short-circuit range. The most sig-nificant advantage of this tool com-pared to every printed representation ina catalogue is that the very specifictrip characteristic which takesaccount of all the actual settings onthe switch, can be generated anddocumented. A prerequisite for thecorrectness of the curve is that identicalswitch types are selected in the tooland the switchgear system, and that allthe switch position settings are cor-rectly entered into the tool. If the toolindicates that modified settings arerequired on the switch, the requiredsettings must be made manually on theswitches. All results can be saved,copied and printed including details foridentifying the devices.

In addition to the trip characteristicsfor the presented new NZM 1 to NZM 4compact circuit-breakers, the tool canalso display the characteristics for theprevious generation of compact devicessuch as the NZM 7, NZM 10 and NZM14, as well as the IZM 1 to IZM 3 opencircuit-breakers and the fuses with gl-characteristic. The tool will beexpanded in the future to include

further components such as the PKZMmotor-protective circuit-breaker andZB overload relay.

Constants and variables for curverepresentation

Protective devices with bimetal releasessuch as the ZB 12, ZB 32 , ZB 65 orZB 150 overload relay only allow forsetting of the rated motor current asthe current setting Ir of the overloadrelease. The further response characte-ristic of the trip characteristics is definedin the construction phase by the ratingof the bimetal, so that the bimetal cha-racteristic corresponds as accurately aspossible to the heat characteristic of themotors. The only non-adjustable side-benefit offered by this variant is a stan-dard-conform single-phasing sensitivity,and all variants feature ambient tempe-rature compensation. They detect andtake the failure of any main pole (phase)into consideration. The same applies forPKZM 01, PKZM 0 and PKZM 4 motor-protective circuit-breakers. On thesecircuit-breakers the response ranges ofthe additional short-circuit release arefixed. The PKZ 2 system and motor-protective circuit-breaker take a furtherstep on the development front as theresponse ranges of the magnetic short-circuit releases are adjustable here.The NZM 1 circuit-breaker and thermo-magnetic circuit-breakers NZM 2 andNZM 3 are directly comparable withthese protective devices.

Protective devices with electronicreleases such as the NZM 2 to 4 or IZM 1to 3 offer additional degrees of free-dom with the setting and definition oftheir protective features as well as inconjunction with further protectivedevices present in the same circuit.Table 4 indicates effective parameterswith differing protective switch types,which are either fixed or variable set-tings. The opportunity to match theseindividual settings to the varying equip-ment is a significant advantage ofcircuit-breakers in comparison to fuses.An example of the improved protectivefeatures by individual adjustable elec-tronic releases is indicated by Figure 6which is a typical motor start-up charac-teristic, which can now be representedusing the tool, and the protection, onthe one hand with a circuit-breakerwith thermal overload releases on


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which a short-circuit release is set to themaximum current, as well as signifi-cantly improved protection with circuit-breaker electronic releases on the otherhand. In the first case, the peak inrushcurrent can still cause a trip release ofthe switch. In the second case the motorhas better protection during run-up.

The adjustable fault current or earth-fault releases are optional accessories

which are not considered in the charac-teristics program. As already described,the short-time delayed switch enablesthe implementation of a time-discrimi-nating system concept. The short-timedelayed releases are also used onmotors with extended run-up times. Inthis application the protective functioncan be extended to include the additio-nal EMT6 thermistor machine protec-tion relay from Moeller.

Handling of the Moeller “CurveSelect” V1.071 software tool

Up to now, it was difficult to representindividual characteristic curves and tocompare them with one another. Quietoften the comparison failed due to thediffering scales for the representationof the coordinates of the curves forcircuit-breakers and fuses. This has

Setting possibilities with current-dependant acting releases with different circuit-breaker types

The releases can be optionally available or the specifications only applywith certain switch variants, see latest Moeller main catalogue

Electromechanical release Electronic release

Parameters with influence on thetripping characteristic

Type ZB... PKZM... PKZ... NZM... NZM... IZM...

Size12, 32, 65, 150

01, 0, 4 2 1, 2 2 3, 4 1, 2, 3

Setting Ir for overload release var. var. var.var.

var. var.-

Response value Irm for instantaneousshort-circuit release

- fixed var.fixed

- -var.

Response value Ii for instantaneousshort-circuit release

- - - -fixed fixed

var. var.

Response value Isd for delayed

short-circuit release- - - - var.

var.

-

Motor protection tripping class CLASS fixed fixed fixed fixed var. -

Time delay setting to overcome current peaks trfor overload release

- - - -fixed fixed

var. var.

Delay time tsd for short delayed

short-circuit release- - - - var. var.

I2t-constant function - - - -fixed fixed

var. var.

Single-phasing sensitivity fixed fixed- - - -

fixed fixed fixed fixed

Rated fault current IΔn - - - -fixed -

-var. -

Delay time tv for residual-current release - - - -fixed -

-var. -

Response value Ig for earth-fault release - - - - - var. var.

Delay time tg for earth-fault release - - - - - var. var.

Table 4: Fixed and variable parameters for current-dependant acting releases with different circuit-breaker types.


11

now changed with the new softwaretool. All curves are now displayed ona single sheet enabling simple visualevaluation.

The handling is very simple as the useris offered the permissible variables inthe type-specific input sheets. He simplyhas to enter the respective variablemanually into the mask. The program isavailable for download on the Internetat www.moeller.net/de/support. Free ofcharge registration is required with theprogram.

1. The program is copied onto a PCas an Excel file on which Micro-soft Excel® is already installed.Further installation is not required.The file can be used for as manyprojects are required.

2. The file is opened by a double-click on “Kennlinien... .xls”.An Excel worksheet opens with themultiple sheets required for thenecessary inputs and the represen-tation of the curves.

3. Comprehensive, advanced informa-tion about the program is containedin the “Read Me” sheet.

4. The required language versionscan be selected in the “General”sheet. On this sheet “Generaldetails” of the project are enteredand are automatically acceptedinto the representation of thecharacteristic curves.With version 1.071 of the program,it is only currently possible to useapplications with an operatingvoltage of between 240 and 690 V,50...60 Hz.

5. It is recommended that you savethe program after entering thebasic program data in any desiredfolder with “File” / “Save as”.This ensures that the original pro-gram file “Kennlinien... .xls” is avail-able for further use and does notcontain project-specific entries. It isalso recommended that you savefurther entries regularly with “File” /“Save as”.

6. With the worksheets “NZM...”,“IZM...”, “PKZ…”, “ZB”, “MCB”circuit-breakers or “Fuses” youcan select the protective devicewhose characteristic curve youwant to represent next.Per sheet and project it is possible toregister the data for 2 to 3 protec-tive devices of the same construc-tion type and size in the “Input”fields. Every product sheet is used amaximum of once per project. Allentries can be erased or overwrittenif required. The respective permissi-ble entries are provided correspon-ding to the selected basic type in the“Permissible setting range” field.The permissible values cant becopied and must be entered manu-ally into the input fields. Invalidentries are indicated in the “Errors”field. If possible, an informationdisplay indicating “Control andlimit values” and “Warnings” willbe indicated if necessary.

Each tripping characteristic canonly be graphically represented

Figure 6: Circuit-breakers with electronic releases enable – by flexible setting features – a more exact matching to the typical current consumption curve ofa starting three-phase motor than is possible with the switch on thermal overload releases.

Tripping characteristicof circuit-breaker with

thermal releases

Circuit-breakers withelectronic releases


Trip

pin

g t

ime

Tripping diagram

General specifications:Company: Moeller GmbH

Installation:Editor:

Date:Line: 400V / 50HzMotor starting curve


12

12k10k7k5k4k3k2,5k2k1,5k1,2k1k700500400300 15k 20k 25k 30k 40k 50k 70k 100k

when the device has been assig-ned with a designation in the“Designation” field.

7. On the worksheets “FSC” (Freestyle curves) and “Mot” (Motorcurves) the freely definable char-acteristics for protective devicesor for a motor run-up curve areentered. Refer to the Read_Me filefor further information concerningthe handling of the freely definablecurves. The freestyle curves are mul-tiple usage oriented and can bereused by simply saving the projectunder different names.

After entering the data for thefirst protective device and aftereach further input, the trippingcharacteristic(s) are displayed onthe “Tripping graphs <> Curves”(Figure 1). Subsequent changes tothe entries on the “Product sheets”are automatically considered bythe next curve display. The repre-sentation is made on a log-logcoordinate system with 5 x 7decades, from 1 A to 100 kAand from 1 ms to 2 h, and asabsolute values.

8. The entire worksheet or justthe “Characteristics <> Curves”can be printed. The project relateddata can be displayed, edited and

printed on every computer whereExcel is installed. The “Characteri-stics <> Curves” worksheet canbe marked and copied into the com-puter clipboard and then insertedinto other documents. After modi-fications on the input sheets, the“Characteristics <> Curves” sheetmust be copied and inserted againif required.

9. After completion of the projectspecific file, it can be protected bythe write protect feature in Win-dows Explorer® if required. (Locateand mark the file in WindowsExplorer and then protect with“Properties” / “Attributes” / “Read-Only”.) It is recommended that yousave the “Characteristics <> Curves”individually with a suitable softwarepackage as a PDF file and to write-protect it if necessary. This savesmemory in the project folder andthe document can be protectedagainst subsequent modifications.

10. The following limiting conditionsmust be observed with the evalua-tion of the diagrams:

All curves are represented assumingthe cold state and without represen-tation of the standard-conform tole-rances of the response ranges, andthe tripping times are represented

as mean values of the parame-terized tripping characteristic.This representation correspondswith the characteristics representedin the catalogues. In the non-delayed overload release range,the minimum command duration isindicated as it is the time for whichthe current must flow before anirreversible trip is initiated. Thiscorresponds to the melting time(minimum melting curve) with fuses.The current, voltage and the phaseposition dependent total openingdelay, which is comprised of theresponse delay, switching delay andarc quenching time is not conside-red by the represented curves.

11. In order to ensure selectivity (dis-crimination) in the overload range,the curves represented for thecircuit-breaker under one another,and the curves for the fuses maynot cross or touch each other at anypoint. Consider the tolerances ofthe curves which are ± 20 % in theoverload range. The overload selec-tivity (discrimination) of the selecteddevices has been reached at themeeting and crossover points.

In the short-circuit range, the elec-trodynamic processes which aredependent on the individual switchconstruction play an important role.

Figure 7: On the lower end range of the curves, a dynamic behaviour of the switch cannot be calculated with a reasonable amount of effort. For a bindingstatement regarding selectivity in this range, you are referred to the test results in the selectivity table in the Moeller main catalogue.

Start of the electrodynamic range

Characteristic endwith Icu



13

Ii = 8 x InI≤t = Ontsd = 0msIsd = 2 x Irtr = 2sIr = 1 x InIn = 630AVE630NZMN3 -Q2

100AglF12h

1h

20min

10min

5min

2min

1min

20s

10s

5s

2s

1s

500ms

200ms

100ms

50ms

20ms

10ms

5ms

2ms

1ms


Q1IZMB1 -U1600In = 1600AIr = 1 x Intr = 8s (I≤t)Isd = 3 x Intsd = 100msI≤t =OnIi = 12 x In

80AglF2

Netz:Datum:Bearb.:Anlage:Firma:

400V / 50Hz13.07.2007Mey1Moeller

Allgemeine Angaben:

Für die Richtigkeit übernimmt Moeller keine Gewähr.Die Haftung ist insoweit mit Ausnahme in Fällen desVorsatzes ausgeschlossen.

Q2NZMN3 -VE630In = 630AIr = 1 x Intr = 2sIsd = 2 x Irtsd = 300msI≤t = OnIi = 8 x In

100AglF12h

1h

20min

10min

5min

2min

1min

20s

10s

5s

2s

1s

500ms

200ms

100ms

50ms

20ms

10ms

5ms

2ms

1ms


Q1IZMB1 -U1600In = 1600AIr = 1 x Intr = 8s (I≤t)Isd = 3 x Intsd = 100msI≤t =OnIi = 12 x In

80AglF2

Netz:Datum:Bearb.:Anlage:Firma:

400V / 50Hz13.07.2007Mey1Moeller

Allgemeine Angaben:

Für die Richtigkeit übernimmt Moeller keine Gewähr.Die Haftung ist insoweit mit Ausnahme in Fällen desVorsatzes ausgeschlossen.

Figure 9: In contrast to Figure 8, the circuit-breaker represented in blue has been reselected. The modified settings provide selectivity in the overload and short-circuit range. The selectivity which is evident in the short-circuit range is confirmed by the selectivity specifications in the main catalogue. The I2tfunction can be switched on and off. It improves the selectivity with fuses.

Figure 8: Non-selective protective devices can be recognised by crossover or (almost) touching curves. The green curve represents an IZM outgoing circuit-breaker in a distribution board. The NZM incoming circuit-breaker of a downstream sub-distribution is represented in blue. In this distribution circuit thefuses indicated in red are intended to protect various motor starters with overload relays.

Non-selectiverange

ActivatedI2t function


Trip

pin

g t

ime

Tripping diagram


Trip

pin

g t

ime

Tripping diagram


Installation: 1Editor: Mey

Date: 13.07.2007Line: 400V / 50Hz


Installation: 1Editor: Mey

Date: 13.07.2007Line: 400V / 50Hz


14

The current limiting properties ofthe circuit-breaker, owing to theelectrody-namic effects on thecontacts and quenching systems,can not be calculated with justifiableeffort by this simple tool in the highcurrent range. The range of thiselectro-dynamic limit is representedon the diagram by the responsevalue of the non-delayed overloadrelease using a dashed vertical line(Figure 7). The short-circuit selecti-vity is verified by comprehensiveshort-circuit testing in the test labo-ratory. For this range the detailsconcerning the selectivity in theselectivity tables in the Moeller maincatalogue are obligatory. The cha-racteristic of the respective circuit-breaker ends with the value of theultimate short-circuit breakingcapacity Icu which depends on thedevice type and rated voltage.

12. Selectivity problems can normallybe remedied by selecting anotherdevice or sometimes by modifieddevice settings (Figures 8 and 9).

Enhanced protection in marginalconditions

At the end of the nineties, Moellerintroduced the protection systemscone model for representation of thesystematics with the protective systems[9]. Moeller arranges well known aswell as innovative protection systemsto the standard definitions or self-

created definitions correspondingwith Figure 10.Definitions such as personnel protec-tion, protection for special workshopsand areas as well as protection ofequipment and the protection ofsystems are generally well known.However new definitions areequipment basic protection and systemfunctional protection. In the systemprotection field, Moeller has taken anindisputable lead with a new techno-logy which has not been challenged todate. The new protection system whichevolved and is already into its second

generation is the highly successfulARCON® arc-fault protection system.The protection systems envisioned forthe very high demands placed in termsof avoidance of damage to systems andprotection of personnel as well as assu-rance of an exceptional level of systemavailability, could not be achieved as thesystems were simply too slow. Masteryof the destructive arc requires its quen-ching within the first two millisecondsof occurrence. On the ARCON® system,the mains voltage which feeds the arcis short-circuited in less than 2 milli-seconds by a pyrotechnic based short-circuiting element (Figure 11) shouldan arc occur. The conventional circuit-breakers simply have “just” the task ofdisconnecting the switchgear systemfrom the mains supply within the nor-mal circuit-breaker related switchingtimes. With this system, the damage tothe swithgear system has been reduceddemonstrably to contamination of thesystem with dirt, or in the worst case todamage of a fraction of the distributionsection. The total failure of a switchgearsystem is reduced to an interruption inoperation of a matter of hours. Furtherliterature presents this unique system indetail [9 to 13]. Its effect extendsbeyond the protective functions whichcan be presented with the features ofthe “CurveSelect” software tool.ARCON ® is also worth mentioning,because the protective functions were

a

b b b

c

d

e

Figure 11: If the conventionally available circuit-breakers are too slow to prevent an arc, the use ofthe ARCON ® arc-fault protection system from Moeller is recommended. It detects arcs and shorts-outthe feed voltage source within 2 ms and quenches the arc.

F Protection of installation functionsE Protection of installations

D Protection of equipment

C Basic protection of equipment

B Protection of special installations and locationsA Protection of persons

Figure 10: Moeller represents the different protection systems in low-voltage engineering as a cone-shaped model. The functions and systems of functional protection extend beyond the functionsof the circuit-breakers presented. Moeller solves these demands for example with the unique ARCON®

arc-fault protection system.

a ARC-EM master

b ARC-EL3 slave for three ARC-SL streamlined sensors

c ARC-SL streamlined optical sensors

d Current transformer

e ARC-AT quenching device

Power feed 1

Section 1 Section 2 Section 3 Section 4 Section 5 Section 6 Section 7


15

difficult to designate in the previousparagraph due to the extremely shorttime range and extremely high currentsinvolved at the same time. This relatesonly to the features of the presentedtool, and does not mean that Moellercould not master this difficult task.

Reliability:

The paper describes the status of thestandards and the state of developmentof the NZM circuit-breaker in March2007, as well as version V 1.071 of theCurveSelect software tool. The basis forthe technical data for the describedMoeller products is the relevant validMoeller main catalogue (HPL). Productinformation from Messrs. Jean Müller,Eltville have been used as the basis forthe fuse characteristics. Subject tochange without notice.

Acknowledgement:

The paper was completed with thefriendly support of the developers ofthe circuit-breaker control units andthe characteristics software, Mr. GerdSchmitz and Mr. Alexander Zumbeck,as well as Mr. Udo Theis from circuit-breaker product support.

Literature:

[1] Wolfgang Esser“Main areas of application of circuit-breakers”Elektropraktiker, Huss-MedienGmbH Berlin, ep Issue 9-2003(German language)

[2] IEC / EN 60 364-4-41, amended orDIN VDE 0100-410 * ClassificationVDE 0100 part 410 “Erection ofpower installations with nominalvoltages up to 1000 V, Part 4:Protection for safety, Part 41:Protection against electric shock”(1992, 1997), German versionHD 384.4.41 S2 (1996) and draftA1 and draft 2003-04

[3] Wolfgang Esser,“Switching and protective devicesin machine controls”Elektropraktiker, Huss-MedienGmbH Berlin, ep Issue 11-2003(German language)

[4] IEC / EN 60 204-1, DIN VDE 0113Part 1 “Safety of machinery ,Electrical equipment of machines ,Part 1 General requirements”(IEC 204-1: 1997 + Corrigendum1998) and draft 2002-09

[5] Wolfgang Esser,“The growing importance of com-munication with circuit-breakers”Elektropraktiker, Huss-MedienGmbH Berlin, ep Heft 1-2003,(German language)Special print VER 1230-930 D,Moeller GmbH

[6] IEC / EN 60 947-1, DIN VDE 0660Part 100 "Low-voltage switchgearand controlgear, Part 1, Generalrules" (1992, 2003)

[7] IEC / EN 60 947-2, VDE 0660 Part101 “Low-voltage switchgearand controlgear, Part 2: Circuit-breakers" (2004)

[8] IEC / EN 60 947-4-1, DIN VDE 0660Part 102 "Low-voltage switchgearand controlgear, Part 4-1: Contactors and motor-starters - Electromechanicalcontactors and motor-starters "(2003, 2004)

[9] Wolfgang Esser“Systematics of the protectionsystems in low-voltageengineering – The protective system conemodel –TB 0200-023 D or GBMoeller GmbH, Bonn, 1998

[10] Peter-Lorenz Könen, Dr. H.Schäfer“Arc-fault protection on low-voltage applications – a challengefor protection engineering –VER 27-869 (German language)Moeller GmbH, Bonn 1998

[11] Peter-Lorenz Könen“Protection of persons andsystems with an arc”„etz“ Issue 15 /2003(German language)

[12] System information“Power Reliably Available andSafely Under Control”W 4600-7542Moeller GmbH, Bonn, 2003

[13] Product Information“ARCON® – The Lightning FastAirbag for Your Switchboard“ARCON® Arc Fault ProtectionSystemW4600-7560GBArticle No. 285245Moeller GmbH, Bonn 2007


Moeller addresses worldwide:www.moeller.net/addressE-Mail: [email protected]

© 2004 by Moeller GmbHSubject to alterationsVER1230-943GB ip/xx 11/07 Printed in the Federal Republic of Germany (11/07)Article No.: 286000

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Xtra Combinations from Moeller offers a range of productsand services, enabling the best possible combination optionsfor switching, protection and control in power distributionand automation.

Using Xtra Combinations enables you to find more efficientsolutions for your tasks while optimising the economic viability of your machines and systems.

It provides:■ flexibility and simplicity■ great system availability■ the highest level of safety

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