Instructions For Digitrip Models 220, 520, 520, 520M, And .

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I.L. 70C1037H02Page 1I.L. 70C1037H02Instructions for Digitrip Models 220, 520, 520i, 520M, and520Mi Trip Units for use only in Cutler-Hammer Magnumand Magnum DS Circuit BreakersTable of 1General Description of Digitrip Trip Units . 2Protection . 4Mode of Trip and Status Information . 4Installation and Removal . 41.3.1 Installation of the Trip Unit . 41.3.2 Rating Plug Installation . 41.3.3 Trip Unit/Rating Plug Removal . 5Wiring . 6Plexiglass Cover . 6Ground Alarm/Power Supply Module(520M Models only) . 61.6.1 Auxiliary Power . 61.6.2 Ground Alarm . 6Display Feature (520M family only) . 7Standards . 7General Description ofMagnum Circuit Breakers . 7General . 7Low Energy Trip Actuator . 8Ground Fault Protection . 82.3.1 General . 92.3.2 Residual Sensing . 92.3.3 Source Ground Sensing . 92.3.4 Zero Sequence Sensing . 92.3.5 Multiple Source/Multiple Ground . 92.3.6 Ground Fault Settings . 9Current Sensors (Magnum Frames less thanor equal to 3200A) . 10Current Sensors (Magnum Frames greaterthan 3200A) . 10Principles of Operation . 10General . 10Trip and Operation Indicators . 15Making Current Release . 15Zone Interlocking (520 family only) . 15Protection Settings . 19General . 19Long Delay Current Setting . 19Long Delay Time Setting . 19Short Delay Current Setting . 20Short Delay Time Setting . 20Instantaneous Current Setting . 20Ground Fault Current Setting . 21Ground Fault Time Delay Setting . 21Test Procedures . 21General . 21Effective 8/13/99Courtesy of NationalSwitchgear.com5.2 When to Test . 225.3 Functional Field Testing . 225.4 Performance Testing for Ground FaultTrip Units . 225.4.1 Code Requirements . 225.4.2 Standards Requirements . 225.4.3 General Test Instructions . 226.0 Battery . 236.1 General . 236.2 Battery Check . 236.3 Battery Installation and Removal . 247.0 Frame Ratings(Sensor Ratings and Rating Plugs) . 10, 248.0 Record Keeping . 259.0 References . 259.1 Magnum and Magnum DS Circuit Breakers . 259.2 Time-Current Curves . 25Appendix A Zone Interlocking Examples . 29Appendix B Troubleshooting Guide . 31Appendix C Typical Breaker MasterConnection Diagram . 33WARNINGDO NOT ATTEMPT TO INSTALL OR PERFORMMAINTENANCE ON EQUIPMENT WHILE IT ISENERGIZED. DEATH OR SEVERE PERSONAL INJURYCAN RESULT FROM CONTACT WITH ENERGIZEDEQUIPMENT. ALWAYS VERIFY THAT NO VOLTAGE ISPRESENT BEFORE PROCEEDING. ALWAYS FOLLOWSAFETY PROCEDURES. CUTLER-HAMMER IS NOTLIABLE FOR THE MISAPPLICA-TION ORMISINSTALLATION OF ITS PRODUCTS.WARNINGOBSERVE ALL RECOMMENDATIONS, NOTES,CAUTIONS, AND WARNINGS RELATING TO THESAFETY OF PERSONNEL AND EQUIPMENT. OBSERVE AND COMPLY WITH ALL GENERAL ANDLOCAL HEALTH AND SAFETY LAWS, CODES, ANDPROCEDURES.

Page 2I.L. 70C1037H02Figure 1.1 Digitrip 520M Trip Unit with Rating PlugNOTE: The recommendations and information containedherein are based on experience and judgement, butshould not be considered to be all inclusive or to coverevery application or circumstance which may arise.If you have any questions or need further information orinstructions, please contact your local representative orthe Customer Support Center at 1-800-356-1234.1.0 GENERAL DESCRIPTION OF DIGITRIP TRIP UNITSThe Digitrip Trip Units are breaker subsystems thatprovide the protective functions of a circuit breaker. Thetrip units are in removable housings, installed in thebreaker, and can be replaced or upgraded in the field bythe customer.This instruction book specifically covers the application ofDigitrip Trip Units, as illustrated in Figure 1.1, installed inMagnum and Magnum DS Breakers. Throughout thisInstructional Leaflet, the use of the term “MagnumBreakers” refers to both the Magnum and Magnum DSlow-voltage, ac power circuit breakers.The Magnum Digitrip line of trip units consists of the 220,520, and 520M for UL standards and models 220, 520i,and 520Mi for IEC standards. Throughout this Instructional Leaflet, the use of the term “DT20 family” refers tothe 220, 520, 520i, 520M, and 520Mi units; the term “520family” refers to only the 520, 520i, 520M, and 520Miunits.Effective 8/13/99Courtesy of

I.L. 70C1037H02Page 3Table 1.1 Protection Types Available for Digitrip Trip UnitsTrip Unit TypeDigitrip 220Digitrip 520/520iDigitrip 520M/520MiAmpere Range200A-3200A200A-6300A200A-6300ARMS WLSIGFixed Rating Plug (In)YesYesYesOvertemperature TripYesYesYesFixed @ 1 x (In)0.4-1.0 x (In)0.4-1.0 x (In)Fixed @ 10 seconds2-24 Seconds2-24 SecondsYesYesYesNo200-1000% x (Ir)200-1000% x (Ir)No100-500 ms100-500 msNo100-500 ms100-500 msNoYesYes200-1000% x (In)200-1000% x (In)200-1000% x (In)Protection and CoordinationProtection Ordering OptionsLongLong Delay SettingDelayI 2tLong Delay Timeat 6 x (Ir)Protection Long Delay Thermal MemoryShortDelayShort DelayPick-Up4I 2tShort Delay Timeat 8 x (Ir)Protection Short Delay Time FLATShort Delay TimeZSI5Pick-Up4Instan-InstantaneoustaneousOff PositionNoYesYesProtection Making Current ReleaseYesYesYesGroundGround Fault OptionNoYesYes(Earth)Ground Fault AlarmNoNoYes3FaultGround Fault Pick-UpNo25-100% x (In)125-100% x (In)1Protection Ground Fault Delay I2t at .625 x (In)No100-500 ms100-500 msGround Fault Delay FlatNo100-500 ms100-500 msNoYesYesNoYesYesYesYesYesCause of Trip LEDsNoYes2Yes2Remote Ground Trip/Alarm ContactsNoNoYes3NoNo4 Char. LCDGround FaultZSI5Ground Fault MemorySystem DiagnosticsStatus/Long Pick-up LEDSystem MeteringDigital DisplayNotes: to 1200 Amperes; this is only for UL versions, not for IEC models.Four cause of trip LEDs–L, S, I, G. Making Current Release is indicated by the Instantaneous LED.Requires optional Ground Alarm/Power Supply Module (see Section 1.6).Additional setting is marked M1 where:800-3200A Frame:M1 14 x /n for Plug Amps 200 through 1250AM1 12 x /n for Plug Amps 1600, 2000, 2500AM1 10 x /n for Plug Amps 3000, 3200A4000-6300A Frame:M1 14 x /n for Plug Amps 2000, 2500A (see Section 2.5)M1 12 x /n for Plug Amps 3200, 4000, 5000AM1 10 x /n for Plug Amps 6300A5. ZSI Zone Selective Interlock (see Section 3.4)Effective 8/13/99Courtesy of

I.L. 70C1037H02Page 4The Digitrip 220, 520, and 520M trip units may be appliedon both 50 and 60 Hz systems.Digitrip DT20 family of trip units are microprocessorbased ac protection devices that provide true RMScurrent sensing for the proper coordination with thethermal characteristics of conductors and equipment. Theprimary function of the Digitrip Trip Unit is circuit protection. The Digitrip analyzes the secondary current signalsfrom the circuit breaker current sensors and, when presetcurrent levels and time delay settings are exceeded, willsend an initiating trip signal to the Trip Actuator of thecircuit breaker.In addition to the basic protection function, the Digitrip 520family of trip units provides mode of trip information suchas: Long Time trip (overload)Short Time tripInstantaneous tripGround (Earth) Fault trip (if supplied).The current sensors provide operating power to the tripunit. As current begins to flow through the breaker, thesensors generate a secondary current which powers thetrip unit.The Digitrip 520 family of trip units provides five phaseand two ground (time-current) curve shaping adjustments.To satisfy the protection needs of any specific installation,the exact selection of the available protection functionadjustments is optional. The short delay and ground faultpick-up adjustments can be set for either FLAT or I2tresponse. A pictorial representation of the applicabletime-current curves for the selected protection functions isprovided, for user reference, on the face of the trip unit asshown in Figure ProtectionEach Digitrip DT20 Trip Unit is completely self-containedand requires no external control power to operate itsprotection systems. It operates from current signal levelsderived through current sensors mounted in the circuitbreaker. The types of protection available for each modelare shown in Table 1.1 and Figures 3.2 through 3.9.NOTE: The Digitrip 220 (LI model), 520 (LSI model), and520M (MLSI model) can be used on 3-pole or 4-polecircuit breakers for the protection of the neutral circuit.Only these three models can provide neutral protection,although models MLSIA,MLSIG, and MWLSIG canprovide neutral metering (see Figures 3.7, 3.8, and 3.9).Refer to the National Electric Code (NEC) for the appropriate application for 4-pole breakers.1.2 Mode of Trip and Status InformationOn all DT20 units, a green light emitting diode (LED),labeled Status, blinks approximately once each second toindicate that the trip unit is operating normally. This StatusLED will also blink at a faster rate if the Digitrip is in apick-up, or overload, mode.Red LEDs on the face of the 520 family of trip units (forLong Delay, Short Delay, and Instantaneous) flash toindicate the cause, or trip mode, for an automatic tripoperation (for example, ground fault, overload, or shortcircuit trip). A battery in the Digitrip unit maintains the tripindication until the Reset/Battery Test button is pushed.The battery is satisfactory if its LED lights green when theBattery Check button is pushed (see Section 6).NOTE: The Digitrip 520 family provides all protectionfunctions regardless of the status of the battery. Thebattery is only needed to maintain the automatic tripindication.1.3 Installation and Removal1.3.1 Installation of the Trip UnitAlign the Digitrip unit with the guide pins and spring clip ofthe Magnum Circuit Breaker. Press the unit into thebreaker until the pins on the trip unit seat firmly into theconnector housing and the unit clicks into place (seeFigure 1.2).1.3.2 Rating Plug InstallationWARNINGDO NOT ENERGIZE THE MAGNUM BREAKER WITHTHE DIGITRIP REMOVED OR DISCONNECTED FROMITS CONNECTOR. DAMAGE TO INTERNAL CURRENTTRANSFORMERS MAY OCCUR DUE TO AN OPENCIRCUIT CONDITION.CAUTIONIF A RATING PLUG IS NOT INSTALLED IN THE TRIPUNIT, THE UNIT WILL TRIP WHEN IT IS ENERGIZED.Insert the rating plug into the cavity on the right-hand sideof the trip unit. Align the three pins on the plug with thesockets in the cavity. The plug should fit with a slightinsertion force.Effective 8/13/99Courtesy of

I.L. 70C1037H02Page 5Figure 1.2 Installation of the Digitrip Unit into a Magnum Breaker (Side View)CAUTIONDO NOT FORCE THE RATING PLUG INTO THE CAVITY.Use a 1/8" (3 mm) wide screwdriver to tighten the M4screw and secure the plug and the trip unit to the circuitbreaker (see Figure 1.3). Close the rating plug door.CAUTIONTHE M4 SCREW SHOULD BE TIGHTENED ONLYUNTIL IT IS SNUG. DO NOT USE A LARGE SCREWDRIVER. A 1/8" (3 mm) WIDE SCREWDRIVER BLADEIS ADEQUATE.1.3.3 Trip Unit/Rating Plug RemovalTo remove the rating plug from the trip unit, open the ratingplug door. Use a 1/8" (3 mm) wide screwdriver to loosenthe M4 screw. Pull the door to release the rating plug fromthe trip unit.To remove the trip unit from the circuit breaker, deflect thespring clip to release the unit from the steel mountingplate. Pull the unit to disengage the two 9-pin connectorsfrom the circuit breaker (see Figure 1.2).Effective 8/13/99Courtesy of NationalSwitchgear.comFigure 1.3 Installation of the Rating Plug and MountingScrew

I.L. 70C1037H02Page 61.4 WiringThe internal components of the breaker, and how they arewired out to the breaker secondary contacts, are shown inthe breaker master connection diagram provided asAppendix C.1.5 Plexiglass CoverA clear, tamper-proof, plexiglass door sits on the breakercover. This door allows the settings to be viewed but notchanged, except by authorized personnel. The plexiglasscover meets applicable tamper-proof requirements. Thecover is held in place by two cover screws. Security isinsured by the insertion of a standard meter seal throughthe holes in both of the cover retention screws. Theplexiglass cover has an access hole for the Step buttonon the 520M and 520Mi units.1.6 Ground Alarm/Power Supply Module (520M Models only)The Ground Alarm/Power Supply Module (see Figure 1.4)is an optional accessory for the Digitrip 520M and 520Mimodels. The module can be installed beneath the metalmounting plate of the trip unit in the Magnum CircuitBreaker. The module covers the following input voltageratings: 120 VAC (7802C83G01), 230 VAC(7802C83G02), and 24/48 VDC (7802C82G01).1.6.1 Auxiliary PowerWhen the module is wired as shown in Figure 1.5, it willprovide an auxiliary power supply so that the 520M/520Miliquid crystal display (LCD) will be functional even whenthe circuit breaker has no load. A Digitrip 520M unitwithout auxiliary power will not display data until loadcurrent reaches approximately 25% 1 phase or 10%3 phase of the (In) rating.Figure 1.4 Optional Ground Alarm/Power Supply Modulefor 520M Trip Unit1.6.2.2 Ground Fault Alarm1.6.2 Ground AlarmA second function of the module is to provide either aground trip or ground alarm only output contact via therelay supplied in the module. On Digitrip 520M modelswith ground fault protection, an LED on the front of theunit also provides an indication of ground fault trip. Ground Fault TripWhen the Ground Alarm/Power Supply module is usedwith the MLSIG model, this unit will provide ground faulttrip contacts when the circuit breaker trips on a groundfault. You must then push the Reset button on the Digitripin order to reset the contacts (see Figure 1.5, Note 3).A ground fault alarm alerts a user to a ground faultcondition without tripping the circuit breaker. A red AlarmOnly LED on the front of the trip unit will indicate thepresence of a ground fault condition that exceeds theprogrammed setting.The ground fault alarm relay is energized when theground current continuously exceeds the ground faultpickup setting for a time in excess of a 0.1 second delay.The alarm relay will reset automatically if the groundcurrent is less than the ground fault pickup (see Figure 1.5, Note 4).Effective 8/13/99Courtesy of

I.L. 70C1037H02Page 7OLOverload (Digitrip in overload mode)Pushing the Step button while the unit is in the OLmode will have the unit again display the overloadcurrent value.HELPThis message can indicate more than one problem with the trip unit. If the rating plug is missing,a HELP message and an Instantaneous trip LEDlight will be observed. The rating plug needs to beinstalled and the Instantaneous trip LED must becleared by pressing the Reset/Battery Test button.This message could also indicate that the trip unitis out of calibration and should be replaced at theearliest opportunity.1.8 StandardsThe Digitrip 220, 520, and 520M Trip Units are listed bythe Underwriters Laboratories, Inc., under UL FileE52096, for use in Magnum Circuit Breakers. These sameunits are also listed by the Canadian Standards Association (CSA) under file LR 43556.Figure 1.5 Wiring Diagram for 520M Models and GroundAlarm/Power Supply ModuleAll Digitrip units have also passed the IEC 947-2 testprogram which includes radiated and conducted emissiontesting. As a result, all units carry the CE mark.2.0 GENERAL DESCRIPTION OF MAGNUM CIRCUIT BREAKERS1.7 Display Feature (520M family only)2.1 GeneralThe Digitrip 520M and 520Mi models have a user interface in addition to the green and red LED trip indicators.This seven element display performs a metering functionand can be used to monitor load currents.Magnum Circuit Breakers are tripped automatically onoverload fault current conditions by the combined action ofthree components:When the Step button on the face of the trip unit ispressed and released, the display will show PH 1, forPhase 1 or A, and the current value. If the Step button isnot pressed again, the display will continue to show thecurrent value for Phase 1. Each time that the Step buttonis pressed, the next monitored function will be displayed.The other readings can be displayed in the sequencebelow:PH 2Phase 2 (B)PH 3Phase 3 (C)PH 4NeutralPH 5Ground (if Ground function is supplied)HIHighest phase currentEffective 8/13/99Courtesy of NationalSwitchgear.com1. The Sensors, which measure the current level2. The Digitrip Trip Unit, which provides a tripping signalto the Trip Actuator when current and time delaysettings are exceeded3. The low-energy Trip Actuator, which actually trips thecircuit breakerFigure 2.1 shows this tripping circuit for a typical MagnumBreaker. This arrangement provides a very flexiblesystem, covering a wide range of tripping characteristicsdescribed by the time-current curves referenced in Section9.2.The automatic overload and short circuit tripping characteristics for a specific circuit breaker are determined bythe ratings of the installed current sensors with a matchingrating plug and the selected functional protection settings.Specific setting instructions are provided in Section 4.

I.L. 70C1037H02Page 8When the functional protection settings are exceeded, theDigitrip unit supplies a trip signal to the Trip Actuator. As aresult, all tripping operations initiated by the protectionfunctions of the Digitrip Trip Unit are performed by itsinternal circuitry. There is no mechanical or direct magnetic action between the primary current and the mechanical tripping parts of the breaker, and external controlpower is not required.WARNINGIMPROPER POLARITY CONNECTIONS ON THE TRIPACTUATOR COIL WILL DEFEAT THE OVERLOADAND SHORT CIRCUIT PROTECTION, WHICH COULDRESULT IN PERSONAL INJURY.OBSERVE POLARITY MARKINGS ON THE TRIPACTUATOR LEADS AND CONNECT THEM PROPERLY, USING THE INSTRUCTIONS PROVIDED.2.2 Low-Energy Trip Actuatorlocated under the black molded platform on which theDigitrip unit is supported. The Trip Actuator contains apermanent magnet assembly, moving and stationary coreassemblies, a spring, and a coil. Nominal coil resistanceis 25 ohms and the black lead is positive. The circuitbreaker mechanism assembly contains amechanism-actuated reset lever and a trip lever toactuate the tripping action of the circuit breaker.When the Trip Actuator is reset by the operating mechanism, the moving core assembly is held in readinessagainst the force of the compressed spring by the permanent magnet. When a tripping action is initiated, the lowenergy Trip Actuator coil receives a tripping pulse fromthe Digitrip unit. This pulse overcomes the holding effectof the permanent magnet, and the moving core is released to trigger the tripping operation via the trip lever.2.3 Ground Fault ProtectionNOTE: The Digitrip Model 220 is not available withground fault protection. Only the 520 family has groundfault types available.The mechanical force required to initiate the trippingaction of a Magnum Circuit Breaker is provided by aspecial low-energy Trip Actuator. The Trip Actuator isFigure 2.1 Tripping Circuit for a Typical Magnum Breaker (Partial)Effective 8/13/99Courtesy of

I.L. 70C1037H02Page 92.3.1 GeneralWhen the Digitrip 520 family includes ground fault protection features, the distribution system characteristics (forexample, system grounding, number of sources, numberand location of ground points, and the like) must beconsidered along with the manner and location in whichthe circuit breaker is applied to the system. These elements are discussed in Sections 2.3.3 through 2.3.6.The Digitrip 520 family uses three modes of sensing todetect ground fault currents: residual, source ground, andzero sequence (see Table 2.1). Magnum Circuit Breakerscan accommodate all three types, except for 4-polebreakers. The breaker secondary contact inputs B-6, B-7are used to configure the breaker cell positions for thethree schemes. No jumper from B-6 to B-7 programs theunit for a residual ground fault scheme, while a jumperfrom B-6 to B-7 programs the trip unit for either a sourceground or zero sequence configuration. If present, thisjumper resides on the stationary side of the switchgearassembly. In all three schemes, the proper current sensorinput is required on the external sensor input terminalsB-4, B-5 of the breaker secondary contacts.Table 2.1 Digitrip Sensing ModesGround (Earth)FaultSensing MethodBreakerSecondaryContacts Req’dApplicableBreakersFigureReferenceResidualNo Jumper3 or 4 pole2.2, 2.3, 2.5, 2.9Digitrip GFSensingElementUsedelement R5Source GroundJumper B6 to B73 pole only2.7element R4Zero SequenceJumper B6 to B73 pole only2.8element R4Note: This information applies to Trip Units with Ground2.3.2 Residual SensingResidual Sensing is the standard mode of ground faultsensing in Magnum Circuit Breakers. This mode utilizesone current sensor on each phase conductor and one onthe neutral for a 4-wire system (shown in Figures 2.2and 2.3). If the system neutral is grounded, but no phaseto neutral loads are used, the Digitrip 520 family of unitsincludes all of the components necessary for ground faultprotection. This mode of sensing vectorially sums theoutputs of the three or four individual current sensors. Forseparately-mounted neutrals, as long as the vectorial sumis zero, then no ground fault exists. The neutral sensormust have characteristics and a ratio which are identicalto the three internally-mounted phase current sensors.Available types of neutral sensors are shown in Figure 2.4. Residual ground fault sensing features areadaptable to main and feeder breaker applications.Available ground fault pick-up settings employing Residual Sensing are given in Table 2.2. Figure 2.5 shows a4-pole breaker with Residual Ground Fault Sensing.Effective 8/13/99Courtesy of NationalSwitchgear.comCAUTIONIF THE SENSOR CONNECTIONS ARE INCORRECT, ANUISANCE TRIP MAY OCCUR. ALWAYS OBSERVETHE POLARITY MARKINGS ON THE INSTALLATIONDRAWINGS. TO INSURE CORRECT GROUND FAULTEQUIPMENT PERFORMANCE, CONDUCT FIELDTESTS TO COMPLY WITH NEC REQUIREMENTSUNDER ARTICLE 230-95(C).2.3.3 Source Ground SensingDepending upon the installation requirements, alternateground fault sensing schemes may be dictated (seeFigures 2.6 and 2.7). The ground return method is usuallyapplied when ground fault protection is desired only on themain circuit breaker in a simple radial system. Thismethod is also applicable to double-ended systems wherea mid-point grounding electrode is employed. For thismode of sensing, a single current sensor mounted on theequipment-bonding jumper directly measures the totalground current flowing in the grounding electrodeconductor and all other equipment-grounding conductors.The settings shown in Table 2.1 will apply when theneutral sensor is not the same as the frame rating in aground return sensing scheme.2.3.4 Zero Sequence SensingZero Sequence Sensing, also referred to as vectorialsummation (see Figure 2.8), is applicable to mains,feeders, and special schemes involving zone protection.Zero Sequence current transformers (4 ½" x 13 ½"[114 mm x 342 mm] rectangular inside dimensions) areavailable with 100:1 and 1000:1 ratios.2.3.5 Multiple Source/Multiple GroundA Multiple Source/Multiple Ground scheme is shown inFigure 2.9. In this figure, a ground fault is shown whichhas two possible return paths, via the neutral, back to itssource. The three neutral sensors are interconnected tosense and detect both ground fault and neutral currents.Call Cutler-Hammer for more details on this scheme.2.3.6 Ground Fault SettingsThe adjustment of the ground fault functional settings(FLAT response or I2t) is discussed in Section 4.8. Theeffect of these settings is illustrated in the ground faulttime-current curve referenced in Section 9. Applicableresidual ground fault pick-up settings and current valuesare given in Table 2.2 as well as in the ground time-currentcurve.

I.L. 70C1037H02Page 10Table 2.2 Ground (Earth) Fault Current Settingsrating specified on the plug label. The current sensorrating can be viewed through openings in the back of thebreaker.Ground Fault Current Settings(Amperes)1InstalledSensor/Rating Plug(Amperes) In.25.30.35200506025063752.5 Current Sensors (Magnum Frames greater than 12375438500625750938125016004004805606408009601200 1600220005006007008001000120015002 920224002 3200216002200022400230002 0023000237502 5000263003157518902205252031503780472563001. Tolerance on settings are 10% of values shown.2. On Models 520 LSIG and 520M LSIG, the shaded values are set to a maximumtrip value of 1200 amperes for NEC.The six (3-pole) or eight (4-pole) current sensors installedin the circuit breaker are located on the lower conductors.The poles are paralleled and the corresponding currentsensors are also paralleled (see Figure 2.3). For example, a 4000A breaker phase rating has two 2000:1current sensors wired in parallel, which provides anoverall ratio of 4000:2. The auxiliary current transformershave a ratio of 20:1 for this size breaker which furthersteps down the rated current to 100 milliamperes and isequivalent to 100% (In) to the Digitrip.3.0 PRINCIPLES OF OPERATION3.1 GeneralThe Digitrip DT20 family of trip units is designed forindustrial circuit breaker environments where the ambienttemperatures can range from –20 C to 85 C but rarelyexceed 70 to 75 C. If, however, temperatures in theneighborhood of the trip unit exceed this range, the tripunit performance may be degraded. In order to insure thatthe tripping function is not compromised due to an overtemperature condition, the Digitrip 520 family microcomputer chip has a built-in over-temperature protectionfeature, factory set to trip the breaker if the chip temperature is excessive. On the 520 family, if over-temperatureis the reason for the trip the red Long Delay Time LED willflash.3. See Section Current Sensors (Magnum Frames less than or equal to3200A)The three (3-pole) or four (4-pole) primary current sensorsare installed internally in the circuit breaker on the lowerconductors of the breaker. The current sensor ratingdefines the breaker rating (In). For example, 2000A:1Asensors are used on a 2000A rated breaker. There arefour auxiliary current transformers with a ratio of 10:1which further step down the rated current to 100 milliamperes, which is equivalent to 100% (In) to the Digitrip.The primary current sensors produce an output proportional to the load current and furnish the Digitrip DT20family with the information and energy required to trip thecircuit breaker when functional protection settings areexceeded.If a set of current sensors with a different ratio are installed in the field, the rating plug must also be changed.The associated rating plug must match the current sensorThe Digitrip uses the Cutler-Hammer custom-designedSµRE chip , an integrated circuit that includes amicrocomputer to perform its numeric and logic functions.The principles of operation of the trip unit are shown inFigure 3.1.In the Digitrip DT20 family of trip units, all sensing andtripping power required to operate the protection functionis derived from the current sensors in the circuit breaker.The secondary currents from these sensors provide thecorrect input information for the protection functions, aswell as tripping power, whenever the circuit breaker iscarrying current. These current signals develop analogvoltages across the current viewing resistors. The resulting a

Magnum and Magnum DS Breakers. Throughout this Instructional Leaflet, the use of the term “Magnum Breakers” refers to both the Magnum and Magnum DS low-voltage, ac power circuit breakers. The Magnum Digitrip line of trip units consists of the 220, 520, and 520M for UL stan

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