Eaton Magnum DS Technical Data Manual

Also see for Magnum DS: Instruction leaflet Instruction booklet Instructions Instructional Leaflet

Technical DataEffective: May 1998 Page 17TD.44A.01.T.ECutler-HammerHigh-Resistance GroundingWhere continuity of service is a highpriority, high-resistance groundingcan add the safety of a grounded sys-tem while minimizing the risk of ser-vice interruptions due to grounds. Theconcept is a simple one: provide a pathfor ground current via a resistance thatlimits the current magnitude, and mon-itor to determine when an abnormalcondition exists.The ground current path is provided atthe point where the service begins, byplacing resistance in the connectionfrom system neutral to ground. Controlequipment continuously measuresground current. A relay detects whenthe current exceeds a predeterminedlevel. An alarm alerts building person-nel that a ground exists. The systemhas built-in fault tracing means toassist in finding the source of theground. An integral transformer pro-vides control power from the primarysource.600 Volt (Maximum) Delta SystemsTo add high-resistance grounding toan ungrounded delta-connected sys-tem, a neutral point must be created.Three single-phase transformers canbe interconnected in a zigzag or wye-broken delta configuration to providesuch a neutral point. The transformersand grounding resistors are chosen tolimit the ground current to a maximumvalue of 5 amperes.Application note –The neutral point may not be used toserve phase-to-neutral loads. Also,this technique may be applied on wye-connected sources when the neutralpoint is not conveniently accessiblefrom the service entrance location.600/347 Volt (Maximum) WyeSystemsTo add high-resistance grounding to awye-connected system, resistors areplaced in series with the neutral-to-ground connection of the powersource. The resistors are chosen tolimit the current to a maximum valueof 5 amperes.Application note – Per1993 NEC 250-5b, exception no. 5 line-to-neutral loads may not be connectedto a system where the neutral isresistance-grounded.Ground Current DetectionAny time a system is energized, a smallground current called the “capacitivecharging current” will be observed. Forlow-voltage (600V and below) systems,this naturally-occurring current is typi-cally 1 ampere or less.When one phase becomes grounded,additional current above the charginglevel will flow. As all ground currentmust flow through the grounding resis-tor/grounding transformer assembly,an ammeter in this circuit will read thetotal amount of ground current. Byplacing a current-sensing relay inseries with the ammeter, the currentrelay can be adjusted to pick up at alevel in excess of the capacitive charg-ing current, thus indicating the abnor-mal condition.Alternatively, an optional voltmeter-relay can be connected across thegrounding resistors. The voltageacross the resistors is proportional tothe amount of ground current. Thevoltmeter-relay’s pickup adjustment isset above the capacitive charging cur-rent, to the desired detection level.In both current and voltage detectionmethods, the ground current ammeterprovides a direct reading of the total,actual ac ground current present in thesystem at that time. It will be helpful toperiodically note the ammeter’s read-ing; a trend towards higher values mayindicate the need for equipment main-tenance, and hence reduce the occur-rence of unplanned shutdowns.Indication and Alarm CircuitsWhen a fault is detected, an adjustabletime delay is provided to override tran-sients. When the time delay has beenexceeded, the green “normal” lightwill turn off, the red “ground fault”light will turn on, and the ground alarmcontacts will transfer. If equipped withthe optional alarm horn, it will sound.When the fault is cleared, the current/voltage relay will reset. If the reset con-trol is set on “auto,” the lights willreturn to “normal” on, “ground fault”off, and the ground alarm contacts willre-transfer. If the reset control is set on“manual,” the lights and relay contactswill remain latched until the operatorturns the reset control to “reset.” Thelights and ground alarm contacts willthen return to normal. The system canbe reset only if the fault has beencleared.During a fault, the optional alarm horncan be silenced at any time by usingthe “alarm silence” pushbutton. It willnot re-sound until either the system isreset, or the re-alarm timer expires.The re-alarm timer is activated by the“alarm silence” control. If the horn hasbeen silenced but the fault has notbeen cleared, the timer will run. It has arange of 2–48 hours. When the timertimes out, the horn will re-sound, alert-ing maintenance personnel that thefault has not been cleared.Test CircuitA test circuit is provided to allow theuser to quickly determine that the sys-tem is working properly. The test cir-cuit will operate only under normalconditions — it will not allow testing ifthe system is sensing a fault. A sepa-rate grounding resistor is provided,connected to a relay operated by the“test” position of the mode selectorswitch. The relay’s contact groundsphase B through the test resistor, caus-ing ground current to flow. The systemthen reacts as it would under actualsystem ground conditions: lights trans-fer, alarm contacts transfer and the(optional) horn sounds.Pulser CircuitThe pulser circuit offers a convenientmeans to locate the faulted feeder andtrace the fault to its origin. The pulser isavailable any time a fault has beendetected. An adjustable recycle timercontrols the pulse intervals. The “pulse”light flashes on and off, correspondingto the on-off cycles of the pulser contac-tor. The pulser contactor switches abank of resistors on and off, thus allow-ing a momentary increase in the groundcurrent (approximately a 5 ampere cur-rent pulse above the ground current).Locating a Ground FaultThe current pulses can be noted with aclamp-on ammeter when the ammeteris placed around the cables or conduitfeeding the fault. The operator testseach conduit or set of cables until thepulsing current is noted. By moving theammeter along the conduit, or check-ing the conduit periodically along itslength, the fault can be traced to its ori-gin. The fault may be located at thepoint where the pulsing current dropsoff or stops.If little or no change in the pulsing cur-rent is noted along the entire length ofa cable, then the fault may be in theconnected load. If the load is a panel-board, distribution switchboard ormotor control center, repeat the pro-cess of checking all outgoing cablegroups to find the faulted feeder. If thefault is not found in an outgoingfeeder, the fault may be internal to thatequipment.Magnum DSMetal-EnclosedLow-Voltage SwitchgearApplicationwww . ElectricalPartManuals . com