power distribution - Siemens

VL Circuit BreakersTrip Unit OverviewThe interchangeability of the VL circuitbreaker trip units allow for easy conversionfrom any of 3 types of protection.They are thermal-magnetic, electronic,or electronic with a built-in LCD display.The thermal-magnetic trip unit featuresan adjustable magnetic trip setting. Theelectronic trip units are microprocessorbased true RMS sensing devices andare available with a variety of adjustabletrip settings, configurations, and informationmenus. With precise controlover the circuit beaker functions andaccess to system status, diagnostics,and information, these trip units allowfor unsurpassed flexibility in circuitcoordination.An example of coordination is the outof the box Ground Fault function on theModel 545 trip units. The pick-up andtime delay settings are fixed for eachVL Trip UnitsSelectionframe and do not overlap with the settingson the other frames. Therefore,when VL breakers are used together ina system the GF protection is automaticallycoordinated. The user also has theability to program a custom coordinationscheme with the high level ofadjustability available on the Model576 trip units.Trip Unit Functions Model 525 Model 545 Model 576Thermal- Electronic Electronic Electronic Electronic Electronic with LCD Electronic with LCDMagnetic LI LIG LSI LSIG LSI LSIGContinuous CurrentSetting (I r)Fixed ◆ ◆ ◆ ◆ ◆ ◆Long Time Delay (t r) ◆ ◆ Fixed Fixed ◆ ◆InstantaneousOvercurrent Setting (I i)◆ ◆ ◆ Fixed Fixed ◆ ◆6MOLDED CASECIRCUIT BREAKERSShort Time Pick-up (I sd) ◆ ◆ (ON/OFF) (ON/OFF)Short Time Delay (t sd) ◆ ◆ ◆ ◆Short Time l 2 t Pick-up ◆ ◆ ◆ ◆Ground Fault Pick-up (l g) Fixed Fixed ◆Ground Fault Delay (t g) Fixed Fixed ◆Alarm & Status LEDs ● ● ● ● Built-in Display (LCD) ● ●Pre-Trip Alarm ● ●Last trip information ● ●Zone Selective ● ●Communications ● ●◆ – Adjustable setting.● – This feature is included.“fixed” – Non-Adjustable setting. – Feature is not included. – Requires the trip unit to be connected to a PC (via a COMPRO or COMMOD communications module) for access or programming.Continuous Amps Rating (I r )This setting is the continuous currentthat the breaker will carry without tripping.It can be set up to 100% of the tripunit’s nominal rating (I n ).Long Time Delay (t r )Sometimes referred to as the “overload”position, this function controls the breaker‘s“pause-in-tripping” time. It allowslow level, temporary inrush currentssuch as those encountered when startinga motor to pass without tripping. Thetime delay begins when the currentreaches 6 x I r .Instantaneous Pick-up (I i )This function sets the breaker to tripinstantaneously during high fault conditions.On Model 545 trip units this settingis fixed on LSI and LSIG trip unitsand adjustable on LI and LIG trip units.These features are fully adjustable onModel 576 trip units.Short Time Pick-Up (l sd )This function controls the level of faultcurrent the breaker will carry for a shorttime without tripping, thus allowingdownstream devices to clear short circuitsahead of up-stream protection.It may be defeated (turned-off) onModel 576 trip units.Short Time Delay (t sd )This controls the interval of time thebreaker will remain closed against a fault(at the Short Time Pick-up current level)without tripping. The time delay may beset at fixed points or at short time intervalsbased on l 2 t curves. This function isused with the Short Time Pick-up toachieve selectivity and better systemcoordination.Ground Fault Pick-Up (I g )This setting controls the level of groundfault current that will cause the breakerto trip. Model 545 Electronic Trip Unitsact on the residual current to senseground current. The Model 576Electronic Trip Unit is programmableand allows the user to select eitherthe residual current method or directdetection (via a separate current transformer)to detect ground current.Ground Fault Time Delay (t g )This controls the interval of time thebreaker will remain closed after a groundfault is detected (at the Ground FaultPick-up current level) without tripping.6-94Siemens Power Distribution & Control, SPEEDFAX 2007-2008 Product Catalog