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A RCLI M ITE R

TM

 

A R C FL A SH M I T I G AT I O N S O LU T I O N FO R LV US I N G U FE S

Phase C could remain energized to the transformer 
primary for an extended time and since most of the 
plant’s SUS are delta-wye, all three transformer 
phases have the same equally applied potential. 
Since there is no difference in potential between 
the delta windings, there is no current flow, there-
fore there is no induction to generate secondary 
potential. 

However, having a sustained bolted line-to-ground 
phase C fault will activate the plant’s ground fault 
alarm system. Maintenance would be chasing the 
wrong problem.

To prevent this nuisance alarm, the MV SWITCH 
should be installed (or retrofitted) with a shunt trip 
activated by one of the QRU1’s trip out contacts. 

Two of the CLFs will still interrupt in about the same 
timeframe, about 1-2 ms, Phase C CLF may not in-
terrupt. This prevents the false alarms.

Upon UFES operation, all three fuses should be re-
placed, since the phase C fuse may be damaged by 
microsecond internal arcing, along with the three 
PSEs. The UFES to ground bonding jumper can be 
small thermally, approximately #2 AWG, since it only 
has to carry current for 5 ms.

Ungrounded Delta MV systems

Summary of Contents for ArcLimiter

Page 1: ... TECHNICAL AND APPLICATION GUIDE ArcLimiterTM Arc flash mitigation solution for low voltage equipment using UFES ultra fast earthing switch ...

Page 2: ...stries are facing internal or external deadlines to implement arc flash AF mitigation solutions within their facilities ABB now offers ArcLimiterTM an arc flash mitigation solution that is unique in the industry It solves the LV arc flash problem at the MV or LV system level ...

Page 3: ... 007 008 Low resistance grounded MV systems 009 010 High resistance grounded MV systems 011 012 Ungrounded Delta MV systems 013 Summary of ArcLimiterTM solution application scenarios 014 MV LV transformers fed by MV breaker 015 ArcLimiterTM solution application at LV system level 016 Available UFES ratings ...

Page 4: ...ltage on the transformer primary extinguishing the LV arc flash quickly approximately 4 ms Test results in dicate the incident energy level peak was 0 5 cal cm2 which is well below the AF threshold of 1 2 cal cm2 where PPE is required A note on the CLF application is in order A fuse will become current limiting when the magnitude of amperes through it is large enough to fully in terrupt in cycle o...

Page 5: ...150E ratio of the SCC to the fuse FLA rating is 67 Fuse will inter rupt in cycle Operations should not be im pacted System SCC 4 600A CLF is a 200E ratio is 23 Fuse will interrupt in cycles Operations could be impacted and the plant needs to be informed up front 01 Internal distribution system configuration Post testing analysis revealed that MV system grounding has an impact on overall system beh...

Page 6: ...ions When phases A and B CLF fully interrupt the entire phase C current briefly appears as a zero sequence current on the traces The only path for fault current is through the phase C fuse to UFES phase C PSE to transformer grounded neutral Since there is no impedance in that path the fault current flow is high only limited by the transformer s short circuit impedance Since phase C is delayed by 1...

Page 7: ...oltage recovery starts with full CLF interrup tion by 1 5 2 ms SCC dependent When phase A and B CLF clear the entire phase C current appears as a zero sequence current on the test traces There is a large reduction in phase C fault current once phases A and B CLF open The only path for fault current is through the phase C fuse to UFES phase C PSE to the transformer s neutral but is now limited by t...

Page 8: ...protection relay x seconds later Review the ground return path in Figure 4 This action shuts down the entire MV BUS resulting in poor reliability for customers plants The 51G 1 or 51G 2 will be faster than a sustained high ground fault value say 1200 A through the CLF To prevent this reliability issue the MV SWITCH should be installed or retrofitted with a shunt trip activated by one of the QRU1 s...

Page 9: ...nues as a plant benefit The UFES closes all three phases to ground simulta neously At this point the LV AF is essentially over Depending upon UFES closing time and phase se quence phase A and B CLF melt in 1 ms MV voltage system recovery starts with full CLF interruption by 1 5 2 ms SCC dependent When phases A and B CLF clear the entire phase C current now very lim ited appears as a zero sequence ...

Page 10: ...n micro seconds However having a sustained bolted line to ground phase C 10 A fault will activate the plant s ground fault alarm system Maintenance would be chasing the wrong problem To prevent this nuisance alarm the MV SWITCH should be installed or retrofitted with a shunt trip activated by one of the QRU1 s trip out contacts Two of the CLFs will still interrupt in about the same timeframe about...

Page 11: ...o not have ground fault protection Indications of a ground fault are usually via installed voltmeters The operating process continues as a plant benefit When triggered the UFES closes all three phases to ground simultaneously At this point the LV AF is essentially over Depending upon the UFES closing time and phase sequence phase A and B fuses melt in 1 ms MV voltage recovery starts with full CLF ...

Page 12: ...will activate the plant s ground fault alarm system Maintenance would be chasing the wrong problem To prevent this nuisance alarm the MV SWITCH should be installed or retrofitted with a shunt trip activated by one of the QRU1 s trip out contacts Two of the CLFs will still interrupt in about the same timeframe about 1 2 ms Phase C CLF may not in terrupt This prevents the false alarms Upon UFES oper...

Page 13: ... C CLF interruption is delayed almost indefinitely Too short a time for ground relay pick up Sustained line to ground phase C fault tripped by the upstream 51G relay Trips entire MV BUS resulting in poor reliability for the plant Sustained line to ground phase C 10 amp fault activates the plant s ground fault alarm system Sustained line to ground phase C fault will activate the plant s ground faul...

Page 14: ...ary windings The X axis is in units of times transformer s full load amps base not top The Y axis in seconds is the time duration capability of the transformer to thermally and mechanically withstand a sustained secondary bolted fault The lower portion of the curve is the mechanical damage area considered the area of most concern from a protection viewpoint The graph s purpose is to assist in the ...

Page 15: ...l see a bolted LV fault collapsing any LV equipment AF That transformer LV through fault of 52kA will be reflected to the MV primary as 1 Z FLA Example 80 of the MV LV transformers are 2500KVA base rated Per ANSI energizing the transformer will produce an inrush of 12 FLA for 0 1s If the transformer has an impedance of 5 75 or 9 the inrush will be 1 0 0575 FLA 17 4 FLA Slightly higher than typical...

Page 16: ...d voltage peak kV 12 95 150 170 Rated frequency Hz 50 60 50 60 50 60 50 60 Rated short time withstand current kA 100 50 63 40 40 Rated peak withstand current kA 220 130 165 104 104 Rated duration of short circuit s 0 5 3 2 3 3 Rated short curcuit making current kA 220 130 165 104 104 Mechanical properties Dimension diameter x height mm in 137 x 210 5 4 x 8 3 Closing time ms 1 5 Contact bounce time...

Page 17: ...formation up to date and correct it makes no representations or warranties of any kind express or implied about the completeness accuracy reliability suitability or availability with respect to the information products services or related graphics contained in the document for any purpose Any reli ance placed on such information is therefore strictly at your own risk ABB reserves the right to disc...

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