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    #91
    Originally posted by mbrooke View Post
    So it is not out of bounds of the discussion we are having and the Peterson coil RJ brought up.
    You don't use a Petersen coil on a MGN system so it is not really relevant.
    BB+/BB=?

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      #92
      Originally posted by mbrooke View Post
      Not if all loads are connected in delta and your zero sequence is set very low.
      Tell me how you propose to set it below shock levels on MV system.
      BB+/BB=?

      Comment


        #93
        Originally posted by romex jockey View Post
        you mean other earthing systems ?


        https://en.wikipedia.org/wiki/Earthing_system


        I always felt it somewhat a challenge getting my head outta the 'nec' box.....

        ~RJ~
        Yes. There are several other systems around the world and more than one in the US but MGN is the one most used in the US for distribution.
        BB+/BB=?

        Comment


          #94
          Originally posted by mivey View Post
          Perhaps you have some setting or breaker selection issues. 2-8 cycles is normal total clearing with 5 pretty common.
          Show me what part of the NESC mandates that an MGN system or any particular system must clear in 2-8 cycles.



          Originally posted by mivey View Post
          You don't use a Petersen coil on a MGN system so it is not really relevant.

          You know the theory which I am referring to. Limit the neutral current, you limit the remote earth voltage which is what RJ was getting at.


          Originally posted by mivey View Post
          Tell me how you propose to set it below shock levels on MV system.

          Definite time ground trip set below the anticipated body current clearing in 5 cycles.



          Honestly, you don't want to admit that tieing the primary neutral into the secondary neutral can get someone hurt or killed.

          Comment


            #95
            Originally posted by mbrooke View Post
            Show me what part of the NESC mandates that an MGN system or any particular system must clear in 2-8 cycles.
            Show me where I said it did. I'm just telling you what I see in switchgear and fault data.

            Where did your get your number of often more than 5 cycles from? My 2-8 cycles comes from many years of experience.

            Originally posted by mbrooke View Post
            You know the theory which I am referring to. Limit the neutral current, you limit the remote earth voltage which is what RJ was getting at.
            Throwing out unrelated applications as a solution to a different application hints at a willingness to throw stuff together because some of the words and terms are used in both applications but not because it is applicable to the situation at hand.

            Originally posted by mbrooke View Post
            Definite time ground trip set below the anticipated body current clearing in 5 cycles.
            and what do you use for ground trip instantaneous settings in a distribution feeder?

            What if I told you for a lot of systems I work on, I set the 50G pickup to ~140-400 amps?

            Originally posted by mbrooke View Post
            Honestly, you don't want to admit that tieing the primary neutral into the secondary neutral can get someone hurt or killed.
            Honestly, speculation with wild assumptions don't fit an engineer mindset. We deal with data. We love data. You can't give an engineer too much data. Do you have any data showing probability studies, mortality rates, etc. or are you just throwing more stuff out there?
            BB+/BB=?

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              #96
              Originally posted by mivey View Post
              Show me where I said it did. I'm just telling you what I see in switchgear and fault data.

              Where did your get your number of often more than 5 cycles from? My 2-8 cycles comes from many years of experience.
              An SPS2 breaker on its best day clears in 3 cycles page 15:

              https://w3.usa.siemens.com/smartgrid...akerFamily.pdf


              A breaker that hasn't opened in a while can take a few extra cycles.


              It takes about 1/2 1 cycle for a microprocessor relay to make a trip decision.


              Of course that is best case scenario tripping on definite time or zone 1 MHO (none delayed).


              Come real world you have oil breakers that just start at 8-10 cycles.

              Breaker failure that can take 35 cycle to complete.

              Eletromechanical relays.

              Inverse time over current tripping if coordinating with a string of other devices.

              All these add time, 5 cycles is best case in a new system, often a pie dream in old ones. Which is why its never assumed when it comes to life safety.

              IE, page 23 assumes 72 cycles:


              https://www.eversource.com/content/d...rsn=f340c162_2



              Throwing out unrelated applications as a solution to a different application hints at a willingness to throw stuff together because some of the words and terms are used in both applications but not because it is applicable to the situation at hand.
              Peterson coils are used in distribution systems.

              As are remote LV grounds to prevent MV neutral voltage from entering the building.


              and what do you use for ground trip instantaneous settings in a distribution feeder?

              Depends on many things, anywhere from 5 amps to 560 amps for a typical feeder.

              What if I told you for a lot of systems I work on, I set the 50G pickup to ~140-400 amps?
              With wye primary distribution transformers, of course!



              Honestly, speculation with wild assumptions don't fit an engineer mindset. We deal with data. We love data. You can't give an engineer too much data. Do you have any data showing probability studies, mortality rates, etc. or are you just throwing more stuff out there?

              Its not a speculation when it clearly violates IEC 60479-1:


              Comment


                #97
                Originally posted by mbrooke View Post
                An SPS2 breaker on its best day clears in 3 cycles page 15:
                would you believe a breaker rated to open in 3 cycles will open in 3 cycles or less? I know because we routinely test them.

                Originally posted by mbrooke View Post
                A breaker that hasn't opened in a while can take a few extra cycles.
                Then it is malfunctioning and needs repair.

                We don't want to depend on broken equipment in our prtection scheme. That is why we perform routine testing and maintenance.

                Originally posted by mbrooke View Post
                It takes about 1/2 1 cycle for a microprocessor relay to make a trip decision.
                yes

                Originally posted by mbrooke View Post
                Of course that is best case scenario tripping on definite time or zone 1 MHO (none delayed).
                and for your scenario of a phase dropping into a neutral, that is what we expect to happen. In fact, that is what I am most likely to see when reviewing the fault data.

                Originally posted by mbrooke View Post
                Come real world you have oil breakers that just start at 8-10 cycles.
                come real world most that I see are rated faster than that and operate within specs. If you are having breakers operate outside specs then you need to re-work your maintenance schedules and procedures.

                Originally posted by mbrooke View Post
                Breaker failure that can take 35 cycle to complete.
                Backup schemes. We use them as a safety net but also recognize the probabilities are very low that we will have to use them (maintenance and testing, remember?).

                You can have an entire station in fault for a very long time. Minutes.

                We had that after a contractor melted a lockout relay during testing and did not reveal their mistake. We found out later when a fault occurred and just sat there cooking everything. The DO called and said "hey, your station has some extremely high currents, would you like us to trip it?" It was dragging down the transmission network. Those are the odd scenarios where equipment and people fail but not our planned protection scheme that we consider to be working as it should.


                Originally posted by mbrooke View Post
                Eletromechanical relays.
                very dependable when maintained.

                Originally posted by mbrooke View Post
                Inverse time over current tripping if coordinating with a string of other devices.
                not our scenario. A bolted L-N fault assumes no fault impedance so we should be hitting 50G and it will win the race (tie at worst) against the 51 relays .

                Originally posted by mbrooke View Post
                All these add time, 5 cycles is best case in a new system, often a pie dream in old ones.
                Quite frankly, you don't know what you are talking about. I work on systems that have been around for 80-100 years and with proper maintenance and testing they don't slow down with age. Where do you get this nonsense?

                We tested breakers a few weeks ago that are 60+ years old and 3-cycle rated. The mechanism operated in about 2.5 cycles and the instantaneous relays in about 1/2 cycle.

                Originally posted by mbrooke View Post
                read the fine print:
                "The fault-clearing times designated above are based on broad-application worst-case relay and/or breaker-failure situations. If other fault-clearing times are substantiated, maximum current single cable ratings may be adjusted by calculation on a case-by-case basis."

                Originally posted by mbrooke View Post
                Peterson coils are used in distribution systems.
                But not in a MGN distribution system.

                Originally posted by mbrooke View Post
                As are remote LV grounds to prevent MV neutral voltage from entering the building.
                Please clarify

                Originally posted by mbrooke View Post
                iwth wye primary distribution transformers, of course!
                Kinda need a wye distribution system to go along with your neutral scenario don't you think?


                Originally posted by mbrooke View Post
                Its not a speculation when it clearly violates IEC 60479-1:
                Not my area of expertise as I don't work under that code.
                BB+/BB=?

                Comment


                  #98
                  Originally posted by mivey View Post
                  would you believe a breaker rated to open in 3 cycles will open in 3 cycles or less? I know because we routinely test them.

                  Then it is malfunctioning and needs repair.
                  Its not malfunctioning. Its been documented in event data. Even in stability reports its assumed 2 extra cycles for a 3 cycle breaker and 1.5 extra cycles for a 2 cycle breaker. PJM, ISO-NE, Ercot, ect assume these extra few cycles for a breaker in stability reports involving critical clearing time. Yes these are transmission breakers, but it still holds true for distribution breakers.





                  and for your scenario of a phase dropping into a neutral, that is what we expect to happen. In fact, that is what I am most likely to see when reviewing the fault data.

                  If the relay is set to trip instantaneously for this type of fault. Add a few reclosers in series and you are "stacking" curves. Fuse blowing in fuse saving schemes will also increase the time.



                  come real world most that I see are rated faster than that and operate within specs. If you are having breakers operate outside specs then you need to re-work your maintenance schedules and procedures.
                  Still more then 5 cycles for that old oil dinosaur.

                  Backup schemes. We use them as a safety net but also recognize the probabilities are very low that we will have to use them (maintenance and testing, remember?).
                  If that was the case, then we could safely eliminate all breaker failure. And use normal clearing times in substation worker protection calcs. Not going to happen.



                  You can have an entire station in fault for a very long time. Minutes.

                  We had that after a contractor melted a lockout relay during testing and did not reveal their mistake. We found out later when a fault occurred and just sat there cooking everything. The DO called and said "hey, your station has some extremely high currents, would you like us to trip it?" It was dragging down the transmission network. Those are the odd scenarios where equipment and people fail but not our planned protection scheme that we consider to be working as it should.
                  Now that is what I would consider a rare enough scenario mitigated by correct maintenance and design- not a stuck breaker.


                  very dependable when maintained.
                  Of course, but slower then MP relays.

                  not our scenario. A bolted L-N fault assumes no fault impedance so we should be hitting 50G and it will win the race (tie at worst) against the 51 relays .
                  For you, yes.

                  Quite frankly, you don't know what you are talking about. I work on systems that have been around for 80-100 years and with proper maintenance and testing they don't slow down with age. Where do you get this nonsense?

                  We tested breakers a few weeks ago that are 60+ years old and 3-cycle rated. The mechanism operated in about 2.5 cycles and the instantaneous relays in about 1/2 cycle.

                  Ok, good.



                  read the fine print:
                  "The fault-clearing times designated above are based on broad-application worst-case relay and/or breaker-failure situations. If other fault-clearing times are substantiated, maximum current single cable ratings may be adjusted by calculation on a case-by-case basis."


                  Yes, if your breaker fail time is less then 72 cycles have at it. But you can't ignore it, nor assume normal high speed clearing.


                  But not in a MGN distribution system.

                  True- unless you insulate everything phase to phase and use only delta loads.

                  Please clarify

                  Already linked it:









                  Kinda need a wye distribution system to go along with your neutral scenario don't you think?

                  You can hook everything phase to phase and just keep the MGN.

                  Not my area of expertise as I don't work under that code.

                  But you should know that graph. Its the foundation for which nearly every step potential, clearing time, loop impedance, bonding and grounding mandate is based upon across most of the globe and soon to be for North America. Its already being used by UL to set the basis for industrial GFCIs.


                  https://www.csemag.com/articles/uls-new-gfci-classes/




                  Ok, for the sake of the argument lets agree on 5 cycle clearing. After all it is very doable. Where in the NESC does it say a bolted L-N fault (on a distribution line) must clear within 5 cycles? That is what I'm trying to get at.
                  Last edited by mbrooke; 07-10-19, 10:21 AM.

                  Comment


                    #99
                    3 cycles is reasonable for a typical distribution breaker whether air or vacuum. I see oil breakers so rarely these days it's hard to say. I've encountered just two in 25 years and both went out of service before it was time to test. If we stack a 50G we have a 1 cycle delay on even old GE and ABB mechanical relays plus another cycle for an Electroswitch pistol grip 86 relay gets us to a maximum 5 cycles. This is for a typical pre-2000 design. If we used a multifunction relay such as a 351 the way it's intended relay delay is 1 cycle worst case for a total cycle time of 4 cycles minimum in a modern design. So for most equipment using 50G 5 cycles is very reasonable. It is a common error to loom at breaker test reports and ignore relay delay times.

                    Since this is safety, NFPA 70E and a dearth of other documents makes it very clear that none of the standards apply to equipment that is not properly maintained. I will concede that a breaker might trip slowly if not maintained but using 6-12 cycles is pure fantasy. And when testing it is well known that trip performance improves as you "work" a malfunctioning relay. Spray a little WD40 in there and it easily passes testing fir a couple days until the lubricant evaporates! Then it is even worse since the residual wax and clays and maybe a little oil are dissolved and cleaned out, leaving metal on metal contact. It is just as likely to trip in 30-60 cycles or simply fail to trip when a breaker malfunctions. Or the 50G can malfunction and trip early or nuisance trip. We don't have design data for this. Backup protection is there but might be pure guess work and might end up being when the fault is consumed by the arc. Standards do not exist for improperly maintained equipment because it's all a guess. So trying to engineer for improper maintenance is not good practice, and violates engineering ethics and professional engineering standards.


                    Sent from my SM-T350 using Tapatalk

                    Comment


                      I still assert that its "normal" for a 3 cycle breaker to clock in at 5 cycles. Let alone an oil unit.

                      Here is a relaying engineer saying the same thing toward the end of a thread:

                      davidbeach (Electrical) 26 Sep 16 12:38
                      A cycle or so for the relay and 2-3 cycles for breaker time plus, maybe, a bit of slop. I like to list the longer end of the time range but I do see the occasional fault that is cleared in 3 cycles (relay + breakers) with a 3 cycle breaker. But I also see a 3 cycle breaker sometimes take an extra cycle or two if it's been closed for a very long time and the go just 3 cycles on the second trip.

                      https://www.eng-tips.com/viewthread.cfm?qid=414455


                      Through out its assumed 3 cycles as the fastest clearing, not the slowest.

                      Comment


                        Originally posted by mbrooke View Post
                        Its not malfunctioning. Its been documented in event data. Even in stability reports its assumed 2 extra cycles for a 3 cycle breaker and 1.5 extra cycles for a 2 cycle breaker. PJM, ISO-NE, Ercot, ect assume these extra few cycles for a breaker in stability reports involving critical clearing time. Yes these are transmission breakers, but it still holds true for distribution breakers.
                        We keep our transmission and distribution breakers maintenanced and tested and don't allow the stickiness you evidently are seeing.

                        Originally posted by mbrooke View Post
                        If the relay is set to trip instantaneously for this type of fault. Add a few reclosers in series and you are "stacking" curves. Fuse blowing in fuse saving schemes will also increase the time.
                        Depends on reach. You would normally want your relay to look further and catch those bolted faults. I wil normally set the instantaneous to see 80% of the main line. I will stop at a recloser if it is catching the remainder.

                        Originally posted by mbrooke View Post
                        Still more then 5 cycles for that old oil dinosaur.
                        Sounds like it is time to tweak the budget.

                        Originally posted by mbrooke View Post
                        If that was the case, then we could safely eliminate all breaker failure. And use normal clearing times in substation worker protection calcs. Not going to happen.
                        We use alternate (faster and no reclosing) settings when working on the line. It may cause a lockout for what would normally be a blink but so be it.

                        Originally posted by mbrooke View Post
                        Now that is what I would consider a rare enough scenario mitigated by correct maintenance and design- not a stuck breaker.
                        That contractor was fired.

                        Originally posted by mbrooke View Post
                        Yes, if your breaker fail time is less then 72 cycles have at it. But you can't ignore it, nor assume normal high speed clearing.
                        We assume our breakers will operate during a fault the same way as they did during testing.

                        Originally posted by mbrooke View Post
                        True- unless you insulate everything phase to phase and use only delta loads.
                        Hey, it is only money.

                        Originally posted by mbrooke View Post
                        Already linked it:
                        But I'm being lazy and want a spoon-fed summary.

                        Originally posted by mbrooke View Post
                        You can hook everything phase to phase and just keep the MGN.
                        Like California.

                        Originally posted by mbrooke View Post
                        But you should know that graph. Its the foundation for which nearly every step potential, clearing time, loop impedance, bonding and grounding mandate is based upon across most of the globe and soon to be for North America. Its already being used by UL to set the basis for industrial GFCIs.
                        OK. Haven't ran across it yet.

                        Originally posted by mbrooke View Post
                        Ok, for the sake of the argument lets agree on 5 cycle clearing. After all it is very doable. Where in the NESC does it say a bolted L-N fault (on a distribution line) must clear within 5 cycles? That is what I'm trying to get at.
                        It doesn't and I have not said it did.
                        BB+/BB=?

                        Comment


                          Originally posted by paulengr View Post
                          3 cycles is reasonable for a typical distribution breaker whether air or vacuum. I see oil breakers so rarely these days it's hard to say. I've encountered just two in 25 years and both went out of service before it was time to test. If we stack a 50G we have a 1 cycle delay on even old GE and ABB mechanical relays plus another cycle for an Electroswitch pistol grip 86 relay gets us to a maximum 5 cycles. This is for a typical pre-2000 design. If we used a multifunction relay such as a 351 the way it's intended relay delay is 1 cycle worst case for a total cycle time of 4 cycles minimum in a modern design. So for most equipment using 50G 5 cycles is very reasonable. It is a common error to loom at breaker test reports and ignore relay delay times.

                          Since this is safety, NFPA 70E and a dearth of other documents makes it very clear that none of the standards apply to equipment that is not properly maintained. I will concede that a breaker might trip slowly if not maintained but using 6-12 cycles is pure fantasy. And when testing it is well known that trip performance improves as you "work" a malfunctioning relay. Spray a little WD40 in there and it easily passes testing fir a couple days until the lubricant evaporates! Then it is even worse since the residual wax and clays and maybe a little oil are dissolved and cleaned out, leaving metal on metal contact. It is just as likely to trip in 30-60 cycles or simply fail to trip when a breaker malfunctions. Or the 50G can malfunction and trip early or nuisance trip. We don't have design data for this. Backup protection is there but might be pure guess work and might end up being when the fault is consumed by the arc. Standards do not exist for improperly maintained equipment because it's all a guess. So trying to engineer for improper maintenance is not good practice, and violates engineering ethics and professional engineering standards.


                          Sent from my SM-T350 using Tapatalk
                          I agree and those have been my experiences as well.
                          BB+/BB=?

                          Comment


                            Originally posted by mbrooke View Post
                            I still assert that its "normal" for a 3 cycle breaker to clock in at 5 cycles. Let alone an oil unit.

                            Here is a relaying engineer saying the same thing toward the end of a thread:




                            https://www.eng-tips.com/viewthread.cfm?qid=414455


                            Through out its assumed 3 cycles as the fastest clearing, not the slowest.
                            But scuffed to operate slower after sitting then operate faster once cycled. If it is sticking it needs work.
                            BB+/BB=?

                            Comment


                              Originally posted by mivey View Post
                              We keep our transmission and distribution breakers maintenanced and tested and don't allow the stickiness you evidently are seeing.
                              This is good, but its difficult to do with tens of thousands of breakers every few years. Especially when for some you need to schedule an outage (straight bus).

                              Depends on reach. You would normally want your relay to look further and catch those bolted faults. I wil normally set the instantaneous to see 80% of the main line. I will stop at a recloser if it is catching the remainder.
                              With multiple reclosers in series it gets complicated, ie recloser loops. Parts of the line loose instantaneous clearing.


                              Sounds like it is time to tweak the budget.
                              I'd agree, but most EEs aren't the bean counters.


                              We use alternate (faster and no reclosing) settings when working on the line. It may cause a lockout for what would normally be a blink but so be it.

                              Yup- work ALWAYS gets a hot line tag.



                              We assume our breakers will operate during a fault the same way as they did during testing.

                              Never, ever assume this. Its asking for a blackouts or injury. Thats why despite everything the relaying is duplicated as well as the DC system and communications. Everything besides a casual SCADA trip gets BF relaying initiated. Over reaching zone 2/3, over lapping 50/51, transformer neutral over current, ect as a last resort. MHO reaching through some transformers or even a dedicated 311C for a transformer. Over seas Substations without dedicated busbar protection typically have not just zone 2 from the first supply substation in the chain but zone 3 from the stations before that despite each breaker having a revere zone for BB protection.

                              Granted every POCO has their own philosophy- but for me and to a lesser degree NERC assume a breaker will fail when called to trip.




                              But I'm being lazy and want a spoon-fed summary.
                              If the MV neutral is capable of significant voltages (to remote earth) during any fault condition its isolated from the LV neutral. The LV neutral is then grounded at least 8 feet away where the sphere of influence from the MV rod does not reach the LV ground rod.

                              Your number of 2.4kv will require that in certain parts of the system the customer neutral must be disconnected and permanently isolated from the MGN.








                              Like California.

                              I like what Cali does. Though so I've heard that on 3 wire systems they do not ground the can

                              OK. Haven't ran across it yet.

                              You will soon enough if you haven't already without knowing.


                              It doesn't and I have not said it did.

                              And thats what I'm getting at. I can legally set my relaying so that a line to neutral fault takes say 60 cycles to clear. 60 cycles of 2.4kv is going to harm someone. Even 5 cycles has risk.


                              I encourage you to run the numbers on an adult person assuming a resistance from hand to two feet and then compare to the IEC graph.

                              Comment


                                Originally posted by mbrooke View Post
                                This is good, but its difficult to do with tens of thousands of breakers every few years. Especially when for some you need to schedule an outage (straight bus).
                                Either be in the utility business or don't. Difficult or not, it is just part of the job.

                                Seems odd to stress over NEV during a fault if you are perfectly willing to skip routine maintenance to ensure your equipment is functioning in the first place.

                                Originally posted by mbrooke View Post
                                I'd agree, but most EEs aren't the bean counters.
                                So true. The Dilbert factor.

                                Originally posted by mbrooke View Post
                                Granted every POCO has their own philosophy- but for me and to a lesser degree NERC assume a breaker will fail when called to trip.
                                I assume, and it proves to be true for a well-maintained system, a breaker will rarely fail when called upon, but do have backups in case.

                                Originally posted by mbrooke View Post
                                If the MV neutral is capable of significant voltages (to remote earth) during any fault condition its isolated from the LV neutral. The LV neutral is then grounded at least 8 feet away where the sphere of influence from the MV rod does not reach the LV ground rod.
                                That would work. How fast does it react and what is the trigger mechanism?
                                BB+/BB=?

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