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    Directional Power & Current Relays

    We are doing a large project and unfortunately the building that we are installing the PV system on is fed by a small spot network in a large metro area. The utility is requiring that our system never export more than 155 kW and in order to guarantee this they are requiring us to install a 67 directional current element relay and a 32 directional power element relay that will disconnect the PV system if power export ever exceeds 155 kW.

    I have never run into this before and don't know anything about these relays, how they work and how they are installed. Has anyone run into this before? Does anyone know where I can learn more about how these relays work and where & how to install them? I'm at a bit of a loss right now on where to find information on this subject. Any help pointing me in the right direction is much appreciated!

    #2
    What type of relay do you have in place now at the export point?
    It may have it on it.
    enable it, set it, and forget it.
    I have them turned on at some of our solar sites on our utility breaker.

    Comment


      #3
      Originally posted by Hv&Lv View Post
      What type of relay do you have in place now at the export point?
      It may have it on it.
      enable it, set it, and forget it.
      I have them turned on at some of our solar sites on our utility breaker.
      There aren't any relays at the export point, at least that I am aware of. The building main service equipment is an extremely antiquated Federal Pacific fused switchgear so we were planning on a supply side connection with a fused disconnect. Unfortunately a load side connection is not possible.

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        #4

        https://www.powellind.com/sites/down...r%20Relays.pdf

        that one is much simpler than this one.
        https://www.myprotectionguide.com/up...ectionaloc.pdf

        look here.https://store.gegridsolutions.com/FA.../GET-8048A.pdf

        I don’t see this happening with fuses. How are you measuring the output? Are you measuring it or just connecting it inside and hoping net metering would take care of it.

        You need voltage, which you have, and CTs installed to a relay. Then it has to be set and tested correctly.
        Got a test set?

        Kind of lazy utility. You get the relay in, set it, commission it, get the site up and running, what’s to keep you from tweaking it and gaining output?
        Last edited by Hv&Lv; 10-04-19, 06:25 PM.

        Comment


          #5
          Get on selinc.com. It’s all phasor math. You look at phase angle of the currents compared to the voltages. You should be able to do it all with a 751 or 751 A, 3 CTs and 2 PTs. At worst you’d need to step up to a 651 with a full set of metering on both sides. I’m on the road so can’t tell you which one right now. The sensors go to the relay. The relay shunt trips your switch. Also use undervoltage release for safety. This is easily done with your main breaker. Also need a power source from the utility side another PT if the PTs aren’t on that side. There is the issue of sync relay, under/over frequency and voltage too never mind basics like current and ground fault. With the SEL relays all of that is built in.

          I will warn you SEL programming can be very intimidating and how you do your wiring for modern (Basler, SEL) relays is totally different and far simpler from traditional approaches.


          Sent from my iPhone using Tapatalk

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            #6
            I can't help with the relay stuff, but it seems like you need to either install the relays on the whole service (ahead of the supply side tap), or you should just downsize the inverters to 155kw or less. Just sayin'.

            Comment


              #7
              Originally posted by paulengr View Post

              I will warn you SEL programming can be very intimidating and how you do your wiring for modern (Basler, SEL) relays is totally different and far simpler from traditional approaches.


              Sent from my iPhone using Tapatalk
              The older SEL programming used the word bits with their and not or (*!+) can be. The newer ones like the 6 or 7 series relays are simpler to program than the old 5 series.

              of course, I say that having programmed these all over our system.
              1st timer, you better call in some help...

              Comment


                #8
                My company just closed out a PV project on a high rise building connected to the downtown network here in Austin where the AHJ will not allow the export of a single fraction of a kW. They have their own relays which will shut down power to the building if they detect any export at all, and NOBODY wants that to happen. The City requires us to monitor the building load and configure three levels of protection on our side of the interconnection to keep any power from being exported.

                We did not realize going in how challenging (and expensive) it would be to comply with their requirements. It was an educational experience, but we are not likely to undertake another project like it.

                Comment


                  #9
                  I also just finished a couple of PV with energy storage projects on a downtown network. This utility required zero export. We were able to use our site controller for the ESS to ramp down the power output of the PV inverters. And then as a fail-safe we installed an SEL-751A relay to trip the breaker feeding the PV and ESS at our interconnection point.

                  Sent from my Pixel 2 using Tapatalk

                  Brian

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                    #10
                    Originally posted by jaggedben View Post
                    or you should just downsize the inverters to 155kw or less. Just sayin'.
                    thats what I was thinking. Isn't that much easier? We had an approx 2 Meg system where the utility required the power to be limited slightly. The inverter manufacturer reprogrammed the inverters to dial back the max output, so that may be an option too.

                    Edit: I guess if the system is quite a bit larger than the utility's max and you are planning on local loads chewing through pv power most of the time, the relay approach makes sense.
                    Ethan Brush - East West Electric. NY, WA. MA

                    "You can't generalize"

                    Comment


                      #11
                      Just a comment here regarding the surprises.

                      Aren’t there engineering studies done on these PV systems and the utility requirements before they are installed?
                      before a PV system is allowed to be grid tied(at least to our system), there must be an engineering study done that is paid for by the PV owner. Wire size, Substation capacity, Substation loads, all are incorporated into this study.
                      When the system is approved, the requirements regarding interconnect are spelled out in the contract regarding export limitations and any safeguards required. Any safeguards required by us that we install, including any infrastructure, breakers, relays, etc (billed T&M) to get to the facility,
                      There are no surprises on these installations.
                      Well, at least not to the PV owner... what they tell the EC we have no control over.

                      Comment


                        #12
                        Originally posted by Hv&Lv View Post
                        Just a comment here regarding the surprises.

                        Aren’t there engineering studies done on these PV systems and the utility requirements before they are installed?
                        ...
                        For a system this size the answer should be yes, if the PV installer knows what they are doing. But the installer requests the utility to do the study, since only the utility is knowledgeable enough about their network to say what can be exported. I hope that our OP is not too far along to change the system design (downsize inverter) before installation, if that is the wiser option for everyone involved.

                        For smaller systems, a study is usually not done before installation, at least in California. Around her, for systems under 30kW, or for services where the customer doesn't have their own dedicated utility transformer, (i.e. residential), the customer is generally not on the hook for utility-side upgrades, and the worst that happens is that permission to operate is delayed if a transformer upgrade is necessary.

                        Comment


                          #13
                          BTW, to clarify my earlier comments, obviously the relay device measurement should be done on the whole service but the disconnection should be done only to the PV. But regardless, you'd still want a disconnection to be an event which would only happen under abnormal circumstances, not something that would be knocking the PV system on and off multiple times a year. The OP is light on details in this regard. Are we talking about a PV system that is substantially larger than 155kW, and if so is there a constant building load that amounts to the difference that would only go off in very unusual circumstances? These are important considerations.

                          Comment


                            #14
                            This is the answer. We use 651R relays on most of our projects and add the 32 element when needed. The key point is you need control logic that stops your system from ever actually tripping the relay so you don’t have nuisance tripping.

                            This would get very expensive for a 155kW system. You need a relay, a trip device (breaker, motorized switch or recloser) and someone to program and test it. Plus all the instrument transformers.


                            Sent from my iPhone using Tapatalk

                            Comment


                              #15
                              Originally posted by pcanning87 View Post
                              This is the answer. We use 651R relays on most of our projects and add the 32 element when needed. The key point is you need control logic that stops your system from ever actually tripping the relay so you don’t have nuisance tripping.

                              This would get very expensive for a 155kW system. You need a relay, a trip device (breaker, motorized switch or recloser) and someone to program and test it. Plus all the instrument transformers.


                              Sent from my iPhone using Tapatalk
                              I’m not sure a 651R is right for a 155kW system, although if the breaker in the invertor can be wired with IO, there might be an application there.
                              if it’s a 200kW invertor with the associated electronics for commercial use, it may already have the capability to do this. It just needs to be turned on.

                              for 25kV installations...
                              651R, Tavrida with VT and CT
                              ~$21,000, plus installation costs.
                              not including the switches for isolation or metering expenses.

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