Centimeter
Member
- Location
- USA
- Occupation
- Farmer
I know this general subject has been discussed in this forum, however I have not found much with regards to this subject in the single phase flavor. So, I am asking for advice and I hope I am not being annoying-- I did look through the forum quite extensively before asking. I also apologize about the length!
I have 240V Single Phase at my location and I am looking to install a service to a center pivot sprinkler system which will require both 120V Single Phase for the control panel and 480V 3 phase for the pump and tower motors (there's good voltage flexibility on these so not too worried about nailing the voltage). I am also hoping to extend the service past the center pivot to another location where I hope to install two 50 amp 120V RV outlets. Greedy I know, but us farmers need to think about all the ways we can make an extra buck.
The three phase will only be necessary for running the pivot and thus will only need to run maybe 24 hours a week. I don't want to run three phase power the whole way as I don't want to run a rotary constantly in order to have the 120V circuits on at all times. Thus my plan is to run single phase 480V the whole way and derive 120V where needed using step-down transformers. For reference, the principle loads on the circuit would be a 10HP 480V Rotary and 2 x 50amp 120V RV circuits.
My plan is to use a 25KVA 240-480 single phase step-down transformer in reverse-- I got it for a song so I'd like to use it. This is an older model Sola HD S5H25, so no high efficiency stuff or anything like that. I am not certain if this was designed for being reversed or not as it uses high (H) and low (x) voltage conventions rather than primary and secondary. I am not able to find any technical documentation on this transformer, however I can access the data for the newer high efficiency one, Sola ES5H25S. It lists the inrush as being ~6-8x normal running current as a step-down and the usual not recommended and no data for using it in reverse. Since it's a transformer running continuous duty with two wires both in and out, I plan to uprate the OCPD on the incoming 240V to 125% FLA and rounding up, which gives an OCPD of 150 Amps. Unfortunately, I am stuck with a Square D Homeline panel, so the best breaker I can get is the HOM2150BB. If I look at its trip curve, I see that at 800 amps (using the 8x inrush spec on the newer transformer) it will trip after ~1 sec at 1C.
Question 1: Is this OCPD for this transformer likely to work or am I asking for constant headaches given the fact that I am running it in reverse? I am hoping that it being an older model will work in my favor... I am fine if I have a couple nuisance trips upon turning the circuit on as long as they don't happen when I'm running at full tilt. I also will have a 15kva step down transformer (for the RV circuits) as a constant load on this 25kva transformer, which I'm hoping will help mellow out this inrush current too. Thoughts? Either way, I want to make sure that this is a safe application!
I intend to run a full size EGC from my main panel with the two 480v conductors and no neutral (since the transformer is being run in reverse). At the pivot point and the RV site, I would like to use a 480-240/120 step down transformer to create the 120V for the control panel and the 50 amp outlets for the RV's.
Question 2: To create the Neutral for the 120V circuits, I was planning on bonding the EGC from the main panel to the neutral tap of the step down transformers at the pivot and the RV site. Is this an effective way to derive a proper neutral and also to provide for proper functioning of the OCPD on the input side of the 25KVA transformer? I expect to drive grounding rods in at both the pivot point and the RV sites as well and connect these to the EGC. If not, how does one go about creating a proper neutral in this situation given the fact that no bonded neutral is being run from the 25KVA transformer?
For reference, I plan to use a Hevi-Duty 15KVA S5H15S step-down transformer for the two 50 amp RV outlets. The 120V for the pivot control panel I haven't figured out yet, but it will just be a small transformer to run the board and contactors.
I have worked a lot with electric but not much with transformers, so please excuse me if this comes off as totally ignorant-- I am just a farmer trying to learn some new tricks and hopefully save some money. Thanks for your patience and for any help you can provide.
I have 240V Single Phase at my location and I am looking to install a service to a center pivot sprinkler system which will require both 120V Single Phase for the control panel and 480V 3 phase for the pump and tower motors (there's good voltage flexibility on these so not too worried about nailing the voltage). I am also hoping to extend the service past the center pivot to another location where I hope to install two 50 amp 120V RV outlets. Greedy I know, but us farmers need to think about all the ways we can make an extra buck.
The three phase will only be necessary for running the pivot and thus will only need to run maybe 24 hours a week. I don't want to run three phase power the whole way as I don't want to run a rotary constantly in order to have the 120V circuits on at all times. Thus my plan is to run single phase 480V the whole way and derive 120V where needed using step-down transformers. For reference, the principle loads on the circuit would be a 10HP 480V Rotary and 2 x 50amp 120V RV circuits.
My plan is to use a 25KVA 240-480 single phase step-down transformer in reverse-- I got it for a song so I'd like to use it. This is an older model Sola HD S5H25, so no high efficiency stuff or anything like that. I am not certain if this was designed for being reversed or not as it uses high (H) and low (x) voltage conventions rather than primary and secondary. I am not able to find any technical documentation on this transformer, however I can access the data for the newer high efficiency one, Sola ES5H25S. It lists the inrush as being ~6-8x normal running current as a step-down and the usual not recommended and no data for using it in reverse. Since it's a transformer running continuous duty with two wires both in and out, I plan to uprate the OCPD on the incoming 240V to 125% FLA and rounding up, which gives an OCPD of 150 Amps. Unfortunately, I am stuck with a Square D Homeline panel, so the best breaker I can get is the HOM2150BB. If I look at its trip curve, I see that at 800 amps (using the 8x inrush spec on the newer transformer) it will trip after ~1 sec at 1C.
Question 1: Is this OCPD for this transformer likely to work or am I asking for constant headaches given the fact that I am running it in reverse? I am hoping that it being an older model will work in my favor... I am fine if I have a couple nuisance trips upon turning the circuit on as long as they don't happen when I'm running at full tilt. I also will have a 15kva step down transformer (for the RV circuits) as a constant load on this 25kva transformer, which I'm hoping will help mellow out this inrush current too. Thoughts? Either way, I want to make sure that this is a safe application!
I intend to run a full size EGC from my main panel with the two 480v conductors and no neutral (since the transformer is being run in reverse). At the pivot point and the RV site, I would like to use a 480-240/120 step down transformer to create the 120V for the control panel and the 50 amp outlets for the RV's.
Question 2: To create the Neutral for the 120V circuits, I was planning on bonding the EGC from the main panel to the neutral tap of the step down transformers at the pivot and the RV site. Is this an effective way to derive a proper neutral and also to provide for proper functioning of the OCPD on the input side of the 25KVA transformer? I expect to drive grounding rods in at both the pivot point and the RV sites as well and connect these to the EGC. If not, how does one go about creating a proper neutral in this situation given the fact that no bonded neutral is being run from the 25KVA transformer?
For reference, I plan to use a Hevi-Duty 15KVA S5H15S step-down transformer for the two 50 amp RV outlets. The 120V for the pivot control panel I haven't figured out yet, but it will just be a small transformer to run the board and contactors.
I have worked a lot with electric but not much with transformers, so please excuse me if this comes off as totally ignorant-- I am just a farmer trying to learn some new tricks and hopefully save some money. Thanks for your patience and for any help you can provide.
