solarken
NABCEP PVIP
- Location
- Hudson, OH, USA
- Occupation
- Solar Design and Installation Professional
I am working on a preliminary design for a commercial customer (a machine tool shop) to fill several needs. One of them is to protect some of the machines in the shp that are damaged periodically after severe powr quality events. I have a rough design to provide an isolated 3-phase power feed to their most sensitive equipment (Basically a UPS) along with solar and storage and a control system to shave demand peaks and reduce ene4gy usage.
However, as I was digging into the details i started looking at their existing utility service, and I am starting to think their power quality issues might be caused or at least contributed to by how the utility is providing their 240V delta service. This is what I see: They have three transformers on the pole just outside their building. Two of them are single phase 50KVA transformers, providing the 3-phase 240V service connected via an Open wye - Open Delta arrangement, with one phase (call it A) coming from one Sgl ph transformer secondary, one phase (Call it B) coming from the other sgl ph transformer, and one phase (call it C) coming from the bare neutral conductor. The third transformer on the pole is a 240V single phase transformer that feeds a separate 240V/120V service for their office and lighting circuits, through a separate meter.
These two services are the last on the feeder line from the utility, i.e. the phase and neutral conductors end on the pole that feeds them, and do not go on to feed any other customers. This is in an industrial park and there are lots of manufacturers, shops, etc in the immediate area, many fed from that feeder.
The customer experiences sags and swells quite often, sometimes lasting three seconds or more, and with voltage dropping to as low as 40-50V, and rising to as high as 310V, often on one or two phases only. Like I said it has been severe enough to blow up some of his CNC machines, including wire EDM, a milling machine with a VFD, and others.
As I have researched this, it seems that an Open Delta service can cause voltage imbalance issues, assymmetric currents into 3-phase motors, power factor issues, and other power quality problems. I am wondering if the way this service is provided/connected, along with the fact that it is on the end of a run, and downstream of other customers with likely heavy variable loads is the main issue. The utility says nothing is wrong, even though the surge suppressors they installed along with a power quality monitor are blown on two phases, and the power quality monitor is logging these sag and swell events periodically. I also know now that open delta capacity is only 86.6% of the nameplate capacity of the two transformers feeding it, so instead of 100kVA, the transformers can only provide 86.6kVA. I see them hit 70kVA at times in the data we collected.
Does anyone have any experience with this kind of issue? Any advice? What to check? I am meeting with the utility engineers soon to discuss, and want to be prepared. They don't seem to have any interest in helping to resolve, but I am thinking is a change in service can help provide more balanced and stable power, I don't have to include a custom UPS (expensive and complicated) into the design and can go with just a routine grid-connected solar design with storage.
Thanks, Ken
However, as I was digging into the details i started looking at their existing utility service, and I am starting to think their power quality issues might be caused or at least contributed to by how the utility is providing their 240V delta service. This is what I see: They have three transformers on the pole just outside their building. Two of them are single phase 50KVA transformers, providing the 3-phase 240V service connected via an Open wye - Open Delta arrangement, with one phase (call it A) coming from one Sgl ph transformer secondary, one phase (Call it B) coming from the other sgl ph transformer, and one phase (call it C) coming from the bare neutral conductor. The third transformer on the pole is a 240V single phase transformer that feeds a separate 240V/120V service for their office and lighting circuits, through a separate meter.
These two services are the last on the feeder line from the utility, i.e. the phase and neutral conductors end on the pole that feeds them, and do not go on to feed any other customers. This is in an industrial park and there are lots of manufacturers, shops, etc in the immediate area, many fed from that feeder.
The customer experiences sags and swells quite often, sometimes lasting three seconds or more, and with voltage dropping to as low as 40-50V, and rising to as high as 310V, often on one or two phases only. Like I said it has been severe enough to blow up some of his CNC machines, including wire EDM, a milling machine with a VFD, and others.
As I have researched this, it seems that an Open Delta service can cause voltage imbalance issues, assymmetric currents into 3-phase motors, power factor issues, and other power quality problems. I am wondering if the way this service is provided/connected, along with the fact that it is on the end of a run, and downstream of other customers with likely heavy variable loads is the main issue. The utility says nothing is wrong, even though the surge suppressors they installed along with a power quality monitor are blown on two phases, and the power quality monitor is logging these sag and swell events periodically. I also know now that open delta capacity is only 86.6% of the nameplate capacity of the two transformers feeding it, so instead of 100kVA, the transformers can only provide 86.6kVA. I see them hit 70kVA at times in the data we collected.
Does anyone have any experience with this kind of issue? Any advice? What to check? I am meeting with the utility engineers soon to discuss, and want to be prepared. They don't seem to have any interest in helping to resolve, but I am thinking is a change in service can help provide more balanced and stable power, I don't have to include a custom UPS (expensive and complicated) into the design and can go with just a routine grid-connected solar design with storage.
Thanks, Ken
