Metering equipment for capturing sub cycle transients
Metering equipment for capturing sub cycle transients
(OP)
I had posted a little while ago that we are experiencing several issues in our facility that we believe are a result of voltage transiens originating either from outside our facility or coming from within our facility.
In an effort to analyze some of these transients I want to try to capture them on some sort of power metering device. I believe some or most of these transients are sub cycle transients lasting less than 1/2 cycle in duration in which case most relays or metering equipment are not quick enough to capture these transients.
Does anyone know of a good power meter for capturing these sub-cycle transients? I would want something that could provide an osilography of the transient as well a indicate magnitude and durations. I would want something that I could permenantly install and put on our SCADA network for viewing present and past events.
Does anyone have any experience with a particular unit?
Does anyone know if the Multilin 750 relay, or Multilin PQMII Power monitor is capable of this?






RE: Metering equipment for capturing sub cycle transients
Metrosonics or Power Monitors for portable units?
Alan
RE: Metering equipment for capturing sub cycle transients
You may want to call up Dranetz/RPM or Fluke or the like.
Also try speaking to some electrical testing company folks in your area.
Rafiq Bulsara
http://www.srengineersct.com
RE: Metering equipment for capturing sub cycle transients
There are numerous other options, including Schweitzer, Electro Industries, and others.
David Castor
www.cvoes.com
RE: Metering equipment for capturing sub cycle transients
Even you get meters installed. How will you tell between "outside our facility or coming from within our facility" without knowing the information of the scheduled or forced outages from both facilities.
RE: Metering equipment for capturing sub cycle transients
Rafiq Bulsara
http://www.srengineersct.com
RE: Metering equipment for capturing sub cycle transients
RE: Metering equipment for capturing sub cycle transients
I looked a little deeper at the PQMII and it appears it is possible to see these subcycle transients with the relays "Trace Memory" setup.
I'm going to try to set this up next week to see if I can catch some of these transients, and I will post my findings.
I'm going to look into someo of the other devices mentioned above.
RE: Metering equipment for capturing sub cycle transients
It also depends on the type of the loads. Some indu. facilities in the system I work have there own Co-gen and big motors adjacent with the others.
To me the most interesting job in power system is to do a post-disturbance analysis. It is not a easy job.
RE: Metering equipment for capturing sub cycle transients
This meter is set up on one of our 4.16kV feeders, and I set the trigger on the meter to trigger at 110% of nominal voltage. This trigger occured at 5:31 EST yesterday evening, and at this time there were no other large loads starting or stopping.
Does anything obvious come to anyones mind when looking at these waveforms? Could this possibly be capacitor switching from outside the facility? Can you tell as davidbeach said weather or not the transients originates within the facility or is coming from outside?
RE: Metering equipment for capturing sub cycle transients
RE: Metering equipment for capturing sub cycle transients
If Ia and Va are the same phase (I doubt it) then you have about 0 for your power factor, but an inductor can't have the currents you show.
RE: Metering equipment for capturing sub cycle transients
Rafiq Bulsara
http://www.srengineersct.com
RE: Metering equipment for capturing sub cycle transients
RE: Metering equipment for capturing sub cycle transients
The meter that I am looking at is located on a feeder breaker on our main 5kV switchgear lineup after the utility transformer. The secondary of the utility transformer is a 4.16kV wye config, feeding a main breaker on this switchgear lineup. On this lineup there are about (8) feeder breakers. I only did a quick setup on the one feeder breaker attached for the I knew the area it served was having problems. I went ahead and set up the PQM's on the main breaker and the rest of the feeder breakers as well to look for this transient.
All of the PQM's are conntect to the same PT which has an open detla secondary, and all of the PQM's have their own CT's for the respective feeder circuit.
davidbeach, why are saying that it looks like we have a power factor of 0? Is it because the phase shift between the Ia and Va waveforms are about 30deg, and since Va is actually the Vab vector then the actual Va vector will be shifted 30deg which will put it in phase with the Ia current as shown? The p.f. for the downstream circuit is about .86 or so and when I glanced at the phasors everthing looked ok. I'll have to look again. I'm curious why the show the voltage a Va as opposed to the actual Vab?
I guess even with the phasors possibly wrong it there is no doubt a transient that is occuring do you guys agree?
Rbulsara what makes you think this is a source transfer? Is this a typical characteristic? I'd be interested to hear davidbeach's reasoning as well as to why he would expect larger currents or think this would have to be a resistive load? Wouldn't a p.f. of 0 indicate a resistive load?
I will continue to monitor and post results.
RE: Metering equipment for capturing sub cycle transients
Because it is very similar to captures I have seen for STS transfers on resistive loads. At voltage waves are just slightly off by a few degrees, on either side of the "transient". A disturbance in the same source, will not have that phase angle difference. Again, I am not drawing conclusions, just pointing out similarity. Knowledge of the actual system is needed to make definitive comments.
Rafiq Bulsara
http://www.srengineersct.com
RE: Metering equipment for capturing sub cycle transients
I looked closely and I see what you are saying about the voltage waves being a few degrees off. It appears that after the event, the voltage wave was shifted forward in time.
So are you suspecting that this was some sort of transfer that transfered to a second source that was slightly leading the origional one at the time of transfer?
How can you tell from these waveforms weather or not the transient originated outside of the plant?
RE: Metering equipment for capturing sub cycle transients
RE: Metering equipment for capturing sub cycle transients
We only have one transfer source in our system which is downstream of this switchgear lineup. I know for a fact that this transfer switch did not operate at this time for it only operates in an emergency case.
RE: Metering equipment for capturing sub cycle transients
You need to dig further upstream of the system.
Rafiq Bulsara
http://www.srengineersct.com
RE: Metering equipment for capturing sub cycle transients
RE: Metering equipment for capturing sub cycle transients
But in any case, I know of nothing that can happen downstream and cause that discontinuity in the voltage wave.
RE: Metering equipment for capturing sub cycle transients
I was able to capture (5) more transient events over the weekend. The strange part is as I mentioned all of these PQM's are on the main and feeder breaker looking at the same PT's on the main switchgear lineup, however all (5) of the attached events seem to be different. I would think that they would all see the same event since they are all looking at the same PT? Relays are set so they must be manuall reset after a trigger.
I have attached the (5) triggered waveforms, along with the trigger time and date proceeding each waveform.
It appears that three of these events seem to have the phase shifted transients as the first one I posted, while the other two events (4/24/10 @ 06:11:48 and 4/24/10 @ 10:53:14) only seem to have a transient on the Va waveform. After seeing this, do you still thinks its possible that the phase shifted transients are a result of a source transfer since it was mentioned above that this was very uncommon? Could the two non-phaseshifted transients be a result of capacitor switching or some other event?
Do these transients look like ones that could trip VFD's on bus overvoltage had we not gone ahead and put line reactors on all of our drives?
The transient on 4/25/10 @ 17:31:10 looks interesting for it appears to have alot of current distortion associated with the current waveforms.
I was able to figure out how to display the Vc waveform and was also able to determine that these Va, Vb, and Vc waveforms are indeed L-L voltages and this can be verfied by the peak of each waveform being close to 5.8kV. Multilin has told me that becuase I am using an Open Delta 2-PT arrangement I am not able so see a Vb waveform, however I questioned this and are waiting for a response from them. Elsewhere in the relay it gives me Vab and Vbc magnitudes but the relay does not give me a Vbc phasor in the phasor metering. I'm not sure whats going on here.
I tried to use the cursers as best I could and came up with close to a 70deg phase shift between the voltages and currents that davidbeach was questioning. And since we now know that voltages are L-L so we need to subtract the 30deg which leaves us with about 40deg and this matches close to the p.f. of about .75 which I was seeing on the relay. Therefore waveforms seem to be correct.
Thanks for the help.
RE: Metering equipment for capturing sub cycle transients
David Castor
www.cvoes.com
RE: Metering equipment for capturing sub cycle transients
No there is not currently something happening here at our facility at the time of these events I've captured. We have had over the past few months several issues with drives tripping out (some of which I've posted on this site) and power supplies failing. Almost like clockwork we would have drives trip while sitting idle overnight and would have to reset them all every morning. I was never able to see what exactly was causing these drives to trip so just assumed it was some sort of transient and installed line reactors on all the drives and havent had a problem since. This whole time I've assumed it was something coming from outside the facility, and put is on my radar to get ahold of a meter that could help me verify this.
I finally got a chance to get back to this issue and after looking at the PQM found that I could possibly capture some of these transients. After seeing some of these (again none caused any issues currently) I became curious as to what I was seeing and thought I would seek the advice of the experts here on this site. These transients look kind of strange to me and I'm wondering if these should be something I should be concerned with and contact the utility, of if these are just natural occurances? I find it hard to see how the phase shifted transient would be a natural occurance?
Thanks for all the help with this.
RE: Metering equipment for capturing sub cycle transients
Rafiq Bulsara
http://www.srengineersct.com
RE: Metering equipment for capturing sub cycle transients
The other two events appear to be voltage spikes on Va.
RE: Metering equipment for capturing sub cycle transients
I've attached (2) more transients that I've recorded over the past two days. I've recorded others but they were more of the phase shift type that appears to be a measurement error of some sort. I am going to ask Multilin for their thoughts on this phases shifted measurement error.
As far as the transient that appers on the Va most of the time, does this appear to be a real transient? Can you tell if this is something that is coming from outside our facility?
Do the peaks of 9kV during these transients indicate that this may be something that could have been causing a disturbance to our drives before we put the line reactors on. (I'm almost half tempted to take the reactor off this drive temporarily to see.)
jghrist
Can you briefly explain why there would be ringing associted with current changing rapidly? Is this ringing only associated when current changes rapidly, or would it occur when the voltage changed rapidly as well?
RE: Metering equipment for capturing sub cycle transients
The other thing that I find strange with these transients is the fact that all of these PQM's are looking at the same PT inside the switchgear, however not every device records the same transient. There may be one transient that shows up on one device and none that show up on the rest. And it doesn't appear that they are even at all triggered from the same transient due to the fact they all have different trigger times.
RE: Metering equipment for capturing sub cycle transients
RE: Metering equipment for capturing sub cycle transients
Yes all trigger points are the same set to trigger at 110% overvoltage.
Some of the transients we have seen are peak at about 9kV which is well over the peak of 110% of L-L voltage (5.88kV)
RE: Metering equipment for capturing sub cycle transients
Sounds like something else to ask Multilin about.