blown fuse detection
blown fuse detection
(OP)
Getting back to the subject of blown fuse protection (thread238-175697: Negative Sequence Protection), one of my clients has experienced a few cases where an automatic transfer switch (custom built breaker transfer-pairs) begin cycling after a transformer primary fuse opens. These cases all involve pad-mount medium voltage to 480V utility-owned transformers supplying the normal source input of the breaker pair ATS.
An article on the Basler web site discusses the phenomenon where wye-wye 5-leg shell-form transformers regenerate voltage on open phases, particularly when there is no load applied. I suspect many pad-mount transformers are of this construction. This would explain the confused ATS's.
The ATS's typically utilize a 47/27 relay, connected through open-delta PT's, for sensing on the utility source.
Possible solutions I see are to add some load upstream of the ATS, so the transformer always has some load, or replace the transformer with delta-wye (may not be an option). The Basler article mentions a "small" load, but how small is small?
Has anyone dealt with this situation or have any other suggestions to deal with this regenerated no-load voltage?
An article on the Basler web site discusses the phenomenon where wye-wye 5-leg shell-form transformers regenerate voltage on open phases, particularly when there is no load applied. I suspect many pad-mount transformers are of this construction. This would explain the confused ATS's.
The ATS's typically utilize a 47/27 relay, connected through open-delta PT's, for sensing on the utility source.
Possible solutions I see are to add some load upstream of the ATS, so the transformer always has some load, or replace the transformer with delta-wye (may not be an option). The Basler article mentions a "small" load, but how small is small?
Has anyone dealt with this situation or have any other suggestions to deal with this regenerated no-load voltage?






RE: blown fuse detection
RE: blown fuse detection
I think you have to register or something to download it.
RE: blown fuse detection
In either case, it's a high impedance phenomena. A small amount of load should collapse the voltage, but the magic question is how much. I'd try about 2% load on the winding, in other words put about 2% of rated current on the winding and see if the voltage collapses.
What kVA size transformer is involved?
RE: blown fuse detection
RE: blown fuse detection
RE: blown fuse detection
It's always good to see a recommendation from another source. It is comforting when the two agree with each other.
RE: blown fuse detection
it's very intresting topic.
I think more from 2% it's not simple value.
According to theory (I haven't any excpirience with 47 protection): several reason of NPS on busbur are:
Conductor broken, asimmetrical load and motor load(voltages unbalance as result of current unbalance of motor).
As I remebare (please correct me), it's more or less linear
proportianal ( about k*Un%---5k*In%). That means
in normal situation with motor load U NPS is not more 2%.
Daviandgo, I assume your setting about 3-4%.
Problem, I think is time delay, it's depend.
I assume, NPS not used as trigger of ATS, it's only prevent transfer.
Alehman, thanks for start of this topic.
Hm, I think , I'll put this function in one of projects
and check what is result. Hey, I know were, next month we'll
install relay for decoupling of plant on 36kV side.
Regards.
Slava
RE: blown fuse detection
B-phase open:
Van: 1.0<0
Vbn: approx. 0.5<-120
Vcn: 1.0<120
V2/V1 = 0.2
C-phase open:
Van: 1.0<0
Vbn: 1.0<-120
Vcn: 0.58<90
V2/V1 = 0.23
RE: blown fuse detection
Pad-Mounted Transformer 2500 kVA, 34.5kV YG/480V YG
System Phase Rotation: CBA
Measured Values:
With all fuses in (Load on transformer)
Negative-to-positive Ratio: 0.2%
With C-phase fuse removed (No load on transformer)
Negative-to-positive Ratio: 4.3%
With B-phase fuse removed (No load on transformer)
Negative-to-positive Ratio: 2.4%
This was the basis of the 2% setting to prevent transfer back to the utility source in the event of a blown fuse.
RE: blown fuse detection
RE: blown fuse detection
Are you check NPS voltage on 34.5kV side ?
Are you check NPS voltage with some load ?
Q?
Why according to Alehman's post ( sorry to Basler) it's 23% and 20%?
According to theory/practic,"first" setting of NPS (47) is 3%.
Regards.
Slava
RE: blown fuse detection
You say "According to theory/practic,"first" setting of NPS (47) is 3%.".
Just curious if you've seen that in a standard somewhere?
RE: blown fuse detection
No, of course no.
I wrote,that I haven't any expirience with this function.
Before some time, we installed protective relay of some
big compnay ( for feeder protection). Those relays are include NPS and PPS ( U2> and U1< )voltage protection.
We never used this protection and I asked mnf.:
What is a typical appl for this protection.
U1< for the decoupling.
U2>, for open conductor, asimmetrical loads.
in manual recommendaed typical setting is 3%.
I'm only translate mnf. recommendation, sorry.
BTW, my second problem, we haven't Y/Y trnasformers in our area, only D/Y.
Why, it's intresting for me, before half year we used
NPS voltage for alarms in VT secondary wiring and it's helped us.
Regards.
Slava
RE: blown fuse detection
Forgot something.
According to Basler result.
U=0.5Un or 0.58Un.
Sorry, for what I need 47 function?
27 is good function for this data.
Regards.
Slava
RE: blown fuse detection
RE: blown fuse detection
RE: blown fuse detection
RE: blown fuse detection