Phase Shift ?
- Thread starter Mike01
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glene77is
Senior Member
- Location
- Memphis, TN
What is the source of your information that Delta/Wye contains a phase shift?
Interesting thought, want to read something about it.
wirenut1980
Senior Member
- Location
- Plainfield, IN
Yes, all delta-wye transformers have a 30 degree phase shift. It is a function of the phase angle differences between how the primary and secondary coils are hooked together. There is no real purpose of the phase shift, however, delta-wye transformers are sometimes used to either trap triplen harmonics in the delta winding, or they are used along with transformers with no phase shift to cancel harmonic currents from six pulse drives.
As far as how to tell if a utility primary is delta or wye...If you are talking about at a transformer: If the transformer is a padmount, you would need to see the nameplate. If the transformer bank is a pole-mount cluster bank, then you would be able to tell from how the primary bushings are wired. Wye would be one or two primary bushing transformers, with one primary phase going to one bushing, the other bushing is tied to ground (if 2 primary bushings). If delta primary, the transformers would have two primary bushings, and these would be connected to each other in all three transformers (I know this last part is not very clear, I am having trouble word-smithing).
As far as how to tell if a utility primary is delta or wye...If you are talking about at a transformer: If the transformer is a padmount, you would need to see the nameplate. If the transformer bank is a pole-mount cluster bank, then you would be able to tell from how the primary bushings are wired. Wye would be one or two primary bushing transformers, with one primary phase going to one bushing, the other bushing is tied to ground (if 2 primary bushings). If delta primary, the transformers would have two primary bushings, and these would be connected to each other in all three transformers (I know this last part is not very clear, I am having trouble word-smithing).
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Follow Up
I was looking at a short circuit study that had indicated some voltage drop calcs. While looking at them I noticed the unit substation to be Delta-Wye (the 30Degree phase shift/positive), however when looking at the voltage drop it gave the voltage drop as a negative integer? How can the voltage drop be negative? When I asked about this I was informed it?s what the software says but how is my question?
Follow Up
I was looking at a short circuit study that had indicated some voltage drop calcs. While looking at them I noticed the unit substation to be Delta-Wye (the 30Degree phase shift/positive), however when looking at the voltage drop it gave the voltage drop as a negative integer? How can the voltage drop be negative? When I asked about this I was informed it?s what the software says but how is my question?
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Does yous model have the transformer taps set to increase the voltage by one or more tap settings? That would do it. Sometimes I do this, in order to provide a VD of below 3% further downstream. That makes the voltage nearer the source come out above 100% nominal, and thus shows up as a negative VD.
It might be worth adding that there is no phase shift between the actual windings on each coil. The phase shift is when you go line to line. The Y side line to line is made up adding two line to neutral voltages with a 120deg angle between them.
Transformers are not particularly good for harmonic attenuation, particularly lower order harmonics.
Many of the contracts we have had for VSD systems specify maximum THD on voltage at the point of common coupling generally in accordance with nationally accepted engineering recommendation.
There are a number of sites where we have had to include harmonic filters in our scope of supply for the overall installation to ensure contract compliance.
Usually we'd do this at the LV switchboard, generally 400V 3ph.
Sometimes, the supply is MV and each VSD has its own MV to LV transformer. In such cases, we put the filters on the MV side.
Not sure I agree with this statement. I do agree that voltages and currents on "complementary" windings are in phase. The shift occurs from the fact that primary windings are connected line-to-line whereas secondary windings are connected line-to-neutral. Note in the following diagram how primary line-to-line "vectors" are the same as the secondary line-to-neutral vectors. Each system's phasing is referenced Line A/a to system neutral, which for delta configured windings is a virtual point at the "center" (can't think of the correct geometric term at present) of the triangle, so indicated with the dashed line.
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richxtlc
Senior Member
- Location
- Tampa Florida
In the diagram you show, the primary is leading the secondary by 30 degrees.Not sure I agree with this statement. I do agree that voltages and currents on "complementary" windings are in phase. The shift occurs from the fact that primary windings are connected line-to-line whereas secondary windings are connected line-to-neutral. Note in the following diagram how primary line-to-line "vectors" are the same as the secondary line-to-neutral vectors. Each system's phasing is referenced Line A/a to system neutral, which for delta configured windings is a virtual point at the "center" (can't think of the correct geometric term at present) of the triangle, so indicated with the dashed line.
drbond24
Senior Member
- Location
- Barboursville, West Virginia
I suspect it was showing it as the decrease to the voltage on the circuit. If the voltage drop was -3%, that would mean there was a 3% drop on the circuit. The negative would just be indicating a decrease in the voltage.
This has nothing to do with the phase angles or transformer, though.
That's what I said.
The shift is between primary line to line and secondary line to line.
ohmhead
Senior Member
- Location
- ORLANDO FLA
Phase shift??
Phase shift??
Well just a simple construction electrician with a question, phase shift between windings pri to sec only happens on a delta wye or a wye delta transfer why ? now its 30 degrees A phase delta to A phase wye on transfer if so how or why ? i just thought its was due to the induction of the coils or windings ac reactance to time in cycles between each pri to sec winding or the way transfer happens to time can you clear this up for me in simple terms ? take care
Phase shift??
Well just a simple construction electrician with a question, phase shift between windings pri to sec only happens on a delta wye or a wye delta transfer why ? now its 30 degrees A phase delta to A phase wye on transfer if so how or why ? i just thought its was due to the induction of the coils or windings ac reactance to time in cycles between each pri to sec winding or the way transfer happens to time can you clear this up for me in simple terms ? take care
OK... I must have been reading your post in a totally different frame of mind (which is not uncommon for me :grin
Let's use delta-wye for this discussion.
If you look at the diagram I posted earlier, note what you are calling primary A phase winding is actually connected A to C. Now note secondary A to N is the same direction in the symbologies to the right. This would be the same phasing, but it is no longer line-to-line on the secondary, but rather line-to-neutral. Line-to-line on the secondary now has a 30? phase shift from the primary's line-to-line phasing.
Is there something you are not saying, or should we just take your comment on face value?
FWIW, the diagram is from a Cooper Power Systems, Inc. publication http://www.cooperpower.com/library/pdf/r201902.pdf
glene77is
Senior Member
- Location
- Memphis, TN
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Every time I read about the "phase shift" between primary and secondary (which is not an actual delay, but just an electrical difference), I wonder why it matters.
It's not like we're going to connect anything between, say, a 480/277v distribution system and a 208/120v panel supply. Why does the difference matter to us?
It's not like we're going to connect anything between, say, a 480/277v distribution system and a 208/120v panel supply. Why does the difference matter to us?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The only time it matters is when sources are being paralleled. If the supply is only a single transformer it is immaterial.
I have an application where I need the 30 degree phase shift.
I have a Liebert UPS that has an isolation transformer.
I have a 2 breaker bypass for the UPS that requires the UPS output breaker be opened before the bypass breaker is closed.
I want to make it able to be bypassed without interupting the load.
I need an isolation transformer on the bypass feeder to match the 30 degree phase shift from the UPS.
Is the isolation transformer just a delta primary, wye secondary transformer?
I have a Liebert UPS that has an isolation transformer.
I have a 2 breaker bypass for the UPS that requires the UPS output breaker be opened before the bypass breaker is closed.
I want to make it able to be bypassed without interupting the load.
I need an isolation transformer on the bypass feeder to match the 30 degree phase shift from the UPS.
Is the isolation transformer just a delta primary, wye secondary transformer?
ohmhead
Senior Member
- Location
- ORLANDO FLA
Smart $Let's use delta-wye for this discussion.
If you look at the diagram I posted earlier, note what you are calling primary A phase winding is actually connected A to C. Now note secondary A to N is the same direction in the symbologies to the right. This would be the same phasing, but it is no longer line-to-line on the secondary, but rather line-to-neutral. Line-to-line on the secondary now has a 30? phase shift from the primary's line-to-line phasing.
WHY? and is this phase shift the the current & voltage shift in degrees on that phase winding of pri to sec . meaning matching phase or is this the difference between just voltage & current on a to c phase of both currents in each seperate winding on common tap ? can power factor effect this shift or loads ? were trying to understand what is phase shift and how or why its there basically ? take care
If you look at the diagram I posted earlier, note what you are calling primary A phase winding is actually connected A to C. Now note secondary A to N is the same direction in the symbologies to the right. This would be the same phasing, but it is no longer line-to-line on the secondary, but rather line-to-neutral. Line-to-line on the secondary now has a 30? phase shift from the primary's line-to-line phasing.
WHY? and is this phase shift the the current & voltage shift in degrees on that phase winding of pri to sec . meaning matching phase or is this the difference between just voltage & current on a to c phase of both currents in each seperate winding on common tap ? can power factor effect this shift or loads ? were trying to understand what is phase shift and how or why its there basically ? take care
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Make sure the UPS vendor is involved.
If the bypass transformer is fed from the same source as the UPS then, you will probably not have any problem.
If the transformer is fed from a different source then you need to be aware of a 'rare' mis-wiring issue often called 'rolled phases'. You are probably aware of the issue of phase rotation ABC vs ACB. Phase rolling is having a 'phasing' of CAB or BCA instead of ABC. A phase rotation meter will not detect rolled phases because they do have the proper rotation.
Always make sure that you take readings of all 9 different L-L voltage combinations prior to connecting two sources in parallel.
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