Vector Group
Vector Group
(OP)
Hello,
Have a transformer with Vector group Yd5. Line come in with C-B-A instead of normal A-B-C phase order.
On terminal A arrives L3, on B arrives L2 and on C arrives L1.
How does this affect the Vector group? Does this transform to Yd7 or Yd1? Or will it remain Yd5?
Three engineers and three opinions, need some assistance to set transformer protection.
(Personally I think Yd7 or maybe Yd1, but not Yd5=)
BR Gestur
Have a transformer with Vector group Yd5. Line come in with C-B-A instead of normal A-B-C phase order.
On terminal A arrives L3, on B arrives L2 and on C arrives L1.
How does this affect the Vector group? Does this transform to Yd7 or Yd1? Or will it remain Yd5?
Three engineers and three opinions, need some assistance to set transformer protection.
(Personally I think Yd7 or maybe Yd1, but not Yd5=)
BR Gestur






RE: Vector Group
RE: Vector Group
Regards
Marmite
RE: Vector Group
See the attached image. The simulation consists of a 3-phase voltage source scaled to reach 100V peak and oscillate once every 12 seconds. The 12 seconds allows me to put units on the # in Yd# - in this simulation there are 12 "seconds" to a full rotation. The top transformer is a normal Yd5, and the load weakly references the secondary symmetrically about the 0V reference.
The top plot shows primary voltages A and B for the top transformer. Phase A's rising zero crossing is at 0 seconds and phase B follows it at 4 seconds.
The next plot shows secondary voltages a and b for the top transformer. Phase a crosses at 5 seconds and phase b follows it 4 seconds later. No surprises there, normal Yd5 behaviour.
The third plot shows the voltages at the primary terminals of the bottom transformer. In this case phases A and C have been swapped, while everything else remains the same. So phase A now crosses at 8 seconds and phase B crosses 4 seconds earlier since the phase rotation is backwards.
The final plot shows the secondary voltages of the bottom transformer. Phase a now crosses at 3 seconds, which is 7 seconds after phase A (or equivalently, 5 seconds before, but we'll stick to the positive convention for vector groups). Phase b crosses 4 seconds before phase a since the secondary reflects the phase rotation of the primary.
In summary, crossing A & C on the primary of a Yd5 will, provided the terminals marked A, B, C and a, b, c do not change, perform as if the transformer was a Yd7 and the phase rotation will be backwards. This makes sense once you study the voltage vectors across individual transformer windings, but I found it much more convincing in simulation.
RE: Vector Group
Yd9?
Diagram attached. Where did I stuff up?
RE: Vector Group
a-n lags A-n by 270 degrees
b-n lags B-n by 150 degrees
c-n lags C-n by 30 degrees
If a & c were also swapped at the secondary, the transformer would stay a Yd5, but the phase rotation would be c-b-a.
RE: Vector Group
RE: Vector Group
If you do the same thing - swapping the same two phases on the primary and secondary - on a Dy1 transformer you end up with the equivalent of a Dy11 connection, and vice versa.
RE: Vector Group
If you are not changing the internal connections, it's pretty straightforward if you just take the phasor diagram on the transformer nameplate and apply your actual system phase sequence to the appropriate transformer terminals.
RE: Vector Group
Same place I did before doing the simulation - you've double dipped on the swapping of the terminals. You've changed which phase is connected to which terminal, but then also changed which terminal you use as the reference. I don't think the result is wrong, it's just that by referencing to a different terminal the number comes out different. The overall effect is the same.
I actually like the convention suggested in the FAQ:
In our case, the Yd5 transformer is still a Yd5 transformer, but by changing the ordering of the phase connections the rotation is flipped and it behaves like a Yd7 (with flipped secondary rotation). If you go one step further, as sibeen did, and consider where the phases go, then it looks like Yd9! At the end of the day the behaviour is the same, it's just that the convention (and reference) has changed.
By the way, thanks for pointing out the FAQ dpc. It's a pity the referenced Basler document seems to have disappeared from the Internet.
RE: Vector Group
LiteYear, fair dinkum, nothing is ever lost on the internet :)
Especially when dumb mongrels like myself made sure we downloaded the document years ago.
See attached - about a 1.3 meg file.
RE: Vector Group
If you like the FAQ, don't forget to rate it; so far I'm only scoring a 6 out of 10. And if you have suggestions, there is a comment form.
RE: Vector Group
RE: Vector Group
Marmite:
"You would need to check the LV connections as well. If A&C are crossed on the secondary the same as they are on the primary then your transformer will act as a Yd7. If not then you are just changing the phase rotation."
LiteYear:
"crossing A & C on the primary of a Yd5 will, provided the terminals marked A, B, C and a, b, c do not change, perform as if the transformer was a Yd7 and the phase rotation will be backwards."
crossing A & C on the primary of a Yd5 and secondary do not change
Marmite=> transformer was a Yd5 and the phase rotation will be backwards
LiteYear=> transformer was a Yd7 and the phase rotation will be backwards
Please clarify my conclusion!
RE: Vector Group
RE: Vector Group
below my interpretation of your post for setting relay
Siemens Transformer Relay Parametrization (extract):
270 Rated Frequency 60 Hz
271 Phase Sequence L3 L2 L1
313 Starpoint of Side 1 is Earthed
314 Transf. Winding Connection Side 1 Y (Wye)
323 Starpoint of Side 2 is Isolated
324 Transf. Winding Connection Side 2 D (Delta)
325 Vector Group Numeral of Side 2 5
RE: Vector Group