Delta start transformers orientation
Delta start transformers orientation
(OP)
I think I have read it somewhere that delta usually faces the power flow direction, I wonder why it is like that?
If the start faces the power flow direction, we may get a float voltages on the secondary (delta), however, if the transformer is not earthed (star), this may lead to similar problem.
If we have a static converter, would it make a difference to face the power flow with a star instead of delta? i.e. delta will be connected to bridge rectifier.
If the start faces the power flow direction, we may get a float voltages on the secondary (delta), however, if the transformer is not earthed (star), this may lead to similar problem.
If we have a static converter, would it make a difference to face the power flow with a star instead of delta? i.e. delta will be connected to bridge rectifier.






RE: Delta start transformers orientation
Any voltage unbalance or phase angle errors will result in circulating currents in the delta limited by the transformer impedance and the source impedance.
Issues:
1> In the event of a ground fault on one primary phase the other two phases will back feed into the fault and the fault current may be higher than expected.
2> In the event of a ground fault on one primary phase the wye/delta bank may blow a primary fuse.
3> In the event that one primary phase is lost, the wye/delta bank will back feed the missing phase. As a result, the wye/delta bank often blows a primary fuse due to overloading.
4> Repair crews have a tendancy to increase the size of primary fuses at banks experiencing frequent fuse blowing. Burned out transformers due to a combination of a loss of one primary phase and over sized fuses are another issue.
5> Distribution transformers are designed for low impedance and are as a result a small voltage or phase angle error will cause quite high circulating currents.
6> Long distribution lines with unbalanced single phase loading are apt to have voltage balance issues.
7> When long distribution lines with unbalanced single phase loading have voltage balance issues, the issues are often addressed by the installation of a bank of single phase voltage regulators. Unfortunately, when unequal line to neutral voltages are corrected by three single phase voltage regulators, line to line voltage unbalances are introduced and phase angle errors are introduced. The voltage and phase angle issues cause heavy circulating currents in a wye/delta bank.
8> When a distribution circuit with a wye/delta bank installed somewhere is energized phase by phase, Refrigerators and freezers on single phase transformers throughout the circuit are severely stressed and may fail.
9> It is well to use caution when considering a delta/wye bank in a co-generation application or any circuit where the power flow may reverse. Should the power flow through a delta wye transformer reverse for any reason the transformer is now a wye/delta transformer and may experience issues.
Other than that and a few things I may have forgotten, a wye/delta bank works great.
Bill
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"Why not the best?"
Jimmy Carter