Three-Phase Transformer Loses One Phase

You have what is termed a single phase condition. Are you speaking of a primary phase loss or a secondary phase loss. Wye or delta?

I would like to know if it is primary phase loss..

lets use any of conditions to for the purpose of explanation. i just want to know the effect when any phase of the the primary is lost.

the output will have little bit of low currents & voltages. & the input phases get imbalanced. the two phases will get more than calculated currents to give a desired output power.

If the transformer is in a balanced 3-phase system and the common point of the coils connected to the system neutral via a Petersen coil the increasing voltage drop on the Petersen will trigger the protection.

Thanks Wareagle for the link. It's a very rich stuff!

If your system is delta-delta connected and you lose a leg, your available power will be 67% of normal.

Let me explain the situation with the following diagrams with a Dyn1 transformer of 11KV/380V. The three coils of the transformer are shown in Black, Red and Green color for explanation. All angles shown here are with respect to the V_BC as reference.

With Healthy condition:

HT voltages are:

V_BC = 11000 < 0

V_CA = 11000 <120

V_AB = 11000 <-120

LT Neutral to Line voltages are:

V_na = 220 < 60

V_nb = 220 < 180

V_nc = 220 <-60

LT Line to Line voltages are:

V_bc = 380 < -30

V_ca = 380 < 90

V_ab = 380 <-150

With Phase A lost condition:

Full V_BC voltage is applied in Red coil and same voltage is also applied in coils Black and Green in series. The voltage V_BC/2 is applied across each of the coils Black and Green. The voltages applied in each of the coils are:

V_BC = 11000 < 0

V_CA = 5500 <-180

V_AB = 5500 <-180

LT Neutral to Line voltages are:

V_na = 110 < 0

V_nb = 220 < -180

V_nc = 110 < 0

LT Line to Line voltages are:

V_bc = 330 < 0

V_ca = 0 < 0

V_ab = 330 <-180

Note: This analysis is done completely on my knowledge in 3 phase electrical system and I appreciate any comments on it.

-MS

Dear Mr. Samad,

Could you please describe about the phase shift due to winding configurations (vector group). Is the phase angle difference is between HV side phase to phase and LV side phase to phase? (or) is it between HV side Phase to Phase and LV side Phase to neutral for a transformer with a vector group of Dyn1. Also what would be the phase angle difference between LV side Phase to Phase and Phase to Neutral?

If it has been correctly designed, installed and commissioned then the protective equipment associated with it will operate as necessary, thereby disconnecting it.

<...GHANA...>

The country of installation is irrelevant to this discussion, it isn't obvious or necessary that this is a person's name, and if this is an acronym then please update GHANA - Definition by AcronymFinder accordingly.