WYE-DELTA-WYE TX BLOWN HS FUSE PROTECTION
WYE-DELTA-WYE TX BLOWN HS FUSE PROTECTION
(OP)
Folks,
We typically protect a 3PH Delta-Wye power transformer from blown high side fuse operations with negative sequence overvoltage detection in the low side tiebreaker. In this case, a dropped phase on the high side of a Delta/Wye produces one phase at nominal and the other two at half nominal values. (I'm not even sure how this is shown in the vector math, but its a method we've employed according to a SEL application guide... I'd like to see the solution to this if anyone can explain!) Anyhow, how would this protection apply to a 115-2.4-12.5 kV Wye-Delta-Wye transformer? (the delta is tertiary) Would the same values result as in a Delta-Wye connection, or would it act like the primary with one phase at zero and the others at nominal....??? Thanks for the help!
We typically protect a 3PH Delta-Wye power transformer from blown high side fuse operations with negative sequence overvoltage detection in the low side tiebreaker. In this case, a dropped phase on the high side of a Delta/Wye produces one phase at nominal and the other two at half nominal values. (I'm not even sure how this is shown in the vector math, but its a method we've employed according to a SEL application guide... I'd like to see the solution to this if anyone can explain!) Anyhow, how would this protection apply to a 115-2.4-12.5 kV Wye-Delta-Wye transformer? (the delta is tertiary) Would the same values result as in a Delta-Wye connection, or would it act like the primary with one phase at zero and the others at nominal....??? Thanks for the help!






RE: WYE-DELTA-WYE TX BLOWN HS FUSE PROTECTION
If there is a fairly large motor running single phased on the system, it will try to replace the missing phase. In this case there will be a phase displacement. The voltages and phase displacements in a particular system will depend to a great extent on the size of the motor relative to the size of the system.
respectfully