Transformer Curve Shift
Transformer Curve Shift
(OP)
IEEE 242 requires 15% margin between the main secondary curve characteristics and the primary fuse. I have seen several expressions in different books.
For example some books just consider .58% curve shift to the left for transformer damage curve and do not consider L-L faults. Like (SKM software and related literature)
Some books require the transformer damage curve to be shifted .15 to the right.
In the first case the closest point of secondary breaker to the primary fuse is the corner of STPU.
Now, I understand that fuse needs to protect the transformer in low current faults that’s why the curve is shifted to the left.
But shifting the transformer curve to the right by .15 percent has already covered by shifting it to the left!
Is this seem right?
For example some books just consider .58% curve shift to the left for transformer damage curve and do not consider L-L faults. Like (SKM software and related literature)
Some books require the transformer damage curve to be shifted .15 to the right.
In the first case the closest point of secondary breaker to the primary fuse is the corner of STPU.
Now, I understand that fuse needs to protect the transformer in low current faults that’s why the curve is shifted to the left.
But shifting the transformer curve to the right by .15 percent has already covered by shifting it to the left!
Is this seem right?






RE: Transformer Curve Shift
The 58% shift you are referring to is for check for transformer through-fault protection by the primary protection for a line-to-ground fault on the secondary side.
These are two different issues.
RE: Transformer Curve Shift
RE: Transformer Curve Shift
RE: Transformer Curve Shift
RE: Transformer Curve Shift
Regards,
RE: Transformer Curve Shift
Keep in mind the transformer damage curve only applies to through-faults, where the fault is external to the transformer on the secondary side. If the fault is inside the transformer, the damage curve is not relevant, since the transformer is already damaged.
RE: Transformer Curve Shift
RE: Transformer Curve Shift
RE: Transformer Curve Shift
I was aware f the 58% curve shift to the left to consider L-G fault. My question was relating 16%-17% curve shift to the right I didn’t know the purpose behind this.
Here dpc, and others suggest that that is required margin (current) , between the secondary protection device and primary protection device. I accepted it; however the curve shift was confusing, because 17% shift would not make that much of a difference in coordination to pick a bigger size fuse and therefore create more margin, so I just ignored the concept of curve shift and stick to the necessary 17% margin between primary and secondary protective curves