DOC. MIE91093 Rev. 1.34
Page 114 of 145
1.15.3 The Restraint and the Differential current
We define IR as Restraint current and it is normally given as
the average between current I
1
and I
2
, where:
I
1
: transformer
primary
side pu current
I
2
: transformer
secondary
side pu current
Depending on the relay manufacturer, the Restraint current is
calculated as:
2
1
I
I
I
R
: this formula is used by Siemens relays
2
2
1
I
I
I
R
: this is the standard formula
3
2
1
I
I
I
R
: this is used by some of GE relays for three
windings transformer
2
1
I
I
I
R
: this is used on Ret316 relays
The differential current is defined as:
2
1
I
I
I
d