The Restraint And The Differential Current - ISA T1000 PLUS User Manual

DOC. MIE91093

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
 I : transformer primary side pu current
1
 I : transformer secondary side pu current
2
Depending on the relay manufacturer, the Restraint current is
calculated as:
 

I I I
R 1 2

I I

1 2

I
R
2

I I

1 2

I
R
3
windings transformer
 

I I I
R 1
The differential current is defined as:
Rev. 1.34
: this formula is used by Siemens relays
: this is the standard formula
: this is used by some of GE relays for three
: this is used on Ret316 relays
2
and I , where:
1 2
Page 114 of 145
 
I I I
d 1 2