Specifications

7SR242 Duobias Description Of Operation
3.1.3 87HS
W2W1
II 
2
II
W2W1

Figure 3-3 Differential Highset Characteristic
Figure 3.1-3 illustrates the differential highset characteristic. Within the relay the fundamental frequency RMS line
currents are modified by the ICT Multiplier and ICT Connection settings (see 3.1.1) before being applied to the
differential highset elements. The differential highset elements calculate the operate current for each phase from
the vector sum of winding 1 and winding 2 currents i.e. I
OPERATE
= I
W1
+ I
W2
.
87HS Setting defines the differential current required to operate the element. The output of 87HS Delay can be
mapped to relay outputs.
Operation of the highset differential elements can be inhibited from:
Inhibit 87HS A binary or virtual input.
87HS Inrush Action: Inhibit Operation of the inrush current detector
87HS Overfluxing Action: Inhibit Operation of the overfluxing detector
©2010 Siemens Protection Devices Limited Chapter 1 Page 23 of 52