Current Protection: High Impedance Restricted Earth Fault (87Ref); Figure 3-19 Logic Diagram: High Impedance Ref (87Ref) - Siemens 7SR17 Rho Manual

Chapter 1) 7SR17 Rho Description Of Operation
3.6 C P
URRENT
One high impedance Restricted Earth Fault (REF) element is provided.
The relay utilises fundamental current measurement values for this function.
The single phase current input is derived from the residual output of line/neutral CTs connected in parallel. An
external stabilising resistor must be connected in series with this input to ensure that this element provides a high
impedance path.
87REF Current Setting sets the pick-up current level. An output is given after elapse of the 87REF Delay setting.
External components – a series stabilising resistor and a non-linear resistor – are used with this function. See
'Applications Guide' for advice in specifying suitable component values.
Operation of the high impedance element can be inhibited from:
Inhibit 87REF
Page 48 of 78
: H I
ROTECTION IGH MPEDANCE
A binary or virtual input

Figure 3-19 Logic Diagram: High Impedance REF (87REF)

R E
ESTRICTED ARTH
©2014 Siemens Protection Devices Limited
F (87REF)
AULT