Current Protection: High Impedance Restricted Ef (64H); Figure 3.5-1 Logic Diagram: High Impedance Ref (64H) - Siemens 7SR224 Technical Manual

7SR224 Argus Description of Operation
3.5

Current Protection: High Impedance Restricted EF (64H)

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. If I is utilised for this purpose, SEF protection cannot be used.
4
64H Current Setting sets the pick-up current level. An output is given after elapse of the 64H 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:
A binary or virtual input.
Inhibit 64H

Figure 3.5-1 Logic Diagram: High Impedance REF (64H)

©2010 Siemens Protection Devices Limited Chapter 1 Page 29 of 70