Siemens 7SR224 - Current Protection: High Impedance Restricted Earth Fault (64 H); Figure 3.5-1 Logic Diagram: High Impedance REF (64 H)

(1) Description of Operation 7SR224
Page 30 of 66 ©2009 Siemens Protection Devices Limited
3.5 CURRENT PROTECTION: HIGH IMPEDANCE RESTRICTED EARTH FAULT (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
4
is utilised for this purpose, SEF protection cannot be
used.
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:
Inhibit 64H A binary or virtual input.
64H
>
c
64H Current Setting
64H Delay
c
Inhibit 64H
64H Element
Enabled
Disabled
&
I
4
(I
G
)
Figure 3.5-1 Logic Diagram: High Impedance REF (64H)