Current Protection: High Impedance Restricted Earth Fault - (64H); Current Protection: Cold Load (51C); Figure 3-16 Logic Diagram: High Impedance Ref (64H) - Siemens 7SR10 Argus Series Manual

3.4.4

Current Protection: High Impedance Restricted Earth Fault - (64H)

One high impedance Restricted Earth Fault (REF) element is provided 64H.
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.
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
64 H Element
Enabled
Disabled
Inhibit 64H
IL
3.4.5

Current Protection: Cold Load (51c)

The setting of each shaped overcurrent element (51-n) can be inhibited and alternative 'cold load' settings (51c-n)
can be applied for a period following circuit switch in.
The Cold Load settings are applied after the circuit breaker has been open for longer than the Pick-Up Time
setting.
Following circuit breaker closure the 'cold load' overcurrent settings will revert to those defined in the Phase
Overcurrent menu (51-n) after either elapse of the Drop-Off Time setting or when the measured current falls
below the Reduced Current Level setting for a time in excess of Reduced Current Time setting.
During cold load settings conditions any directional settings applied in the Phase Overcurrent menu are still
applicable.
A CB 'Don't Believe It' (DBI) alarm condition, see Section 4.3, is not acted on, causing the element to remain
operating in accordance with the relevant 51-n settings. Where the Reduced Current setting is set to OFF
reversion to 51-n settings will only occur at the end of the Drop-Off Time. If any element is picked up on expiry of
Drop-Off Time the relay will issue a trip (and lockout if a recloser is present).
If the circuit breaker is re-opened before expiry of the Drop-Off Time the drop-off timer is held but not reset.
Resetting the timer for each trip could result in damaging levels of current flowing for a prolonged period during a
rapid sequence of trips/closes.
Cold load trips use the same binary output(s) as the associated 51-n element.
Operation of the cold load element can be inhibited from:
Inhibit Cold Load
©2018 Siemens Protection Devices Limited
A binary or virtual input.
64 H Current Setting
&
c
>
(I or I )
4 g SEF

Figure 3-16 Logic Diagram: High Impedance REF (64H)

A binary or virtual input.
7SR10 Description of Operation
64 H Delay
c
Chapter 1 Page 40 of 77
General Pickup
64H