Operation logic
67YN supports three operation modes selected with setting Operation mode: “General
EF”, “Alarming EF” and “Intermittent EF”.
Operation mode “General EF” is applicable in all kinds of ground faults in ungrounded
and compensated networks. It is intended to detect all kinds of ground faults regardless of
their type (transient, intermittent or restriking, permanent, high or low ohmic). The setting
Voltage pickup value
defines the basic sensitivity of the 67YN function.
In “General EF” mode, the operate timer is started in the following conditions.
•
Ground fault is detected by the General Fault Criterion (GFC)
•
Fault direction equals
Directional mode
setting
•
Estimated stabilized fundamental frequency residual current exceeds the set
Min trip
current
level
The
PICKUP
output is activated once
Pickup delay time
has elapsed.
TRIP
output is
activated once
Trip delay time
has elapsed and the above three conditions are valid. Reset
timer is started if any of the above three conditions is not valid. In case fault is transient and
self-extinguishes,
PICKUP
output stays activated until the elapse of reset timer (setting
Reset delay time). After
TRIP
output activation,
PICKUP
and
TRIP
outputs are reset
immediately, if any of the above three conditions is not valid. The pickup duration value
PICKUP_DUR, available in the Monitored data view, indicates the percentage ratio of the
pickup situation and the set operating time.
In case detection of temporary ground faults is not desired, the activation
of
PICKUP
output can be delayed with setting
Pickup delay time
. The
same setting can be also used to avoid restarting of the function during
long lasting post-fault oscillations, if time constant of post-fault
oscillations is very long (network losses and damping is low).
To keep the operate timer activated between current spikes during
intermittent or restriking ground fault, the
Reset delay time
should be set
to a value exceeding the maximum expected time interval between fault
spikes (obtained at full resonance condition). Recommended value is at
least 300 ms.
Section 4
1MAC059074-MB A
Protection functions
450
615 series ANSI
Technical Manual
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