Protections
52
Part No. 057-129 DSE871x mono remote display ISSUE 2.1 21/09/2010 ADM
6.8 SHORT CIRCUIT AND EARTH FAULT SHUTDOWN / ELECTRICAL TRIP ALARM
When the module is suitably connected using the ‘Earth Fault CT’. The module measures Earth Fault and can
optionally be configured to generate an alarm condition (shutdown or electrical trip) when a specified level is
surpassed.
Short Circuit alarm operates in the same way as the Earth Fault, using the same curve formula, but typically uses a
lower value for K (time multiplier) to give a faster acting trip.
If the Alarm is enabled, the DSE8710 Series controller begins following the IDMT ‘curve’. If the current surpasses
the Trip for an excess of time, the Alarm triggers (Shutdown or Electric trip as selected in Action).
The higher the fault, the faster the trip. The speed of the trip is dependent upon the fixed formula:
T = K x 0.14 / ( ( I / I
s
)
0.02
-1 )
Where:
T is the tripping time in seconds (accurate to +/- 5% or +/- 50ms (whichever is the greater)
K is the time multiplier setting
I is the actual earth current measured
Is is the trip setting value
The settings shown in the example above are a screen capture of the DSE factory settings, taken from the DSE
Configuration Suite software.
I
S
(Trip setting
value)
K (time multiplier setting)
K (time multiplier setting)
I
S
(Trip setting
value)
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