Recorded Values Of The Latest Eight Faults; Inverse Time Operation; Stage Specific Inverse Delay; Operation Modes - Allen-Bradley Rockwell Automation 857 User Manual

Inverse Time Operation

Recorded Values of the Latest Eight Faults

Detailed information is available on the eight latest faults: Time
stamp, fault type, fault value, load current before the fault and
elapsed delay.
Table 3.48 – Recorded Values of the Arc Protection Stages Arcl>, Arcl
Arcl > (50 ARC / 50N ARC)
02
Parameter Value
yyyy-mm-dd
hh:mm:ss.ms
Type
Flt
Load
EDly
The inverse time operation – i.e. inverse delay minimum time
(IDMT) type of operation – is available for several protection
functions. The common principle, formulae and graphic
representations of the available inverse delay types are described in
this chapter.
Inverse delay means that the operation time depends on the measured
real time process values during a fault. For example with an
overcurrent stage using inverse delay a bigger a fault current gives
faster operation. The alternative to inverse delay is definite delay.
With definite delay a preset time is used and the operation time does
not depend on the size of a fault.

Stage Specific Inverse Delay

Some protection functions have their own specific type of inverse
delay. Details of these dedicated inverse delays are described with
the appropriate protection function.

Operation Modes

There are three operation modes to use the inverse time
characteristics:
Standard delays
Using standard delay characteristics by selecting a curve family
(IEC, IEEE, IEEE2, RI) and a delay type (Normal inverse, Very
inverse etc).
Standard delay formulae with free parameters
Selecting a curve family (IEC, IEEE, IEEE2) and defining one's
own parameters for the selected delay formula. This mode is
activated by setting delay type to 'Parameters', and then editing
the delay function parameters A ... E. (See "Free Parameter
Settings using IEC, IEEE and IEEE2 Equations").
Protection Functions
Unit Description
Time stamp of the recording, date
Time stamp, time of day
pu Fault type value. Only for ArcI> stage.
pu Fault value
pu Pre fault current. Only for ArcI> stage.
% Elapsed time of the operating time setting.
100% = trip
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A,
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857-UM001A-EN-P – July 2009