The operation of NSPTOC can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
OPERATE
START
t
Timer
t
Level
detector
I3P
BLOCK
ENA_MULT
I
2
Blocking
logic
Figure 466: Functional module diagram
Level detector
The measured negative-sequence current is compared to the set
Start value
. If
the measured value exceeds the set
Start value
, Level detector activates the Timer
module. If the ENA_MULT input is active, the set
Start value
is multiplied by the set
Start value Mult
.
The protection relay does not accept the
Start value
or
Start value Mult
setting if the product of the settings exceeds the
Start value
setting
range.
Timer
Once activated, Timer activates the START output. Depending on the value of the
Operating curve type
setting, the time characteristics are according to DT or IDMT.
When the operation timer has reached the value of Operate delay time in the DT
mode or the maximum value defined by the inverse time curve, the OPERATE output
is activated.
When the user-programmable IDMT curve is selected, the operation time
characteristics are defined by the parameters
Curve parameter A
,
Curve parameter
B
,
Curve parameter C
,
Curve parameter D
and
Curve parameter E
.
If a drop-off situation happens, that is, a fault suddenly disappears before the
operate delay is exceeded, the timer reset state is activated. The functionality of
the timer in the reset state depends on the combination of the
Operating curve
type
,
Type of reset curve
and
Reset delay time
settings. When the DT characteristic
is selected, the reset timer runs until the set
Reset delay time
value is exceeded.
When the IDMT curves are selected, the
Type of reset curve
setting can be set to
"Immediate", "Def time reset" or "Inverse reset". The reset curve type "Immediate"
causes an immediate reset. With the reset curve type "Def time reset", the reset
time depends on the
Reset delay time
setting. With the reset curve type "Inverse
reset", the reset time depends on the current during the drop-off situation. The
START output is deactivated when the reset timer has elapsed.
If a drop-off situation happens, that is, a fault suddenly disappears before the
operate delay is exceeded, the timer reset state is activated. The functionality of
the timer in the reset state depends on the combination of the
Operating curve
type
,
Type of reset curve
and
Reset delay time
settings. When the DT characteristic
1MRS759142 F
Protection functions
REX640
Technical Manual
821
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