Table 451: Values of the Enable reference use setting
Enable reference use
Functionality
Standalone
In the standalone mode, depending on the value
of the
Operating curve type
setting, the time char-
acteristics are according to DT or IDMT. When the
operation timer has reached the value of the
Oper-
ate delay time
setting in the DT mode or the value
defined by the inverse time curve, the
OPERATE
output is activated.
Reference use
Communication
valid
When using the horizontal communication, the
function is forced to use the DT characteristics.
When the operation timer has reached the value of
the
Minimum operate time
setting and simultane-
ously the enabling signal from the Current compari-
son module is active, the
OPERATE
signal is activa-
ted.
Communication
invalid
Function operates as in the standalone mode.
The
Enable reference use setting forces the function to use the DT
characteristics where the operating time is set with the
Minimum
operate time setting.
If the communication for some reason fails, the function switches to use the
Operation curve type setting, and if DT is selected, Operate delay time is used. If the
IDMT curve is selected, the time characteristics are according to the selected curve
and the
Minimum operate time setting is used for restricting too fast an operation
time.
In case of a communication failure, the start duration may change substantially
depending on the user settings.
When the programmable IDMT curve is selected, the operation time characteristics
are defined with the
Curve parameter A, Curve parameter B, Curve parameter C,
Curve parameter D and Curve parameter E parameters.
If a drop-off situation happens, that is, a fault suddenly disappears before the
operation delay is exceeded, the Timer reset state is activated. The functionality
of 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 value of the
Reset delay time setting 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.
If the drop-off situation continues, the reset timer is reset and the
START
output is
deactivated.
The "Inverse reset" selection is only supported with ANSI or the
programmable types of the IDMT operating curves. If another operating
curve type is selected, an immediate reset occurs during the drop-off
situation.
The setting
Time multiplier is used for scaling the IDMT operation and reset times.
1MRS757644 H
Protection functions
620 series
Technical Manual
463
