If ENA
U
MULT isTRUE
Effective start value
Start value low
_
_
:
=
(Equation 29)
If ENA
U
MULT is FALSE
Effective start value
Start value
_
_
:
=
(Equation 30)
Voltage and input control mode
If
Control mode is set to "Voltage and input Ctrl", both the "Voltage control"
and "Input control" modes are used. However, the “Input control” functionality is
dominant over the “Voltage control” mode when
ENA_LOW_LIM
is active.
No voltage dependency mode
When
Control mode is set to "No Volt dependency", the effective start value has no
voltage dependency and the function acts as a normal time overcurrent function
with effective start value being equal to the
Start value setting.
Level detector
The measured phase currents are compared phasewise to the calculated effective
start value. If the measured value exceeds the calculated effective start value, the
Level detector reports the exceeding value to the phase selection logic. If the
ENA_MULT
input is active, the effective start value is multiplied by the
Start value
Mult setting.
Do not set the multiplier
Start value Mult setting higher than necessary. If
the value is too high, the function may not operate at all during an inrush
followed by a fault, no matter how severe the fault is.
The start value multiplication is normally done when the inrush detection function
INRPHAR is connected to the
ENA_MULT
input.
Phase selection logic
If the fault criteria are fulfilled in the level detector, the phase selection logic detects
the phase or phases in which the measured current exceeds the setting. If the phase
information matches the
Num of start phases setting, the phase selection logic
activates the Timer module.
Timer
Once activated, the Timer module 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 settings
Curve parameter A, Curve parameter B,
Curve parameter C, Curve parameter D and Curve parameter E.
1MRS759142 F
Protection functions
REX640
Technical Manual
373