4.2.1.4 Operation principle
The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of non-directional earth-fault protection can be described by using a
module diagram. All the modules in the diagram are explained in the next sections.
A070437 V3 EN
Figure 132: Functional module diagram. Io represents the residual current.
Level detector
The operating quantity can be selected with the setting Io signal Sel. The selectable
options are "Measured Io" and "Calculated Io". The operating quantity is compared
to the set Start value. If the measured value exceeds the set Start value, the level
detector sends an enable-signal to the timer module. If the ENA_MULT input is
active, the Start value setting is multiplied by the Start value Mult setting.
The IED does not accept the Start value or Start value Mult setting
if the product of these settings exceeds the Start value setting range.
The start value multiplication is normally done when the inrush detection function
(INRPHAR) is connected to the ENA_MULT input.
Timer
Once activated, the 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
Section 4 1YHT530004D05 D
Protection functions
264 615 series
Technical Manual
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