Operation Principle - ABB 615 series Technical Manual

1MAC059074-MB A
4.2.1.4
615 series ANSI
Technical Manual
The function picks up and trips when the residual current exceeds the set limit. The trip
time characteristic for low stage 51N, 51G and high stage 50N, 50G can be selected to be
either definite time (DT) or inverse definite minimum time (IDMT). The instantaneous
stage 50N-3, 50G-3 always trips with the DT characteristic.
In the DT mode, the function trips after a predefined trip time and resets when the fault
current disappears. The IDMT mode provides current-dependent timer characteristics.
The function contains a blocking functionality. It is possible to block function outputs,
timers or the function itself, if desired.

Operation principle

The function can be enabled and disabled with the Operation setting. The corresponding
parameter values are "Enable" and "Disable".
A070437-ANSI V1 EN
Figure 149: Functional module diagram
Level detector
The operating quantity can be selected with the setting IG/I0 signal Sel. The selectable
options are "Measured IG" and "Calculated I0". The operating quantity is compared to the
set Pickup value. If the measured value exceeds the set Pickup value, the level detector
sends an enable-signal to the timer module. If the ENA_MULT input is active, the Pickup
value setting is multiplied by the Pickup value Mult setting.
The protection relay does not accept the Pickup value or Pickup value
Mult setting if the product of these settings exceeds the Pickup value
setting range.
The pickup value multiplication is normally done when the inrush detection function
(INR) is connected to the ENA_MULT input.
Section 4
Protection functions
315