Operation Principle - ABB RELION Series Technical Manual

Section 4
Protection functions
4.3.1.4
396
The function is based on the measurement of the negative sequence current. In a fault
situation, the function starts when the negative sequence current exceeds the set limit.
The operate time characteristics can be selected to be either definite time (DT) or
inverse definite minimum time (IDMT). In the DT mode, the function operates after
a predefined operate 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 "On" and "Off".
The operation of NSPTOC can be described using a module diagram. All the modules
in the diagram are explained in the next sections.
A070660 V1 EN
Figure 206: 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, the 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, 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.
1MRS758755 A
REC615 and RER615
Technical Manual