Application Guide - NP900 Series
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A996A
Protection function is run in a completely digital environment with protection CPU
microprocessor which also processes the analog signals transferred to digital form.
Figure 3.2.1-21 Principle diagram of NP900 protection relay platform.
In following chapters are presented the common functionalities of protection functions. If in
some protection function is deviation of this basic structure the difference is described in
the corresponding chapter of the manual.
3.2.1.1
P
ICK
-
UP CHARACTERISTICS
Pick-up of the function is controlled by X
set
setting parameter, which defines the
maximum allowed measured magnitude in per unit, absolute or percentage value before
action from the function. The function constantly calculates the ratio in between of the
user set pick-up parameter and measured magnitude (Im). Reset ratio of 97 % is inbuilt in
the function and is always related to the
Xset
value. If function pick-up characteristics
vary from this described, it is defined in the function part of the manual.
