Ice NP900 Series, Инструкция по применению

Страница: 123 / 504

Application Guide - NP900 Series 123 (504
)
A996A
User settable variables are binary signals from the system. Blocking signal needs to reach
the IED minimum of 5 ms before the set operating delay has passed for blocking to be
active in time.
In following figures are presented typical applications for this function.
Figure 3.2.10.3-61 Cable end differential with natural unbalance in the phase current
measurement.
When calculating the residual current from phase currents the natural unbalance may be
in total around 10% and still the used CT:s are in the promised 5P class (probably most
common CT accuracy class). When the current natural unbalance is compensated in this
same situation the differential settings may be set more sensitive and the natural
unbalance does not affect into the calculation.
Figure 3.2.10.3-62 Cable end differential when fault happens.
0.00
1.00
2.00
0 1 2 3 4 5 6 7
I D
if
f
I Bias
Differential characteristics
Characteristics
DIFF
0.00
1.00
2.00
0 1 2 3 4 5 6 7
I D
if
f
I Bias
Differential characteristics
Characteristics
DIFF