Application Guide - NP900 Series
340 (504
)
A996A
For HV side:
HV
I0d
_
Bias
_
AVG
=
�
( IL1
������⃗
HV
+ IL2
������⃗
HV
+ IL3
������⃗
HV
) + I0
���⃗
HVMEAS
�
2
HV
I0d
_
Bias
_
MAX
= max
�
( IL1
������⃗
HV
+ IL2
������⃗
HV
+ IL3
������⃗
HV
�
, I0
���⃗
HVMEAS
)
HV
I0d>
_
diff
_
add
=
�
( IL1
������⃗
HV
+ IL2
������⃗
HV
+ IL3
������⃗
HV
) + I0
���⃗
HVMEAS
�
HV
I0d>
_
diff
_
substract
=
�
( IL1
������⃗
HV
+ IL2
������⃗
HV
+ IL3
������⃗
HV
)-I0
���⃗
HVMEAS
�
For LV side:
LV
I0d
_
Bias
_
AVG
=
�
( IL1
������⃗
LV
+ IL2
������⃗
LV
+ IL3
������⃗
LV
) + I0
���⃗
LVMEAS
�
2
LV
I0d
_
Bias
_
MAX
= max
�
( IL1
������⃗
LV
+ IL2
������⃗
LV
+ IL3
������⃗
LV
�
, I0
���⃗
LVMEAS
)
LV
I0d>
_
diff
_
add
=
�
( IL1
������⃗
LV
+ IL2
������⃗
LV
+ IL3
������⃗
LV
) + I0
���⃗
LVMEAS
�
LV
I0d>
_
diff
_
subtract
=
�
( IL1
������⃗
LV
+ IL2
������⃗
LV
+ IL3
������⃗
LV
)-I0
���⃗
LVMEAS
�
For both sides REF stages have average and maximum bias current calculation setting
option as well as the add or subtract differential current calculation options similarly to the
phase differential stages (depend of the installation directions of the CTs and desired
sensitivity for bias calculation).
In NP900 differential stage the reference current for the REF protection for transformers is
always the protected side nominal current (HV, LV), which is calculated in the relay TRF
module.
For transformer application the setting of the REF stage, whether it is located in the HV or
LV side may be set a lot more sensitive than phase differential. Basically the setting
sensitivity should be defined by the fact if there is expected CT saturation or not
(Transformer maximum single phase output compared to neutral point CT ratings). The
tripping characteristics may be set differently in case if the network is directly grounded or
through impedance and the fault current may be expected to saturate CTs in the external
fault also.
For this reason there are three sections in the REF function characteristics also, non-
biased, slightly biased and heavily biased. For high impedance or close to neutral winding
fault the first non biased section should consider the possible measurement errors of the
Содержание NP900 Series
Страница 1: ......
Страница 49: ...Application Guide NP900 Series 49 504 A996A Figure 3 2 1 3 25 Definite time operating characteristics...
Страница 50: ...Application Guide NP900 Series 50 504 A996A Figure 3 2 1 3 26 IEC predefined characteristics NI VI LTI and EI...
Страница 52: ...Application Guide NP900 Series 52 504 A996A Figure 3 2 1 3 28 IEEE predefined characteristics EI MI and VI...
Страница 243: ...Application Guide NP900 Series 243 504 A996A Figure 3 3 2 1 122 NPS biased thermal trip curves with kNPS values 7 and 10...
Страница 491: ...Application Guide NP900 Series 491 504 A996A 3 7 5 6 SETTING EXAMPLE...
Страница 504: ...Application Guide NP900 Series 504 504 A996A A996A...