Application Guide - NP900 Series
329 (504
)
A996A
Next is calculated the currents flowing in this situation at HV and LV sides, when the
loading of the transformer is e.g. 1.5 times its rated power.
For LV side currents will be
I
LV
=
�
I
NLV
× 1.5
�
CT
LVPRI
CT
LVSEC
�
�
CT
LVSEC
× IpuPRI
LV
=
�
1154.7A × 1.5
�
1200A
5A
�
�
5A × 0.96
= 1.5xIn
And for HV side currents will be
I
HV
=
�
�
I
NLV
× 1.5
TR
CORR
�
�
CT
HVPRI
CT
HVSEC
�
�
CT
HVSEC
× IpuPRI
HV
=
�
�
1154.7A × 1.5
8.75
�
�
150A
5A
�
�
5A × 0.77
= 1.7xIn
By calculating this way these currents now present the worst possible case caused by tap
changer effect into the differential relay measured currents.
Now there is two possible ways to use biasing calculation and in practice one way to
calculate differential current (even there are add and subtract modes, the effect will be the
same since the differential current shall basically always be calculated as:
�
I
HV
-I
LV
�
, thus
giving the absolute difference in measured currents, add and subtract just compensate
differently connected CTs when the starpoint is either towards to transformer or away from
it)
When more sensitive settings are wanted “Average” mode is selected
LxBIAS
AVG
=
|ILx
HV
| + |ILx
LV
|
2
If more stabile settings are wanted “Maximum” mode is selected:
LxBIAS
MAX
= max (|ILx
HV
|, |ILx
LV
|)
With “Average” mode selected the slope is calculated as follows:
Slope 1 =
Idiff TP2
LxBIAS
AVG
×
100%
=
|I
LV
-I
HV
|
�
I
LV
+ I
HV
2
�
×
100%
=
1.5-1.7
�
1.5 + 1.7
2
�
×
100%
= 12.
5%
With “Maximum” mode selected the slope is calculated as follows:
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...