Application Guide - NP900 Series
318 (504
)
A996A
Primary side per unit factor and current calculation
In
HV
=
Sn
√
3 × U
HV
=
2000000VA
√
3 × 10000V
= 115.47 A
IpuPRI
HV
=
In
HV
CTpri
HV
=
115.47A
150 A = 0.77
IpuSEC
HV
= IpuPRI
HV
× CTsec
HV
= 0.77 × 5A = 3.85 A
Secondary side per unit factor and current calculation
In
LV
=
Sn
√
3 × U
LV
=
2000000VA
√
3 × 1000V
= 1154.7 A
IpuPRI
LV
=
In
LV
CTpri
LV
=
1154.7A
1200 A = 0.96
IpuSEC
LV
= IpuPRI
LV
× CTsec
LV
= 0.96 × 5A = 4.81 A
So now what this means is that if the transformer outputs power of 2 MVA through it the
HV side CT secondary current will be 3.85A and LV side CT secondary current will be
4.81A. Differential function uses these values for per unitizing the measured currents so
that in this case the HV side measurement will show 1.0 xIn and LV side measurement
will show 1.0 xIn as well even the measured currents are different. This is called amplitude
matching of HV and LV sides. In NP900 differential relay this is done automatically by
setting the transformer nominal values and CT ratings so these calculations are not
needed to be applied by used. This is just for informational purpose that where these
values come from.
Содержание NP900 Series
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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...