FUNCTION CHARACTERISTICS
46
NA30 - Manual - 04 - 2022
Example 2
The residual CT primary current I
Enp
must be set as: I
Enp
= 100 A
• Relay residual nominal voltage U
En
The residual nominal voltage U
En
may be estimated by means of the following general formula (ef-
fective for insulated neutral or impedance-ground connected grids):
If open delta VT with primary nominal voltage balances to the grid voltage divided by √3, the follow-
ing streamlined calculus may be used:
U
En
= 3 · VT open delta secondary nominal voltage [V] for insulated or impedance-ground neutral
grids.
Example A1
The relay residual nominal voltage U
En
must be estimated by means of the following general for-
mula:
U
En
= √3 · U
ng
/K
VT
= √3 · 6900 / (√3 · 100) = 69 V
Example A2
The relay residual nominal voltage U
En
must be indifferently estimated by means of the following
general formula:
U
En
= √3 · U
ng
/K
VT
= √3 · 6000 / (√3 · 60) = 100 V
or by means the following streamlined formula:
U
En
= 3 · U
ns
= 3 · 100 / 3 = 100 V
The U
np
setting must be adjusted to: U
np
= U
ng
= 6.9 kV
• Measurement reading mode
Measures may be displayed according the following operating modes:
- With RELATIVE setting all measures are related to the nominal value,
- With PRIMARY setting all measures are related to the primary value.
Es2-IEn.ai
3x
K
CT
= 100A / 5A
52
I
En
= 5 A
NA30
VT ratio K
VT
Grid nominal voltage U
ng
where the VTs [V] x √3 are connected
U
En
=
Es1-UEn.ai
K
VT
=
/
/
V
V
10000
3
100 3
3
= 100 ·
3
= 100 ·
/
/
V
V
10000
3
100 3
Grid nominal voltage U
ng
= 6.9 kV
VT ratio: K
VT
=
Insulated or impedance-ground neutral
/
U
ng
= 6.9 kV
U
En
52
NA30
Es2-UEn.ai
K
VT
=
/ V
V
6000
3
100 / 3
3
= 60 ·
Insulated or impedance-ground neutral
U
np
= 6 kV
U
En
52
NA30
3
= 60 ·
/
/
V
V
6000
3
100 3
Grid nominal voltage U
ng
= 6 kV
VT ratio: K
VT
=
/
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