FUNCTION CHARACTERISTICS
77
Example 2
The relay rated voltage U
n
may be defined as: U
n
= U
ng
/K
VT
= 6000 / 60 = 100 V
or with the formula: U
n
= √3 · U
ns
= √3 ·100 / √3 = 100 V
For the U
R
= 400 V versions, the relay rated voltage must be set to the grid nominal voltage (direct
measure of the line voltage without VTs).
Example 3
The rated voltage U
n
must be set as: U
n
= U
ng
= 400 V
• Relay residual rated voltage U
En
Three instances are expected:
A) residual voltage acquired with open delta VT.
B) residual voltage measure by means VT connected from star-point and earth.
C) residual voltage measure by vector calculus.
Case A
The residual nominal voltage U
En
may be estimated by means of the following general formula
(effective 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 fol-
lowing 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 general formula:
U
En
= √3 · U
ng
/K
VT
= √3 · 6900 / (√3 · 100) = 69 V
Example A2
Es2-Un.ai
K
VT
=
/
/
V
V
6000
3
100 3
= 60
/
/
V
V
6000
3
100 3
= 60
Grid rated voltage U
ng
= 6 kV
VTs ratio K
VT
= U
ng
/U
ns
=
U
ng
= 6 kV
U
n
52
XMR-x
Es3-Un.ai
U
ng
= 400 V
U
n
= 400 V
52
XMR-x
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 rated voltage U
ng
= 6.9 kV
VT ratio: K
VT
=
Insulated or impedance-ground neutral
/
U
ng
= 6.9 kV
U
En
52
XMR-x
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
3
= 60 ·
/
/
V
V
6000
3
100 3
Grid rated voltage U
ng
= 6 kV
VT ratio: K
VT
=
/
XMR-x
XMR-D EQUIPMENT MANUAL
Ed. 2.9 - 02/2021
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