VAMP 257 - Page 82

VAMP 257 Feeder and motor manager
Technical description
VAMP Ltd
40
VAMP 24h support phone : +358 (0)20 753 3264
VM257.EN002
For the I
0
and U
0
measurement, the fundamental frequency
components are used. Thus, the degree of the third harmonic
attenuation is at least 60 dB, which contributes to the
extremely high accuracy of the earth fault protection.
The directional earth fault protection measures the residual
voltage U
0
, earth fault current I
0
and the phase angle ϕ
between U
0
and I
0
.
The directional earth fault protection includes two separate
protection stages, that is, I
0
ϕ
> and I
0
ϕ
>>. Both the stages have
their own operation time settings. The protection stage starts
when the setting values of I
0
ϕ> and U
0
> are simultaneously
exceeded.
The I
0Res
mode (I
0cos
ϕ
) is used in rigidly, resistance and resonant
earthed networks, and in the I
0Cap
mode (I
0sin
ϕ
) in isolated
networks. The user can set this characteristic, or it can be
controlled dynamically using any digital input. The control
input is usually used in compensated applications, where the
compensation coil can be switched on and off.
Figure 2.3.11-1. Block diagram of the directional earth fault stages I
0
ϕ
> and
I
0
ϕ
>>
Figure 2.3.11-2. Operation characteristic of the directional I
0
in Res or Cap
mode