Vt Supervision - ABB RELION REB500 Technical Manual

Section 5
Bay protection functions
and the rated power system frequency, that is, the memory voltage is used for 15 periods at
rated system frequency and for a proportionally reduced number of periods as the frequency
deviates from rated power system frequency.
As long as the reference voltage U
determine fault direction.
In this case, a forwards fault satisfies the condition:
-90° < arg Z
A reverse fault satisfies the condition:
+90° < arg Z
Z is the impedance measured by the protection, which contains a component of the source
ref
impedance Z
mathematically transformed in order to make the influence of the source impedance visible. If
the reference voltage is less than 0.5% of the rated voltage, direction is not taken into account
for the phase-to-ground loop and tripping is blocked. In the case of the phase-to-phase loops,
tripping is either enabled or blocked, depending on the setting of the parameter
5.1.7.3

VT supervision

The purpose of the VT supervision function is to monitor the VT leads with respect to
asymmetrical short-circuits and open-circuits. An MCB can be included for three-phase VT
short-circuits and arranged to block the protection via a separate optocoupler input.
The input variables monitored by the VT supervision function are the three voltages U
and U
L3
(U , I ) components are calculated for both the three-phase voltage and three-phase current
2 2
systems:
3U = U
0
3U = U
2
3I = I
0 L1
3I = I
2 L1
64
< +90°
ref
< -90°
ref
in addition to the line impedance Z
S
and the three currents I
+ U + U
L1 L2 L3
+ U × a2 + U × a
L1 L2 L3
+ I + I
L2 L3
+ I × a2 + I × a
L2 L3
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is greater than 0.5% of the rated voltage, it is used to
ref
. The operating characteristic has to be
L
, I , I . The zero-sequence (U
L1 L2 L3
3
   
a 0.5 j 1/120
2
1MRK 505 406-UEN B
MemDirMode .
GUID-66C20810-64C5-419C-9A32-29BBE2A3DA00 v1
, I ) and negative-sequence
0 0

Bay protection functions REB500
Technical manual
, U ,
L1 L2