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based on the busbar voltage as shown below:
whereas, ‘VT ratio at Line’ is obtained from the actual value in VCT
ratio setting corresponding with scheme switch [SYN-VLine], and ‘VT ratio
at busbar’ is obtained from the actual one corresponding with the scheme
switch [SYN-VBus]. We shall see the scheme switches in the succeeding
section.
(iii) Frequency difference
The frequency differences between the running voltage and the incoming voltage
(Δf1 and Δf2) are smaller than the SYN1 and SYN2 settings:
For SYN1 setting: Δf1
≥
| fV
B
− fV
L
| ≤ [SYN1-df]
For SYN2 setting: Δf2
≥
| f
L2
− fV
L
| ≤ [SYN2-df]
Note: When Off is set for the scheme switch [SYN1-dfEN], the VCHK abandons
the frequency difference condition from synchronism requirements.
Similarly, the frequency difference condition is not valid when [SYN2-dfEN]
= Off.
(iv) Phase angle difference
The phase differences between the running voltage and the incoming voltage (θ1
and θ2) are smaller than the SYN1 and SYN2 settings:
For SYN1 setting: V
B
× V
L
cosθ1 ≥ 0
V
B
× V
L
sin ([SYN1-Angle]) ≥ V
B
× V
L
sin θ1
For SYN2 setting: V
L2
× V
L
cosθ2 ≥ 0
V
L2
× V
L
sin ([SYN2-Angle]) ≥ V
L2
×V
L
sin θ2
(v) Notice and tips
If the frequency difference between the V
L
and the V
B
is shown very large, the
VCHK may fail to make the decision for the synchronism, although Off is set for the
[SYN1-dfEN] to abandon checking the frequency difference. This is because; the
vector passes the [SYN1-Angle] zone very quickly. As a result, the VCHK may fail
to issue the permission command. To avoid the failure, the user has to set values for
settings [SYN1-Angle] and [T_SYN1] depending on the assumed frequency
difference (Δf):
SYN1-Angle
T_SYN1
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