Hitachi Relion 650 Series Technical Manual page 330

Section 12
Monitoring
• transformer core type
• electrical configuration and grounding (vector group) of the transformer
• to which winding the load VT is connected
• electrical configuration of the load VT
The required calculations for most common transformer configurations are described in the PWC600
User Manual and are implemented in the Switchsync Setting Tool (SST).
The resulting streams of limb voltage samples are published at the outputs LIMBU1, LIMBU2, and
LIMBU3. Internally, these limb voltages are normalized to p.u. using UBase setting (selected by
GlobalBaseSel), for calculating the residual fluxes in the next step.
Most power transformers have coupling between the phases, either through a delta winding
(electrical coupling) or through a three-limb core (magnetic coupling). Due to this inter-phase
coupling, energization of the first phase causes voltage to appear also in the other phase(s) although
the respective CB poles are still not closed. This makes it difficult to detect the actual making instant
in the later phase(s) to close. However, as the three voltages sum up to zero it is possible to detect
the later making instants from a suitable algebraic combination of limb voltages. In TRAFOSWT, the
TrafoType setting determines the appropriate combination as listed in
Table 287: Differential limb voltage signal outputs
Switch Case
1
2
3
4
5
6
7
8
9
The differential limb voltages are provided at the outputs DIFFLU1, DIFFLU2 and DIFFLU3. The
three-phase grouped signal for the same is the DIFFLU3P output.
324
Description Differential voltage outputs
DIFFLU1
Yn, non-coupled LIMBU1
Yn, coupled (LIMBU1 - LIMBU2)/√3
Y, coupled/non- LIMBU1
coupled
D, 30° (D1) (LIMBU2 - LIMBU3)/√3
D, 330° (D11) (LIMBU1 - LIMBU2)/√3
D, 210° (D7) (LIMBU2 - LIMBU3)/√3
D, 150° (D5) (LIMBU1 - LIMBU2)/√3
Z, 30° (Z1) LIMBU1
Z, 330° (Z11) LIMBU1
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Table 287.
DIFFLU2 DIFFLU3
LIMBU2 LIMBU3
(LIMBU3 - LIMBU1)/ (LIMBU2 - LIMBU3)/
√3 √3
LIMBU2 LIMBU3
(LIMBU1 - LIMBU2)/ (LIMBU3 - LIMBU1)/
√3 √3
(LIMBU2 - LIMBU3)/ (LIMBU3 - LIMBU1)/
√3 √3
(LIMBU1 - LIMBU2)/ (LIMBU3 - LIMBU1)/
√3 √3
(LIMBU2 - LIMBU3)/ (LIMBU3 - LIMBU1)/
√3 √3
LIMBU3 LIMBU2
LIMBU2 LIMBU3
Technical Manual