Siemens SENTRON Manual page 212

Applications
13.4 Transfer between three sources with two outgoing loads
Transfer with T1 (kVA) < T2 (kVA) and T2 (kVA) > T3 (kVA)
As well as the previously described applications, applications comprising 3 transformers (T1,
T2, T3) where the power of the transformer T2 is greater than that of the other two
(T1 (kVA) < T2 (kVA) and T2 (kVA) > T3 (kVA)) can also be implemented with the transfer
switching equipment. By using two transfer switches, this complex application can be
realized, thus enabling the power supply to be maintained.
Figure 13-7
* Dependent on the priority setting on the transfer switching equipment
212
Transfer T1 (kVA) < T2 (kVA) and T2 (kVA) > T3 (kVA)
T1 T2
0 0
1 0
0 1
0 0
1 0
0 1
1 1
1 1
T3 Switching state
of the transfer
switching
equipment
0 x
0 P1
0 P2 + P3
1 P4
1 P1 + P4
1 P2
+ (P3 or P4)*
0 (P1 or P2)*
+ P3
1 (P1 or P2)*
+ (P3 or P4)*
Manual, 08/2017, L1V30368969104A-02
Non-critical Critical
load 1 load 2
OFF OFF
ON OFF
ON ON
OFF ON
ON ON
ON ON
ON ON
ON ON