Static Excitation Pt. 5: Compound Boost CT revisited

[n1mr0d]

Hi, i managed to obtain some information about a special wound CT used in a compound-source static excitation system. There was a 'nameplate' located on the back of the CT, which in turn was directed to the wall. It seems the wound CT has one primary and 2 secondary coils. The primary has 3 windings, the secondary 19 & 3. The secondary coils are connected in series in a 'delta' way. As CT's are current sources, isn't it illegal to connect two current sources in series?

Can someone explain to me why the secondaries are connected to each other in this way. Maybe it has something to do with fault currents etc?

 

[n1mr0d]

Just got a stroke of genius: it looks like a weird kind of zigzag or interconnected wye connection.

This is my interpretation of it:

 

[n1mr0d]

I've read that the zigzag winding is used for absorbing triple-N harmonics, but doesn't the secondaries have to be symmetrical? What is the effect of 2 asymmetrical secondaries?

(PS: I hate it when you can't edit your own threads)

 

[n1mr0d]

After reading a PDF, i was finally able to assign a vector group to the CT. The primary side has vector group Y0, and the secondary Z7uw. 0-7=-7 or +5 phase shift (150 degrees) --> Yzn5

Another PDF mentions the following:
"Taking no special measures, following connection modes amount to 100% load of neutral point:
Delta-star connection with secondary extended neutral point Dy5
Star-zigzag connection with secondary extended neutral point Yz5
If three-phase sets are formed via 3 single-phase transformers, then load of neutral point must definitely be avoided"

Is this 'neutral loading' of any significance of the CT in relation to the exciter?