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Zero Sequence Impedance of Autotransformer with Tertiary Winding 1

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anggapra

anggapra

Electrical
Jun 28, 2018
29
Hi,

How to determine the zero sequence impedance of an autotransformer with a tertiary winding?

The following are the specifications I received from the manufacturer, the positive sequence impedance is stated as 0.2%, but there is no data for zero sequence impedance, is there a rule of thumb to calculate it?
Autotrafo_chwocz.png


Note: Currently, its tertiary is delta connected, and the neutral point is connected to ground

Regards,
 
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Absent any zero sequence test data, and assuming a single 3-phase unit (probably a safe assumption at that size), I'd go with R0 = R1 and X0 = 0.85 * X1. Seems to work.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982
 
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Thanks David,

Does the construction of an autotransformer winding affect its zero sequence impedance?

The transformer above consists of 2 different cores, here is the drawing and photo below
untank_tgzpxa.png

Autotrafo_ZELP_skig6i.png


Meanwhile, we have another autotransformer with a drawing like this, unfortunately, there is no photo, but it seems that there is only 1 core in this autotransformer.
Autotrafo_KARA_wt4rqo.png
 
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This is a special transformer -an autotransformer with a series booster transformer on the secondary. So, the impedance will be the sum of these two transformers. Better contact the manufacturer. You can roughly estimate the zero sequence from Table 1 of IEC 60076-8 -Transformer Application Guide for regular transformers with different connections.
 
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Thanks prc, IEC 60076-8 is such a good read.

Based on that table, I think X0 = 0.85 * X1 is a good estimation
 
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