Secondary Bushing CT resistance of 150 MVA Transformer

082399 · Oct 26, 2023

Hi,

A client in a Petrochemical plant specified a requirement of 150MVA Transformer with a primary BCT rated at 3000:5, 2000:5. According to the specification, it is mentioned that "The secondary resistance of the CT shall not exceed 0.0025 ohms per turn". The transformer vendor however offers them the same Transformer but with a secondary BCT that would not exceed "0.005 ohms per turn" for client's approval.
If the client accepts what the vendor is offering, does this will cause issues in the future? are there any consequences?

Appreciated the quick response.
Thanks.

RRaghunath · Oct 26, 2023

Depends on what for the BCT is proposed to be used. If it is for the High impedance Restricted Earth fault protection, the resistance parameter needs to be matched with the CT at the other end of the zone. If it is for transformer differential protection, the parameter could deviate considering the protection is biased type.
Then, you also have to look at the Vk and magnetising current parameters when it comes to HiZ protection.
Better to involve your protection engineer as well when you take up the issue with the client.

R Raghunath

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Secondary Bushing CT resistance of 150 MVA Transformer

082399

Electrical

RRaghunath

Electrical

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