Failures and failure rates for 5MVAR transformers at 24hrs soak test

[MacCB]

Hi Lds & Gent's,
Can anyone out there refer to any report on the subject?
The only argument I've found is: "That is common recommendation from the trf vendors manual to complete a 24hrs soak test at commissioning".
But what kind of failures or malfunction would you reveal during this period, and especially after 23hrs, 59minutes and 59seconds?
BR

 

[cuky2000]

It is very hard to find any statistic during the short time range.
This number is expected to be relatively low in the region of infant mortality of the transformer.
A general idea of failure in this region is shown below.
Good luck

 

[prc]

Trust the "soak test" means keeping the transformer energized at no-load. Clause 5.11 of IEEE C57.93-2019 Installation and maintenance of Transformers cover this procedure. This standard suggests 12 hours for energization without load for voltage classes 230 kV and above and 8 hours for below 230 kV. The purpose of this keeping under no-load is to is to limit damage from any fault arising from incipient defects from improper transport, storage or installation. Standard mentions " While this period of energization at no-load is not required, it is helpful to understand and evaluate the transformer in this condition prior to applying load" .I have experienced at least half a dozen cases of transformer failures during this soak test.