CT standard BS3938-1965

[reactive]

Can anyone help me with a copy of obsolete CT standard BS3938-1965 or if this is not possible, more specifically the following :
- What is the primary continuous current rating as specified by the standard. Is it simply the primary rated ratio current or is there an overcurrent factor ?
- I need an explanation of the codes e.g. what is a 7.5C15S10 CT (VA, class etc.)?

We have some existing CTs on a fairly old site in Zambia and wan't to know if we can run them above their primary rated ratio current and also would like to calculate approximate saturation levels during faults.

Thanks.

 

[peterb]

From memory, the permissible overload level should be somewhere around 20-30%, but I would try to verify that with the manufacturer if they are still in business.
As for the saturation level, do a magnetizing current test to draw the CT mag curve. Measure the secondary resistance and you will have everything that you need to calculate CT performance.

 

[scottf]

The only BS standard I have for CTs is BS 3938-1973.

In this standard protection cores are rated like in the IEC standard (i.e. 5P20 - 30 VA) or as the BS Class X designation. I do not recognize the designation you list above.

The continuous primary current rating should be marked seperately on the nameplate...like "RF1.5" , etc... By the current BS standard, if the nameplate does not state a rating factor, you must assume that the rated primary current is the maximum continuous current.