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Re: potential transformers
From: Dick Gray[SMTP:rjgray-at-rmii-dot-com]
Reply To: Dick Gray
Sent: Thursday, October 30, 1997 11:04 AM
To: Tesla List
Subject: Re: potential transformers
On Mon, 27 Oct 1997 23:57:58 -0600, Tesla List wrote:
>
>From: Jim Lux[SMTP:jimlux-at-earthlink-dot-net]
>Sent: Monday, October 27, 1997 11:16 AM
>To: Tesla List
>Subject: Re: potential transformers
>
>>
>> Can any of the list members tell me if an instrument transformer is the
>> same as a potential transfomer? There is a site that has a pile of them
>> for sale!
>>
>>
>>
>> http://www.austin.inter-dot-net/
>
>Sorry, those are current transformers, rated for various insulation classes
>(e.g. 600 V). You can tell because the specs are something like 500:5,
>which means it is designed to monitor a 500 Amp current on a 5 Amp meter. 5
>Amp meters are standard in the industry. This is really a 100:1 current
>transformer...
>
>
>
Just for general information, instrument transformers may be either
CT's or PT's. It is the accuracy class that determines the use for
PT's. These may be anything from 1200:120 up to as high as 750,000:120
for revenue metering purposes. In some substations, buss PT,s may be
classed as instrument transformers because of their accuracy as well as
being used for protective relaying. These transformers usually have
more than one secondary winding or a tapped secondary winding, the tap
being used for protective relaying.
Current transformers also can vary as to accuracy, depending on whether
they ars used for revenue metering or protective relaying. The best way
to tell is to look at the nameplate if possible. Otherwise a general
rule of thumb for smaller transformers is to look at the terminals. The
PT's primary terminals will usually be for small (#8 or less) for the
lower voltages and 500 mcm or larger for the big transformers. The CT's
will usually have flat bar primary terminals and two or more lead or
screw-type secondary terminals, depening on whether they are single or
multi-ratio transformers. It is a tapped secondary winding for CT's.
I hope that this additional info is useful.
Dick