All about PT's 2

[mel127]

Greetings,
We are on the process of upgrading various components on our substations which was built when I wasn't even born. We tried contacting vendors and suppliers for them to recommend a replacement for PT's.They come out with a lot of queries:
1. Location of application - Outdoor type
2. Connection type - Line to ground
3. Secondary voltage - 115 V
4. Ratio - 175

These are the questions that needs clarification from you experts:
1. Accuracy and burden.Highest burden for .3 ACC CL;Thermal rating?
2. Also do you recommend to fuse this or not?

I know this are very basic questions for experts like most of you guys in this forum.But for a newbie like me I need your expert opinion.

By the way our system is 34.5 KV.

Thanks in advance.

 

[slavag]

Hi Mel127.
We had topic on the issue.
Please see attached thread:
thread238-209138
For the start.
Regards.
Slava

 

[apowerengr]

The answers to your questions depend on what the pt secondaries are being used for - revenue/billing metering or protection? If this is metering, the company owning the meter will have their requirements for burden and accuracy class. If its protection only, what relay functions rely on the pt outputs, what are the aggregate relay burdens and what are the allowable input voltage range to the relays? Then, you need to answer whether what the system configuration looks like as it can affect the BIL requirements of the PT's based on the system connection to the bus supplying the PT's (grounded, ungrounded, impedance-grounded).

And, many times the systems have changed over the years, pt connections which were used years ago might be better changed during this process which could require relay changeouts as well. Fusing or not depends on what the PT outputs are used for, opinions will range based on utility practices.

 

[mel127]

Thanks guys. This is good start for me. Keep doing what you do. Great site for newbies like me