HoJoCo
Electrical
- Apr 3, 2002
- 9
Hello!
I have a customer with a 34.5 KV delta system feeding a Electric Arc Furnace (EAF). The facility asked me to meter the system due to past equipment failures. (blown fuses, damaged PACS breaker).
They have three PT's in the metering vault, single terminal, rated 20,125V, 300:1. I originaly offered fusing to connect these into the system (PH-Gnd.) but after reading a few threads, was concerned about ferro-resonance and damage.
I then offered 2-34.5 KV PT's, connected open delta (Ph-Ph). The customer is concerned about being able to accurately monitor the usage (for electrode regulation/Load balancing) with only two PT's?
Should I just offer a third PT or should I consider PT's with dual secondary (wye & Delta connected)
Thanks! See below.
Howard
******************
Posting from RCWILSON
"7 May 08 13:56
I recall that Y-Y PT connections can be susceptible to ferro-resonance and that open-delta PT's are not. Is my memory fuzzy or is this true?
We usually apply a Y-Y set of VT's with dual secondary windings, one connected in grounded wye and one wired broken delta with a loading resistor. The broken delta with resistor minimizes ferro-resonance and gives a 3Vo voltage for ground detection."
I have a customer with a 34.5 KV delta system feeding a Electric Arc Furnace (EAF). The facility asked me to meter the system due to past equipment failures. (blown fuses, damaged PACS breaker).
They have three PT's in the metering vault, single terminal, rated 20,125V, 300:1. I originaly offered fusing to connect these into the system (PH-Gnd.) but after reading a few threads, was concerned about ferro-resonance and damage.
I then offered 2-34.5 KV PT's, connected open delta (Ph-Ph). The customer is concerned about being able to accurately monitor the usage (for electrode regulation/Load balancing) with only two PT's?
Should I just offer a third PT or should I consider PT's with dual secondary (wye & Delta connected)
Thanks! See below.
Howard
******************
Posting from RCWILSON
"7 May 08 13:56
I recall that Y-Y PT connections can be susceptible to ferro-resonance and that open-delta PT's are not. Is my memory fuzzy or is this true?
We usually apply a Y-Y set of VT's with dual secondary windings, one connected in grounded wye and one wired broken delta with a loading resistor. The broken delta with resistor minimizes ferro-resonance and gives a 3Vo voltage for ground detection."