Real World Problem With an SEL-300G Synch-Check

Here is a story from one of our Customers at Manta Test Systems:

“I had to troubleshoot a Schweitzer SEL-300G relay yesterday that had the (25) Sync-Check element enabled, but wouldn’t assert the close permissive. My customer had had extreme problems synchronizing the 16MW generator on-line. They sometimes had to try up to 10 times to close the generator breaker, and without success. And, as you know, steam turbines don’t like to spin unloaded; they overheat, etc. The Substation was rebuilt in 2009, and all relays were upgraded to SELs; hence, the problem has existed since then—and I just learned of it!

Thanks to the MTS-5000, I discovered the problem. The SEL-300G, actually all SEL relays configured with Sync-Check, must be connected with the generator voltage (SYNCP) on terminals Z09-Z10-Z11-Z12, and the System voltage (VS) on terminals Z15 & Z16. Regardless of the Synchronizing settings, the close permissive contact(s) (25A1 and/or25A2) will only assert if the generator frequency is above 60 Hz, or more correctly stated, faster than the System voltage. I found the voltage connections reversed! SYNCP was actually connected to the Bus Voltage & VS was actually connected to a PT on the generator leads.

I thought you may have already run into this situation, or may in the future. If so, you are now armed with the ultimate knowledge for sync problems with SEL relays.”