Sparking was found this morning inside HV cover on TCS in TH while TM3 was HV conditioning at TCS. The TCS bias was set to 50KV when I found this spark. It sparks between HV cover front side wall to a KF 25 clamp on HS water terminal. The KF 25clamp is used in this situation on HS water line top because the HS line is opened inside module, and we need a vacuum seal on the top of this line.  Actually, The clap is much smaller than the corona ring on HS terminal, and the corona ring is more close to side wall. But there is a 90 degree straight corner on this clam. So the spark happened between the side wall and this 90degree corner on the clamp. We can not change the clap now since it will break vacuum. So, we decide to do HV test without HV cover installed onTM3 at TCS. A work permit is issued for  this. Lock out procedure: Document-70039 is clarified in WP.