Recent content by Kyle2022

Are you saying that neighboring companies have elected to leave the cleared breakers open while the disconnects are opened on the failed breaker? Are the disconnects motor-operated? Do the disconnects automatically open on a failed breaker as a result of a BFI timeout and after checking for no...

Thanks davidbeach. The polarity marks do look perfectly normal. I was just confused why there were two sets. I thought maybe someone was trying to depict a different type of CT (bushing or otherwise). Now that I understand these are placed in series to increase their rating, all is OK...

The drawing is from Siemens Germany, which is why I figured this was some sort of German and/or IEC symbol. Apparently this is not the case. That aside, do you agree with scottf as to why it is used OR do you believe this is a mistake altogether? Thank you. I appreciate your responses.

Yeah, I guess that's the real question. I figured it showed the 2 CTs in series. Why is it done at all? Thanks for the response scottf.

Good afternoon, I am attempting to figure out what is meant by the CT symbol in the attached picture. I work in the US and I have never seen a CT shown like this, especially with two polarity marks. Thank you! Kyle

BJC, I did just look up 'a' vs 'aa' and 'b' vs 'bb' in the ANSI standards. It is just as you've stated. Anyway, thanks for all your help. The problem that drove this discussion has been resolved. I was wondering why an 'aa' and 'bb' from a disconnect in series directly tripped a breaker...

Thank you all for your comments. My belief that the switches behave as I have stated has no reasoning other than assumption. I was hoping that 'aa' and 'bb' contacts were standard which apparently is not the case. The client is several states away, so I have no immediate means of testing said...

Rbulsara, Thank you sir. I am also very familiar with "a" and "b" contacts, but not so much with "aa" and "bb" Kyle

I'm having a hard time finding exactly how the 52aa and 52bb contacts work for a disconnect switch. I believe they work as follows, but please correct me if I'm wrong: As the disconnect closes from open: 52bb opens, 52aa closes, 52b stays closed, 52a stays open When the disconnect is closed...

I'm glad that there is an intern with interest in this field. I am a 26-year old electrical engineer in the power industry, and there seem to be few of us. Wbd's recommendation, "The Art and Science of Protective Relaying", is the book I started with. It's an excellent resource. Although...

Good afternoon, It has been mentioned in some seminars that I've attended that the PPE requirements of an arc flash study can be lowered by 2 categories if the switchgear door is closed (closed-door racking, etc). Is this an industry-wide assumption or the ramblings of the un-educated? If it...

Good morning folks, I am trying to size some 15kV cables that will be laid in cable trench. I would rather not use ventilated cable trench though some have said these can achieve "free-air" ratings. I've gotten my hands on a study titled "Ampacity of Conductors in Ventilated Cable Trench" by...

Thanks jghrist, I just wanted to be sure I wasn't missing something. I am positive this is just one of those things that has been wrong for years. It looks like it might have come about from a lack of contacts on the bus differential lockout, but there is no way the unit differential lockout...

I've come across an odd situation in a switchyard outside of a power plant. An electro-mechanical high impedance differential relay (KAB) is used as bus differential protection. As is practice, a lockout contact is used to short-circuit the varistor in order to prevent it from overheating. I...

Zogzog is right on with his equipment suggestions. You mentioned that you are looking for specific brands. We use the following: Megger: AVO (as he said voltage depends on transformer) TTR: Biddle Winding Resistance: AVO Power Factor: Doble M4000 Microohmeter: Biddle