Hello,

Can anyone please help me with the below questions?

1. Regarding arc flash labeling for a 195MVA combustion generator operating at 18kV, since the voltage range falls outside the scope of IEEE 1584-2018, I am forced to evaluate it using the Ralph Lee method. However, I am unsure about the appropriate value for the working distance in the calculations. Are there any typical values mentioned in specific standards that I can consider for determining the working distance?

2. I would like to inquire about the behavior of a combustion generator during a fault condition in the absence of protective devices. Does a combustion generator continue to contribute a steady fault current for a 2-second duration, or does it stop generating power due to specific reasons such as a terminal voltage dip?

Thanks

Look I can answer both questions very easily. But these are basic questions. What your questions say is that you are plugging data into power analysis software but you have no clue how it works or what you are doing. Thus you can’t validate the results. It would be irresponsible on my part to give you the answers, kind of like giving you answers on a test. You will know and understand this with a basic power system analysis training class either through a local university or through Jim Phillips.



Why? The standard you mentioned, 1910.269, specifically tells you not to use Lee. Did you bother to read it? Even if you don’t, try this. Decrease your system voltage from 18 to 15 kV. That puts you inside 1584. Notice that Lee is incorrect by over an order of magnitude. So why do it wrong? Are you using the standards or blindly taking advice from a software program?



This is well publicized in the arc flash standards. OSHA tells you how to do this in the annexes to 1910.269. Even without that ergonomics standards tell you what to use. Did you read these or receive training?



You have an electro-mechanical system. There are trips other than just overcurrent that are relevant here. I’ve popped field fuses stalling a generator. Your question and assumptions aren’t even relevant. Why do you assume that a generator powering an arcing fault won’t reach its stall limit and go into cycle slipping? Are you aware of what happens in a paralleling system when we exceed lead/lag limits? As you stall out a synchronous motor it not only lags but when it lags too much suddenly and instantly it is leading at 180 degrees, leading to massive electrical transients. So there is your voltage “drop� concern. In addition this massive torque and negative power draw puts a huge torque as well as very high jerk (dT/dt) on the coupling, bearings, and shaft, then massive oscillations. If not controlled it results in damage and often to the building around it as parts go flying. The protective devices are there to prevent those things from happening and significant damage to the generator, never mind mechanical damage to the coupling, bearings, and shaft. Why do you think companies spend such an insane amount of money on the protective devices (with significant redundancy) that you are so flippant to ignore?

All this is again covered in the engineering standards. Again I know the answers. 2 seconds is well covered in IEEE 1584. Yes we are outside 1584 but this part is still relevant. Jim Phillips also published “Why 2 Seconds?� Very relevant. But before going there please read IEEE 1584.1 and make sure you are compliant (you aren’t).

I understand that you have strong opinions on this matter, but I would appreciate it if you could express your viewpoint in a more respectful manner. Dismissing my questions and resorting to derogatory language is not conducive to a constructive conversation.

I asked for assistance because I am seeking to learn and understand better. While I acknowledge that I may not have all the necessary knowledge or training at this moment, I am open to receiving guidance and suggestions from experienced individuals like yourself.

If you are willing to provide further explanations or point me in the direction of specific resources that can help me improve my understanding, I would be grateful for your assistance. However, I kindly request that we maintain a respectful and constructive dialogue.