I appreciate all the lively dialog!
The arc flash calcs are a function of the fault energy and the clearing time. The above discussion surrounds the arc energy. The problem usually seems most aggravating with main breakers, which are often applied without instantaneous elements, or settings...
I guess the imple,entation varies. I deal with a lot of large industrials, and their position varies according to my post - hence I ask the question.
According to OSHA, they have not directly adopted NFPA 70E (although there ared indirect incorporations of it), but they can make the case.
OSHA...
I had to do it a number of years ago, Frank, at a steel mill to give equal BIL protection for phase-phase transients as phase - ground transients.
GE mounted all 3 on a plate, then supported the plate with post insulators, and then tied the plate to ground with a single arrestor of the same rating.
For those of you involved at plant sites, have you or are you being encourged to look at the new regulations regarding Arc Flash, and applying Personal Protective Equipment?
Are you (a)complying, (b)ignoring, or (c)stumped on how to respond? I'm trying to figure out just what kind of an impact...
You probably know this, but the symptoms you describe sounds a lot like what happens if all phases and neutrals are not run in the same raceway, per NEC. In other words, if the vector sum of all currents in all phases plus neutral in each raceway do not cancel, you will get eddy currents like...
One more thing - Teck cable was (apparently) developed specifically for installation in cold climates. It remains flexible at temperatures below other cable types, and is approved for installation at temperatures lower than other cable types.
It is also approved for direct burial.
sounds like it's OK.
I've spent 2 days in meetings dealing with a large (30,000 hp) centrifugal natural gas compressor on VFD's & my brain is a little tilted -
Thanks
;-)
Check with the compressor vendor. I can't recall if a screw is a positive displacement or not.
The concern is whether it would surge - but you would know more than I might about the characteristics.
I assume the compressor is a reciprocating (positive displacement) type.
If it a screw operated in parallel with other machines, you may need to look more closely.
Just my 2 cents worth -
If I understand all the above dialog, you applied a vector drive to the application. With the application, a vector drive works very hard to maintain constant speed on the shaft. When a transient torque is applied (when the dough is 'thrown up' as you put it) the vector...
One other suggestion - using instantaneous elements for fault detection or sometimes called 'zone selective interlocking' is a cheap way to gain some speed & selectivity.
The principal uses an instantaneous element to detect a fault.
Logic is developed that compares the fault detectors...
jraef:
I understand & appreciate your input. I might point out the following:
1) RVSS are very poor performeds when it comes to starting torque. SS starters are no better than series reactors when it comes to reduced voltage starting, and when you are trying to maintain minimum starting...
Just an update:
1) My calcs show that the capacitor assist will work, (long story here - they're already doing it with a 15,000 hp motor), but only if they have their two substation transformers in service (in parallel for redundancy). If they lose one, starting is out of the question. Hence...
Be sure the drive manufacturer is aware of the motor type.
For years it was standard design to use LCI type drives on the largest VFD applications, and synchronous motors are perfect for this application. However, LCI is an old technology (in fact the original technology for large drives). It...
