I have an application where I need to use a breaker that has four sets of 300/5 CT's in its bushings. I need a much lower CT ratio (around 75/5 would be ok). Is there any reason why we cannot connect the CT's in parallel to acheive an effective ratio of 75/5? Is this something that anyone has...
Hi,
I have a proportional valve driven by a 4-20mA signal. This directly ports oil to an amplifier stage (another valve mounted directly to the proportional valve). The amplifier spool moves very slow (can take up to 30 seconds to move from one position to the null position). The...
I am looking for information on power system stability. In particular, we use synchronous condensers and many synchronous motors, and I'm wondering how this affects the stability of our power system (increases it or decreases it). Any informatin would be appreciated.
Thanks.
How would one select the appropriate size resistor for a LV system. We are trying to select between 100 and 200 ohm to limit the ground fault. Is there any guidance out there for this?
Hi, I'm trying to put together a safe work procedure for a tripped mobile substation (delta-wye) that is resistance grounded. When we have a ground fault, is there a safe way to approach the substation? While most codes say we should limit our GPR to 5000V, we have the possibility of reaching...
We have multiple 46/4160 transformers in our substation that feed switchgear inside our facility. The power cables are teck, and run in multiple cable trays. In a recent inspection we noticed that there was no bare ground to each switchgear (they are old installations). Should we have...
We use a trailing cable to feed mobile mine equipment at 4160 V. I am trying to find any direction from the IEEE, NEC, or NFPA about how to handle this energized cable. The cable is appropriately insulated to be laid on the ground to feed the equipment, however there are concerns about...
We have a large (3500 hp) motor, that sometimes trips on start up on a false ph-ph fault. It often starts on the second attempt. Any ideas on what the problem could be? We have changed the relay, and the CT's have been checked.
I have a section of 4160 overhead line that is 336ACSR and then drops down to 2/0 ACSR. According to the code I'm suppose to set my upstream breaker to protect the 2/0 ACSR. However this will cause nuisance trips as the heavier 336 ACSR has heavy loads. I've been told that the other option is...
Is there any recommendation for setting the ground pick up level for an induction motor. Our current setting is just based on co-ordination with upstream protection. However, outside of that, is there any standard setting to protect different motors from ground faults?
I am in the process of reruiting a number of 4160 distribution lines. I am finding it difficult to locate the current rating of various ACSR conductors. If someone could point me in the right direction it would be appreciated. Also, what is the usual acceptable temperature rise in overhead...
Our MCC's have a symmetrical fault current rating. I was wondering if that was 1/2 cycle or 3-5 cycle fault current rating? Also, for what applications would one use the 1/2 cycle vs the 3.5 cycle fault levels (eg. which one for relay coordination)?
Thanks.
My company is currently considering changing our standard impedance of new 1000 kVA (4160/600) transformers from 6% to 8% to keep our fault levels low. However there are concerns about voltage regulation as we have a lot of connected motor loads. Is there any appropriate documentation that...
