Spoke with utility and they tell me that the are regulating secondary voltage (tap changer) to 120V on the secondary of the 2400V to 120V PT's with the PT connected L-N on 4.16kV secondary. They said that there is a 2V bandwitdh on tap changer.
This means that they are regulating secondary to...
We've also noticed that this drop is occuring plant wide and even measuring minimums of 109V in office receptacles during certain times. Would this be an indication that we should raise or incoming voltage to some amount?
I'm going to look into the two measurment errors mentioned. Might be PT...
We are having an issue where an 120V branch circuit is dropping to 112V during the starting of a motor and causing problems with electronics. This voltage drop is causing several problems and we are searching for answers as to what we are seeing and where to make corrections.
Our system has a...
dpmac
I have seen the same MSHA standards that you are referring to, and although they do state that these systems need to be tested anually, they are very vauge in what they are looking for.
Its hard to decipher weather or not they are looking for a test to be performed at every transformer...
Zogzog
I am indeed having a NETA certified testing company perform this testing. I am confident that they indeed know how to perform a 3-point fall of potential test, however there seems to be some confusion even with them as to may many points we need to test, and at what locatins since grid...
I have been requested to perfrom an earth resistance test here at our industrial facility. This tested is mandated by MSHA requirements that govern our site.
Our distribution voltage is 4.16kV and our utilization voltage is 480V.
I have been researching this test and plan on performeing a...
I jsut recieved a quote for the same drive in a 40hp and it still came in at $15,960.00 which is high. I'm probably going to do just as DickDV mentioned and get rid of the additional HMI if I pursue this drive.
Do you guys think that after removing the HMI I should be paying under 5k for this...
I just recieved a quote for one of these Powerflex 70 50Hp drives at about $17,300.00. This included the drive mounted in a NEMA 4 enclosure with an HMI mounted on the front of the enclosure. It also included a 3% line reactor installed in the cabinet on the line side of the drive as well as...
Thanks for all the responses guys. After reading all of the respones it sounds like trying to use one drive to control both motor will be too complex to integrate into the existing control system and may only lead to problems with maintnance and operation. I am still awaiting pricing on...
Waross
Good point about adding a second breaker for redundancy on the bypass contactor. I was thinking as well that if one of the motors failed and tripped the breaker it would leave us dead in the water.
I am awaiting on pricing for just the standard drive to see how much each drive costs to...
Just thought of an idea to run the motors DOL if there is a problem with the drive.
Where the drive is located, or in the drive enclosure I will add a 3rd contactor which esentially bypasses the drive if there is a problem with the drive. The contactor will be on the load side of the thermal...
I apoligize but I realize now I forgot to mention a key piece to all of this in that these two motors are already connected to individual starters running across the line. I am wanting to retrofit this setup to incorporate a vfd.
Davidbeach brings up a good point in that with only 1 drive we...
I am putting together a design for a VFD controlling two 40hp motors on centrifugal water pumps which are pumping water from a tank.
Only 1 motor ever runs at a time and the other motor is strictly sitting on standby as a backup. The idea is to control the speed of the motor and thus the flow...
The motor that I am referencing is a 350hp 4.16kV induction motor started with a DOL starting method.
The motor came equipped with 6 stator rtds which are connected to a motor protection relay for monitoring. It was discovered recently that one of the rtd's was damaged (failed open) and was...
Getting back to Turbogen's comment above about "Induced Eddy Currents".
Aren't these induced currents and eddy currents that you spoke of magnetic flux currents as opposed to actual electrical currents.
Wouldn't it be the same as if you wrapped a coil of wire around a core, with the current in...
Is it true also that for a given load a larger motor will accelerate the load faster then a smaller motor at a set speed?
I would think so due to the fact that acceleration time is esentially the difference between motor torque and load torque. If the torque produced by a larger motor is...
Thanks for the response guys!
So is the current more related to the slip being greater during faster ramps, or the motor trying to accelerate quicker and producing more torque? Or are these two aspects one in the same?
Is it true that the faster a VFD is ramped during a start then the more current will be drawn by the motor. I have heard this and both seen this in the field. My question now is why?
I'm thinking that for a faster ramp, the faster the VFD changes frequency fast compared to how fast the motor...
I finally got a chance to go down to the VFD and take some meeasurements. Looking at the bus voltage when the drive was idle I saw about 687V DC. I had the operator then ramp the drive up to 60Hz and then give the drive a stop command. During this Decel period I did not see the drive DC...
I want to first start by apoligizing if it seems as if I was ignoring other recommendations regarding the use of a line reactor. I understood from the first responses that this reactor was not a solution to my problem, however I wanted to understand in depth the reasons why this was not the...
