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  1. Thanks Marke, i had heard about the pitfalls of pigtails, but wanted to confirm from an expert. Your alternative suggestions are excellent. Cheers.
  2. We use 3 pole isolators between VSd and motor. If we put a screened cable, then is it Ok to pigtail the screen and join at isolators,or it is better to use a straight uninterrupted run of cable to the motor. cheers.
  3. Hi Marke, Just a quick check..does the incomer cable to the VSD also needs to be screened type..? And will Isolation transformer help in reducing the noise..? Cheers.
  4. Thanks Marke for your usual prompt and precise answer. Cheers and have a nice day.
  5. We have 4 ABB make ACS 550 series drives (30kw) in a dairy facility. There are few computers on the same location which constantly have harddisk failures...we measured the common mode noise and found 5 volts.(output of UPS) The online (APC make) UPS does filter some of the noise but still some noise is seen at its output. I propose, 1.Replacing the existing unarmoured cable (VSD to motor) into armoured cable and the armour grounded at both sides. 2. Putting isolation transformer at the output of the UPS. 3. Putting line chokes for the VSD. Are there any other known culprits which cause common mode noise... ( I have used Fluke 435 and found THDVN going as high 233% range 50-233%) Are there any other things which can be done to protect the computers. Any ideas appreciated.
  6. Are you already using them...are you facing any problems?.....like voltage dip when they start etc? if yes ..then go for soft-starters... cheers
  7. Hello Osama, My first line of action will be to check the CT. you can cross check the CT by checking the secondary current of CT with clampmeter and then multipliying with the ratio for example....if you read 4 amps on the secondary of CT and your CT ratio is 1000/5 then your primary currnt is 4 X 1000/5= 800 amps. Cheers
  8. See the difference in the turn ratio of a CT and a normal distribution transformer.....moreover the impedance comes into play ..the secondary of a current transformer when disconnected from its load while current is flowing in the primary will mean transformer secondary to continue driving current across the effectively infinite impedance This will produce a very high voltage across the open secondary (into the range of several kilovolts in some cases). Cheers.
  9. It should not cause problems...but wait till some other members chime in...with their views.. But what is the duty cycle? should not be started/stopped more than 3 times per hour.
  10. Hi !! I have attached a sketch for grounding setup for parralleling 3 LV generators with stepup transformers. Can anybody comment on pros and cons of this arrengement of earthing, and any suggestions/comments about choice of transformers are appreciated. Cheers. Gensetup.doc
  11. This VFD is used for driving the winder/unwinder ? Which part of the machine is it driving? Is there any analog feedback coming from the machine to VFD.? If you have some sort of arrangement to have the feedback (speed) given to VFD then you don't have to change PI values everytime.
  12. Incomplete info Jony ..220 kw at what voltage? Are you using a conventional Y-D starter or a softstarter.. See the nameplate FLA and multiply it by 5 Cheers.
  13. I am trying to understand your question..are you saying that by mistake, the ref signals shorted with a live line? In that case VSD will have problems in the control card. However if it is tripping, the incoming breaker then it is a serious problem. Personally, i avoid using contactors in input/output side of VSD. Try opening the drive cover and see for some arcings or blackspots. Power supply card or some thyristors might be grounded. Cheers...and do not let problems spoil the spirit...
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