Search results for query: *

Thanks scottf!! This is what I want to hear:) I have heard before that burden is related to the saturating point. I dont know what the burden is but its a differential input to an electronic relay (siemens 7SJ). Electronic relays have low burdens in general? 3-5VA? I know that modern day...

We are to comission a system with 1200/1 10p10 CTs. The fault level is 18kA at 11kV. At what point will the CTs saturate? They are connected to Siemens 7SJ protection relays. Kevin Bosch Rainbow Technologies

Its a Sepam M87 relay (it has current to voltage plug in transducers at the CT input) Kevin Bosch Rainbow Technologies

I need to spec differential CTs for a 3400kW Induction motor. I wish to use 3CTs instead of 6 (by running the phase and neutral through one CT. The FLC is 204A. The CT supplier is asking for a detailed spec before they make the CTs to order. They need knee point voltage as well as volts per...

I Love the Engineering Fraternity. We do detailed analysis on the suspicion as to what accronym SA is... Kevin Bosch Rainbow Technologies

Both from China - probably both Parafinic - but you have to do the tests. And dont forget the breakdown test, crackle test, dissolved gasses etc whilst you are about it. Dont want to do the job twice. Kevin Bosch Rainbow Technologies

My instinct would say that the Chinese trafo is using a parafinic (single chain molecule oil). The naphthenic (branch chain) is more expensive. Its not good practice to mix oils. I made that mistake before on a 40MVA Crompton Greaves Trafo. I was thinking (its English - must be Naphthenic). They...

Im thinking that Im connected to the wrong tap and am actually BOOSTING the voltage to the motor. The guys on site never did a ratio test... 15min extra on commissioning could of saved so much time, not to mention caning the windings of that poor machine... :/ Kevin Bosch Rainbow Technologies

TYPO!!! Its 5MVAr of caps for the start. We have used this method with great success. We boost the voltage by about 1000V to help her start, ie offset the motors volt drop. Kevin Bosch Rainbow Technologies

Is the star point of an HV induction motor always earthed? Where is the star point normally brought out to earth? It is here that I need to mount a neutral CT for a motor differential protection scheme. The three line CTs need to be mounted as close as possible to the motor terminations to the...

We have had issues starting a 3.6MW Squirrel Cage motor with an 85% auto transformer tap. The inrush current is higher than the DOL inrush! We measured the inrush as 1050A with a 15% volt drop. The DOL inrush should be around 850A with a lower volt drop. The manual shows a 1140A inrush for DOL...

Fuses are Bussman made in UK and guaranteed to be each individually xrayed before shipping... Kevin Bosch Rainbow Technologies

To all, thank you for valuable posts. What is happening here is as follows: Striker pin operation on one or two fuses. Fuses replaced (not all) and then on start up ... BANG!!! HUGE damage. This has been happening since 2006 about once every 6months, and now more frequently :(( About 18fuses...

We have recently been rupturing 3.3kV fuses (not just striker pin but full flash over with shattered fuses and partially vapourised busbar spouts!!) This happens when two 375kW DOL motors start (off the same 3.3kV fused contactor) for a conveyor at a coal depo. This has happened intermittently...

Thanks for the input gents. Pity my output is fried. Would a ramp down help the situation? We are getting new parts airfreighted and we would hate to fry them (and our jobs!!) My understanding was that it could be the rapidly collapsing field on a coasted stop, or the "generating" action when...

Skogsgurra There is no check valve :/ Its a vacon drive (PWM) with teco motor (standard induction motor - 4pole) The drive stop has been set to coasting stop - not ramped. Kevin Bosch Rainbow Technologies

We have the output damaged on a VSD driving a 1200kW cyclone pump on a mine. After three weeks of operation the drive did not restart after it was switched off. The power unit on the white phase had burn marks on and the fuses driving the power unit from the dc bus were open. Can this of been...

Kiribanda: We have blown arrestors when closing the fuses in. Usually we get an almighty bang when the second fuse goes in!! jghrist: The line is overhead (2km) with a couple of road crossings (cables). Both the transformers being energised when the fuses go in are delta primary and are...

We have recently energised a section of Almond (35mm2) powerline at 33kV via single phase fuses. The feeder powerline was live when we energised. We have blown 5 surge arrestors over three days. They split open and caused all three fuses to open at the feed end (125A fuses). We were told that...

Hi Stefan, This topic has bothered me for some time. Why not use a common neutral bar and run it with isolation from the hull. This would prevent hull heating and welds etc. Atleast then personell who make contact with a motor that has an earth fault will NOT be shocked. The literature...