LIQUID RESTISTANCE STARTER

[naglow]

H ow do you determine the type of salt solution to put in a liquid resistance starter (slip ring)
The motor in a 415v 230KW Rotor volts 559 rotor amp 275

 

[teco]

naglo:- please advise :- do you have a characteristic curve for the liquid resistor? what is the full volume of water in the tank? what starting torque is required,and what is the internal resistance of the rotor circiut.
would reccomend a sodium solution rather than salt.
kind regds.

 

[nbucska]

There is no such thing as sodium solution.
The Na is a metall, if you dissolve it
you create a compound e.g. salt.

Don't try to put sodium in water !!!!
Use sodium hydroxid. (caution, caustic)
<nbucska@pcperipherals.com>

 

[teco]

sorry my mistake:-should have read we reccomend sodium carbonate.
kind regds

 

[naglow]

The water volume of the tank is 25 litres.The motor is not matched to the starter both items were obtained independantly, the duty is extreme with the motor starting a large ring mill crusher and no figures are available on the inertia .The crusher is designed to crush 700 tons per hour at 230kw.The Supply Athority has requested that the motor only draw 1.5 times full load on start up.
Is it possable to measure tank liquid resitance when full and do a calculation to determine current draw.

 

[busbar]

Empirical trial may be the only means. Resistance checks of several concentrations of the salt might be scalable. The resistor likely has more than two electrodes.

Simply, the rate of change of fluid temperature versus acceleration time seems like the biggest unknown. Six gallons of a salt solution, 559A 3ø, time to acceleration of a ‘large ring mill crusher’ and resistor energy dissipation (a/k/a fluid state change) may not result in stable operation, making it infeasible. Sorry, but defining anything for “area under the curve” integration is out of my league. I’d take advantage of increased physical isolation during starting.

The span between 1.5x inrush and stalling could be narrow (or negative; ie, not possible.)

 

[teco]

naglowlease advise fax # and we will send you a typical liquid mix procedure along with typical liqid rheostat characteristic curve.
kind regds

 

[naglow]

fax number 61 63512099 for info on salt solution

 

[teco]

naglow :- we have tried to send fax but comes up wrong number . please check and advise ie country code.
kind regds

 

[nbucska]

Obviously you must start the crusher empty so 1.5 I must be
enough to accelerate.

The &quot;resistor&quot; looks like a large variable capacitor--
multiple stator and rotor plates.

You may have to provide cooling if you start often.

I think Na2Co3 will be converted to NaOH by electrolysis
anyway which will increase the conductivity.


<nbucska@pcperipherals.com>

 

[busbar]

nbucska, I don't doubt it's intended for the purpose, but 25 l seems a bit small for a 200kW+ 400V motor.

Is the resistor fluid in an open vessel? Can you turn a &quot;knob&quot; to adjust the &quot;capacitance&quot;/resistance?

Won’t the CO3 will reduce to OH, because of heat? Not sure about electrolysis with alternating current.

 

[nbucska]

Busbar:
25 l may be enough if you have time between starts to cool down. Even without cooling, you may loose some water but
one start won't boil away 25 l ! You mey have to add destilled water more often...

Open vessel, you may turn it. I have seen one when I was a kid...

Electrolysis with AC is slower and less effective . The bubbles which are large enough bubble out, the very small ones dissolve back ,when the current changes direction.


<nbucska@pcperipherals.com>

 

[busbar]

Thanks for the followup, nb. I try not to read postings with a &quot;been there...done that&quot; or well-frog view. There is a lot to be learned from how others do it. Because I haven't seem it, or found it in an ANSI standard doesn’t automatically make it wrong. My apologies for questioning a tried-and-true method.

 

[naglow]

fax number 610263512099 Australia

hope to have trial start of motor next week with no load.

 

[nbucska]

Hi Busbar:

Yes, it has a number of interdigitated stator and rotor electrodes.

The CO3 solution can heat up only to about 100 C --
it is not high enough to disintegrate it.

The NaOH adsorbs some CO2 but I suspect most of the
solution remains hydroxid.
<nbucska@pcperipherals.com>

 

[busbar]

Thank you for the follow up, nbucska. It makes sense that excessive energy release would have to accompanty a state change.

 

Naglow as you are in Australia can I suggest an expert who builds these for a living as a source of knowledge to help you out. He is Bill Mairs of NHP in the Melbourne Office. For a very helpful source on motors try Graham Hannah of TECO in their Sydney Office. These gentlemen do this for a living and from my experience are very helpful.

Cheers from QLD

 

[jbartos]

Suggestion: Check with the liquid resistor producers and marketers. Visit

http://www.mdresistor.com/mdus/resistancespointneutreus.htm

http://www.rabin.com/site/Auction.nsf/WebAnnounce/2E3FCA7E18BDB16788256B14000163A5?OpenDocument

http://cmcltd.uhome.net/

(specific data available)

http://rftechnologies.net/sys/standard.htm

http://rftechnologies.net/sys/load.jpg

etc. for more info