Well what is my best choice ??

ANOTHER STUDENT QUESTION

I think the next two steps in my PLC education are
1. to control a motor using a VFD and PLC.
2. Learn more about AND how to do PID

I DO NOT want to just make a motor run, I want to connect it to a variable load and control for load variation.

QUESTION What is my best learning opportunity and is most applicable to the real world you work in?? In other words what should I do to to make me most employable??

The two quickest choices at the school lab are
1. They have AC motor / generator coupled to DC motor / generator and with a brake unit. This is a lab unit so all internal leads are brought out. The AC unit can be run as motor (synchronous would rotor or strait induction) or generator. DC unit is compound wound.
2. Hydraulic system (simple mostly hooked up). Would need to connect a throttle valve to simulate a load or connect a load. They have motors on hand so those may be an option.

Have AB micorlogix, 5 02 and O4 and RS logix 500 software.
VFD are Toshiba

PLUSES and MINUSES
Instructor is better at electrical than hydraulics.
Probably have just about anything to do with electrical. They have complete switchboard setup for operating generators (AC and DC) loadbanks etc etc.

I could set this up and control AC drive motor (synchronous) and overexcite for PF correction -- I never had luxury of a PF meter on submarine electric plant. Supposedly we did it but I never saw the results (on PF meter). This would be for my own curiosity. Motor speed would vary with DC load (variable resistors). PLC via VFD would control motor speed, PF, AC excitation, DC excitation.
DRAWBACKS
1. Very limited real world application. Most industry does not worry about PF they let utility correct at switchyard and pay the PF penalty. In many cases this is a good decision. They do not have generation except standby package units.
2. I already know much of MG set operation we had quite a few on submarine - other than the VFD portion that is and how to program the PLC to make all this work.
3. May be difficult to setup current control on PLC and or VFD. Exitation or field current would be on order of 5 to 10 amps. (this part would be learning experience)

ADVANTAGE
Easier to setup. Have switchboard with all meters.

HYDRAULICS Pros Cons
DRAWBACKS
1. Mainly setup -- I would have to get a pressure transmitter. Probably should get it in a 4 to 20 mA version to learn more about this control method -- familar with 50 or 100 mV methods etc etc.
Would have to get a throttle valve and pipe that in OR connect hydraulic motor(s) or maybe a piston or two.
ADVANTAGE
More applicable to real world.
Hydraulic tank pump relief valve bypass valve already setup.
Load (demand) would be measured by discharge pressure of pump and controlled by speeding or slowing motor.

The PID will come in after I get the PLC and VFD to control the motor with varying load. THEN I will learn how to use PID to more accurately control the motor.

Other thoughts feedback etc etc??

Thanks
Dan Bentler

PID is used for a lot of things, and I'm not sure how your test bench translates to real world functions.

For real world, I have used PID for the following applications:
VSD, controlling a blower, To control pressure.
VSD, controlling a blower, to control air flow.
Control valve controlling water flow.
Speed and position control for a servo drive.
Tank level control, although this was a long time ago and I cannot remember if this was for a pump or valve.
One thing I have noted, is that I have never used the "D" part of the controller.

The process industry is built on PID control, and use it for controlling flows, pressures, temperatures and levels. Any or all of these would be good. (but you have already shown this in not available to you.

The motor generator set could also work, you could set it up as a speed controller and vary the load. You could then test and see what happens when you have too little (and too much) P, I and D.

In my experience, I find that people generally like to use too much I and way too much D.

Doug

In my experience, I find that people generally like to use too much I and way too much D.

Click to expand...

In my experience, when things are not working as desired, most people tend to use too much of everything!

Dan,

Where did you get this idea?

1. Very limited real world application. Most industry does not worry about PF they let utility correct at switchyard and pay the PF penalty. In many cases this is a good decision. They do not have generation except standby package units.

Click to expand...

In my experience, just about all industrial plants of any size worry tremendously about the dreaded low (lagging) Power Factor (PF), because it adds significantly to power costs and reduces profits. I have spent a lot of time at different plants figuring out how many capacitors are needed to bring the power factor up high enough to avoid penalty charges. Generators are not necessarily needed to improve the power factor, although some larger plants do use other methods in addition to capacitor banks, such as large synchronous motors (compressors, large blowers) running with a field-controlled leading power factor to offset the lagging power factor of the other non-synchronous induction motors. Do not write off power factor control just yet--you might find a better mouse trap.

Lancie

I served on the Seattle Light Citizen Rate Advisory Committee. One of the issues we studied was Power Factor. City Light presented data showing only very largest industries did anything about power factor. The rest ("medium" and small) did nothing. The conclusion we drew was PF correction had to be done of course, most cost effective was for smaller industry to let City Light do it at substation. By very large I mean the steel mill with electric arc furnace (3 phase 440 volt and 50 K amps)or Boeing wind tunnel 13,000 HP motor. I was fortunate to do the study assisted by an independent engineer who had installed PF correction at the wind tunnel and at the steel mill.

I briefly looked into using synch motors for PF correction - ws told it is not cost effective until get up to 250 HP (if memory is right). Now if that is NOT the case there are lots and lots of 50 and 100 HP motors out there that COULD be used for PF correction. The trick of course is to start the darn thing then there is the added cost of regulating the field and rotor sliprings etc etc. For now this idea is being stored in the pipe dream locker in my brain can take it out and play with it.

Thank you very much for making me defend my statement.

I made my decision and am going with the hydraulic setup. The nice thing about this is it all lab gear so it is setup for quick setup and teardown - don't have to have a bucket of pipe fittings. Also it is "low" pressure (up to 600). Have 1.5 HP 3 ph 208 motor drivng hydrualic pump. Load will be a hydraulic motor. The motor is part of a lab setup so it has a gear train with a DC tach gen and some kind of position sensing switch (need to learn about that it is about 1/2" dia and 3/4 inch long with 3 wires). VFD is Toshiba L100. Hooked it up and did test familiarity run. Interestingly peak motor amps (displayed on Toshiba display) was at approx 30 HZ -- we theorize this is caused by the relief valve coming off seat (max spring pressure). Speed (hydraulic motor) to that of pump had good correlation ie double speed of pump (15 to 30 Hz) doubled speed of hydraulic motor.

SO THE PLAN
plan is to control hydraulic motor speed with speed of electric motor. Maybe later on I will add a cylinder to make the situation a little tougher (more real world) to deal with.

Dan Bentler

PF correction

Lancie

Just took the PF correction pipe dream off the shelf and played with ti. One of the reported problems was how to match PF correction (ie capacitor bank) to existing condition. many smaller industries do not have people qualified to to deal with this. Boeing (at old wind tunnel) leaves PF correction caps on line -- they are afraid of wearnig out the circuit breaker (vintage WW II) -- drives City light nuts because they have to readjust swithchyard when Boeing turns on/off the wind tunnel. PLC would be able to do this nicely. Main trick is to get the sensors and the controls.

Oneof my big faults is I care the least about large industry. I am more interested in the little guys.

Dan

Dan,
The company I worked for in Texas,have been making PF correction units for years. and still do for the little companys.They make both fixed and automatic PF correction. It is a big busness for them although it started yrs. ago as a side line for them.
Regards,
Tom


http://www.capacitorconvertors.com/autocap.html

I figured someone would have a product meeting the need. One of the things I DID NOT mention is that City Light (like many / most) utilities have a PF penalty -- they do not have a PF reward. So in many cases there is no benefit driver for small industry to install correction.

To quote my brother "When the power company makes it worth my while to change then I will do so. If they wont pay me to help reduce their peak load I wont bother. Until then I will use all the power I want whenever I want.

Kind of shortsighted from the big picture overall system perspective but he does have a point.

Dan

I know what he means,In Mobile,Al. I was working at a plant that had 7.5 Mw of induction heat.needless to say the harmonics were something to worry about.All the power company said was "if you do'nt do something about it we will have to charge acordingly" dos'nt leave you much choise.

Regards,
Tom

I helped out as a consultant on a retrofit of old equipment into a new gas scrubbing plant (called an Amine plant) around the year 2000 (gas was about 88 cents per gallon in Texas around that time).

Anyway, they had two 1200 Hp 600V VFD's going into place (I think they were Alstom drives), and the power company came out with a ton of capacitors to hang off the line for PF correction. I told them we already had about 1200 KVAR of caps in the filters, and I didn't think they should install so many for pf correction.

Of course, they had their work order, and put them in anyway.

And they didn't even acknowledge I was right when they came back two days later to take them out again.

The company I work for makes PFC's, with harmonic reduction thrown in for free. You need to do a quick line quality check and then the rest is easy. I wrote a paper on their design about 20 years ago (more or less), and probably still have a copy somewhere.

Don,

You might have someone contact the link below,they might be interested in buying from you. As they build PF correction and filters for sell to the public. The last time I checked they were using small caps.
Regards,
Tom

http://www.capacitorconvertors.com/

We have 3, 4800 hp sync and 1, 1250 hp sync motor and for 35 years were producing overall leading power factor at no benefit to ourselves. (Our incoming metering wouldn't measure past unity)
We recently installed new static exciters that monitor PF and found we were needlessly overexciting. I think the utility (Ontario Hydro)owes us for compensating for all those laggers for the last 35 years!

So PF monitoring has real-world significance,

Brian.

I am at the moment installing a 400KVAR cap bank for a plant. The load they draw is about 1500amps at 600volt.. They pay on average about $6-9,000 a month. Payback is 1 year. The unit is self regulating..only bring in caps when required. Engineer sizes the units adds in the features for Harmonics we install.. Plant forgets its there, we re torque once a year.. I dint think you need qualified engineers on staff to run these??
Another case.. A hotel downtown..also uses cap correction again fit it and forget it(For at least 10 years) after that time you have made enough money to toss out the old and bring in the new...

Maybe the states is different but up here cap banks are a common thing..

leitmotif,

For the purposes of furthering your education, how about a project to set up the AC motor you mentioned, with the Power Factor meter measuring its power factor. Now get some motor starters and some small capacitors (you probably have some in the school lab & shop) and build yourself an automatic variable power factor controller. Measure the PF, and use a PLC to bring the capacitors on line as needed. You could also control the speed and loading of the motor to vary the power factor.

Pf

SLIVER
If I recall correct Seattle City Light has a "jam" in their meter so it will not record lead PF. Not only do they not measure it but they do not pay for it. We never got that far but one of my recommendations was for them to pay for leading PF. I think that is not only stupid but unfair but what do I know I am just a citizen ratepayer. They claim they can do it cheaper in the switchyard / substation. I think you should send them a bill.

LANCIE 1. Right now will concentrate on the hydraulic setup - it has more applicability to industry and in theory should make me more marketable. After that the PF project may be a possibility.

The power factory project would be good education I agree. Like I said it is in the pipe dream locker. Am thinking on it. Equipment wise the school has it all AC DC switchboards with all meters, paralleling capability, load banks (resist, induct, capacitive etc).
LET US KEEP KICKING PF AROUND who knows maybe we will think of something all the manufacturers of PF correction gear have not thought of.

Dan Bentler