Any motors with no manual start and stop?

Einstein_86 · Oct 27, 2011

I have to write a PLC program for a whole water treatment plant (it's a practical project) but I dont have detailed data about each motor so I am making reasonable assumptions. I just need to ask about certain points :

1-Is it a must that i make a manual start and stop for each motor ? (I am thinking of making them fully automated i.e. operate when a level switch signals and stop when another level switch signals , hence there wont be any manual buttons or switchs, but is this practical ?? I mean in real there are motors with no manual buttons or i will have to use them ??

2- I have assumed that all motors are DOL started, they are of ratings 2.5kW, 3.4 kW, 4.5kW and 5.5 kW. Is that okay or i will have to use delta star or soft starter ? I think the ratings are low enough for DOL except that of 5.5kW, actually i am confused about it and i think it may need a current reducing starting method.

I hope you help me with what you think is practical for my above points, as I did not work with factories before and still miss this practical part.

Clay B. · Oct 27, 2011

1) Having a manual control is something the maintenance guys would realy like to have. THis way when they change a motor they can manually start it to check rotation.

2) Starting method depends on load. If you load has a high inertia then yes a softstart may be required. The relation between the motor and the load decides what is required. This is something you should be provided by whoever sized the motors.

James Mcquade · Oct 27, 2011

As i see it, you need the following information:

1. electrical schematics - that gives you the motor sizes(if done properly) and wiring method.

2. piping schematics with valves shown.
3. scope of work detailing how the plant is to operate.

other wise, you are going to make assumptions (as always, your wrong) and will end up not having the correct i/o, analog sensors, wrong sequence of events, and the list goes on and on.

i am all the time being yelled at for wanting lots of details.
its a pain for those wanting to do the job, but its the little details that make a big difference. Most of the time, they see why i ask so many questions when the project is complete and the machine is running.

regards,
james

leitmotif · Oct 28, 2011

Einstein_86 said:
I have to write a PLC program for a whole water treatment plant (it's a practical project) but I dont have detailed data about each motor so I am making reasonable assumptions. I just need to ask about certain points :

1-Is it a must that i make a manual start and stop for each motor ? (I am thinking of making them fully automated i.e. operate when a level switch signals and stop when another level switch signals , hence there wont be any manual buttons or switchs, but is this practical ?? I mean in real there are motors with no manual buttons or i will have to use them ??

2- I have assumed that all motors are DOL started, they are of ratings 2.5kW, 3.4 kW, 4.5kW and 5.5 kW. Is that okay or i will have to use delta star or soft starter ? I think the ratings are low enough for DOL except that of 5.5kW, actually i am confused about it and i think it may need a current reducing starting method.

I hope you help me with what you think is practical for my above points, as I did not work with factories before and still miss this practical part.

YES in USA there is supposed to be a disconnecting means within sight of the motor OR it must be lockable in OFF.
NO you do not have to use local start stop switches.
HOwever I would put in local control on off to allow for ease of maintenance AND for when float switch sticks so you can turn the pump off to avoid burning it out.

You COULD do wye delta starting but seems kind of expensive for these small motors. I would consider using VFD and control pump speed - assuming centrifugals and IF you can do it - to reduce starting current and reduce power consumption from slower pump speed. CHECK the pump curve to ensure you are not running it too slow and end up burning out the seals.

Otherwise DOL is a good way to go if you NEVER need variable flow.

Dan Bentler

Karsten · Oct 28, 2011

Seriously, stop asuming things.

Is there no specification for the plant?

You can at least make it possible to run the motors manually from the HMI.

Einstein_86 · Oct 28, 2011

Re

Thanks a lot for your help it added to me, but actually this project is like a test for me to test my abilities for handling such projects (PLC coding, wiring diagrams and control panel design) so I do not have details or any sheets, just I have the AUTOCAD drawing of the plant and i was told what steps does this plant follow but of course not with the very specific details that any engineer requires, that's why i am making assumptions, but i am willing to make them as close as possible to the real application, as my work will be compared to the actual project design and results.

The most silly part which makes me suffer - so far- is the PLC cases, i keep thinking what if... what if... and all are assumptions i made with my own mind, it really makes it hard !

Thank you all again and i wish i can get more advices from you

Karsten · Oct 28, 2011

If it's only for fun and no one has to pay for it then go ahead with manual start and stop since it gives you more of a challange and no one will have anything against it.

In the real world of course somone needs to pay for it.

Oceansoul · Oct 28, 2011

I work at a WTW. We have like 30 PLC's.......each with hundreds of lines of code. Good Luck =]

Tom Jenkins · Oct 28, 2011

You should alwasy keep in mind the difference between what is required by code or law and what is good practice.

In your example, there isn't any specific code requiring manual pushbuttons. However, good practice dictates that a Emergency Stop pushbutton be provided and that a Hand-Off-Auto or similar control be provided for testing and emergency operation. PLCs and SCADA sstems fail, just like everything else made by the hand of man!

Electric utilities often have requirements for reduced voltage starting for motors above a certain size, often around 40 hp or 50 hp on 480/3/60 power. Good practice also dictates this. Your largest motor is 7.5 hp, so I would say reduced voltage is an unnecessary expense.

Note that these comments are based on US practice - your local codes and norms may be different. See if you can find a local mentor to help you with that.

Any motors with no manual start and stop?

Einstein_86

Member

Clay B.

Lifetime Supporting Member

James Mcquade

Member

leitmotif

Member

Karsten

Member

Einstein_86

Member

Karsten

Member

Oceansoul

Member

Tom Jenkins

Lifetime Supporting Member

Similar Topics