Plc control of WYE/Delta motor?

I am in the process of building a 150 hp hydraulic power unit to operate a hay press. This is a new installation into my business and I would like to set it up nice, but economically. I have many different issues to work through, but I have a few I really need advice on. The motor I am using is an ABB 150 hp wye start, delta run motor. I have the 3 contactors and do not want to spend the money for a 150hp soft start. It will be tied to 2 variable displacement, electronic pressure comp pumps, so I can start the motor under no load. My questions are as follows:

Is it a good idea to control the wye/delta start-up sequence with a plc?

Should I use the plc to control overload monitoring on my motor with a CT to analog?

Should I CT to analog all three phases or just 1?

I have a spare plc and a touchscreen and the need to monitor many different things. I just thought it would be nice to have a command center monitoring all of the electrical system and the start up and shut down.

Cooling Circuit
Cooling Fan
Pump Comps
Oil Temp
Oil Level
Pressures
Motor Temp

Any advice and product information would be appreciated.

Tim

Should I use the plc to control overload monitoring on my motor with a CT to analog?

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This part has me confused a little, DO NOT control the overload in the PLC. What you can do is monitor if an OL condition has happened (or may happen) and take appropriate action.

When I say "may happen" is monitoring for conditions that exceed what you want but prior to an overload being engaged. An example may be that your running load is 150 amps but for X amount of time you are running 175 amps, this may be an alarm condition.

The more phases you monitor the more precise you can be when monitoring for alarm conditions.

Most reduced voltage starters come with circuitry to control the sequencing of the transition to full voltage. I would suggest using that hardware to control the starter, with auxiliary contacts on the starters to indicate status to the PLC. Similarly, the starters should have overloads with auxilary contacts that will protect the motors from overload and indicate a fault to the PLC. When all is said and done, by the time you are done programming and testing it is probably just as economical and certainly more reliable to not try to replace this hardware with the PLC.

If you are just monitoring loading for informational purposes, monitoring current on one leg is probably sufficient. Taking all of the signals you indicate, plus those from the starter, back to a PLC for indication and alarming is a good idea.

The PLC will allow you to control the timing of the shift from wye to delta. Monitoring one phase is usually enough but you do need a UL rated thermal overload between the contactors and the motor and it must be 3 phase. I highly recommend you use interposing relays between the PLC output and the contactor coil windings.

You can get a simple or complex as you want with this setup. If you have the time to program and monitor the things you list and display them on a hmi, I say go for it. Especially if you are getting paid to do the programming.

You will need several analog input modules. Since you possibly will be using numerous pressure transducer's I recommend you settle on either 4-20ma signals or 0-10 vdc signals. Do all of them the same. It will simplify things a bit by not mixing the signal levels you are working with.

IF you need help with the programming etc I have the time and desire...no charges involved but tips are welcome.

Check with your power co. they may let you start your motor accross the line and the motor would rather start this way. As for plc control we do every thing with the plc anymore, if it`s monitoring it might as well control. We`ve tried it both ways. Even with our autotransformer starters we can set a bit in the plc and it becomes an accross the line starter until we fix the problem.
2 cents :site:

The big issue with DOL is not the utility company but having the power and circuitry to handle it. With a 150HP motor you would need a CB or fusing around 1200 amps, or more, the problem with this is that may not be appropriate to protect in a short circuit condition.

Another issue with this type current is cost. You have to realize in many situations power companies charge extra for "surge current.". If you have a large motor that is started several times a day then you may pay more for DOL than you would "slow" starting it.

Thanks for the quick responses. First of all, I am in a county where well irrigation is abundant and there are Hundreds of 100-150hp motors started DOL every day. I am also in a peak usage/surge charge electrical system. I still would like to start the motor wye/delta with the starters I have. This unit was origionally built in Germany, and the starters they used have no built in overload. They were using a seimens overload relay that I cant find much info about to control motor overload. When I bought this unit, the control was for a concrete pump and had about 40 relays and several other components in it and alot of people did their part to make the box a wiring nightmare. I basically gutted the box and now am rebuilding a new control system. I am trying to figure out the best way to design a motor overload circuit. There is also a thermistor in the motor that I know nothing about and would like to learn.

I already have a DL06 with analog cards and interposing relay module. I also have a 10" Touchscreen mounted in an empty box from another earlier project. I am a farmer and this is my new processing plant, so my time is basically worth nothing so that is not an issue. I will also be the maintainence tech, so I want to have a system that I can understand and be able to "trick out".

Thanks alot
Tim

I defineitely recommend a "conventional" overload relay for each starter, and code probably requires it. It may be an old style overload with heaters or a newer solid state overload with current sensors, but either way one should be used to protect the motor.

Thermistors in motor winding are usually PTC (Positive Temperature Coefficient) resistors that change resistance values suddenly and dramatically above a fixed threshold temperature. Generally special relays are used to monitor them. Klixon / TI makes them, but they have been bought out and I don't know the name of the successor company. A web search may uncover it.

Dold, Siemens and Klockner Moeller are just a few manufacturers that make PTC Relay Modules that will interface the ptc's in a motor to a plc's Digital Inputs.

PTC's are not a substitute for a proper overload relay though.

I know we are not supposed to try and advertise here but check out;

www.benshaw.com

I have used a bunch of their softstarts and recommend them very highly. You would be surprised at how inexpensive a 150HP softstart can be had.

allscott said:

I know we are not supposed to try and advertise here but check out;

www.benshaw.com

I have used a bunch of their softstarts and recommend them very highly. You would be surprised at how inexpensive a 150HP softstart can be had.

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Recommending a product you have used and think is good is i believe different to blatent advertising.... My Opinion

Well i have just finished a 75Hp Rootes Blower installation, used a Siemens 3RW Soft Start.........

I will rarely again be tempted to use Star/Delta (Wye Delta). It was just such a nice piece of kit, even had a tiny fan to blow air through the heatsink whilst starting and for a few seconds after switching to by-pass.

I am trying to figure out the best way to design a motor overload circuit.

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Here is link that will explain one type of overload. As you will see changing temp. makes a difference. This is one reason a newer solid state overload with current sensors might be better. You can get a stand alone overload section from ab ch or sq.d to use with your contactors. i believe when you figure the current for the heaters you will take the full load current * .57 and then depending on which overload type you use, use this answer in your next calculations. If you use fusetrons you can size them at 1.15 to 1.25 of full load current for easy to start motors and this will also protect your motor. In rewiring your wye delta starter you could add a second timer that proves the transition has been made from y to delta. As fast as this motor is going to start i doubt if it`s going to make any difference in your bill how you start it. Like allscot said don`t advertise, but i like DANFOSS!

Thomas Sullens said:

i believe when you figure the current for the heaters you will take the full load current * .57

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I always use 0.58 for the delta loop current for sizing overloads.

We've been using the following overload/motor protectors for the last 5 or 6 years. They are really great. We currently use them as stand alone, but they can be attached to a modbus network. They are relatively small and very functional. I recommend them to almost anyone that is looking for good motor protection at a decent price.

http://www.symcominc.com/catalog/motor_protection/777.html