Conveyor System Control

[Wooly]

Hi all,

Not sure if anybody can help, or even if I'm in the right place.

A bit of background info first, I've been working as a maintenance electrician for 10years now, and have just been asked by a friend to help with a new installation. Having not really designed anything from scratch before, I was wondering if I could get any advice.

The system consists of 1x30kW motor, 1x15kW motor and 1x3kW magnet. Both motors to be inverter driven, with the magnet DOL. I was curious as to whether I would need a main contactor directly after the isolator, as well as one after each inverter, and one for the magnet control. I have many ideas, but am not really sure how viable they are.

Thanks in advance for any feedback.

Wooly

 

[ashrow]

wooly

after 10 years you should know how things work and how the stages of set up are
Good luck

 

[Wooly]

Thanks for the reply, but I'm just a bit unsure on the design side. Just wondered if anyone could give me any pointers. If you'd rather not, then thanks anyway.

 

[grantr37]

what's the system for? that's quite the magnet you got there

 

[Wooly]

Filtering recyclable waste. Thats just the info I've been given. Have you any advice? Was going to have main isolator, split out to 3 seperate breakers, then to the inverters, then through contactors. Was going to have 24Vdc control circuit, using a Pilz relay for estop control of the contactors, and drive enable signals? Sound along the right lines?

 

[grantr37]

thought that it would be for grabbing cans from recycling or something like that.... make sure that your emergency stop set up is good, a good number of Emergency stop buttons and put overload breakers at each motor incase one gets jammed by rubbish to stop it blowing the drive inverter or its windings...

- - - Updated - - -

just to add that all 3 motors should be stopped by 1 of them overloading/jamming

 

[Wooly]

Thanks for that advice.

So, would that be putting the overloads in series with the estop circuit?

One other thing would be whether the estop should drop the signal to drive enable, and the contactor coils simultaneously, or if I would need some kind of delay.

 

[Knobhead]

You do not go from the inverter through a contactor. You’ll damage the inverter!

Draw out what you propose (electrical and product flow) and lets have a look at it.

 

[stef]

Thanks for that advice.

So, would that be putting the overloads in series with the estop circuit?

no, emergency stop chain has to be separate. Link the overloads into the control start/stop circuit.

One other thing would be whether the estop should drop the signal to drive enable, and the contactor coils simultaneously, or if I would need some kind of delay.

No, estop has to stop straight away. For this purpose you will need a contactor before the inverter, not after. This would, as Tony said, wreck the inverter. Needless to say that you need to have a two channel safety relay in the emergency stop chain.

an auxilliary contact of the safety relay provides the enable signal.

 

[Knobhead]

E-Stops are a bit of a nightmare with inverter drives.
I redesigned a centrifuge control system. It had always been a standing joke that if the E-Stop was pressed it would take the best part of five minutes to stop. I altered the system so the E-Stop didn't kill the power to the centrifuge but put it in to maximum ramp down. I brought it to a halt in 10 seconds. Even saved on the lecky bill, on ramp down the regenerative braking pumped 200KW back in to the mains.

Don't know about the legal side of it (that's NBP's field), but it was a bloody site safer that the official method!

 

[Wooly]

Thanks for all the feedback guys.

I meant to say contactors first, don't know why I said after.

I was going to have a seperate 24Vdc power supply to control the start/stop and control circuits, putting the inverter 24V control through relays for the drive enable and FWD commands.

The PILZ unit will be dual channel, and will drop off control voltage, and coil voltage to all contactors. I was thinking of having the drive enable signal going through an auxilliary contact on the preceding contactor, so when the contactor drops out, so will the drive enable. The FWD command would then be operated through a relay in the stop/start circuit.

Does this sound ok?

 

[paulr57]

Operate the magnet with a DOL starter, adequate overload protection and E.stop cct.

Feed each inverter with adequate overcurrent protection - see manual.

Feed each motor DIRECTLY from each inverter. Do not use contactors, or BANG!

The safety relay controls the inverter drive voltages and magnet E.stop cct.

That's it.

You MUST learn all about the inverters, current/torque ramps, acceleration/deceleration, etc and DC injection to brake freewheeling motors.

At these power levels MAKE SURE you know what you're doing.

Good luck!

 

[paulr57]

Yes, I've come across this problem many times in the manufacturing industry.

Most common way round this is a DC operated clutch type brake which stops the motor
freewheeling. Alternatively, some inverters inject a DC voltage into the motor to act
as a brake.

 

[Wooly]

So, would you have a DOL starter and not have another contactor with stop/start control on the main panel door?

Having to make the panel as well, I was going to have: estop reset, control on/off, and three sets of Start/stop buttons on the main door, all with indicator lights.

One other thing, would it really be wise to estop the magnet, as it may be potentially more dangerous to turn off than leave on?

Also, given the conveyor sizes and weight of material on these, I would imagine that there will be little, if no run on, so would some sort of braking really be necessary?

This whole thing is giving me a headache!

 

[Robotstar5]

You could fit positive guided safety contactors and monitor the N/C of each through the reset line on the safety relay.