3 Phase Motor Overload Problem?

[gerard]

The conveyor jams because of the nature of the product. It's just high volume food belting down the line and unless someone just stands there and polices the line all day, jam-ups will happen. I will be able to install the Inverter myself, I was just trying to see what you guys would do in a similar situation.

 

[ericks]

Hi Darkwood,
You might have misunderstood me.
We use MCB's and motor overload / protection devices.
Not just a MCB to protect the motor. The whole design is carefully done to match the motor to the mech. drive unit. We always!!! use motor overload devices whether it be thermal / electronic overloads. Depending on the application we would consider whether to use thermal / electronic or even vsd's.
We tend not to overdesign as cost is important. What i tried to say is that you should start with the MCB sizing as this gives a "degree" of protection. If your application is wrong, where your motor might be too powerfull for the application you should solve this first. We start and protect 0.55Kw to 2500Kw motors in our plant. I presumed having a overload device in the starter came without saying!!

Working in a plant with about 2000 motors we regulary have either conveyors and or pumps jamming. Where there are thermal overloads fitted we never have damage as the MCB always trips. I agree the MCB alone is def not an ideal motor protection device. When you have a steady overcurrent over a long period of time the MCB won't trip, that is the job of the overload device.

Thanks

 

[Quadrant]

Hi Guys,I am getting the same reply to a thread(3ph Overload problem) twice a week with no new content.Does any one know what im doing wrong?
Roy
Quadrant

 

[Darkwood]

Hi Darkwood,
You might have misunderstood me.
We use MCB's and motor overload / protection devices.
Not just a MCB to protect the motor. The whole design is carefully done to match the motor to the mech. drive unit. We always!!! use motor overload devices whether it be thermal / electronic overloads. Depending on the application we would consider whether to use thermal / electronic or even vsd's.
We tend not to overdesign as cost is important. What i tried to say is that you should start with the MCB sizing as this gives a "degree" of protection. If your application is wrong, where your motor might be too powerfull for the application you should solve this first. We start and protect 0.55Kw to 2500Kw motors in our plant. I presumed having a overload device in the starter came without saying!!

Working in a plant with about 2000 motors we regulary have either conveyors and or pumps jamming. Where there are thermal overloads fitted we never have damage as the MCB always trips. I agree the MCB alone is def not an ideal motor protection device. When you have a steady overcurrent over a long period of time the MCB won't trip, that is the job of the overload device.

Thanks

Was just a short post you put and it gave the wrong impression but your obviously putting all this into the design, sorry for the mix up but not everyone is fluent in motor control and protection but obviously you are.

 

[TF and the wire]

I think you are correct to go for an invertor.

Overloads are supposed to be coarse enough to avoid tripping on start up and short heavy loads.

I had one on a conveyor recently that was tripping after about 30 seconds. It was set at 4 amps, as the motor plate stated but was actually taking 15amps. The cause was that it had been wired in delta instead of star. So it was taking that long with almost 400% overload.

I usually use Allen Bradley powerflex 4 invertors. Dead easy to get hold of, wire up and program. You can select the current to be displayed so you can watch what it takes on normal loading. You can then set the overload trip current accordingly.

 

[gerard]

Cheers,

Just wondering, the motor has a gear box so it is running at a low speed with high torque. So there is quite a lot of power going through it. Will the Inverter do its job - i.e. cut out the motor when a fault current is detected?