375kw squirrel cage 415v motor starting issues

[Thomas_h]

Hey everyone thanks for reading.

We are having an issue with our cone crusher and starting. We have had engineers design the motor and starter know the full application and torque requirements of the cone crusher.

We are having intermittent starting issues. And have been for 2 years no one has been able to work out what is happening. We are using a soft starter and we change current limit settings. Does not matter if we increase it or then decrease it back to original settings it will then start. It will run and run and start then just not start. We change current limiting start up settings then it will start.

Bit of context on the site. A lot of electricians have been through and we have come to a common theory of it being a power quality issue. The whole site is run on diesel gensets and our power factor correction, due to lightning damage, is limited. We have our smallest filter and largest filter and we have a rectiformer that is always increasing and decreasing its draw and forever chasing the ideal power factor and at times crushing start up is an issue due to the sizes of our only 2 filters left that have to be manually controlled.

We get fitters to remove the guard and can spin freely and have removed belts and always starts up.

Can anyone shed some light on the effects of power quality with motor start up? The soft starter faults out on F4 - current limit start time expired.

 

[James]

Have you considered changing it to star - delta starting, it will not be affected much by power quality issues unlike the electronic soft start unit.

 

[Thomas_h]

Have you considered changing it to star - delta starting, it will not be affected much by power quality issues unlike the electronic

No we haven’t. The design has come the electrical and mechanical engineers who are contractors.

I don’t know a lot about star delta starting but I don’t think we’d have the torque requirements for starting it.

I have been on this site for 6 months and always having call outs to this particular motor and now all I did is slightly adjust the current limit on startup and it will then work. Operators think I’m a genius. Next time it won’t start I’ll adjust it back to what the engineer has specified and it works..

 

[James]

start-up torque should be about 1/3 of the rated motor torque in delta.

 

[Darkwood]

Have you talked to the gen' suppliers, certain equipment can massively reduce the gen's full load capability, I look after a stone yard and we lose 30%-40% of the generators plated FLC due to large VSD's been on the system, you say its a soft start but functionally the do start a motor up in a similar fashion so could be putting limitations on the generator.

 

[Thomas_h]

Have you talked to the gen' suppliers, certain equipment can massively reduce the gen's full load capability, I look after a stone yard and we lose 30%-40% of the generators plated FLC due to large VSD's been on the system, you say its a soft start but functionally the do start a motor up in a similar fashion so could be putting limitations on the generator.

Yeah when we start up the cone crusher the power factor can drop from .9 to .5. I’ve seen it drop down to .4 during start up. We have more than enough spinning reserve to supply the start up load but the power factor drops so much you can see the lights dim/flicker shortly.

reactive power would increase so much which would then decrease the FLC of the generators. We have about 1.5Mw spinning reserve. It has knocked the site out before but usually when our PF is low for start up.

It makes us all think about the effect of reactive power of the motor on startup when the PF can drop so low.

we can’t get instantaneous readings during startup with the system we have there is a bit of a delay. We are thinking of installing a data logger on the cone crusher so we can see it when it doesn’t startup verse when it starts and go from there.