Overspeed limit protection for VSD pumps

[Sawsan311]

Dear All,

Appreciate advising if it the inherent design of VSD pumps can avail the trip of the pump at a specific overspeed limit and whether the speed set point at which pump must trip can be tuned/adjusted during design/implementation stage?

Thanks

Regards,

 

[LittleInch]

The speed is set by the VFD drive. This varies between set limits and is adjusted either manually or via a control input from the control system. "Overspeed" doesn't exist.

Your question doesn't make sense.

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Also: If you get a response it's polite to respond to it.

 

[TiCl4]

I'm not sure I understand the question. VFDs can be used to increase frequency to the motor beyond the standard 60/50 Hz. Disagreeing with LI here: Increasing the output frequency to the motor above the nameplate is often called over-speeding. The limit is dictated by the various components of the pump (motor, pump type, gearbox limit, etc). The VFD is typically set so that the 0-100% of the drive corresponds to a certain frequency range. So, if setting up for 150% overspeed for a 60 Hz motor, the 0-100% would be set to 0-90 Hz.

Given this is all set in the VFD when commissioning, I don't know how you could get into an over-speed situation accidentally. Why would you need an over-speed trip?

 

[LittleInch]

Noted. But the question implies that something other than the motor is causing the pump to go faster which isn't possible. Maybe.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Sawsan311]

Dear All, thanks for your replies,

I was mainly referring to whether there is a scenario for overspeed beyond the specified range on the pump curve. Considering it feeds the motor with a variable frequency. As <r. TiCl4 explained, frequency may exceed the range corresponding to maximum pump speed. So does pump vendor consider any protection against the failure of the variable frequency drive before the system enters into an unstable state outside its design envelope (with respect to head and low).

Or would the consequence of such failure be reflected in the pump's vibration monitoring system?

Thanks

regards,

 

[LittleInch]

You're in danger of overthinking this...

The pump doesn't feed the motor with anything.

If the pump has a maximum speed then you enter that as max speed / frequency into the VFD.

I'm not aware of a VFD failure by where it suddenly decided to increase the speed or frequency beyond the maximum it has been programmed to do.

The vibration, bearing temp and other pump process parameters ( pressure, temperature, flow) can all alarm and trip the pump if they exceed the required limits.

what more do you need?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TiCl4]

Sawsan311,

LI was correct in saying that you are making this more convoluted than necessary.

Firstly, if you think a VFD failure could lead to an overspeed condition, you could not then rely on that same VFD to reliably provide overspeed protection.

Secondly, I know of no failure mechanism that could lead to a VFD allowing greater than 100% output. The failure would need to be in the initial programming (or reprogramming after a power surge necessitated re-entry of key parameters). In such a case, the VFD would not have any role in stopping pump overspeed.

Lastly, LI is again correct in stating that your other process parameters (vibration probes, flow measurement, bearing temp monitoring, etc) that you normally measure can all be used as a proxy for a pump operating at a dangerous condition.

So in summary, there is no need to try to wrangle a specific overspeed protection into a VFD.

 

[danschwind]

I've also never seen any consideration regarding possible failure of the VFD which would increase the motor speed beyond its programmed limit.

Daniel
Rio de Janeiro - Brazil

 

[Sawsan311]

Thank you All