TRUE motor running indication with current monitor 1

[classIdiv2]

How could I get a "true" motor running indication? I was using the motor starter N.O. contacts but since my control circuit is 24VDC and my motors are running at460VAC so it is not a "true" motor running indication when 460VAC is down. My client also asked a current indication for the motor on the door.

Where can I get a device which can show the running current on the door but also has a dry contact output to indicate if there is any current has been detected? I don't want this device to have any over-current or under-current or any sort fo protection. Just a simply current amps indication and a relay output or dry contact output to show motor is running or not running.

 

[fabiosm]

Does your motor starter have phase failure protection function and an analog output? If it has you can use the phase failure protection to ensure the starter contact that you use for motor running indication is "true" and the analog output for current measurement.

 

[controlsdude]

Not sure what overload protection functions you have. Do you monitor these overload protections on the motor circuit with your controls? I mean if you monitor these functions then you can ensure that 480vac is on the motor.

 

[badservo]

see

http://www.automationdirect.com/adc...s_(AC_-a-_DC)/Current_Switches_-a-_Indicators

 

[OperaHouse]

There are GO/NO GO self powered current relays that provide a set of dry contacts. These are placed on one leg of the power going to the motor. This assumes that if the motor is drawing current it is running and and any motor fault would trip the MCR off.

 

[itsmoked]

Be careful since just current does not prove rotation. Make sure you understand exactly why the customer needs to know why it's running. You might really need to know it's turning.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[FreddyZ]

Or... they might actually need to know that the thing which the motor drives, is actually turning. Failure of a coupling might produce a turning motor with a dead machine on the far side of the failed coupling.

 

[itsmoked]

Excellent point.

I can imagine a lot of cases where doing something when somethings has to be turning and it's not could lead to very bad things.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[catserveng]

Take a look at these guys,

http://www.time-mark.com/Default.aspx

Mike L.

 

[itsmoked]

catserveng;

I saw nothing there that would work.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[catserveng]

I haven't found a single device exactly like the OP is looking for, but have used the phase voltage monitor and the three phase over/under current monitor from Time Mark with their contacts wired in series with the aux contact of the contactor to provide a "better" running indication at a customers request, for a fairly economical price.

Of course I've also used an SEL motor protection relay, and more recently an SEL 751A relay to provide a similar indication as the OP is looking for, just depends on how big the motor is, how important the process and how much money they are willing to spend.

Mike L.

 

[controlsdude]

Well if the customer needs to know the motor is turning, then either an encoder or a prox on a gear box is necessary. Of course additonal inputs needed for this to a plc.

Motor running starts the timer
reset the timer with the prox or encoder
alarm and stop the motor output contactor or vfd if the timer times out.

 

[zeusfaber]

I'd talk to the client to understand the application better. It might emerge that there is a measurable property on the driven machine (like boost pressure on a hydraulic pump, or oil pressure on a compressor).
A.

 

[itsmoked]

Earth to classIdiv2... Come in classIdiv2!

Are you here or are we wasting our time?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

You scared him off now Keith... nice going

classIdiv2 (if you are still with us)
Here is an example of a motor protection relay that will give you load monitoring indication that your motor is actually turning, without an external sensor.

Click image for link

The key difference that would make this more reliable is below:

Load Monitor Under or over kW trip or alarm. Setting: Off or 20 - 100% of motor kW with 1-20sec delay
Power Factor Monitor Leading or lagging PF, trip or alarm. Setting: Off or 0.1 - 1.0PF (lead or lag) with 1-20 second delay

I would program it so that after XX seconds, if the kW is not at least 20% of the motor rating and the PF is not at least .3, then you can know that the motor is NOT rotating. This works better than just monitoring current, because current will fluctuate with voltage regardless of load. kW will not, kW is always load. Adding in the PF monitoring isn't absolutely necessary, but it's there and it would function as a double-check. This would replace your Over Load Relay and on this unit, the display can be mounted on the door. There are several others on the market just like this; Load Monitors Corp has one, Siemens has one, and there is another one from Canada that I can't remember the name of and I'm sure several others. The key is, look for one that is a kW monitor

I would not use that from a personnel safety standpoint however, there are other more specific rotation monitors for that which will require an external sensor. But from a machine or process standpoint, this works great.

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