control power monitor 2

[tulum]

Hey Folks,

Anyone now of a really cheap montior for control power status?

I have a job that has ten feeders with ten separate CPT's on each feeder and the design engineer has requested that the 120VAC secondary of each CPT be monitored... this is lots of $ for something we have never done here before...

I have checked with AB and Carlo Gavazzi and found a couple however they are in the $200-$300 dollar range.

Anyone have experience with this?

Regards,
TULUM

 

[wbd]

I would install a small control relay that has a 120V coil and wire up a contact (either NO or NC) depends on your control. Then when ac power is lost, the coil drops out and the contact changes state. Something like a Potter Brumfield KRP series would work. Depending on the model, they range from $12 - $50.

 

[tulum]

Thanks WBD I will look into the relay...

I am not familiar with what a CPT monitor should do? Is it supposed to warn of a dip in voltage?

A control relay would drop out basically at 30% voltage and pickup again around 80%. Is this an acceptable method in industry for monitoring control...

My thought is - what is required? To let the scada know the Control power is gone, or let the SCADA know that there is a dip and you may loose it?

Regards,
TULUM

 

[wbd]

I would ask the design engineer on why he wants the power to be monitored. If he is worried about dips in the voltage causing equipment such a motor contactors to drop out, what's monitoring going to do? You'll know you had a dip since your motors will shut down.
If it is to monitor the power and send a signal that power is lost, then a simple relay will work fine.
I would find out what the designer is trying to accomplish.

 

[waross]

Hello tulum;
I am sure that monitoring for voltage dips and recording the time of events is already done at the main panel, on the incoming lines and possibly on the feeders.
Any voltage dips on the feeders will be passed on to the secondaries of the control transformers.
A problem or impending failure that shows up as a voltage dip only on the secondary of a control transformer will certainly develop into a complete failure in a short period of time. Probably before it can be located by the technicions.

Typically monitoring of control power transformer secondaries is used to warn of complete failure of control power. This would be open fuses or breakers and/or a failed control transformer.

I would consider an economical PLC. Connect each transformer output to a seperate input on the pLC.
You would want to verify the threshold voltage of the input interface on the PLC.
With a PLC installed, it will be simple to communicate the status to a DCS or SCADA system.
respectfully

 

[tulum]

Thanks folks,

I will look at both options...

 

[unclebob]

IQ 200 series are really cheap, check Eaton Cutler-Hammer.

 

[jraef]

You really need to find out the purpose of the CPT monitoring. The problem with the relay is in matching the control power requirements of other devices. Contactors are typically designed around a "low voltage dropout" range of 70%, whereas small cheap "ice cube" relays will sometimes hold in down to 30% as previously mentioned. (By the way wbd, control power monitors are often used so that you can discriminate between a control power failure and a device failure when the contactor drops out).

There are inexpensive adjustable voltage monitor relays available from plenty of sources, $200-$300 seems grossly excessive. Time Mark has one for less than $100 that plugs into an octal socket, this one needs just one screw in the center and is only about $65.

http://sacramentoelectronics.com/ncc/SSR5-5.htm

JRaef.com
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[BJC]

Monitoring the control power will tell you if the breaker in an MCC cubical is open or the bucket is drawn out. Way back it wasn't uncommon for some plants to use 3 indicator lights on a motor circuit. Red = run, green = stoped and white = control power on. Some places used amber for power on. The white light had to be neon else the control power could be on and the buld burned out.

 

[rcw retired EE]

Some processes need a back-up pump in standby, ready to run automatically. The CPT monitor can be set up to tell teh PLC or other control system that the standby unit is powered and ready to go.

Some schemes wire this "Ready Relay" between the motor overload and the Auto switch so the relay only picks up when the motor starter control circuit is powered, the H-O-A switch is in Auto and the overload protection is OK.

 

[RalphChristie]

Can anyone explain the term CPT?

Thanx

Regards
Ralph

 

[waross]

I think that it is Control Power Transformer. That fits the context, but it is a new term to me also.
respectfully

 

[davidbeach]

Yes, Control Power Transformer.