Can a PLC provide custom overcurrent protection settings of a circuit breaker with trip unit?

[Dvhez]

I’m modeling a system with an Eaton IZMX-16 (1600A) circuit breaker equipped with a PXR25 trip unit, and I need to configure the overcurrent protection to 350A. However, the lowest setting I can achieve is 640A, based on the PXR25 trip unit’s minimum multiplier (Ir x 0.4).

Is there a cost-effective solution that doesn’t involve replacing the circuit breaker with a lower frame unit? Additionally, is it possible to use a PLC to communicate with the circuit breaker and "bypass" the PXR25 multipliers to define a custom protection curve? The PLC would receive data from a power and energy meter.

Thank you for your help!

 

[cranky108]

A PLC? As in Power Line Carrier?
Try using a different CT ratio.

 

[Dvhez]

Hi cranky108, I apologize for any confusion earlier. When I mentioned "PLC," I was referring to a Programmable Logic Controller. For instance, certain Kohler generators use an AMP403 Controller, which provides genset protection. My understanding is that this controller sends a signal to the main breaker. However, I’m not sure if this approach can be similarly applied to a circuit breaker that has a trip unit (PXR25), specifically for programming the long-time pickup current or defining an specific IEC or IEEE curve.

 

[Coco_HueHueHue]

You can definitely implement genset protections into a PLC (temperature, oil level, etc.) to initiate a trip of the main breaker. The PLC could send an input to an electrical protection relay managing the main breaker. But electrical protections need to be implemented using approved protection relays.

 

[dpc]

Not familiar with this breaker, but you may be able to simply replace the trip unit, not the entire breaker. Have you talked with Eaton?

IMO, trying to use a PLC to monitor current is not a good idea. The PLC will be too slow for one thing. And you will be dependent on the PLC for basic electrical circuit protection - this is almost certain to create problems and confusion in the YEARS to come. I would never do this.

Assuming this breaker can accept a dry contact trip signal, a better approach would be to install a utility-grade protective relay and use that to trip the breaker. However this would still require installation of three CTs at the breaker (preferably the line side) and this may prove to be an issue.

Best option to work with Eaton and come up with a workable solution that keeps the protection functions within the breaker. Generally for low voltage power circuit breakers, the entire trip unit is replaceable. But I'm not sure about these breakers.

 

[che12345]

@ Mr Dvhez (Electrical)(OP)
I am not familiar with IZMX-16 with PXR25.
1. It is normal for a 1600 A, or any current ratings with the lowest setting at say 0.4 Ir. In most cases, a 1600 A trip unit is NOT able to be set to lower. Consult the OEM, they may have a say 800 A trip unit with 0.4 Ir = 320 A min., which would meet your need. No change in your existing frame size or the 1600 A breaker.
2. A basic PLC is an input/output + time delay + sequencing... switching device. It is NOT a protective relay. The protective relay detects the fault may send it to the PLC for sequencing etc. The PLC N.O. or N.C. dry contact output effects the final action ....
Che Kuan Yau (Singapore)

 

[thermionic1]

Imagine the PLC protection, then a fault occurs, then PLC fails to trip. Someone or something very expensive gets hurt. Investigation finds faulty PLC as root cause.

 

[cranky108]

Besides during a fault, power can be lost, and if that power also powers the PLC, you will not trip. Most protection uses a stored energy device to ride over the loss in ac power.

 

[BrianPetersen]

If there are any safety consequences of the protection component failing to do its job, then a standard PLC is not a permissible component in the critical chain of events.