Simple power monitor questions

[scadaguy]

Dear all,

For a VCB, normally what parameters would you measure and monitor? (eg, CB status, tripping/closing current, battery terminal voltage...) How many order harmonic would be measured?

Instead of standalone power monitor module (like schneider or rockwell), are there any existing applications to achieve above by integrating or adding additional functionality to RTU/PLC? The purpose of this is to achieve low-cost solutions but still maintain reliability and moderate maintainability.

Thank you for sharing.

 

[dpc]

This is going to depend almost entirely on what load is being served or the breaker application.

Breaker status (OPEN/CLOSED) would certainly always be monitored. Low Battery voltage is typically alarmed, but not usually on a per-breaker basis. New digital relays have a trouble/watchdog alarm that should be brought back.

The breaker doesn't care much about harmonics. The need for power monitoring depends on the load being served.

If you have a new digital relaying system, there isn't much need for an RTU or PLC, per se. You might have a small PLC in a substation just to handle miscellaneous contact inputs/outputs, but often that can be handled by the digital relays.

A PLC will be too slow to be of much use for power quality monitoring.

 

[scadaguy]

Thanks dpc for your quick reply.

The existing installations are several 11kv distribution boards (~800A) in a substation which is monitored and controlled by RTU (just digital status, alarms and load current). The RTU provides limited remote control functions thru modem or other network means. Actually I should describe it as a SCADA system.

I perceive my senior may want to add modules to the "upgraded" RTU with ease so that it would provide further information of power quality.

My proposal is to replace RTU with PLC (AB or Siemens) and interface with some low-end PQ monitor. But most of them are not cheap solutions that's opposite to our original project objective.

Let's discuss and all suggestions are welcomed.

 

[dpc]

It might be simpler to replace the existing protective relays with digital relays that provide built-in power quality monitoring. The relays can include Modbus, Ethernet or other communications capabilities and provide complete monitoring and control of the circuit breakers. With this approach, you don't really need the PLC.

 

[davidbeach]

I would agree that dpc's solution would probably be better than trying to put something together using various components and a PLC. You'd get your desired results, plus the protection will be greatly improved at the same time.