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Motor networking control

In the days before networked motors, all inputs were accounted for in the Input list and all outputs were accounted for in the Output list. The IO count was then evaluated to help determine the complexity of a system. IO counts directly impacted many various costs in the project such as cost of hardware, cost of wiring, and the cost of installation. The complexity of the system was used to estimate how much engineering time would be required for the project.

Networking of devices (MCCs as well as valves and instruments) makes the task of estimating a project much less straightforward.

1. "Smart MCC" implies the use of some type of network which supports each individual motor, whether a "two-state on/off" motor, "three-state off/forward/reverse motor" or "variable speed drive".

With each motor device, certain components which were traditionally discrete IO points are now wired at the motor controller itself component and communicated to the control system via the network. Common components include the "bucket disconnect", the "running status", and the "overload status". Therefore, your IO count may be less in a networked environment, but the complexity of the control may actually be greater.

2. Automatic Change over between running and standby motors

I interpret this as being a requirement to automatically switch from the normal motor to its designated backup when some type of fault is detected. If so, then you must somehow account for this in your motor list, MCC design, and complexity of the control system.

3. Dry run Protection

Sounds like an interlock for pumps to prevent running if the liquid level in the supply tank is below a safe level.

If so, then you may be quoting things which you are not qualified to do. This is not an "instrumentation" issue or an "electrical" issue, but rather a "process knowledge" issue.

4. Variable speed drives

If your MCCs are "smart", then these parameters are communicated over the network and you no longer need speed reference signals (analog outputs to the variable speed drive) or speed feedback signals (analog inputs from the drive)

5. Various trips (from DCS and SIS) that are coming to motors.

What is required for controlling the motor? I have never worked with SISs (Safety Instrumented Systems), but have used "safety relays" in motor controls which impacted wiring details without impacting "IO count".

You need to understand the requirements in order to quote or design the system -- Period.

6. There is only Local start and no DCS start.

It sounds like some motors have a local start button which is a "Manual" function, not an "Automatic" function. If so, there is probably a discrete input for this function.

Bear in mind that there may be also be a local Hand-Off-Auto selector switch for certain motors. If so, the Hand position and the Auto position require discrete inputs to the control system.

7. Apart from this I have considered few DI's for MCC Incomer's open or closed status.

Is it about the status of MCC Main Circuit Breakers? Does each motor "bucket" have an auxiliary switch to monitor its status? If so, these are often wired to the "smart motor" so that their status is communicated via the network rather than using discrete inputs. This cuts down on "IO count", but does not cut down on "complexity".

8. Interposing Relays

Interposing Relays are used when the amperage requirements of the final motor starter coil exceed the available amperage rating of the "first line" output device. This is a function of the hardware and how you propose to control the motors and must be addressed on a case-by case basis.

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