You've correctly identified the core issue: a motor-operated disconnect (MOD) switch behaves like a breaker for interlocking and control but doesn't have the same interrupting capability. Here's a breakdown of how to model a 1200A, 138kV MOD in ETAP, considering the control aspect with the 125VDC motor operator

Recommended Approach: Modified Breaker Model

This is likely the simplest and most effective approach. Here's why and how to do it:1. Use a High-Voltage Breaker

Start with a standard ETAP high-voltage breaker component. This gives you the necessary terminals for the 138kV system, as well as the inherent interlocking and control capabilities.2.

Adjust Ratings to Reflect Disconnect Characteristics

This is the crucial part. Modify the breaker's characteristics to match the MOD:

Interrupting Rating (kA)

Critically important. Set the interrupting rating to a very low value, essentially zero. This is vital. The idea is to let etap know this component is incapable of interrupting overcurrent or fault current.

Continuous Current Rating (Amps)

Set this to the MOD's continuous current rating (1200A in your case).

Close and Latch Rating (kA)

Set this to a reasonable value corresponding to the fault current that the disconnect must withstand while closed. It is typical for disconnects to have no 'make/latch' rating since they're not supposed to close during a fault. Check the nameplate data or manufacturer's specs. If the nameplate is unavailable, it's best to leave this to default values.



Operating Times (Opening & Closing)

Adjust these to match the MOD's actual operating times, considering the motor operator. You'll find these in the manufacturer's specifications. These are normally slower than breakers.3.

Control Logic and Interlocking

ETAP's breaker component already has the necessary control functions (Open, Close, Trip). Leverage these:

Remote Open/Close

Use ETAP's control functions to simulate remote operation. Connect these to your control system or create simple switches in ETAP's control panel.

Interlocks

This is where you'll define the conditions under which the MOD can or cannot be operated. Common interlocks include: Preventing operation when upstream or downstream breakers are closed (load break scenario).

Interlocking with ground switches. Position indication (from the disconnect's auxiliary contacts). Supervisory Trips

Connect any supervisory trip signals (from protective relays, etc.) to the breaker's trip input.4.

DC Control Power (Motor Operator)



Auxiliary Power

In the breaker properties, there is a tab for Auxiliary Power, ensure the type is set to DC. From there you can define the voltage, and also use a DC source. You can use this DC source to model the battery system as well.

Why This Approach is Good



Simplicity

It's relatively straightforward to implement.

Integration

You get full integration with ETAP's power flow, short-circuit, and protection coordination modules.

Control Modeling

ETAP's breaker component is well-suited for modeling the control aspects of the MOD.

Accuracy

By carefully adjusting the breaker's ratings, you accurately represent the MOD's limitations.

What to Consider



Arc Flash

Remember that while the MOD can't interrupt fault current, it can still be a point of arc flash hazard if it's switched under load or if a fault occurs downstream while it's closed. Ensure that arc flash calculations consider this.

Coordination Studies

The MOD itself isn't a protective device, so it won't be part of your coordination studies. However, its position (open or closed) can affect the coordination of other devices.

Manufacturer Data

Always consult the manufacturer's specifications for the MOD's ratings, operating times, and any specific application recommendations.

Alternative Approach (Less Recommended): Switch + Separate Motor

You mentioned modeling the MOD as a switch and a separate DC motor. While technically possible, it's usually more complex and doesn't integrate as well with ETAP's protection and control features. You'd have to manually build all the interlocking logic using status and syncs, which can become cumbersome.

In summary, I recommend starting with a standard ETAP high-voltage breaker component and carefully adjusting its ratings to match the MOD's characteristics. Pay close attention to the interrupting rating (setting it to a very low value) and model the DC control power for the motor operator.

Good luck! Let me know if you have any more questions. Flag for review