How do I analyse breaker selectivity using the Curves and Selectivity tool in EcoSet Design?

The Curves and Selectivity tool allow users to compare the protection curves of upstream and downstream circuit breakers and evaluate the selectivity of the electrical installation.

Selectivity ensures that, during a fault condition, only the protective device closest to the fault trips, while upstream devices remain closed, improving system availability and minimizing unnecessary power interruptions.

How to Open the Curves and Selectivity Window

1. Select a circuit breaker in the Single Line Diagram (SLD).
2. Click Curves in the Property Sheet.
3. The Curves and Selectivity window open, displaying the protection curves of the selected breaker and its associated upstream breaker.

Understanding the Curve Display

The graph displays:

• Horizontal Axis (X-axis): Current (A)
• Vertical Axis (Y-axis): Time (s)
• Breaker Protection Curves: Time-current characteristics of each breaker
• Fault Current Markers: Available short-circuit current levels
• Selectivity Analysis Results: Coordination status between breakers

In the example shown:

• Q_1 (NSXm160E TM-D 160 A) is the upstream breaker.
• Q_2 (CVS100B TM-D 100 A) is the downstream breaker.

How to Adjust Protection Settings

From the left panel, users can modify:

• Ir (Long-Time Pickup Current)
• Isd (Short-Time Pickup Current) (if available)
• Trip settings of the selected breaker

After adjusting the settings:

1. Review the updated protection curves.
2. Verify whether the downstream breaker trips before the upstream breaker.
3. Save the settings if the desired selectivity is achieved.

How to Interpret Selectivity Results

The application provides a selectivity assessment at the bottom of the window.

Possible results include:

• Total Selectivity: The downstream device operates first under all relevant fault conditions.
• Partial Selectivity: Selectivity is maintained only up to a certain fault current level.
• No Selectivity: The upstream and downstream devices may trip simultaneously.

In the example shown, the result indicates:

"Selectivity By Table: No Selectivity"

This means the selected breaker combination does not provide selective coordination under the evaluated conditions.

Released for: Schneider Electric Egypt and North East Africa