How to read trip characteristc curve of a breaker

A trip characteristic curve, also known as a trip curve, is a graphical representation of the relationship between the current and voltage of a circuit breaker. It shows how the breaker responds to various fault currents and voltages. Here's a step-by-step guide to reading a trip characteristic curve:

Understanding the Curve:

The trip curve is typically a plot of the breaker's trip current (I) against the system voltage (V). The curve is divided into three main regions:

  1. Normal Operating Region: This is the region where the breaker operates normally, with the current flowing within the rated capacity of the breaker.
  2. Fault Current Region: This region represents the area where the breaker trips due to a fault current exceeding its rated capacity.
  3. Inrush Current Region: This region represents the area where the breaker trips due to an inrush current, such as a motor starting current.

Key Features to Look For:

  1. Trip Current: The point where the curve intersects the horizontal axis represents the trip current, which is the current at which the breaker trips.
  2. Dropout Voltage: The point where the curve intersects the vertical axis represents the dropout voltage, which is the voltage at which the breaker trips.
  3. Inrush Current: The inrush current region is typically represented by a steep slope on the curve, indicating a rapid increase in current.
  4. Fault Current Region: The fault current region is typically represented by a flat or slightly sloping section of the curve, indicating a relatively constant current.

How to Read the Curve:

  1. Identify the normal operating region: This is the region where the breaker operates normally, with the current flowing within the rated capacity of the breaker.
  2. Identify the fault current region: This region represents the area where the breaker trips due to a fault current exceeding its rated capacity.
  3. Identify the inrush current region: This region represents the area where the breaker trips due to an inrush current, such as a motor starting current.
  4. Determine the trip current: The trip current is the current at which the breaker trips, which is represented by the point where the curve intersects the horizontal axis.
  5. Determine the dropout voltage: The dropout voltage is the voltage at which the breaker trips, which is represented by the point where the curve intersects the vertical axis.
  6. Identify any other features: Other features on the curve, such as the slope of the fault current region or the inrush current region, can provide additional information about the breaker's behavior.

Interpretation:

The trip characteristic curve provides valuable information about the breaker's performance and behavior under various fault conditions. By analyzing the curve, you can:

  1. Determine the breaker's trip current and dropout voltage.
  2. Identify the breaker's response to different fault currents and voltages.
  3. Determine the breaker's ability to handle inrush currents.
  4. Compare the breaker's performance with other breakers or with the manufacturer's specifications.

By following these steps and understanding the key features of a trip characteristic curve, you can effectively read and interpret the curve to gain valuable insights into the breaker's behavior and performance.