Principle of controlled switching (CS) in circuit breaker

Controlled Switching (CS) Method

Controlled Switching (CS) is a technique used to eliminate harmful transients by precisely timing the switching operations of circuit breakers (CBs). The closing or opening commands to the CB are delayed in such a way that the contacts make or separate at an optimal phase angle, minimizing transient effects.

Key Principles:

• Voltage Zero Crossing for Closing: To avoid switching transients, the moment of contact closure should ideally occur at the voltage zero crossing point. This ensures that the current starts flowing when the voltage is at its minimum, reducing inrush currents and associated transients.
• Bypassing Protection Commands: When controlled opening is applied, it is crucial that all protection trip commands, especially those triggered during fault interruptions, bypass the controlled switching controller. This ensures that the system can quickly respond to faults without delay.
• Example Scenario: Energizing a Capacitor Bank
• Input Command: When a capacitor bank needs to be energized, an input command is sent to the controlled switching controller.
• Reference Time Instant: The controller determines a reference time instant based on the phase angle of the busbar voltage.
• Waiting Time Calculation: After calculating an internally generated waiting time, the controller issues a closing command to the CB.
• Closing Command Timing: The exact timing of the closing command is determined by considering both the predictable make time of the CB and the target point for making (typically the voltage zero crossing).
• These parameters are pre-programmed into the controller.
• Minimizing Transients: The CB then closes at the correct time instant, thereby minimizing switching transients.

Time Sequence in Controlled Switching

The following steps outline the sequence of events in controlled switching for a single phase of a circuit breaker:

• Initial Command: An input command is received to either close or open the CB.
• Phase Angle Detection: The controller detects the phase angle of the busbar voltage.
• Waiting Period: The controller calculates and waits for the appropriate internal delay.
• Closing Command Issued: Once the calculated waiting period elapses, the controller sends a closing command to the CB.
• Contact Closure: The CB makes contact at the predetermined optimal time (voltage zero crossing), minimizing transients.

Visual Representation

A diagram would typically show the time sequence involved in controlled switching, highlighting the relationship between the busbar voltage waveform, the internal waiting time, and the precise moment of contact closure.