Why should a disconnect never be left closed on an open EHV breaker?

Leaving a disconnect closed on an open Extra High Voltage (EHV) breaker can lead to capacitor failure due to prolonged duty. When a disconnect is closed while the breaker is open, it essentially isolates the breaker from the rest of the system. This configuration can allow reactive power to flow into the stray capacitance of the transmission line without proper controlling mechanisms, leading to high voltages being sustained over time. Capacitors are designed to operate within specific voltage ranges, and continuous exposure to elevated voltage conditions can result in overheating, dielectric breakdown, and ultimately failure.

In this context, it's crucial to recognize that correct operational protocols are essential for maintaining the integrity of both the equipment and the electrical system overall. Proper supervision and adherence to stringent safety and operational standards help prevent such detrimental scenarios.