Which of the following measures is crucial for maintaining system stability?

Maintaining system stability in a transmission network is multifaceted, and each measure plays an essential role. Keeping voltage constant is crucial because voltage fluctuations can lead to equipment failure, operational inefficiencies, and can negatively impact system reliability. A stable voltage ensures that the electrical equipment operates within its design parameters, preventing damage and maintaining power quality.

Controlling current levels is equally important as it directly affects the flow of electricity through the transmission lines. Excessive current can result in overheating, increased losses in the system, and potential equipment damage. By ensuring that current levels are within acceptable limits, the system can operate safely and efficiently.

Monitoring surge impedance is also vital. Surge impedance refers to the characteristic impedance of a transmission line that affects how signals and transients propagate. Proper management of surge impedance can help mitigate issues like voltage spikes or reflections, contributing to overall system stability.

Recognizing the importance of all of these measures reinforces that they collectively ensure the stable and efficient operation of the transmission system. Therefore, the inclusion of all these aspects as crucial to maintaining system stability is the correct understanding.