Explain the function of a 'surge arrester' in an electrical system.

The function of a surge arrester, also known as a surge protector or lightning arrester, in an electrical system is to protect electrical equipment from transient voltage surges, which are short-duration, high-voltage spikes that can damage or destroy sensitive electronic components. These surges can be caused by lightning strikes, switching operations, or equipment faults. A surge arrester is designed to divert the surge current to ground, limiting the voltage across the protected equipment to a safe level. Under normal operating conditions, the surge arrester acts as an open circuit, allowing normal current to flow through the electrical system. When a voltage surge occurs, the surge arrester's internal components, typically metal oxide varistors (MOVs) or gas discharge tubes (GDTs), rapidly switch to a low-impedance state, providing a path for the surge current to flow to ground. This clamping action limits the voltage across the protected equipment to a level that it can withstand without damage. After the surge has passed, the surge arrester automatically returns to its high-impedance state, allowing normal operation to resume. Surge arresters are typically installed at the service entrance of a building or at the input of sensitive equipment to provide comprehensive protection against voltage surges.