An electrical surge suppressor

An electrical surge suppressor configured to be connected between earth and a phase of a switch controlled, AC electric load circuit, the surge suppressor including:

• a capacitive component incorporated inside a housing and immersed in, or filled with, oil;
• a linear resistive component having a linear V-I characteristic and being connected to the earth;
• a non-linear resistive component connected or connectable in parallel with the linear resistive component and having a pre-determined knee-point voltage value;
• a monitoring circuit configured to measure at least one operating characteristic of the linear and/or non-linear resistive and capacitive components;
• and
• an auxiliary power supply integrated within the capacitive component to provide an auxiliary supply voltage to the monitoring circuit,
• wherein:
• the capacitive component is connected in series with the parallel connected linear and non-linear resistive components and connected to a phase contact;
• the phase contact is connected or connectable to the load circuit;
• the capacitive component is configured to provide a high impedance connection to the linear and non-linear resistive components, at nominal power supply frequencies and, during switching transients, to provide a low impedance to a combined resistive impedance of the linear and non-linear resistive components effectively into the load circuit at frequencies associated with wavefront rise times of up to 5 μs;
• the capacitive component is configured to increase the rise time of a portion of a steep-fronted surge which exceeds a knee-point voltage value of the non-linear resistive component;
• and
• an external contact is arranged between the linear resistive component and the capacitive component.