A combustion system includes a burner assembly, an electrode positioned within a combustion volume and configured to apply electrical energy to a flame supported by the burner assembly, and a dielectric electrode support extending through a furnace wall into the combustion volume and configured to support the electrode and further configured to be cooled by a coolant fluid circulated therethrough. The electrode support has coolant ports in fluid communication with a coolant channel extending within electrode support. During operation of the combustion system, a fluid coolant flows through the electrode support, holding a temperature of the electrode to within a selected range.