What type of device uses materials like insulating oils and gases for interrupting power system current?

The device that uses materials like insulating oils and gases to interrupt power system current is a circuit breaker. Circuit breakers are essential components in electrical systems, designed to protect circuits from overloads and faults by interrupting the current under fault conditions. The insulating oils and gases serve several purposes: they not only help to extinguish the arc that forms when the circuit is interrupted but also provide insulation to prevent unintended discharges.

In contrast, transformers function to transfer electrical energy between circuits, primarily by using magnetic fields and do not interrupt current. Fuses are overcurrent protection devices that melt to break the circuit under overload conditions but do not use insulating materials like oils or gases for their operation. Switches function primarily to open or close circuits but also do not involve the use of insulating materials for interrupting current. Therefore, circuit breakers are specifically designed to handle fault conditions effectively using the mentioned insulating materials.