Power transformers are used in power transmission and distribution. They step - up voltage at the power plant to reduce transmission losses and step - down at the consumer end. Instrument transformers, like current transformers (CTs) and potential transformers (PTs), are for measurement and protection. CTs step - down high currents for measurement, and PTs step - down high voltages.

A tap changer regulates a transformer's output voltage. As load varies, the output voltage can fluctuate. The tap changer adjusts the turns ratio of the transformer. For example, in a residential distribution transformer, if the voltage drops during peak load, the tap changer can increase the output voltage. There are on - load and off - load tap changers.

Transformers are rated in kVA because they handle both real and reactive power. They don't change the power factor, which is determined by the load. Also, transformer losses (core and copper losses) are related to voltage and current (components of apparent power, measured in kVA), not the power factor.

Inrush current is the high - magnitude current a transformer draws when first energized. It can be several times the rated current and lasts for a few cycles. When the transformer is initially connected, the magnetic core is unmagnetized. As voltage is applied, the core builds up magnetic flux. The inductor - like behavior of the windings and the initial low - impedance state of the core cause this large inrush.

Core losses include hysteresis and eddy current losses. To minimize hysteresis losses, use high - quality magnetic materials like cold - rolled grain - oriented (CRGO) steel. Eddy current losses can be reduced by laminating the core. Thinner laminations and proper magnetic circuit design also help minimize core losses and improve efficiency.

In a clean, dry environment, annual inspections and servicing are usually sufficient. This includes checking for oil leaks (in oil - filled transformers), measuring insulation resistance, and inspecting bushings. In environments with dust, chemical fumes, or moisture, more frequent inspections (every 3 - 6 months) may be needed. Transformers in high - load or critical applications also require closer monitoring.