Voltage transformer: A voltage transformer is a voltage conversion device. It converts high voltage to low voltage so that the low voltage value reflects the change of the high voltage value. Therefore, it is possible to directly measure voltage with ordinary electrical instruments through the voltage transformer. Voltage transformer, also known as instrument transformer, is a voltage conversion device; the capacity of the voltage transformer is very small, usually only tens to hundreds of VA; the primary voltage of the voltage transformer is the grid voltage and is not affected by the secondary load , And its load is constant in most cases; the secondary side load is mainly meters and relay coils, their impedance is very large, and the current passing through is very small. If the secondary load is increased indefinitely, the secondary voltage will decrease, causing measurement errors to increase; using a voltage transformer to indirectly measure the voltage can accurately reflect the value of the high-voltage side and ensure the measurement accuracy; regardless of the primary voltage of the voltage transformer How high, the secondary rated voltage is generally 100V, making the manufacturing of measuring instruments and relay voltage coils standardized. Moreover, the safety of instrument measurement and relay protection work is ensured, and the insulation and manufacturing process difficulties of high-voltage measurement are also solved.