Instrument transformer: the core “safety guardian” for high-voltage power grid measurement

In power scenarios involving kilovolt-level high voltage and kiloampere-level high current, direct measurement is impossible for safe and precise electric energy metering. Extremely high voltage and massive current can not only instantly damage precise metering instruments but also pose a fatal threat to the safety of on-site operators. The core solution to this challenge lies in the indispensable “bridge and converter” in the power system – the instrument transformer. With its precise voltage and current transformation capabilities, it makes the measurement of high-voltage and high-current electric energy safe and reliable.

The core function of an instrument transformer is highly unified: it converts high current and high voltage from the high-voltage system into standardized low-level signals of 5A/1A current or 100V/110V, providing adapted signals that can be safely collected and processed for measuring instruments, protective relays, electric energy metering, and automatic control systems.

CT – Current Transformer

Working principle: It converts a high current (such as 1000A) into a standard low current of 5A or 1A according to a precise transformation ratio (such as 1000:5), and outputs it to devices such as ammeters, electric energy meters, and protective relays.

In layman’s terms: a current scaling device connected in series in an electric circuit.

Core Iron Law: Open circuits are strictly prohibited in secondary circuits! Once an open circuit occurs, the primary current will all become excitation current, generating strong magnetic flux, which can induce thousands of volts of high voltage in the secondary winding, easily damaging equipment and causing personal safety accidents.

Voltage transformer (VT/PT – potential transformer)

Working principle: It reduces the voltage of high-voltage lines (such as 110kV) to a standard safe voltage of 100V or 110V according to a precise transformation ratio, providing an adapted signal for subsequent equipment.

In layman’s terms: a high-precision micro step-down transformer connected in parallel in an electrical circuit.

Core Iron Law: Short circuits are strictly prohibited in secondary circuits! Contrary to current transformers, secondary short circuits can generate huge currents, instantly burning out windings and damaging equipment.

Pro Tip: The “S” suffix means “Special” — accurate from 1% load, critical for modern grids with variable renewable generation.

Conclusion

Current transformers (CTs) and voltage transformers (VTs) jointly constitute the core sensing system of the power grid. As precision sensing units of the power system, they safely and accurately transmit electrical parameters from the high-voltage side to the “nerve center” of the grid – the protection and control relay system.Without the support of both, accurate electric energy metering, sensitive fault detection, and safe system control would be impossible. It is these “electricity interpreters” that operate continuously in substations, laying a solid foundation for the safe, stable, and efficient operation of the entire power system.