What is Working Principle of Current Transformers?

A Current Transformer (CT) is a critical metering and protection device widely used in power systems. Its primary function is to convert high-voltage, large currents into proportional low-voltage, small currents for measuring instruments and protective relays, ensuring accurate energy metering and safe system operation.

In power plants, substations, and user-side high-voltage metering systems, CT accuracy directly affects stakeholders across generation, transmission, and consumption. Therefore, CTs must be verified in accordance with IEC 61869 Instrument Transformers series standards (e.g., IEC 61869-2 for current transformers, IEC 61869-3 for voltage transformers) and related IEC 60044 standards.

Working Principle

The operating principle of a CT is based on electromagnetic induction. It consists of a primary winding, secondary winding, and magnetic core:

• The primary winding is connected in series with the high-voltage circuit and carries a large current.

• The secondary winding delivers a proportionally reduced current (typically 5A or 1A) for metering and protection devices.

• Through the transformation ratio, the CT accurately reflects the magnitude of the primary current.

To ensure measurement accuracy, CT errors must be strictly controlled within specified IEC accuracy classes (e.g., Class 0.2S, 0.5S).

Next-Generation On-Site Calibration Technology

Traditional CT verification methods often require bulky auxiliary equipment such as reference transformers, current boosters, and load boxes—leading to complex wiring, heavy workloads, and low efficiency.

Our newly developed Next-Generation CT Field Calibrator addresses these challenges through advanced innovations:

• Recursive Error Measurement & Impedance-Admittance Algorithms for high-precision deduction.

• Near-Power-Frequency Excitation to suppress electromagnetic interference.

• Built-in IEC Class 0.05 reference CT/VT, eliminating the need for external reference devices.

With these technologies, on-site verification becomes simple, fast, and reliable:

• Ultra-Wide Measurement Range: 5A/5A to 31,500A/5A.

• Instant Compliance Verdict: 1-second “Pass/Fail” judgment.

• Smart Diagnostics: Automatic detection of wiring, ratio, and polarity errors.

• Efficient Data Management: Stores up to 1,000 test results with direct report printing.

This breakthrough reduces the workload dramatically, enabling a single technician to perform verification tasks that previously required multiple staff, while significantly improving efficiency and accuracy.