Instrument Transformer Characteristic Tester, often referred to as "Voltage-Current Characteristic Tester" or "CT/PT Analyzer", is a core instrument in the power system specifically used to test the electrical performance of current transformers (CT) and voltage transformers (PT/VT). It is key equipment to ensure the correct operation of relay protection devices and accurate energy metering, widely used in acceptance tests, preventive tests, and fault troubleshooting in power plants and substations. 1. Core Test Functions Modern instrument transformer characteristic testers are typically multi-functional, capable of automatically completing the following key tests: A. Current Transformer (CT) Tests Voltage-Current Characteristics (Excitation Characteristics): Measures the relationship curve between voltage and current of the secondary winding (U-I curve), which is the basis for judging CT saturation characteristics and calculating the 10% error curve. Ratio Test: Automatically measures the actual current ratio to verify the accuracy of nameplate parameters. Polarity Check: Automatically determines subtractive or additive polarity to prevent incorrect protection connections. DC Resistance Test: Measures the DC resistance of the secondary winding to check coil integrity. Demagnetization: Automatically demagnetizes the core to eliminate the influence of residual magnetism on measurement accuracy and protection operation. Ratio Error and Phase Error: Some high-precision models can measure the ratio error and phase error of metering CTs. Secondary Burden: Measures the actual impedance of the secondary circuit. Transient Characteristics (TP Class): For TPY/TPZ class CTs used in ultra-high voltage systems, tests the transient factor and time constant. B. Voltage Transformer (PT/VT) Tests Excitation Characteristics: Measures the U-I curve on the secondary side of the PT. Ratio Test: Verifies the voltage transformation ratio. Polarity Check: Determines wiring polarity. DC Resistance Test: Measures the DC resistance of the winding. Secondary Burden: Measures the load of the secondary circuit. Power Frequency Withstand Voltage: Some models have a simple power frequency withstand voltage output function (note capacity limitations). 2. Working Principle and Technical Advantages Frequency Conversion Anti-Interference Technology: Traditional methods use power frequency (50Hz) testing, which is susceptible to on-site electromagnetic interference. Modern instruments use frequency conversion methods (such as 45Hz-65Hz automatic scanning or higher frequencies), using digital filtering algorithms to eliminate interference signals, allowing high-precision data acquisition in strong interference environments without removing primary leads. High Voltage/High Current Output: Voltage Output: Typically up to 0~1000V (or even 1800V), sufficient to saturate large protection-class CTs. Current Output: Some models have built-in high-current sources, allowing direct ratio testing without external current boosters. High Automation: One-button operation; the instrument automatically increases voltage, collects data, plots curves, calculates knee point voltage, calculates 10% error multiples, and directly generates reports. Safety: Equipped with overvoltage, overcurrent, and overheat protection, and the test process automatically discharges. 3. Mainstream Technical Parameters and Features for 2025-2026 According to the latest standards (such as GB/T 20840 series, DL/T 596-2025, IEC 61869), current high-end models have the following features: Table Feature Dimension Detailed Description Output Capability Voltage: 0~1000V/1800V; Current: 0~5A/10A (built-in); supports external current booster to expand to over 1000A. Measurement Accuracy Voltage/current accuracy better than 0.05%, ratio error < 0.1%. Test Speed A single group of CT voltage-current characteristic tests is usually completed within 30 seconds to 1 minute. Intelligent Analysis Automatically calculates knee point voltage, saturation voltage, 10% error curve, limit electromotive force, ALF (Accuracy Limit Factor). Display Interaction 7-inch to 10-inch high-definition color touch screen, real-time display of U-I curve, error curve, supports gesture zoom. Wireless Function Supports Bluetooth connection to micro printers, or uploads data to cloud/PMS systems via Wi-Fi/4G. Applicable Types Covers all types including protection class (P), metering class (M), transient class (TPY/TPZ), and zero-sequence CTs. Portability Lightweight main unit (<10kg), built-in lithium battery, suitable for field work without power supply.
