The working principle of secondary circuit testing equipment varies depending on its specific type, but the core principle is based on electrical measurement to evaluate the accuracy and safety of key parameters in the secondary circuit. The following are the working principles of several common types of equipment:
Current Transformer Secondary Load Tester:
Used to measure the secondary load of current transformers (CTs) and voltage transformers (PTs). It applies a test signal to the secondary circuit, measures voltage and current, and calculates parameters such as impedance, admittance, resistance, and reactance. It uses clamp-on ammeter sampling technology to achieve uninterrupted testing and supports dual-mode impedance and admittance measurement, ensuring efficient and safe on-site testing.
Secondary Voltage Drop and Load Measuring Instrument:
Integrates voltage drop and load testing functions. Secondary voltage drop measurement uses the differential measurement principle, simultaneously acquiring the voltage amplitude and phase at the PT output and the energy meter terminal, calculating the ratio difference, phase difference, and combined error. Secondary load measurement uses injected test signals, combined with high-precision sampling and digital signal processing algorithms (such as FFT analysis) to resist interference and improve accuracy. Modern equipment employs GPS/BeiDou synchronization or current zero-crossing synchronization technology to achieve wireless master-slave communication, avoiding long-distance wiring.
Secondary circuit resistance testers, based on the
DC voltage drop method (R=U/I), apply a stable large current (e.g., 100A) to the circuit under test (e.g., circuit breaker contacts), measuring the minute voltage drop across it. The four-terminal (Kelvin) wiring method eliminates the influence of lead resistance, thus accurately calculating the circuit resistance value. This method complies with the requirements of power preventive testing regulations and is widely used in switchgear maintenance.
These devices generally employ high-resolution ADCs, digital filtering technology, and intelligent algorithms, maintaining stable readings even in strong electromagnetic environments, ensuring the reliability of power system relay protection and metering.
