The transformer calibration instrument is a core precision instrument used in the power system for detecting and calibrating the performance of current transformers (CT) and voltage transformers (PT/VT). It plays a crucial role in power metering, relay protection, and power system monitoring. This article will comprehensively analyze the transformer calibration instrument from aspects such as core functions, working principles, and main types.
I. Core Functions
The core function of the transformer calibration instrument is to measure and evaluate multiple key performance parameters of the transformer, including:
Ratio Difference (Ratio Error): It refers to the percentage error between the actual secondary output value of the transformer and the converted value of the rated ratio, which is the core indicator for measuring the accuracy of the transformer’s ratio.
Phase Difference (Phase Angle): It refers to the phase angle difference between the primary and secondary signals of the transformer, usually measured in degrees (′) or centi-radians (crad).
Excitation Characteristics (V-A Characteristics): It measures the relationship curve between the excitation current and voltage of the CT, through which two key parameters can be calculated: one is the turning point voltage/current, which is the core basis for judging whether the CT has saturation phenomenon; the other is the composite error, used to evaluate the operation performance of the protective CT in short-circuit fault conditions.
Secondary Load (Load): It measures the actual impedance (Ω) or apparent power (VA) of the secondary circuit connected to the transformer, ensuring the matching of the secondary circuit operation.
Polarity Check: It determines whether the polarity of the primary and secondary windings of the transformer is correct. In the power system, transformers usually adopt the negative polarity connection method.
Secondary Circuit Integrity Check: It detects whether there are open circuits, short circuits, or poor contact in the secondary winding, to avoid affecting the normal operation of the transformer due to circuit problems.
II. Working Principle
Modern transformer calibration instruments generally adopt high-precision electronic comparison principles, and are divided into two main technical routes:
Standard Source Method: This is an early commonly used technical solution. The core is to use a highly accurate standard transformer as the reference benchmark, comparing and analyzing the output data of the tested transformer with that of the standard device, thereby obtaining the error parameters of the tested transformer.
Electronic Direct Comparison Method: This is the current mainstream technical solution. Its working process is that the instrument internally generates or collects the current and voltage signals of the primary and secondary sides of the transformer, through high-precision sampling modules, A/D conversion modules, and digital signal processing technology, directly calculating the amplitude ratio and phase difference between the two signals, and ultimately obtaining the ratio error and phase angle error data. This method does not require a bulky standard transformer, and the equipment is smaller in size and lighter in weight, while having a higher degree of automation.
III. Main Types
According to different functional positioning and application scenarios, transformer calibration instruments can be classified into the following three types:
Multifunctional Comprehensive Calibration Instrument: This is the most widely used mainstream type, capable of simultaneously testing CT and PT, integrating excitation characteristic testing, load testing, direct resistance testing, and other functions, and meeting the comprehensive detection requirements in multiple scenarios.
Special CT Analyzer: Its function positioning focuses on the comprehensive performance testing of CT, especially having advantages in excitation curve drawing and saturation characteristic analysis, playing a key role in relay protection debugging.
Field Portable Calibration Instrument: It adopts a lightweight design, with a small volume and light weight, more suitable for on-site operation and inspection scenarios. The functional configuration of this type of instrument is relatively simplified, but retains core functions such as ratio error, phase angle error, and polarity test, capable of meeting the basic needs for rapid detection on-site.
Post time: Jan-14-2026