I. Classification of Transformer Ratio Testers
Based on technical principles, application scenarios, and integration level, the transformer ratio testers available in the market are mainly classified as follows:
(1) By technical principle
Traditional type (ratio bridge)
Characteristics: Based on the classic bridge balance principle, manual adjustment of the resistor box is required to balance the bridge, and then the ratio value is read.
Current situation: only used as basic tools in some teaching or specific calibration sites.
Digital type (fully automatic transformer ratio tester)
Characteristics： Utilizing modern digital sampling and DSP (digital signal processing) technology， a low-voltage test power supply (usually three-phase or single-phase) is generated internally. Through a high-speed ADC (analog-to-digital converter) to simultaneously collect the voltage waveforms on the high and low voltage sides, the fundamental component ratio value is calculated to obtain the ratio and phase angle.
Advantages: Fast speed, high accuracy, strong anti-interference ability, supports automatic identification of complex connection groups, and is currently the mainstream product in the market.
(2) By function and application scenarios
General type (portable)
Application： Mainly used for 35kV and below， smaller capacity distribution transformers for daily maintenance.
Features： Small size， light weight (3-5kg)， simple operation， often equipped with lithium battery power supply， convenient for on-site carrying.
Professional type (three-phase / special transformer dedicated)
Application： Suitable for 110kV and above voltage level power transformers， as well as Z-type transformers， rectifier transformers， Scott transformers， etc.， special transformers.
Features： Usually equipped with a large screen， capable of drawing vector diagrams； stronger anti-interference ability， can work stably in the strong electromagnetic environment of the substation； wide measurement range， up to 0.9-10000 or even higher.
Handheld (dumb / rapid screening type)
Application： Used for on-site rapid inspection to determine if the transformer has obvious short circuits between windings.
Features： Extremely portable， small screen， relatively simple functions， usually only displays ratio and error， without complex vector analysis functions.
(3) By winding test method
Single-phase tester： Can test single-phase or three-phase transformers in single-phase mode.
Three-phase tester： Equipped with a three-phase power supply output internally， one connection can complete the three-phase ratio test without manual line change， high testing efficiency， and is currently the mainstream power test recommended equipment.
II. Core considerations for transformer ratio tester selection
In addition to the measurement range and accuracy， when selecting， key elements to focus on include：
Connection group testing capability
Not only need to pay attention to the number of connection groups supported by the instrument (such as 0-11 groups)， but also need to confirm whether it has the automatic group discrimination function. For imported foreign or old non-standard transformers， it is necessary to verify whether the instrument can automatically measure and obtain results， or whether it requires manual pre-selection of the group.
Special transformer testing algorithm
If it involves electric furnace transformers， rectifier transformers， or Scott transformers， it is necessary to confirm that the menu of the tester clearly includes the corresponding dedicated testing algorithm. Ordinary algorithms will generate large phase errors， resulting in invalid test results.
Voltage transformer (PT) and current transformer (CT) ratio measurement
This function is an extended function. Some high-end testers， in addition to transformer testing， can measure the ratio of voltage transformers through external standard voltage transformers or direct low-voltage excitation. When there are many types of equipment， it can save the cost of separately purchasing transformer testing instruments.
Anti-interference performance
Suitable for transformer testing in substations， especially GIS (gas-insulated fully enclosed combined electrical equipment) or near operating busbars. When selecting， check the anti-interference indicators in the manual， and preferentially choose equipment that supports non-frequent measurement (using 45Hz/55Hz etc.， avoiding interference from the site) as it directly affects the stability of on-site testing.
Waveform display and analysis function The model with real-time display function of hexagonal diagrams (vector diagrams) is of high-end type. Besides verifying whether the transformation ratio is qualified, it can also assist in analyzing the wiring polarity of CT/PT and checking for potential phase angle differences inside the transformer.
Post time: Mar-03-2026