Selection is a systematic process of gradually matching the performance of the instrument based on one’s own needs. Please follow the following five steps:
Step 1: The primary task – Clearly define the test object and core requirements
This is the foundation of the selection process. It is necessary to clearly identify the main test object of the instrument. Common test objects include power transformers, ranging from distribution transformers to large power transformers, followed by generators, windings of large motors, reactors, and transformers.
The selection of test current is a key parameter in this step, and its magnitude directly determines the measurement speed and the ability to detect hidden defects. The larger the current, the faster the transformer core can be magnetized and saturated, significantly reducing the waiting time for stable readings, and providing a stronger signal-to-noise ratio, which is helpful in detecting subtle issues such as inter-turn short circuits.
Selection reference standards are as follows: For 10kV/35kV and capacity below 2500kVA distribution transformers, choose an instrument with a 5A or 10A output, which can achieve a good balance between speed and portability; for large power transformers of 110kV and above, a large current model of 20A, 40A, or even above is required; for equipment with thinner windings such as voltage transformers, choose a small current gear such as 1A or 3A to avoid overheating of the equipment.
Step 2: Review core performance – Accuracy, speed, and stability
After determining the current level, it is necessary to evaluate the intrinsic quality of the instrument.
Measurement accuracy
This is a key indicator for measuring the professionalism of the instrument. The basic model accuracy is usually at the ±(0.2% reading + several digits) level, which can meet the needs of most on-site inspection; if used for strict交接试验， fault diagnosis， or manufacturing quality inspection， then a model with an accuracy of ±0.1% or higher should be selected. Resolution
The instrument requires a high resolution capable of displaying down to 1 micro-ohm (μΩ) or even 0.1 μΩ. High resolution can sensitively capture the subtle changes in winding resistance, making it a powerful tool for detecting early defects in equipment.
The value of the three-channel instrument
A true three-channel instrument must be capable of applying current simultaneously to three-phase windings and conducting synchronous voltage measurement. This design ensures that the three sets of measurement data are obtained under the same magnetic state of the core, making the calculated three-phase resistance imbalance rate highly comparable and diagnostic in value. At the same time, the measurement efficiency is much higher than the single-channel sequential measurement mode.
Anti-interference and stability
There are a large number of power frequency electromagnetic interferences in the field environment. Professional handheld three-channel DC resistance testers must have strong anti-power frequency interference capabilities, such as using frequency conversion methods, and can quickly obtain stable and non-jumping readings even under high current output. This performance directly affects the efficiency of on-site work and the credibility of measurement data.
The third step: Evaluate key functions – Enhance efficiency and value
The instrument’s functions determine whether it can solve deeper working problems. Key functions to focus on include:
Demagnetization function
This function is a strongly recommended feature. The test current will cause the transformer core to generate residual magnetism, which may affect the excitation surge and operational safety after equipment commissioning. The demagnetization function can automatically attenuate the current after the test, effectively eliminating the residual magnetism of the core, which is an important function of responsibility towards the equipment and professionalism in operation, especially suitable for the testing of large-capacity transformers.
Temperature rise test function
By monitoring the changes in winding resistance over a long period, the average temperature rise of the winding can be calculated more accurately. This function is an important project support in transformer research and development, type testing, and acceptance work.
Intelligent data management
It is necessary to pay attention to whether the instrument supports large-capacity data storage, whether it can export data through USB, Bluetooth, or Wi-Fi, and whether it is equipped with professional computer analysis software. This function is crucial for generating test reports, comparing historical data, and conducting trend analysis.
Automatic calculation and diagnosis
The instrument should be able to automatically calculate the three-phase resistance imbalance rate based on the measurement results and can automatically give “qualified / unqualified” judgment prompts according to national standards or user-defined thresholds, thereby simplifying the workflow of on-site data judgment.
The fourth step: Consider on-site adaptability – Portability, battery life, and environment
The core application scenario of handheld equipment is on-site work. It is necessary to evaluate its on-site adaptability from the following dimensions:
Portability
The instrument’s weight should be well controlled within 5 kilograms, and it should have a small size, facilitating single-person carrying and climbing operations. Some high-current models may have a relatively higher weight, which needs to be weighed against actual needs.
Battery life
It is necessary to ensure that the instrument can meet the needs of a full day of field work with a single charge. Generally, it is recommended that the battery life be above 8 hours.
Environmental adaptability
The working temperature range of the instrument should be wide, such as -10°C to 50°C, and it should have certain dustproof and moisture-proof capabilities to adapt to complex on-site environments such as substations and outdoors.
The fifth step: Examine brand and service – Long-term use guarantee
It is necessary to choose a reputable brand. Such brands usually provide more reliable product quality and longer equipment service life. At the same time, it is necessary to understand the coverage of the brand’s after-sales service network, the convenience of calibration services, and the technical support capabilities, which are important backbones for ensuring the continuous and stable operation of the instrument.
Post time: Jan-19-2026