Instrument Overview

DC Resistance Quick Tester (0-40A) Product



Measuring the DC resistance of transformer windings is a very important test item. In the "Regulations for Power Equipment Testing," it is ranked second among transformer test items. The regulations stipulate that during transformer handover, major repairs, minor repairs, tap changer position changes, fault inspections, and preventive tests, the DC resistance of transformer windings must be measured. The purposes are: [1]



① Check the welding quality of internal winding conductors and leads



② Check whether the contacts at each position of the tap changer are good



③ Check whether there are any broken points in the windings or leads



④ Check the correctness of parallel branches, whether there is a situation where one or more breaks occur in a winding made of several parallel conductors



⑤ Check for short circuits between layers and turns



This product complies with the requirements of national standards GB6587-86 "General Outline for Environmental Testing of Electronic Measuring Instruments" and GB6593-86 "Quality Inspection Rules for Electronic Instruments."



Alternative names for the DC Resistance Quick Tester:



DC Resistance Rapid Tester, Transformer DC Resistance Tester, Transformer Winding DC Resistance Tester, Transformer DC Resistance Rapid Tester, Transformer DC Resistance Quick Tester, Inductive Load DC Resistance Rapid Tester, Inductive Load DC Resistance Quick Tester, Inductive Load DC Resistance Tester



Overview



Transformer DC resistance testing is a mandatory test item for power equipment manufacturers and power generation and supply departments during factory inspection, handover tests, and preventive tests. It effectively improves product quality and prevents power accidents. The Transformer DC Resistance Tester consists of a high-power switching power supply circuit, precision small-signal measurement circuit, protection circuit, and high-speed microcontroller control circuit. It has functions such as instrument self-check, signal measurement, data processing, rapid discharge, and print results.



2 Main Features of the Instrument

1. Uses a high-speed 16-bit A/D converter, providing stable measurement data and good repeatability.



2. Automatic program-controlled current source technology. The current source has 1000 current levels, automatically controlled by the internal microcontroller based on the measured resistance, achieving a wide measurement range and optimal measurement state without manual current switching.



3. Fast response speed. The tap changer can be switched directly during measurement, and the instrument will automatically prompt, with the new resistance value displayed quickly.



4. Highly intelligent design with clever and advanced function settings, capable of automatically detecting faults such as loose test leads or broken wires.



5. Comprehensive protection functions, reliably protecting the instrument from back EMF impacts, with automatic discharge indication.



6. Displays measurement current and measurement time.



7. Intelligent power management technology effectively reduces internal heating of the instrument.



8. Can store 120 measurement data sets, which are not lost after power-off.



9. All Chinese menus and operation prompts, intuitive and convenient.







3 Structural Characteristics and Working Principle

This tester adopts the typical four-wire measurement method to improve the accuracy of measuring resistance (especially low resistance). The program-controlled constant current source, program-controlled preamplifier, and A/D converter form the main body of the measurement circuit. The central control unit applies a constant, high-precision current to the external load under test by controlling the constant current source, then processes the obtained data (including test voltage and current test current) to obtain the actual resistance value.



This instrument can store 255 test data sets and can print all stored test data. The stored data is not lost upon reset or power-off.



[Instrument Technical Specifications] (Taking HT-40A as an example)



1. Output four current levels: 40A, 20A, 10A, 5A



2. Resolution: 0.1μΩ



3. Range: 20mΩ - 4Ω (5A level); 10mΩ - 2Ω (10A level);



0.2mΩ - 1Ω (20A level); 0.1mΩ - 0.5Ω (40A level);



4. Accuracy: 0.2%



5. Ambient temperature: 0～40℃



6. Ambient humidity: <90%RH



7. Working power supply: AC220V±10%, (50±1)HZ



8. Dimensions: 400×200×350mm



9. Weight: 13kg



Test current 5A, 10A, 20A, 40A



Measurement range



5A: 1μΩ~4Ω



10A: 1μΩ~2Ω



20A: 1μΩ~1Ω



40A: 1μΩ~0.5Ω



Measurement accuracy ±0.2% (full scale)



Display method 128×64 dot matrix display, resistance displayed as 4 1/2 digits



Maximum resolution 0.1μΩ



Power supply AC 220V±22V, 50Hz±2 Hz, fuse 5A



Maximum power consumption 600W when test current is 40A



Working environment Ambient temperature: 0°～40°



Relative humidity: ≤80%



Volume 400╳200╳425(mm)



Weight 12kg with accessories



Features:



① Microcomputer-controlled intelligent instrument, can store test results;



② AC powered, portable design, easy to use and carry;



③ Uses advanced constant current power supply technology, greatly reducing the instrument's volume, weight, and power consumption, further shortening measurement time, and ensuring more stable and reliable measurement data.



④ Built-in micro printer, directly outputs printed results



⑤ This instrument is suitable for measurement and analysis of inductive, low-resistance values such as various power transformer and instrument transformer windings.



[Instrument Precautions]



1. Before switching the tap changer of an on-load tap-changing transformer, be sure to reset. After discharge ends, wait for the discharge prompt sound to end and the prompt message to disappear before switching the tap changer.



3. After the test, press the "Reset" button. Be sure to wait for the discharge indicator light to go out and the prompt message to disappear before turning off the power and disconnecting the wires.



4. During the test, avoid power outages or test clamp detachment.



5. Connect the ground wire before turning on the power, and disconnect the ground wire last after the test.