I. Overview 

The DC resistance of a transformer is a necessary measuring item in the testing, installation, commissioning testing and electric power department’s preventive testing of semi-finished products and finished products in transformer manufacturing. It can be used to effectively detect the selection of transformer coils, welding, loose connection parts, missing strands, broken wires, etc.In order to meet the needs of Fast measurement of DC resistance of transformers, huazheng has developed a new generation of huazheng series DC resistance test instrument using its own technological advantages. The instrument uses a new power supply technology and has features such as small size, light weight, large output current, etc. It is a test instrument optimized for measuring the three-phase winding DC resistances of large-capacity transformers. The instrument can be used to measure the three-phase winding DC resistances of a transformer at the same time. For an on-load tap changing transformer, there is no need for discharging and tapping is directly adjusted with the instrument; the measuring time is 1/3 of traditional single-phase measuring time, which can greatly shorten working time. The whole instrument is controlled by SCM and automatically achieves functions such as self-check, data processing, display, etc. Moreover, the instrument has functions such as automatic discharging, audible alarming of discharging, etc. The instrument has advantages such as stable test data, high accuracy, quick speed and good repeatability, and is the best choice for measuring the DC resistance of transformer on site.

II. Safety Measures

1.Be sure to carefully read the operation manual before using the instrument.

2.The instrument operator shall have general knowledge about the use of general electrical equipment or instruments.

3.The instrument can be used both indoors and outdoors. However, be sure to avoid using it at the following places with rain, corrosive gas, too high dust concentration, high temperature, or direct sunlight, etc.

4.The instrument is a high-precision instrument; therefore, it is required to avoid severe vibration of the instrument, and some shock absorption measures shall be taken during transportation.

5.Repair, maintenance and commissioning of the instrument shall be performed by professional personnel.

6.To ensure personal safety, a reliable ground wire shall be connected before turning on the power; in addition, the ground wire shall be removed after removing the power.

7.It is forbidden to dismantle and move test clips and power supply lines during test. The test lines can be removed after discharging alarm sound is ended upon test completion.

8.For no-load voltage regulation winding, it is forbidden to switch the no-load tap changer when test is being conducted or discharging is not completed.

9.When the power supply suddenly fails during the test, the instrument will start to discharge automatically. At this time, it is forbidden to immediately remove the test lines; they can be removed after the discharging alarm sound is ended.

III. Performance Characteristics 

1.Fixed current output (20mA-40A totaling 9 ranges);automatic current output (0.1-40A the optimal current is set automatically based on the resistance of the test product).

2.Wide measuring range (0Ω-20KΩ); able to measure the inductive DC resistance of transformers, mutual inductors, etc.

3.Functions of single channel measurement, YN three-phase simultaneous measurement, YN three-phase compensation simultaneous measurement (including O-phase resistance), automatic YND11 transformer magnetic, YN three-phase selection measurement, D/Y three-phase selection measurement,etc., and can calculate three-phase resistance balance rate automatically.

4.Function of auxiliary judgment of data stabilization. Automatically calculate the percentage of 5′′, 15′′ or 30′′ resistance deviation, accurately judge the readability of data, and prevent misreading of data.

5.Temperature conversion according to test product materials (copper, aluminum), for convenience of comparison with historical data

6.Transformer demagnetizing function; able to effectively reduce transformer remanence

7.Functions such as perpetual calendar, storage of 99 sets of data, Chinese and English interface selection, etc.; no data loss after shutdown. The instrument is provided with micro-printer and “U disk” interfaces.

8.6" color touch LCD

9.Dual RS485 communication interfaces for convenience of inter-device cascading. In cooperation with the control software of the upper computer, the instrument can achieve remote control and measurement. The instrument can be fitted with an optional built-in bluetooth module to achieve bluetooth wireless communication.

10.Audible discharging alarm, and clear discharging indication to reduce misoperation

11.The instrument is protected from wrong connection of AC380V power; after the protection function is activated, an audible alarm is given to reduce the damage caused by misoperation to the instrument. The instrument also has perfect counter emf protection function and strong arc discharge resistance.

12.The instrument has features such as dust prevention, shock prevention, moisture prevention, high measuring accuracy, good stability and repeatability, high portability, etc.

IV. Specifications 

1.Output current: automatic, 40A, 20A, 10A, 5A, 2A, 1A, 200mA, 100mA, 20mA

2.Range:                       

Automatic (0.1-40A)   0 - 200Ω (three-phase simultaneous measurement 0 - 120Ω)

40A   0 – 0.5Ω         (three-phase simultaneous measurement 0 – 0.3Ω)

20A   0.0005 – 1.0Ω    (three-phase simultaneous measurement0.001–0.6Ω)

10A   0.001 – 2.0Ω     (three-phase simultaneous measurement0.002–1.2Ω)

5A    0.002 – 4.0Ω    (three-phase simultaneous measurement0.005–2.5Ω)

2A    0.005 –  10Ω    (three-phase simultaneous measurement0.01 – 6.0Ω)

1A    0.01 –  20Ω    (three-phase simultaneous measurement0.02 - 12Ω)

200m A  0.1 – 100Ω      (three-phase simultaneous measurement0.1 - 60Ω)

100m A   0.5 – 200Ω     (three-phase simultaneous measurement0.5 - 120Ω)

20m A    10 – 20kΩ      only single-phase test)

1. Accuracy: 0.2%±0.1μΩ

2. Minimum resolution: 0.01μΩ

3. Working temperature: -20~ 40℃

4. Ambient humidity: ≤80%RH, no dewing  

5. Working power supply: AC: AC220V±10%, 50Hz±1Hz

6. Volume: length 420mm× width 320mm× height 200mm

7. Net weight: 14.8kg