I. General

DC resistance of transformer is one testing item which must be tested during ex-work test of semi-finished products and final products, installation, acceptance test and preventive test of electric power department, which can effectively find out material selection of transformer coil, welding, looseness of connection part, missing strand, broken wire etc manufacturing defect and existing hidden problems after operation. The traditional high and low voltage series connection test of the constant current source can’t be applied during temperature rise test of the power transmission transformer because difference between high and low voltage windings of the transformer is great. Now if two testing meters are applied for testing, it is liable to damage the instrument because of mutual induction between high and low voltage windings of the transformer. Our company has developed and researched this instrument, which solves this problem. The instrument applies double constant current source design, CUP program controlled charging and discharging sequence and perfect protection measures, which is highly applicable to temperature rise test of the transformer with great difference between high and low voltage windings.

II. Safety Measures

1. Ensure to carefully read the manual prior to use the instrument.

2. The instrument operator shall have general application knowledge about electric equipments or instruments.

3. The instrument can used indoor and outdoor, it shall avoid application location with rain, corrosive gas, heavy dust, high temperature, direct sun shining etc.

4. The instrument is high precision instrument, it shall avoid violent vibration.

5. Only professional personnel is allowed to carry out repair, maintenance and commissioning of the instrument.

6. When testing is complete, ensure to switch off power supply and disconnect testing line after discharging alarm is stop.

7. Switch shift of transformer only after discharge alarm is stop during measurement of no-load voltage regulating transformer.

8. Prohibit disconnect and move testing clip and power supply line during testing.

III. Performance Characteristic

1. Output current of the instrument is great (maximum output is 20A) and testing scope is wide(maximum 2KΩ), which is applicable to temperature rise test and measurement of DC resistance of all transformers at 35KV voltage class and below.

2. Perfect double power supply design. Simultaneous testing and individual testing function of high voltage side and low voltage side.

3. This machine has protection alarm function for input mis-connection of AC380V power supply, wire breakage and arcing resistant protection function and sound discharging alarm function, indication is clear and mis-operation is reduced. With perfect protection circuit, reliability is strong.

4. Large colourful screen, touching control operation and display data is clear and legible.

5. Temperature rise testing is printed out automatically according to setting time, and temperature rise data are stored, which facilitate recording.

6. The instrument is equipped with the perpetual calendar, 100 groups of conventional data storage, and result storages of 3 temperature rise tests. Data will not be lost after shutdown, which facilitate review. It is equipped with the “U disc” interface which conveniently export data for the machine to generate the temperature rise curve.

7. The instrument is equipped with RS485 communication interface, remote control measurement can be realized after upper position machine operation and control software is installed.

8. This machine is equipped with temperature rise software, which can carry out data processing and generate temperature rise curve automatically.

IV. Technical Index

1. Output current:

High voltage CH1:   5A, 1A, 0.3A,0.1A, 0.01A

Low voltage CH2:   20A, 10A, 5A, 2A

2. Measuring scope:

(High voltage CH1---5A)：   0Ω——4Ω

(High voltage CH1---1A)：   20mΩ——20Ω

(High voltage CH1---0.3A)： 60mΩ——60Ω

(High voltage CH1---0.1A)： 200mΩ——200Ω

(High voltage CH1---0.01A)：2Ω——2000Ω

(Low voltage CH2---20A)： 0Ω——0.1Ω

(Low voltage CH2---10A)： 2mΩ——0.4Ω

(Low voltage CH2---5A)：  4mΩ——0.8Ω

(Low voltage CH2---2A)：  10mΩ——2Ω

3. Accuracy: (high voltage CH1): 0.2%±1μΩ

(Low voltage CH2):0.2%±0.2μΩ

4. Minimum resolution: 0.1μΩ

5. Interval for temperature rise record data: 5s-90s (Can be set at 5s interval)

6. Working temperature: -20～40℃

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

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

9. Volume: 360mm length × 280mm width × 170mm height

10. Net weight: 8 kg