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Zhejiang ERG Technology Joint Stock Co.,Ltd

Mobile: 86-18257346462

Tel: 86-576-83200088


Contacts: Wu Nick/Bella Zheng/Blanca Chen

Add: 135 Haisha Road, Shaliu Economic DevelopmentZone, Sanmen County, Zhejiang, P.R.China

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Transformer DC Resistance Tester Measurement Methods And Considerations
- May 07, 2018 -

Transformer DC Resistance Tester Measurement Methods and Considerations

Transformer DC resistance tester is referred to as a DC resistance tester, a direct resistance tester, and an inductive load DC resistance tester. Text name: Transformer DC Resistance Tester. Transformer DC resistance tester is a new type of instrument designed to measure the DC resistance of large-capacity transformers. It is a high-precision steady-state power supply and test part that is designed as a whole. The test process is controlled by a microcomputer, and the steady flow judgment, data acquisition, data processing, and resistance are automatically completed. Value display and print. The instrument can be completed with one-time power supply for the on-load voltage regulator longitudinal test, fully saving test time, and set up a temperature rise test function for transformer manufacturers. It can achieve fast and accurate measurement of various types of transformers, with simple operation, high precision, Anti-jamming and other features. The following describes the measurement method and precautions of the transformer DC resistance tester.

1. Measuring method of transformer DC resistance tester

Measuring DC resistance is an important item in transformer testing. Through the measurement, it can be checked whether the conductive loop of the device has any defects such as poor contact, poor welding, coil failure, and incorrect wiring. In the actual measurement of small and medium-sized transformers, most of them use the direct current bridge method. When the resistance value of the tested coil is more than 1 ohm, it is usually measured by a single-arm bridge, and when it is less than 1 ohm, it is measured by a double-arm bridge. When using two-arm bridges, the potential head of the bridge should be close to the measured resistance, and the current head should be connected to the top of the potential pile head. Before measuring, first estimate the resistance of the coil under test, place the bridge override button in the appropriate position, short-circuit and ground the non-tested coil, and then turn on the power switch to charge. Press the galvanometer switch after sufficient power. Quickly adjust the measuring arm so that the galvanometer hand moves towards the zero line in the middle of the galvanometer scale, fine-tune it, and record the resistance value when the pointer is stationary at the zero position. At this time, the measured resistance value of the coil = magnification × Measurement arm resistance. After the measurement is completed, first open the galvanometer button and then release the power switch

2. Precautions for transformer DC resistance tester

In the measurement process, in addition to the strict observance of electrical safety regulations and equipment test procedures, special attention should also be paid to:

1) When the coil temperature is stable, the temperature difference between the upper and lower parts of the transformer tank should not exceed 3°C;

2) Since the transformer coil has inductance, the charging current during measurement is not stable, and it must be counted after the current is stable. If necessary, measures must be taken to shorten the charging time.

3) Minimize the contact resistance of the wire in the test circuit. The transformer tap in operation is often exposed to poor contact due to the influence of oil film and other dirt. Generally, it needs to be measured several times before switching to avoid discriminating errors.

4) When measuring the low-voltage side of the transformer, all personnel should maintain a proper safety distance from the high-voltage side.

5) The instrument should avoid strong vibration, direct sunlight and magnetic field during transportation, storage and work. When storing and keeping the instrument, attention should be paid to the ambient temperature and humidity. It should be placed in a dry, ventilated, non-corrosive gas place. When exposed to moisture, rain, or sun exposure, use it gently and gently. Do not drop it.

Thank you for your kindly attention. Hope everything goes well with you.


This is Blanca Chen, from Zhejiang ERG Technology Joint Stock Co.,Ltd. We manufacturer and design transformers accessories. 

Products: (Sorry that for the e-mail not to be sent back,our catalogue and web are not attached for our first contact.)

1. All kinds of transformer cooler
2. Oil pump
3. Butterfly valve
4. Oil flow relay 
5. Control cabinet

6. Terminal box etc.
ERG join the draft of the standard for chinese government in transformers accessories, with certifications:CE, CRCC,IRIS,EUP,TS,CNAS,BV etc. 


Whatsapp/Wechat/Tel: 86 13626615457



Best Regards,

Blanca Chen