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Megohm meters troubleshoot transformers

time:2020/6/14   source:华天电力  reading:308 time

Transformer has many shape, size and type, voltage transformer and current transformer, power transformer, audio and signal transformer, a step-up transformer and step-down transformer, autotransformer and isolation transformer, as well as many other types, no matter what their purpose is, they all suffer from the same basic problems, for example, into a short circuit, open winding, winding grounding short circuit, all these problems can be through some simple tests and megohm meter to test.


Insulation Resistance Tester.png


Use megohm meter to test the power transformer


Step 1


Test whether the primary winding of the transformer is short circuiting to the secondary winding, set the megohm meter to a high resistance range (for example, 2 megohm), and then contact the primary winding terminal with one probe, and contact the secondary winding terminal with another probe; If the transformer has multiple secondary windings, repeat this test for each secondary winding, and your Megabyte should record the "infinite" resistance and read "open" to indicate a good transformer. Different meters indicate this situation in different ways. The megometer displays "1" and indicates open circuit on its LCD. The continuous reading here indicates short circuit between windings, transformer is damaged and needs to be replaced.


Step 2


Test short circuit of transformer winding to laminate. As set in the first step is megohmmeter, by placing a probe on a winding terminal, will be another probe on the metal frame transformer, check each winding, respectively, to ensure that the transformer enclosure probe contact bare metal, and didn't stay in May be used as an insulator, a type of surface treatment on the scratching tip back and forth, until it contact with the base metal.


Step 3


Megabyte probes are placed on the terminals of each winding to test the conductivity of the primary and secondary windings, and the Megabyte is set in a relatively low range, such as 200 ohms. It is normal for most small power transformers to have very low DC resistance, where a high or "open" reading indicates partial or complete disconnection of the windings and the need to replace the transformer.


Step 4


Check the output voltage of the transformer and connect the primary transformer to the 110-volt power supply using the test jumper. Take care that the alligator clips do not touch or touch certain ground surfaces. After inserting the power cord, do not touch the clip or the main terminal, otherwise it may cause fatal electric shock. Set the Megabyte to the appropriate AC voltage range and test each individual secondary winding by placing the probe on the terminal and noting the voltage.


Step 5


Check the inter-turn short circuit in the primary winding and the secondary winding, the output voltage reading is significantly higher than the rated output of the transformer, indicating the inter-turn short circuit in the primary winding; If the output voltage is significantly lower than the rated output of the winding, indicating an interturn short circuit of the secondary winding, the output voltage may vary by ± 10% and within the acceptable range, but anything above or below this value indicates a transformer fault.


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