What are the safety requirements for control transformers?

07 02, 2020

1. Insulation resistance: the insulation resistance of the control transformer in the cold state should be no less than 10MΩ; the insulation resistance of the control transformer in the hot state and the wet state should be no less than 2MΩ.

2. Insulation strength: The electrical insulation strength of the control transformer should be able to withstand the withstand voltage test of AC 50Hz, 2000V sinusoidal AC voltage, and no breakdown or flashover will occur for 1min.

3. Leakage current: The leakage current of the control transformer shall not exceed 3mA.

4. Temperature rise: the limit temperature rise of the coil of the control transformer (Class E insulation) shall not exceed 75K (resistance method); the limit temperature rise of the iron core (class E insulation) shall not exceed 55K (semiconductor point thermometer method).

5. Grounding: The control transformer should have a dedicated terminal for grounding and marked with a grounding symbol.


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