What are the safety requirements for controlling transformers?

1. Insulation resistance: The insulation resistance of the control transformer under cold conditions should be no less than 10MΩ; the insulation resistance of the control transformer under hot and tidal conditions 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 and 2000V sinusoidal AC voltage. No breakdown or flashover will occur after 1min.

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

4. Temperature rise: The limit temperature rise of the coil of the control transformer (E-class insulation) shall not exceed 75K (resistance method) measurement; the limit temperature rise of the iron core (E-class insulation) shall not exceed 55K (Semiconductor Point Thermometer Method) measurement.

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