Convert 60V AC 50Hz to 60V AC 25Hz
Summarizing your problem, you need 25Hz AC from a 50Hz AC source. This is the job of a Step-Down Cycloconverter.
Check this out: https://everycircuit.com/circuit/5551505345871872/step-down-cycloconverter
(Click on the graph window to expand)
In the linked example, 50Hz is reduced to 16.7Hz, or 1/3rd of the input frequency. By re-configuring the control circuit to meet your needs, you can get 1/2 of the input frequency.
You can find more information about Cycloconverters on wikipedia.