Please have a read of point 11 here.
Create a template binary sensor that is on when your power is above 30W.
Then use that binary sensor in the history stats integration.
template:
- binary_sensor:
- name: "Kamin Leistung akt > 30 W"
state: "{{ states('sensor.plug7_kamin_energy_power') | float(0) > 30 }}"
device_class: power