"never ever give up"
Hello to all
In the meantime i solved my problem as follows 
In the " [[inputs.mqtt_consumer]] " part of the telegraf.conf file i added the following …
==> fielddrop = [“ENERGY_ApparentPower”,"_Factor","_Period","*_ReactivePower"]
… and now only the relevant/desired data are stored in the influxdb database.
Best regards
