* Output from Troll gas field reduced by 34 mcm/d
* Production at Karstoe gas plant down by 21 mcm/d
OSLO, May 19 (Reuters) - Norway's gas output will be reduced by a further 34 million cubic metres (mcm) per day due to an unexpected outage on Sunday at the country's biggest gas field, Troll, gas system operator Gassco said.
The outage caused by power supply interruption, which shut down compressors at Statoil (Xetra: 676685 - news) -operated Troll A platform, comes on top of a 21 mcm per day reduction at Karstoe gas processing plant, announced earlier.
Both outages are expected to last for 24 hours, reducing gas deliveries from Norway, Europe's second-largest gas supplier, by 55 mcm per day, Gassco added.
Troll A platform in the North Sea is powered from onshore, and it feeds gas to another gas processing plant, Kollsnes.
Norway's pipeline gas exports to Europe totalled 285 mcm per day by 0647 GMT, same as Saturday average, flows data from Gassco showed.
The export figures are based on gas fed into the system at a certain time and calculated to a daily average.
(Reporting by Nerijus Adomaitis)