* Working on processing unit at Edmonton refinery
* Maintenance to continue into May
* No supply shortages expected (Adds details on duration of shutdown)
CALGARY, Alberta, April 19 (Reuters) - Imperial Oil Ltd (IMO.TO) said on Monday it has started planned maintenance on a processing unit at its 187,000 barrel per day Strathcona refinery in Edmonton, Alberta.
The shutdown of the unit began on Sunday and is expected to last into May, said Jon Harding, a spokesman for Imperial.
Harding declined to say which of the refinery's units was being worked on or how much daily output was affected by the shutdown. However the company does not expect supplies to customers to be affected by the work. (Reporting by Scott Haggett)