I don’t know if you can alter the behavior of the power chart. You can put this script in a separate button. It will query the tag historian and return a dataset with a value every 30 seconds. You can use either system.dataset.exportExcel or system.dataset.toExcel + system.perspective.download to ‘export’ to the user.
Note: Property names are vision syntax. Replace these properties with the appropriate Perspective properties and you can use it there too.
data = system.tag.queryTagHistory(
# you can have more than one tag path in the list. They'll show up as separate columns
startDate=event.source.parent.getComponent('Easy Chart').startDate, # replace
endDate=event.source.parent.getComponent('Easy Chart').endDate, #replace
aggregationMode='Average', #read about various aggregation modes. Pick the one you like
intervalSeconds=30, # only available in 8.1.0 or later
noInterpolation=0 # Investigate whether you want this on or off
# this line is for testing. You'd actually want to do something with the dataset.
event.source.parent.getComponent('Table').data = data
For more, see docs on system.tag.queryTagHistory.