The AEMO operating procedures are clear that this calculation works in the following direction:
Dispatch Error = Target (for the Dispatch Interval) – Final MW (for the same dispatch Interval)
Hence as a raw number, the ‘Dispatch Error’ presents a view of the deviation of the unit’s output (for Scheduled and Semi-Scheduled plant) from what the AEMO expected it to be within NEMDE. It should be obvious that ‘Dispatch Error’ cannot be calculated for Non-Scheduled plant.
In terms of the direction of the number:
Positive Dispatch Error indicates that Output was below the AEMO dispatch target (under-production); and
Hence, in this case, large positive Off-Target would be a possible Unit Trip.
Negative Dispatch Error indicates that Output was higher than the AEMO dispatch target (over-production).