Determines the active source for an Electrical Study. Possible values for this property are -1 - stNone: None (default), 0 - stActiveSource: Active Source, 1 - stScada: SCADA, 2 - stOperator: Operator, 3 - stCCLink: Control Center, 4 - stBilling: Billing, 5 - stCalculated: Calculated, or 6 - stDatabase: Database. The selected source type must exist in the Analog Measurement to be set as an input of an Electrical Study. If this property is set to 0 (zero, Active Source), it follows the configuration performed in the ActiveSource property. Users cannot select type 0 (zero, Active Source) if the ActiveSource property is set to 100, 101, 102, 103, 104, 105, or 106 (outputs of Electrical Studies). In case the selected source is deleted, this property assumes a value of -1 (minus one, None).