TTC - Total Transfer Capacity
Total Transfer Capacity is defined as the maximum exchange programme between two areas compatible, on a given technical profile, with operational security standards applicable at each system if future network conditions, generation and load patterns were perfectly known in advance.
TRM - Transmission Reliability Margin
Transmission Reliability Margin is the reserve cross-border transmission capacity maintained in case of possible emergency events and due to uncertainty as to the accuracy of data used in determining of TTC value.
NTC - Net Transfer Capacity
Net Transfer Capacity is the maximum capacity for exchange of power between two areas, compatible with security standards applicable in both areas and taking into account the technical uncertainties on future network conditions. NTC is defined as:
NTC = TTC - TRM
AAC - Already Allocated Capacity
Already Allocated Capacity is the total amount of allocated transmission rights i.e. transmission capacity reserved by virtue of historical long-term contracts and the previously held transmission capacity reservation auctions.
ATC - Available Transfer Capacity
Available Transfer Capacity is the transmission capacity that remains available, after allocation procedure, to be used under the physical conditions of the transmission system. ATC value is defined as:
ATC = NTC - AAC
The figure below represents the technical volumes of the cross-border exchange transmission capacity:
TSO determines offered transmission capacities in auctions according to the rules described in the document "Rules for determination of interconnections transmission capacities" (only in Polish).