On-line Security Constrained ATC Calculations (SC-ATC)

SC-ATC accurately determines the ATC and the required ancillary service of large-scale interconnected power systems. SC-ATC employs advanced techniques to handle the following static and dynamic security constraints of a list of credible contingencies: (i) thermal limits, (ii) voltage limits, (iii) voltage stability limits and (iv) transient stability limits. SC-ATC also determines the required ancillary services such as VAR control and the service components that facilitate power transfers. The current version of SC-ATC can handle power systems up to 40,000 buses. The modeling capability of SC-ATC is very comprehensive.

Comprehensive Modeling and Scope

Due to the nonlinear nature of interconnected electric systems, ATC's between two areas and their associated binding constraints depend on the system operating condition. The ATC's and their associated binding constraints can be significantly different for another system operating condition, such as a different pattern of system load demands, a different network configuration, or a different generation dispatch policy. Hence, ATC evaluations must be sufficient in system modeling and scope to ensure that all equipments as well as system limits of the entire interconnected systems network are properly taken into account. The SC-ATC package handles all the relevant physical constraints, as well as, engineering constraints. It uses a full AC detailed power system model, which includes the sending area, the receiving area, as well as, all neighboring areas needed for accurate calculation of ATC. The system model and conditions upon which the SC-ATC calculation is based satisfies the following three FERC-mandated conditions: it represents a realistic operating condition or expected future operating condition, it conforms with the requirements of ATC definition, and it considers single contingency facility outages that result in conditions most restrictive to electric power transfers. SC-ATC provides two modes of ATC calculation stated as follows: (1) Preventive-mode ATC and (2) Corrective-mode ATC.

Subject to: (i) parameterized power flow equations, (ii) soft limits of credible con­tingencies (i.e. line thermal limits, bus voltage limits and transmission corridor flow limits and MW reserves limits), (iii) hard limits of credible contingencies (i.e. steady-state stability limits and transient stability limits) The control modeled in SC-ATC allows the participation of generators, loads, ULTC taps, phase-shifter settings, shunt capacitors, and DC links as either active control or passive control to maximize simultaneous power transfer. Violation of a hard limit will immediately result in system instability. Hence, preventive controls are essential for hard limits while timely corrective controls may prove appropriate for handling soft limits.

BSI SC-ATC Distinguished Features

Functional Viewpoint: It computes the ATC and FCITC, and identifies the corresponding (the most severe) contingency (including the locations and types of contingency), and the associated binding constraints (i.e. the types of violation such as voltage violation, thermal limit, steady-state stability limit or transient stability limit). It identifies and ranks the top severe contingencies in terms of their impacts on the ATC and FCITC. It computes the corresponding ATC and FCITC and the associated binding constraints for each ranked contingency. It pinpoints the bottlenecks of system ATC in terms of the locations of bottlenecks, types of binding constraint and the associated binding contingency. It determines the required ancillary services

Model Viewpoint: It is based on a full power system nonlinear modeling. It takes into account the effects of control devices. It models the general characteristic of power system operating environments

Computational Speed: Its enhanced processing speed is suitable for on-line applications.

Probabilistic Analysis: SC-ATC allows a probabilistic treatment of each contingency to compute the corresponding load margin.

Field Proven SC-ATC

SC-ATC is installed and in operating at a large utility in Asia . This utility handles its 26,000 MW load using SC-ATC for ATC evaluation and enhancement on the power grid.