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Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
superlattice a stack of ultrathin layers of material. Layer thicknesses are sufficiently thin to produce quantum-confined effects, typically 100- 1000 angstroms; generally, there are two different layer compositions, and the superlattice is built with layer composition in an alternating scheme. supernode a cluster of nodes, interconnected with voltage sources, such that the voltage between any two nodes in the group is known. superparamagnetism a form of magnetism in which the spins in small particles are exchange coupled by may be collectively switched by thermal energy. superpipelined processor a processor where more than one instruction is fetched during a cycle in a staggered manner. That is, in an n-issue superpipelined processor, an instruction is fetched every 1/n of a cycle. For example, in the MIPS R4000, which is two-issue superpipeline, a new instruction is fetched every half cycle. Thus, in effect, the instruction pipeline runs at a frequency double than the system (in the R4000 the pipeline frequency is 100 MHz, while the external frequency
Power Flow Tracing in Power Systems with Active and Reactive Circulating Power Flows
Published in Electric Power Components and Systems, 2023
Victor J. Gutierrez-Martinez, Claudio R. Fuerte-Esquivel, Enrique A. Zamora-Cardenas
CPFs have adverse effects on the operation of power systems because they cause additional losses and reduce power transfer capability and voltage regulation. Many possible causes may generate CPFs ranging from economical to operational. Some of them may be scheduled/unscheduled imports/exports between areas (loop flows) [9], power balance obligation [6,7], power purchase agreements [8], the existence of devices with phase-shifting capabilities such as the unified power flow controller (UPFC) [2] or phase shifters (solid-state or conventional) [5], etc. In general, when a CPF is presented, there may be at least one branch where the active power flows from a node with a smaller phase angle to a node with a larger phase angle. The main problem with the power flow tracing algorithms when dealing with systems presenting CPFs is their inability to identify where a flow starts and ends, impeding the allocation of the contribution of the domains to the lines, nodes, and loads. In addition, when the reactive power flow tracing is performed, failure in considering the different directions the reactive power may take in transmission lines and transformers may lead to inaccuracies caused by the “masking” of the CPFs. To overcome these drawbacks, a novel active and reactive CPFs identification and handling algorithm is proposed in this paper. At first, the set of lines through which a possible CPF exists is identified and the circular path is fully traced. Then, all nodes, branches, and loads involved in the CPF are merged in a so-called supernode; in this way, the CPF is considered as flowing internally in the supernode, allowing the power flow tracing algorithm to properly apply the sharing principle even in the supernode. It is highlighting that the domain of the nodes comprising the supernode is preserved such that tracing the power flowing through lines belonging to the supernode is possible because all inflows to the supernode are handled as a total inflow. As a result, the capability of dealing with CPFs of the proposed algorithm overcomes the shortcomings of previously proposed approaches.