Allocation of synchronous condensers for restoration of system short-circuit power

Abstract

Modern power systems, employing an increasing number of converter-based renewable energy sources (RES) and decreasing the usage of conventional power plants, are leading to lower levels of short-circuit power and rotational inertia. A solution to this is the employment of synchronous condensers in the grid, in order to provide sufficient short-circuit power. This results in the increase of the short-circuit ratio (SCR) at transmission system busbars serving as points of interconnection (POI) to renewable generation. Evaluation of the required capacity and grid-location of the synchronous condensers, is inherently a mixed integer nonlinear optimization problem, which could not be done on manual basis considering each type of machine and all bus-bars. This study therefore proposes a method of optimal allocation of synchronous condensers in a hypothetic future scenario of a transmission system fed by renewable generation. Total cost of synchronous condenser installations in the system is minimized and the SCRs at the POIs of central renewable power plants are strengthened. The method has potential for application on larger grids, aiding grid-integration of RES.

Impact of VSC Control Strategies and Incorporation of Synchronous Condensers on Distance Protection Under Unbalanced Faults

“…As shown in Fig. 1-2 and derived in (23)- (29), constant active power control yields the most similar short circuit current to that of synchronous sources, while constant reactive power control gives the largest deviation in terms of phases. Therefore, due to the differences in the current phases, the application of SC2 at the PCC may even further reduce the short circuit current level when constant reactive power control is used.…”

“…As the currents are restricted in magnitudes and the phase information is of interest here, M 5 -M 8 are not given explicitly for brevity. If the currents expressed by (26)- (29) are referred back to the wye-winding side, the current in phase-A and phase-B will be out of phase (similiar to that of synchronous generators during A-B faults) with (26) and (27). However, for constant reactive power control with (28) and (29), the current in phase-A and phase-B will be in phase with the same magnitude, which is significantly different from that of a synchronous source.…”

“…This could raise problems such as voltage instability, undesirable dynamic behaviors of converters and malfunctions of protection systems. Since the short circuit response of a synchronous condenser (SC) resembles that of a synchronous generator, SCs may serve as an alternative to improve the system short circuit strength and thus the application of SCs has gained increasing attention in recent years [25]- [29]. The refurbishment of conventional power plants to SCs have been proposed in [27], [28] to address dynamic voltage control issues and improve system short circuit ratios.…”

“…However, conventional power plants may not always serve as the best locations for SCs and newly-installed SCs can be anticipated. The studies in [28], [29] have presented methods on the optimal allocation of SCs minimizing the total cost. The results have suggested that there is a need of installing new SCs for more VSCs.…”

A Technical & Economic Evaluation of Inertial Response From Wind Generators and Synchronous Condensers

“…However, for the case of synchronous condensers where the capital costs are already known, studies are needed to estimate the distribution of costs across the various and ever increasing number of ancillary services which SCs can provide, for instance power oscillation damping controller as investigated in [29]. Furthermore, the size and location of synchronous condensers should also be considered in investment [30].…”