Effects of the Tap Staggering Volt/VAr Control Method on Online and Adaptive Protection System in Grids with Wind Energy Sources

This paper investigates the impact of applying the tap staggering VoltNAr control method on the Online and Adaptive Protection system. The tap staggering method utilizes differences in taps between parallel transformers to create circulating current, enabling the absorption of reactive power from the grid to maintain network reactive power balance and voltage. However, this reactive power absorption at the primary substation through tap staggering poses potential risks for the Directional Overcurrent (DOC) with the Load Blinder protection scheme, which can result in faults or unnecessary alarms under normal load conditions. In this study, simplified part of a real network with the Wind Energy Sources was modeled in PSS®CAPE, and four different operation scenarios were created based on varying generation/demand profiles. The results indicate that the operation of the DOC with Load Blinder scheme is affected in all scenarios due to the changes in tap staggering, altering short-circuit currents and the values of active-reactive power measured by the Load Blinder Relay. A special macro was developed to evaluate the network changes and adapt parameters, including the DOC pickup (I
> DOC
), Load Blinder maximum resistance (R
LB
), and Load Blinder maximum angle ($\alpha$), based on the effects of tap staggering. Following the adaptation process, an online adaptive system communicates the adjusted parameters via the IEC61850 protocol and configures the real relay device with the adapted settings. As a result, the protection system operates reliably with the adapted protection scheme, enabling more efficient power delivery from Wind Energy Sources to the transmission system without interference from the protection scheme or tap staggering operations.