Stability enhancement of multi-machine systems using adaptive reclosing of transmission lines

• To enhance transient stability, a new method for dead time evaluation is proposed.
• SIME method is used as transient stability assessment tool.
• The calculations are shortened, providing the feasibility of on-line implementation.
• Impact of each stage of delayed reclosing is comprehensively investigated.
• The eligibility of the proposed method is examined on a real nine-machine network.

When a fault occurs in high voltage (HV) and Extra High Voltage (EHV) lines, they could automatically be re-entered to the circuit by auto-reclosing operation of transmission switches after passing a certain time from the first tripping operation. It is due to the fact that most of the faults occurred in HV/EHV transmission systems have a corresponding arc which could be removed just after de-energizing the line. To ensure successful reclosing, de-energizing interval addressed as dead time is conventionally determined, based on the calculation of the time needed for quenching subsequent weakened secondary arc. However, on-fault reclosing is probable even if dead time is conservatively selected. It can lead to severe power swings and put the system in danger of instability especially in vastly loaded networks. These swings will be intensified or weakened upon rotor angular speeds of dominant generators in reclosing instant, which is the key factor in acceleration or deceleration of power swing. Therefore power oscillation can be mitigated by adaptive selection of dead time. In this paper, a new method for dead time calculation is proposed in order to mitigate power oscillations effectively. The proposed method can also be implemented in on-line monitoring and control algorithms due to low amount of calculation. In this approach, single machine infinite bus equivalent (SIME) method is used for the evaluation of power oscillations.