Question

2: Sustained oscillation below the fundamental system
frequency can be caused by
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Series capacitive compensation
Shunt capacitive compensation
series reactor compensation
Shunt reactor compensation​

Answer 1

Sustained oscillation below the fundamental system frequency is generated by  series capacitive compensation.

• The developed system of typically enhancing the device voltage by a capacitor connection in continuous series with the transmission line represents the series compensation.
• The said phenomenon is also referred to as the Sub synchronous Resonance.
• An interaction between the condenser-compensated transmission line array oscillates at the characteristic resonant frequency.
• The turbine-generator mechanical device is set in torsional with the consequent mutual reinforcement of the electric and mechanical oscillations, which can typically result in negative damping.