True/false: load rejection raises terminal voltage

TRUE.

Justification: When a large load is suddenly disconnected (load rejection), the voltage at the generator and line terminals rises, for these reasons:

1. Loss of internal voltage drop. The load current had caused a voltage drop across the generator and transformer reactances. After rejection, the terminal voltage rises to about the internal emf $E'$ (1.1–1.2 pu) until the AVR reduces the excitation.
2. Ferranti effect. The long line becomes unloaded, and its charging current raises the receiving-end voltage by the factor $1/\cos\beta l$ (about 9.5% for 400 km at 50 Hz, where $\beta l = 24^\circ$).
3. Overspeed. The turbine input cannot be reduced at once, so the generator speeds up. The emf rises roughly in proportion to speed, so the effect is largest for hydro sets, which can overspeed by 30–50%.
4. Self-excitation of a generator feeding a long open line can raise the voltage further.

 V (pu)
 1.5 |    __
     |   /  \__
 1.0 |__/      \______  (AVR/governor act)
     +-----------------> t
       ^ load rejected

This temporary overvoltage can reach 1.5 pu and last for seconds. It is limited with shunt reactors, fast AVR and governor action, and SVCs.