In order to protect the capacitor bank

metal oxide varistor（MOV）is commonly used in series compensation. During the operation of series compensation

the MOV units may be damaged. If there is a reduction in the number of MOV units on the basis of damage to the backup unit

it may affect the safe operation of the series compensation. In this paper

the effect of the reduction of MOV units on the series compensator is analyzed

including the following aspects:MOV reliability under swing current;the applicability of MOV current and energy protection setting values;protective level of series compensator. rationality of MOV capacity configuration;the reliability of the devices during the discharge process of the capacitor bank.Inthispaper

the corresponding analysis results are obtained

and the countermeasures are given.