The vacuum tightness test was always used to evaluate the vacuum system's tightness for thermal power units with wet cooling.This method can evaluate the vacuum system's leakage rate effectively for units with average load rate of more than 80%

which ensures the unit economy.However

for units suffering from peak load operation

especially deep peak regulation

the existing industry standards have no specific rules on vacuum tightness evaluation methods for units under low load conditions.When the units are during peak load operation with low load

the condenser heat load

air entering the system

vacuum system and the total volume of vacuum suction device capacity changes will all affect the qualified value of vacuum tightness

to different degrees.Therefore

taking a supercritical 350 MW unit as an example

the qualitative evaluation method at low load of peak shaving and the quantitative correction methods considering the above factors were discussed.The results show that the qualified standard of the vaccum tightness of this unit under 60%load condition is 304Pa/min.This method is simple and has strong practicality

which can provide references for wet cooling units for which peak load operation has become norm state.