If the ejector is equipped with a main extraction steam turbine, why is an auxiliary extraction steam turbine still needed?

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If the ejector is equipped with a main steam extractor, why is an auxiliary steam extractor still needed? The answer is that the main steam extractor is used to maintain vacuum during the normal operation of the turbine. Because during the normal operation of the turbine, there is a small amount of non-condensable gases in the condenser, and in order to save steam, the design capacity of the main extraction pump is kept low ； However, when the turbine is started, the vacuum system contains a large amount of air and other non-condensable gases. In order to establish a vacuum in the system as quickly as possible and accelerate the formation of vacuum in the condenser, an auxiliary extraction pump is used. This is a single-stage extraction pump without an external cooler; after the steam-air mixture is cooled, the non-condensable gases are released into the atmosphere. As a result, it consumes a large amount of steam, and therefore it is only used temporarily during startup, when the vacuum level drops, or when the main extraction pump fails. During normal operation, the main extraction pump alone is sufficient to maintain the required vacuum level.