Spring cron expression for every after 30 minutes

I have following Spring job to run after every 30 minutes. Please check my cron expression, is that correct?

0 0 0 * * 30

Here is a full cron job definition from the related Spring configuration file:

<bean id="autoWeblogPingTrigger" class="org.springframework.scheduling.quartz.CronTriggerBean">
    <property name="jobDetail" ref="jobDetailForWeblogPing"/>
    <!-- run every 35 minutes -->
    <property name="cronExpression" value="0 0 0 * * 30" />
</bean>