With the modern electric system becoming more complicated and voltage grade keeping elevated , the probability that system comes forth some problems is increasing . therefore , it is necessary for us to take adequate measures to ensure the security of the system and minimize the loss when the system fails to function . relay protection technique is the most important one among diversified safety precautions 随着现代电力系统日趋复杂,电压等级的升高,系统出现问题的可能性比以往有所增加,因此,必须有足够的措施保障系统的安全,将电力系统出现故障时所造成的损失减到最低,继电保护技术是各种安全措施中最为重要的一种。
In this way , in case any subsystem failure , general system can on - line maintain in stead of stopping to maintain , so other subsystems can keep working normally during the maintenance of the failure subsystem ; secondly the general system can quickly resume to normal work state with high quality within the common working permission time of integrating system in case of any system development or failure maintenance 当子系统出现故障时，并不需要以停止整个系统的工作为代价，在维护故障子系统期间，其它子系统仍然能够正常工作，独立的完成其自身的功能；其次在实现系统扩展或系统出现故障时，系统能够保持正常生产的许可条件下，力求高质量、迅速恢复正常的生产状态。
It is essential for distributed databases to have backup and recovery functions to ensure it is properly running , though they are only be invoked when problems occur in database . the database ' s safety issue is not cognized as much important as operating system ' s . however , in case of the datum in the database involved some business secret information , once they were stolen , the potential loss would be considerable 在实现中对数据传输过程中的数据进行加密传送；分布式数据库的维护中数据库的备份和恢复是一个必须面对的问题，虽然只有数据库出现故障时，才会用到它，但是备份是保证数据库正常运行的不可缺少的一个功能；对于数据库的安全可能大家对这个问题的认识，远没有操作系统的安全那么重要，但是当数据库里存储的数据涉及商业机密信息时，一旦被盗用，由此将产生不可估量的损失。
