Hi,
The local user command "authorization-attribute level 3" is working within a comware 5 user-framework.
The HP 5510 is a comware 7 switch. Comware 7 uses a Role based access framework.
Luckily, it has some predefined user roles. I think you might be looking for a network administrator.
use
[HP_CORE_SLAVE-luser-manage-admin]authorization-attribute user-role network-admin
Which is a predefined role - that sort of matches the comware 5 level 3 superuser.
NB: You should read up on Role Based Access Control (RBAC) if you havent already. Its mentioned in the "HPE FlexNetwork 5510 HI Switch Series Fundamentals Configuration Guide"
Regards