There could be various reasons why the SQL Server 2016 SP2 Standard Edition (WinCC) setup is unable to complete the installation. Here are some steps you can try:

1. Check the system requirements: Make sure that your system meets all the minimum requirements for installing SQL Server 2016 SP2 Standard Edition (WinCC). Check the documentation or the Microsoft website for the exact requirements.

2. Check the installation media: Sometimes, the installation media may have issues. Try downloading a fresh copy of the installation files and attempt the installation again.

3. Check for conflicting software: Make sure there are no other applications or software running on your system that may conflict with the installation process. Disable any antivirus software and close any open applications before attempting the installation.

4. Check the installation logs: If the installation fails, look for any error messages in the installation logs. These logs can often provide information on what went wrong during the installation process.

5. Try a different installation method: If none of the above steps work, try using a different method of installation. For example, you can try installing SQL Server 2016 SP2 Standard Edition (WinCC) using an ISO file instead of a setup.exe file.

6. Check out the methods provided in this link

If you still cannot complete the installation after trying these steps, it may be best to contact Microsoft support or seek the assistance of a qualified IT professional.