what is diskmanagment disenter error -119930878

Well, based on that narrative I would guess you have a bad download. If you normally use Wi-Fi to connect to the Internet, then I suggest you try using Ethernet instead.

Clean Install of El Capitan or Later on a Clean Disk

1. Restart the computer. Immediately after the chime hold down the (Command-Option-R) keys until a globe appears.
2. The Utility Menu will appear in from 5-20 minutes. Be patient.
3. Select Disk Utility and click on the Continue button.
4. When Disk Utility loads select the drive (usually, the out-dented entry) from the side list.
5. Click on the Erase tab in Disk Utility's main window. A panel will drop down.
6. Set the partition scheme to GUID.
7. Set the Format type to Mac OS Extended (Journaled.)
8. Click on the Apply button, then click on the Done button when it activates.
9. Quit Disk Utility and return to the Utility Menu.
10. Select Reinstall OS X and click on the Continue button.

Note:

1. To install the version of OS X that was currently installed use Command-Option-R.

2. To install the original factory version when the computer was new use Command-Option-Shift-R.

You erased the drive before attempting to reinstall macOS, is that correct? If not, then I suggest you try that next.

What is the exact Mac model that you have? To find the model identifier open System Profiler in the Utilities' folder. It's displayed in the panel on the right. You may also find the complete model information by selecting About This Mac from the Apple menu.

What version of macOS were you upgrading?

It's possible that there is a soft error on your drive where the installer resides that is causing the error. I've had that happen a couple of times. I use Disk Utility to perform First Aid, then try again. If that doesn't work you can try adding another file to the drive which will cause the installer to download to a different location. This will only work on an HDD, not on an SSD. Nevertheless, having erased the drive before you tried installing macOS suggests there may be a problem with the drive or the RAM that is causing that error. I have never seen it but the type of error, diskmanagement, suggest looking at the drive.

If you have an external USB 3.0 drive, then you might try installing on it. If that works then your drive most likely is the culprit.

Sorry, but we are users, only. We don't have that information. Furthermore, you haven't provided enough information. Please read Writing an effective Apple Support Communities question.

How large is the downloaded file? It should be about 5GBs. When you tried re-downloading did you put the first file in the Trash?