Try using
open -rawsettings FtpPingInterval=10
See
https://winscp.net/eng/docs/scriptcommand_open
(You need to use 5.0.x to use -rawsettings switch).

Anyway, I recommend you use the WinSCP .NET assembly:
https://winscp.net/eng/docs/library

I am attempting to set the Keepalives setting for FTP (Executing dummy protocol commands) Seconds between keepalives to 10 seconds in a custom INI file. I have put the following seetings in a INI file called myinifile(FSProtocol=5, FtpPingInterval=10,FtpPasvMode=1). My process start info looks like this:
With startInfo
.FileName = "WinSCP.com"
.Arguments "/ini=myinifile.ini /log=log.txt"
.RedirectStandardInput = True
.RedirectStandardOutput = True
.RedirectStandardError = True
.UseShellExecute = False
.CreateNoWindow = True
.WindowStyle = ProcessWindowStyle.Hidden
End With

My custom ini file is being written to but it does not appear to be setting the Keepalives in the ftp. The log file shows (Transfer Protocol: FTP Ping type: C, Ping interval: 30 sec; Timeout: 15 sec) How can I confirm that the keepalives is being set and working correctly.