If you're just looking to convert a given number of seconds into HH:MI:SS format, this should do it
SELECT
TO_CHAR(TRUNC(x/3600),'FM9900') || ':' ||
TO_CHAR(TRUNC(MOD(x,3600)/60),'FM00') || ':' ||
TO_CHAR(MOD(x,60),'FM00')
FROM DUAL
where x
is the number of seconds.