def sec2HMS(sec):
    """Convert time in sec to H:M:S string
    
    :param sec: time in seconds
    :return: H:M:S string (to nearest 100th second)
    
    """
    H = int(sec//3600)
    M = int(sec//60-H*60)
    S = sec-3600*H-60*M
    return '%d:%2d:%.2f'%(H,M,S)