If you can skip validation, you can generate a simple sql insert and execute it once. like:
$count = 0;
$sql = '';
foreach ($sheetData as $data)
{
if(!$count)
$sql .= 'INSERT INTO tbl_main (id ,name ,unit) Values ('.$data['A'].','$data['B']','$data['C']') ';
else
$sql .= ' , ('.$data['A'].','$data['B']','$data['C']')';
$count++;
}
Yii::app()->db->createCommand($sql)->execute();