Are there any hook or filter when refund is done through admin -woocommerce

Although this answer is little late but anyone else may get benefit from it. The woocommerce_order_refunded hook is called when an order is refunded. Use the following example:

// add the action 
add_action( 'woocommerce_order_refunded', 'action_woocommerce_order_refunded', 10, 2 ); 
// Do the magic
function action_woocommerce_order_refunded( $order_id, $refund_id ) 
{ 
  // Your code here
}