Local vs global ado.net objects

public class DataOperations
    {
        string strConnString =  ConfigurationManager.ConnectionStrings["dbconn"].ToString();
        private static DataOperations singleInstance = null;
        private SqlConnection sqlConn;
        public SqlCommand sqlCmd;
        public SqlDataAdapter sqlAda;

        DataOperations()
        {
            sqlConn=new SqlConnection(strConnString);
            sqlCmd = new SqlCommand();
            sqlCmd.Connection = sqlConn;
            sqlCmd.CommandType = System.Data.CommandType.Text;
            sqlAda = new SqlDataAdapter();

        }

public bool InsertAlumniDetails(.....some values)

        {
            bool bRetVal = false;
            
            
            string strSqlInsert = @"some sql";

            try
            {
                OpenConnection();
                sqlCmd.Parameters.Clear();
                sqlCmd.Parameters.AddWithValue("name", strName);
                sqlCmd.Parameters.AddWithValue("gender", strGender);
                sqlCmd.CommandText = strSqlInsert;
                sqlCmd.ExecuteNonQuery();