Magento 2 ignores a custom XML schema (_perFileSchema)

I’m developing an extension that have custom xml/xsd configuration files. When I’m trying to load extension url, it’s giving me following error:

Warning: DOMDocument::schemaValidate(): Invalid Schema source in /var/www/html/mage202/vendor/magento/framework/Config/Dom.php on line 290

Example:
in customconfig.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Ktpl_Customconfig:etc/customconfig.xsd">
    <mynode1>HELLO</mynode1>
    <mynode>HELLO 2</mynode2>
</config>

in customconfig.xsd

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="config">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="mynode1" type="xs:string" maxOccurs="10"/>
            <xs:element name="mynode2" type="xs:string" maxOccurs="10"/>
        </xs:sequence>
    </xs:complexType>
</xs:element>
</xs:schema>

in SchemaLocator.php class

namespace Ktpl\Customconfig\Model\Table;
use Magento\Framework\Module\Dir;

class SchemaLocator implements \Magento\Framework\Config\SchemaLocatorInterface
{
 /**
 * Path to corresponding XSD file with validation rules for merged config
 *
 * @var string
 */
protected $_schema = null;

/**
 * Path to corresponding XSD file with validation rules for separate config files
 *
 * @var string
 */
protected $_perFileSchema = null;

/**
 * @param \Magento\Framework\Module\Dir\Reader $moduleReader
 */
public function __construct(\Magento\Framework\Module\Dir\Reader $moduleReader)
{
    $etcDir = $moduleReader->getModuleDir(Dir::MODULE_ETC_DIR, 'Ktpl_Customconfig');
    $this->_perFileSchema = $etcDir . '/customconfig.xsd';
}

/**
 * Get path to merged config schema
 *
 * @return string|null
 */
public function getSchema()
{
    return $this->_schema;
}

/**
 * Get path to pre file validation schema
 *
 * @return string|null
 */
public function getPerFileSchema()
{
    return $this->_perFileSchema;
}
}

How can I create custom xml file and read data from this custom xml file?

I saw in a similar situation that Magento 2 ignores _perFileSchema:

https://github.com/magento/magento2/issues/2372