please enter a valid url. protocol is required (http // https // or ftp //) in magento instaltion

For this you need to remove the validation for the particular section.
1. Open \app\design\install\default\default\template\install\config.phtml
2. Find the textbox where the base url is entered. It will be around line no 85 with name ‘config[unsecure_base_url]‘
3.  Remove ‘validate-url’ from its class and save the file.

Replace

<li>
<label for=”base_url”><?php echo $this->__(‘Base URL’) ?> <span class=”required”>*</span></label><br />
<input type=”text” name=”config[unsecure_base_url]” id=”base_url” value=”<?php echo $this->getFormData()->getUnsecureBaseUrl() ?>” title=”<?php echo Mage::helper(‘core’)->quoteEscape($this->__(‘Base URL’)) ?>” class=”required-entry validate-url input-text” />
</li>

with

<li>
<label for=”base_url”><?php echo $this->__(‘Base URL’) ?> <span class=”required”>*</span></label><br />
<input type=”text” name=”config[unsecure_base_url]” id=”base_url” value=”<?php echo $this->getFormData()->getUnsecureBaseUrl() ?>” title=”<?php echo Mage::helper(‘core’)->quoteEscape($this->__(‘Base URL’)) ?>” class=”required-entry input-text” />
</li>

OR

Just set your url with http://127.0.0.1/your_folder_name

Now continue your installation