PhD Cover Letter

I'm applying to a 1+3 PhD programme and part of the application form asks for a cover letter. I don't need to include a detailed thesis synopsis yet because that is done in the first year. I'm applying to a consortium of universities so this is making it difficult on how to format the cover letter.

My question is: is it acceptable to write a cover letter addressed to "Dear Sir/Madam" as there's no one specific I can address it to? Or should I write it more like a personal statement?