LACEY — State regulators on Thursday approved a multi-year rate plan for Northwest Natural Gas that will raise bills for Southwest Washington customers beginning August 1, though the increases are smaller than the company originally sought. Northwest Natural, also known as NW Natural, is the largest standalone natural gas utility in the state. The commission left unchanged Northwest Natural’s tariff for line extension allowances, which helps cover connection costs for new gas customers. Agencies that collect debt for Northwest Natural may no longer report late gas bill payments to credit bureaus. Northwest Natural must develop a plan by Dec. 31 to provide customers with information and bill details in their preferred language.