Any corporation authorized to do business in this state, which, under the present laws of the state, is authorized to condemn property for the purpose of generating and transmitting electrical power for the operation of railroads or railways, or for municipal lighting, and which by its charter or articles of incorporation, assumes the additional right to sell electric power and electric light to private consumers outside the limits of a municipality and to sell electric power to private consumers within the limits of a municipality, which shall provide in its articles that in respect of the purposes mentioned in this section it will assume and undertake to the state and to the inhabitants thereof the duties and obligations of a public service corporation, shall be deemed to be in respect of such purposes a public service corporation, and shall be held to all the duties, obligations and control, which by law are or may be imposed upon public service corporations. Any such corporation shall have the right to sell electric light outside the limits of a municipality and electric power both inside and outside such limits to private consumers from the electricity generated and transmitted by it for public purposes and not needed by it therefor: PROVIDED, That such corporation shall furnish such excess power at equal rates, quantity and conditions considered, to all consumers alike, and shall supply it to the first applicants therefor until the amount available shall be exhausted: PROVIDED FURTHER, That no such corporation shall be obliged to furnish such excess power to any one consumer to an amount exceeding twenty-five percent of the total amount of such excess power generated or transmitted by it. In exercising the power of eminent domain for public purposes it shall not be an objection thereto that a portion of the electric current generated will be applied to private purposes, provided the principal uses intended are public: PROVIDED, That all public service or quasi public service corporations shall at no time sell, deliver and dispose of electrical power in bulk to manufacturing concerns at the expense of its public service functions, and any person, firm or corporation that is a patron of such corporation as to such public function, shall have the right to apply to any court of competent jurisdiction to correct any violation of the provisions of RCW 80.32.080 through 80.32.100.