PHOENIX — Incumbents Andy Tobin, Bob Burns and retired Superior Court Judge Boyd Dunn have emerged as winners of the Republican primary in the race for three seats on the Arizona Corporation Commission.

The three defeated former state Sen. Al Melvin and state Rep. Rick Gray and will face Democrats Bill Mundell and Tom Chabin in the Nov. 8 general election. Mundell and Chabin automatically advanced to the general election.

Three of the commission’s five seats are up for grabs this year.

The Corporation Commission regulates electric utilities, telecommunications, securities and railroads. It makes decisions that affect the wallets of consumers and has executive, judicial and legislative power over the firms it regulates.

Tobin and Burns have battled over Burns’ effort to force Arizona Public Service, the state’s largest utility, to disclose whether it spent $3.2 million in the 2014 commission election. The utility has neither confirmed nor denied it spent money to back two winning Republican candidates, Tom Forese and Doug Little.

APS’ parent company, Pinnacle West Capital Corp., confirmed in a Securities and Exchange Commission filing this month that it has received two federal grand jury subpoenas related to the 2014 secretary of state and Corporation Commission races.

All four candidates say Burns should drop his effort to force APS to reveal whether it spent money on the election.

Tobin pointed to advertising beneficial to Burns that is paid for by an outside group funded by nonregulated company SolarCity. The company has been battling utilities’ efforts to change how rooftop solar customers are paid for electricity they sell back to the utility.

Burns said SolarCity is independent of his campaign and is disclosing its backing, while APS apparently didn’t. He noted he has urged all outside groups not to spend money in this year’s election.