Topeka ? With the state’s largest electric utility looking to build new generating plants to meet customers’ increasing demands for power during the next decade, a state consumer advocate is expecting rates to rise.

“This period where we’ve had very slow and stable rates and not had big resource commitments is coming to an end,” said David Springe, lead attorney for the Citizens’ Utility Ratepayers Board, an agency that represents residential and small-business consumers. “It’s been good, but it’s going to change.”

Westar wants to build two generating units fueled by natural gas to add between 150 megawatts and 200 megawatts of capacity by 2008, spokeswoman Karla Olsen said. That’s enough capacity to provide power to up to 146,000 homes.

The company also wants to build a coal-fueled generating plant with at least 800 megawatts of capacity by 2013, Olsen said.

Westar doesn’t know how much such plants would cost or how the expenses would be divided between investors and ratepayers. But it has hired a Kansas City, Mo., firm to study potential sites and evaluate them by the end of the year.

Westar can more than meet peak loads now, Olsen said, but the utility wants extra capacity in case of an emergency or unexpected event. Overall electricity use among Westar’s 655,000 customers also is growing about 2 percent a year.

“What if a plant went down?” Olsen said. “You need to be able to know that you can pick up the slack with other plants.”

Westar has asked state regulators for permission to increase its annual rates by at least $84 million to cover rising expenses. But that request doesn’t include costs associated with building new generating plants.

“We’ll have to raise capital,” Olsen said. “That can be done in part through investors.”

Westar has 10 plants – including the Lawrence Energy Center north of the Kansas Turnpike at the edge of town – with 38 generating turbines, powered by coal, natural gas or diesel fuel, as well as a 47 percent interest in the Wolf Creek nuclear power plant near Burlington.