TOPEKA, Kan. — Stockholders have overwhelmingly approved the $12.2 billion sale of Topeka-based electric company Westar Energy to Missouri-based Great Plains Energy, the two firms announced Monday.

Westar is Kansas’ largest electric company, and after the acquisition, Great Plains would serve more than 1.5 million customers in the two states. The two companies say combining operations would result in $200 million in annual savings after three years, keeping rates in check.

Each company had a special shareholders’ meeting Monday to finish the voting. Great Plains said the holders of 81 percent of its shares participated, and the holders of 95 percent of that group approved the sale. Westar said holders of 63 percent of its stock voted, with an approval rate of 96 percent.

“The combination makes really good sense for the region and our ratepayers,” Charles Chandler IV, the chairman of Westar’s board of directors, said after its meeting in Topeka.

The companies hope to complete the sale next spring. Federal and state regulators must sign off, though Great Plains has argued that the Missouri Public Service Commission doesn’t have jurisdiction because Westar is a Kansas company.

The Missouri commission’s staff has questioned whether that state’s economy and consumers would benefit. However, Terry Bassham, Great Plains chairman and CEO, said in a statement Monday that the larger company would be “more diverse and sustainable” in generating electricity.

Westar shareholders would receive $51 in cash and $9 in Great Plains stock for each Westar share.

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