STATE HOUSE, BOSTON, SEPT. 8, 2014.....Secretary of State William Galvin on Monday said he expects around 550,000 Democratic ballots will be pulled during Tuesday's primary elections, with 165,000 to 170,000 voters participating in Republican primaries.

That works out to a turnout rate of 15 percent to 20 percent of 4.2 million registered Bay State voters for an election that features contested battles among Democrats for major offices such as governor, lieutenant governor, attorney general and state treasurer.

"I hope I'm wrong," Galvin said during a press conference where he predicted many unenrolled or independent voters, who make up the majority of voters, are likely to sit out Tuesday's voting. "I hope it goes higher and higher. We're prepared for everyone to come out."

Gov. Deval Patrick is not seeking re-election this year and voters on Tuesday will choose from a field of three Democrats who hope to move on to the general election on Nov. 4.

In 2006, the last time the governor's seat was open, over 900,000 Democratic ballots were cast in the primary, as Patrick defeated Attorney General Thomas Riley and businessman Christopher Gabrieli.

Patrick, who won the general election in 2006 over Republican Lt. Gov. Kerry Healey, generated "a lot of enthusiasm" that year, Galvin said.

"You don't have that this time," Galvin added.

Galvin, a Brighton Democrat who has served as secretary since 1995, based his estimates on the number of absentee ballots requested and inquiries from residents on where they're voting.

"All these projections, of course, are subject to the ability of candidates to bring out the vote," he said. "That is to say, candidates using grassroots or field operations to try to bring people they suspect they support them out to vote, which can enhance turnout. It's certainly an opportunity for candidates to influence the turnout by having an effect on the vote."

Attorney General Martha Coakley, Treasurer Steve Grossman and pediatrician Don Berwick are in a three-way Democratic primary for governor. Former state official and health insurance executive Charlie Baker is making his second bid for governor and facing a Republican primary challenge from Shrewsbury businessman Mark Fisher.

In 2010, when Patrick and Baker ran unopposed in their respective primaries, 487,000 people pulled Democratic ballots and a little over 240,000 pulled Republican ballots.

Massachusetts has 4.2 million eligible registered voters, and 53.1 percent are registered as unenrolled voters, who have not chosen either party. Democrats make up 35.4 percent of the enrolled electorate, while Republicans make up 10.9 percent.

Party members can only vote in their own party primaries, but independents, or unenrolled voters, can choose to vote in either primary.

"My instinct is that there will be relatively few independents taking party ballots," he said. "Very accomplished and sophisticated" unenrolled voters may participate, Galvin said, "but generally speaking primaries that aren't going to draw a lot of interest from the party members are unlikely to attract a lot of independents."

Galvin said a lack of highly competitive local races, and apparent low voter enthusiasm, will be contributing factors on Tuesday.

Bristol County has one contested House seat and a race for county commissioner, which is unlikely to drive people to the polls, he said.

Middlesex County has a few contested legislative races and a hotly contested primary race for district attorney, Galvin noted. District Attorney Marian Ryan, appointed by Patrick in 2013, is being challenged by Michael Sullivan, clerk of courts in Middlesex Court.

A wide open race for Hampden district attorney, an open Senate seat and other races in western Massachusetts could drive turnout up in pockets, Galvin said, noting the likelihood that turnout may also be enhanced in Worcester County due to legislative races there.

Rattling off some of the other counties, Galvin said, "Franklin County almost nothing; Berkshire County, nothing, just like Norfolk, no down ballot races at all, no contests."

Galvin, who is unopposed in his own primary on Tuesday, said he would be "thrilled" if his predictions are wrong.

Massachusetts shares a primary date this year - a week earlier than usual - with New Hampshire, Rhode Island, Delaware and New York.

Galvin said the earlier primary is due to the federal law governing the availability of federal absentee ballots to overseas military balloters.

Polls open at 7 a.m. and close at 8 p.m.