The healthcare bill that the Senate is expected to pass on Christmas Eve has protections that ensure Massachusetts' pioneering health insurance overhaul will remain intact, and it also includes $500 million in extra money for the state, Senator John F. Kerry said during a quick visit to Boston between votes on the measure. The legislation also contains an additional $200 million for Massachusetts hospitals that say they have not been adequately reimbursed by the state for treating a large share of the poor. The Senate's bill is largely based on the Massachusetts plan and adopts some of its hallmark provisions, including a requirement that nearly everyone obtain health insurance coverage or pay a tax penalty, and subsidies to help low- and middle-income residents afford coverage. Yet in some respects, the Senate's plan is more expansive than the program in Massachusetts because it will allow many more people with higher incomes to qualify for subsidized health insurance coverage.