  This letter proposes a mass-matrix differential-algebraic equation (DAE)
formulation for transient stability simulation. This formulation has two
prominent advantages: compatible with a multitude of implicit DAE solvers and
can be conveniently implemented based on the traditional formulation, for
example, by separating the parameters in denominators into the diagonals of the
mass matrix. It also allows reducing the dynamics using null time constants.
Benchmark studies are presented on the time and accuracy of 17 implicit solvers
for the proposed formulation using the Kundur's two-area system and a 2,000 bus
system.
