Turbine-electric transmission enters a turbine, where it expands down to the exhaust pressure, producing a shaft work output in the process. The exhaust is fed into the power turbine used to power an output shaft for whatever desired application. The power turbine is also connected to the electric generator, which converts mechanical energy into electrical energy. The electric generator driven by the power turbine charges the battery needed in order to drive the motor that supplies compressed air into the combustor. During cruise speed the electric motor does not have to be functioning, only the gas turbine engine is required to continue
Potential energy distance at which "U" becomes zero: formula_34 and formula_35. The choice of formula_36 at infinity may seem peculiar, and the consequence that gravitational energy is always negative may seem counterintuitive, but this choice allows gravitational potential energy values to be finite, albeit negative. The singularity at formula_34 in the formula for gravitational potential energy means that the only other apparently reasonable alternative choice of convention, with formula_36 for formula_34, would result in potential energy being positive, but infinitely large for all nonzero values of "r", and would make calculations involving sums or differences of potential energies beyond what is possible