Energy Losses

Power train energy losses are modelled as a combination of mechanical losses and electrical losses in the generator (including the frequency converter in the case of variable speed turbines).

Mechanical Losses

Mechanical losses in the gearbox and/or shaft bearings are simulated as friction applied on the shaft where the brake is attached. The friction may be constant or interpolated linearly from a lookup table. The lookup table option can be defined against rotor speed, gearbox torque or shaft power, or a two-dimensional lookup table against both rotor speed and one of either shaft torque or power.

Mechanical losses modelled in terms of power are inappropriate if calculations are to be carried out at low or zero rotational speeds, e.g. for starts, stops, idling and parked calculations. In these cases, the losses are better expressed in terms of torque.

Electrical Losses

The electrical losses may specified by one of two methods:

Linear Model

This requires a no-load power loss \(L_N\) and an efficiency \(\varepsilon\), where the electrical power output \(P_e\) is related to the generator shaft input power \(P_s\) by:

\[ \begin{equation} P_e = \varepsilon (P_s - L_N) \label{eq:elecLossLinearModel} \end{equation} \]

lookup Table

The power loss \(L(P_s)\) is specified as a function of generator shaft input power \(P_s\) by means of a lookup table. The electrical power output \(P_e\) is given by:

\[ \begin{equation} P_e = P_s - L(P_s) \label{eq:elecLosslook up} \end{equation} \]

Linear interpolation is used between points on the lookup table.