Type of Setting for Initial Conditions
The general method of initialization and start-up, which is used normally, is based on firstly entering the terminal voltage magnitude and phase. The start-up sequence is:
At time=0, machine is a fixed source at its terminals whose voltage magnitude and phase is as entered by the user which might correspond to the values obtained from a load flow program solution of the network.
The network solution progresses from the start-up with the voltage source firmly fixed so that the network can reach its steady state condition. To ensure that the steady state condition of the network is reached smoothly the source voltage magnitude may ramp to its specified value over a time interval entered by the user.
When the steady state of the network has been reached, the user may choose to 'switch' the voltage sources representing each machine to a constant speed condition with the machine model in place. The machine equations will hold. However, the mechanical dynamics will not be in place during this period and the rotor will be spinning at a constant speed corresponding to the base angular frequency specified by the user.
At the time of transition from source to machine model, IEEE exciter and stabilizer models (if used with the machine model) can be conditioned to give an 'initialized' output so that the transition from source to machine is seamless. The exciter and stabilizer models are initialized during the period the machine is acting as a source. Information for initialization can be fed to these models (terminal voltage, current etc.) from the machine model.
If for some reason, parts of the system still need to reach steady state, the machine in its 'constant speed' state with the excitation system active can be run until the user is satisfied. At this point in time, the rotor can be 'unlocked' on all machines. When this transition occurs, any IEEE governor/turbine system including any torsional multi-mass model of the turbines, shaft and the generator can be conditioned to give the proper input to the machine (if proper initialization procedures have been followed) so that the whole system will now run free and hopefully in steady state.
If for some reason a perturbation is evident or the system is not settling down to a steady state condition, investigate whether initialization procedures have been followed correctly or whether the system is dynamically stable. For example, excitation systems may not be adequately designed and may contribute to electromechanical instability. When systems with many synchronous machines are being modelled, it is always a good idea to be satisfied the system is dynamically stable when run on a power system stability program.
At the point in time when the machines are running free and the excitation and governor systems are stable a snapshot can be taken. Faults and disturbances can be applied to the system with start-up commencing from the snapshot.
These options only apply when the machine is started as a machine instead of as a source at time = 0.0. The preferred option for the non-advanced user is 'None'. The three options are:
None: Preferred option, which simply allows entry of terminal voltage magnitude and phase for initialization. If a source is also initially applied at time = 0.0, the power and reactive power is determined by the source, and the network to which it is connected.
Powers: This option allows entry of terminal power and reactive power for a specified terminal voltage magnitude and phase. The machine can start directly in locked rotor or running free and will do so without a transient, provided that the power and reactive power have been specified according to a correct load flow, and with a correctly initialized AC network corresponding to the load flow.
Currents: This advanced option requires the entry of initial rotor angle with respect to the phase A phase angle of the steady state terminal voltage, initial currents in d-axis armature, q-axis armature and field, which may be difficult to determine for initialization. It also requires the initial machine speed. This is only useful if the machine is started in free running (torque control) mode.