Do you have an example of a detailed synchronous motor starting (asynchronous starting)?
A synchronous motor is typically started as an induction machine while a field winding resistance is also used. The "asynchronous" motor starting of a synchronous machine implies the use of rotor damper windings and a bypass of the normal excitation voltage control by inserting a resistance in the excitation winding. The synchronous machine must be modelled either using a "Standard", "Model 3.3" or "Asynchronous Starting" type, but not a "Classical" one - for which the field current is not available.
Furthermore, a dedicated user defined dynamic model for the dynamic load is associated to the simulation model, as to represent typical behaviour of the motor load: initially a speed dependent load model is used (a starting load) - in which the load follows a certain characteristic. Once the motor has been started, the load on the machine is switched from speed-dependent to time-dependent in which a user defined time characteristic can be programmed (for the purpose of ramping up power to normal operation setpoint). If the motor is already started then the load is constant and equal to the load flow setpoint.
The model supports constant power factor and constant reactive power control. The type of the dynamic controller is automatically selected based on the "Local controller" setting in the motor's Edit dialog (element) under the page "Load Flow". The dynamic setpoints (power factor and reactive power are automatically read from the load flow page).
- Download and import the project "SynchronousMotorStartup.pfd". Activate it and work on the default study case.
- Observe the simple power system included: two synchronous motors SM1 and SM2 (both initially disconnected) and a general load are connected to a 20 kV mains supply. Observe also the switching events considered within the study case "SC01 - Starting all motors (in sequence)": SM1 is switched in at 1 s, SM2 is switched in at 30 s in the simulation.
- Observe also the dynamic control model of one of the synchronous motors. For example, "SM1 Controller" is the composite model of motor SM1. It contains the "Excitation" controller and two load models: "Load (ramp up)" and "Load (starting)".
- The load for ramp up is time dependent (user defined DSL model), whereas the starting load is speed dependent (built-in model of type ElmMdm3 in this case). The load for ramp up to normal operation can be customised via two gradient parameters (DSL parameters named "TORQUE_GRADIENT_DOWN" and "TORQUE_GRADIENT_UP") which will decide the rate of change of the load (irrespective of the time characteristic of the model). The time characteristic of the load can be customised via the characteristic object "LoadTimeCharacteristic" (of class IntMat), accessible via the edit dialog of the "Load (normal operation)" DSL model, then "Basic Data" page, then "Advanced 1" tab. The characteristic is saved inside the "Load (normal operation)" DSL model. It contains two columns (first one for time and second one for output torque in p.u.). Any number of time entries can be added (as many rows as wished) whereas the time column must always contain values in ascending order. The time characteristic is activated as soon as the MotorStarted flag is set. This flag is activated by the "Excitation" control model which detects the successful motor starting.
- With respect to the "Excitation" controller, the model supports the asynchronous starting procedure. The field resistance can be changed via parameter "R_field". The field winding will have the resistor inserted for as long as the motor speed is lower than a certain threshold, defined by parameter "Speed_sw". As soon as the speed crosses this threshold, the field resistance is disconnected and the normal operation excitation control system is used. The excitation control supports both power factor as well as constant reactive power control via the parameter "PF_VAR_CONTROL". This parameter is automatically set via the associated configuration script, The "MotorStarted" flag (which activates the load under normal operating conditions) is set as soon as the excitation control is activated (motor speed greater than threshold "Speed_sw") but with a delayed action defined by parameter "T_DELAY_NORMAL_OPERATION".
- Perform an RMS simulation for 100 seconds without changing any of the settings. Click on the plot "SM1" and "SM2" and observe the time curves.
- Simulate all other study cases and observe the results.