However, utilising timing signals and setting these individually may make the model logic easier to follow. Note: from a modelling perspective it may have been easier to use actual speed signals to control the change over. To investigate this rule, we will look at three scenarios with changeovers occurring at 70%, 80% and 90% of full speed. When to change from start to delta is often quoted as being the time when the motor has run up to 75 to 85% of it's operating speed. The model examples use timing signals to mimic this behaviour. Practical implementation of star-delta starters typically use timer relays to control the switchover. In open transition, there is a break in power while switching between star and delta, whereas in closed transition resistors are employed to eliminate any power break. Models for star-delta starting will cover the two common implementations of open-transition and closed-transition. The direct-on-line model output also give us a base-line performance against which to compare the results of star-delta starting. If you are unfamiliar with these types of circuit, you can refer to a short introductory eBook on the topic - "Motor Starting and Control Primer."īy first constructing a direct-on-line model, we can verify the output is in-line with expectations and that the model is functioning correctly. In writing the post, it is assumed that the reader has some understanding of motor starting circuits. modifying (2) to model a star-delta closed transition starter.modifying (1) to model an star-delta open-transition starter.creating a direct-on-line starting model.To illustrate and understand the performance of the motor starter, modelling is carried out in three stages: stator zero sequence inductance L o = 0.930 pu.magnetising inductance, L m = 1.7562 pu.rotor resistance, R r' = 0.0145 pu and reactance L r' = 0.0424 pu (referred to stator).stator resistance, R s = 0.0258 pu and reactance L s = 0.0930 pu.15 kW, 380 V, 50 Hz, 1 pole pair squirrel cage motor.The technical parameters of the model are: It will be easier to examine and understand the principles by keeping the model simple.
The ExampleĪ relative simple example of a 15 kW motor supplied directly from a source and with the load modelled by a simple inertia will be investigated. This note illustrates by example one possible approach to studying the performance of a star-delta motor starting circuit. Carrying out a software study allows both the electrical performance and that of the connected mechanical systems to be evaluated. For all but the simplest application, there is merit in performing a more detailed study. Many questions sent in to the site are in connection with motor starting and in particular star-delta.
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