Synchronous Machine Introduction

Introduction

The purpose of this laboratory session was to simulate the concepts behind synchronous generator systems and the criteria a system must adhere to before being connected to the mains system.

Procedure

In the first part of the lab, various combinations of the line voltages and phase voltages on a 3-phase power supply were visualised using the oscilloscope program on the computer. Various screenshots were taken of these visualisations. The objective of the lab was to find the relationship between the phase and line voltages using these visualisations.

After this relationship was found and understood, the next objective of the laboratory was to set up a DC motor to be connected to the 3-phase supply via a switch that must only be pressed when the motor system was in phase with the mains. This was measured using a synchroscope. When the needle was seen to be in the “12 o’clock” position, both sides of the switch were in phase with each other.

Results/ Discussion

3-Phase Power System

Before connecting the 3-phase power supply to the computer oscilloscope, it had to be connected through an interface box to decrease the voltage, as the oscilloscope can only read voltages below 10V. When the oscilloscope was ready, the line voltage was kept constant while different combinations of phase voltages & line voltages were read by the oscilloscope. The oscilloscope could read & display up to 2 readings at any one time.

Various screenshots were taken of the oscilloscope during the laboratory, though only a few are needed. In Figure 1, only one reading is present, that of a single Line Voltage. The peak value of the curve is 2√2. Each box from side to side represents 90 degrees of phase (i.e. there are 4 boxes in each oscillation). Also note that each full oscillation takes 20ms, giving a predictable frequency of 50Hz.

Figure 1: Reading from oscilloscope with only one Line Voltage

This next screenshot was taken of 2 Phase Voltages...