Question

Question 1 (25 marks) For a large aircraft with more than one generators, all generator electric outputs must be synchronized on the power buses. Indicate how many parameters those affect the synchronization of AC and DC multi-generator system. Briefly describe the system or the method used to control the parameters. (25 marks)

Answer 1

The process of matching parameters such as voltage, frequency, phase angle, phase sequence and waveform of alternator (generator) or other source with a healthy or running power system is called synchronization.

Synchronisation parameters

For proper synchronization of generator and ac power grid, basically four parameters have to consider:
Sequence of phases of generator and grid.
Voltage Magnitude of both.
Frequency level.
Phase Angle of each phase.
A. Phase Sequence
It is important that, the three phases of both generator and ac network grid should be in same sequence for proper synchronizing.
Generator alternator has three 120ͦ degree apart phases which can be delta or star connected. This phase sequence should be
perfectly matched with grid phase sequence for correct synchronization.
B. Voltage Magnitude
Every generator is designed to give specific output voltage magnitude. While synchronizing generator to respective grid, voltage
level should satisfy essential condition in which the voltage magnitude (sinusoidal) generated by must be equivalent to the
magnitude of the grid voltage.
C. Frequency
Generator produces electrical energy at certain specific frequency designed by manufacturer as per requirement. The generator
frequency should be equal to the frequency on which grid operating. Frequency matching is very important in order to reduce post
synchronization transients on overall system. Generally Syncroscope is used to consider frequency parameter.
D. Phase Angle
Similar to phase sequence, the phase angle also very important parameter of generator synchronization to grid. Phase angle is an
angle between the voltage generated by the generator and the voltage of grid. This phase angle difference must be zero while
synchronizing a generator to grid. From observation of peaks and zero crossing incidence of the sinusoidal waveform (i.e. 0 to
360°), the phase angle can be measured.

echniques for Synchronization

There are different techniques being available for the synchronization of alternators. The primary purpose of these techniques is to check all four conditions discussed above. The common methods used for synchronizing the alternators are given below.

1. Three Dark Lamps Method

2. Two Bright, One Dark Method

3. Synchroscope Method