Question

7. State the different power quality issues associated with different types of distributed generation systems.

Answer 1

Distribution Generation system refers to a variety of technologies that generates electricity at or near where it will be used.This may include solar plant or combined heat and power, hydroelectric dams,wind farms etc.There are numerous problems associated with direct generation system and power quality is one of them.Power quality refers to the electrical system's ability to create a perfect power supply and to maintain a pure waveform if supply voltage and frequency are kept constant.

The following points are some of the power quality issues associated with direct generation system:

1.Voltage Regulation: This is one of the basic problem of DG system.It seems initially that the system will be able to improve the voltage regulation of the feeder as generator controls are faster and smoother compared to conventional tap changing transformers.But when the system is located far away from the substation,it becomes an issue of real concern considering no changes in the utility system is desired.

2.Sustained Interruptions: Many of the generators are designed to provide backup power to the load in case of power interruption.However frequency of interuption may increase in case of distribution Generation system. The common technology used for backup generation is is diesel gensets.the bulk of the capacity can be realised by transferring the load to the backup system. However not all distributed generation system can operate with power quality is their parallel operation involves great expense.

3.Harmonics: harmonics of rotating machines cannot be always neglected specially in grid parallel operation. The utility power system acts as short circuit to zero sequence and it multiplies the voltage by three times. So the resultant current will be very high.

4. Voltage Sag: The most common problem associated with direct generation is voltage sag.the ability to alleviate sag depends upon the type of generation and interconnection location. The system's influence on sag is added by the importance of the service transformer which provides isolation from the source of the sag on the utility system.However it also hinders the ability of DG System to provide any relief to loads of other feeders.