CHAPTER In Figure 4.2 the load current waveform

CHAPTER 4

Results and
discussion

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1.1.                                                                       
Simulation Results

Based on the proposed model of UPQC, the system is presented at
normal operating condition and faulted operating condition scenarios without
and with UPQC with comparison.

1.1.1.                                                                   
 Simulation results in normal operating
conditions

Simulation results
Without Using UPQC

As the model presented in Figure 3.10 with the test parameters
which is connected to a non-linear load has the following detail result
summaries. It is analyzed with different operating conditions. Load voltage and
load current waveforms with Fast Fourier Transform (FFT) analysis with time
domain and frequency domains to determine the difference in percentage of Total
Harmonic Distortion (THD).

In Figure 4.1 the load voltage waveform tells that until 0.3
seconds the load is at starting condition and after 0.3 second it works in its
normal operating condition. It is observed that the harmonic level of load
voltage with a THD of 11.17% and its magnitude is 0.9794p.u.

 

Figure 4.1: Load Voltage Waveform without UPQC

In Figure 4.2 the load current waveform shows that the magnitude
is somehow very low due to the nature of the load which causes a great
fluctuation and after 0.3 second it seems retaining steady state condition with
a harmonic level of THD 26.43% and magnitude is about 12.72p.u.

 

Figure 4.2. Load Current
Waveform without UPQC

Simulation results
Using UPQC

When
UPQC is inserted to the network it is clear that it can compensate both the
voltage and current related power quality issues and it can be seen that the
voltage harmonics level is reduced to 2.11% from 11.17%, which is a permissible
value according to the limit imposed by IEEE 519-1995 as shown in Figure 4.3.

Figure 4.3. Load Voltage
Waveform using UPQC

In Figure 4.4 with the insertion of UPQC to the network at normal
operating condition the load side harmonics is well compensated from a THD of
26.43% to 2.92% which is less than 5%.

Figure 4.4. Load Current
Waveform using UPQC

The value of total harmonic distortion in both cases signifies the
use of UPQC in distribution system.

1.2.Simulation
results in faulted operating conditions

4.2.1       
Simulation results Without Using UPQC

At this scenario a single line to ground fault is applied in the
network near the load. The applied fault duration is is specified between
0.1-0.3 seconds. It is clear that during the fault the voltage level should be
reduced greatly and the current level is increased considerably.

After the fault is cleared the voltage and current waveforms will
retain is steady state condition.

In Figure 4.5, it is showed that for a single line to ground fault
voltage for a faulted line is approximately zero and the effect is also
propagated in the other two lines in a reduction of magnitude for the applied
fault duration.

Conversely, it also presents exaggerated current level for a
faulted phase and approximate current level to zero for the other two phases
for the applied/ chosen transition time / fault duration and after the fault is
cleared the system reaches its steady state condition.

For the above condition FFT analysis is also presented in the time
domain and frequency domain to determine the harmonic level with THD for the
fault duration and steady state condition. 

Figure 4.5. Voltage &
Current level during Transition time

In Figure 4.6 the load voltage without UPQC is seen as FFT form
and it is observed that for 0.1-0.3 second the voltage level is zero and after
the fault is cleared the level is about 0.979p.u, and Figure 11b shows a
frequency domain FFT chart with a THD of .11%.

In Figures 4.7 the load current without UPQC is presented with
time domain and frequency domain FFT analysis and it is seen that for 0.1-0.3
seconds the current is increased greatly because of the fault and after the
fault is cleared it retains its steady state condition. The frequency domain
FFT analysis shows that the harmonics level of the load current is about a THD
of 0.01% , which is very minimum and uniform because of the fault.

Figure 4.6. Load Voltage
Waveform without UPQC

Figure 4.7. Load Current
Waveform without UPQC

Simulation results
Using UPQC

Figure 4.8 shows load voltage with    UPQC in the network at fault condition of single line to ground
fault and it is observed that the voltage level is zero for the fault condition
of 0.1-0.3 seconds and the magnitude is about 0.979p.u after fault clearance in
the time domain analysis.

The frequency domain FFT analysis waveform shows the level of
voltage harmonics with THD of about 1.98% at 50Hz fundamental power frequency
and it is permissible by a standard limit imposed by the IEEE 519-1995.

Figure 4.9 shows the time domain FFT analysis shows a great
current level during fault duration time. The frequency domain current
harmonics level is about 1.7% which is maintained at a permissible limit.

Figure 4.8. Load Voltage
Waveform using UPQC

Figure 4.9. Load Current
Waveform using UPQC

Similarly, the waveforms for double line to ground fault can also
be observed.