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ECE 4821L 12/05/2018 Final Project
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Transmission Grid Simulation
ECE 4821L 12/05/2018 Final Project
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Table of Contents
Objectives ..................................................................................................................................................... 3
Lab Proposals ................................................................................................................................................ 3
PSCAD Simulation Schematics ..................................................................................................................... 4
Lab Simulation Runs ..................................................................................................................................... 5
Report Structure ........................................................................................................................................... 5
System Overview .......................................................................................................................................... 5
Generator ..................................................................................................................................................... 6
Step-Up Transformation to High-Voltage ................................................................................................... 7
Transmission Lines ....................................................................................................................................... 8
Step-Down Transformation to Medium-Voltage (Substation 2) ................................................................ 8
Step-Down Transformation to Local Distribution (Substations 3 & 4) ....................................................... 9
Local Step-Down-Transformation (Substations 5 - 7) ............................................................................... 10
Load Scenario 1 – Factory with Inductive Load ........................................................................................ 11
Load Scenario 2 – Pure Resistive Load ...................................................................................................... 13
Load Scenario 3 – Capacitive Load ............................................................................................................ 14
Load Scenario 4 – Resistive Delta Load ..................................................................................................... 15
Influence of Transmission Line Length ...................................................................................................... 16
Conclusion .................................................................................................................................................. 17
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Objectives
The objective of this lab was to utilize the PSCAD software to simulate a real-world transmission
grid consisting of generator, transmission lines, various substations for up and down
transformations, and multiple load scenarios.
Lab Proposals
The following list summarizes the lab goals as discussed and approved by Professor Monemi
during the planning phase of the lab.
• Simulate grid system from generator to high-voltage up-scaling for transmission to down-
scaling for local cities
• Design multiple transformers (substations) that are needed for proper voltage
scaling/transformation
• Substations that will connect different voltage-levels
• Each simulated city will have a different load scenario (e.g. resistive, inductive,
capacitive)
• Perform power-factor correction for some loads
• Plot various voltages, currents, and powers in the entire grid system
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PSCAD Simulation Schematics
Figure 1 shows the entire simulation schematics that has been designed in PSCAD for this lab
project. Due to the size of the schematics, it is presented in a landscape orientation.
Figure 1: PSCAD Schematics
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Lab Simulation Runs
We run several simulations for this project, which are documented in detail in the remainder of
this report.
In the first simulation, we left out both of the transmission pi-section. At the end, we included
them in the simulation and observed their influence on the entire circuit.
We also run two different simulation runs to observe power-factor correction. First, we omitted
the capacitor at substation 4 and measure the power factor and reactive power. We then
repeated the simulation with capacitor connected and compared the measurements.
Report Structure
The report has been separated into several sub-parts, each of which describes a crucial part of
the entire circuit. Each section explains the background behind the use of the components and
includes important calculation, measurements, and plots.
System Overview
Figure 2 shows the general high-level structure of the project.
Figure 2: System Overview
Generator
Power Plant
[22kV]
Substation 1
Step-Up
High-Voltage
[230kV]
Transportation
over long
distance
Substation 2
Step-Down
[69kV]
Transportation
over short
distance
Substation 3
Step-Down
[13kV]
Substation 4
Step-Down
Factory
Substation
[13kV]
Factory with own substation
and inductive
load
Transportation
over short
distance
Substation 5
Step-Down
[110V]
Substation 6
Step-Down
[110V]
Substation 7
Step-Down
[110V]
Residential
Consumer:
Resistive Y- load
Residential
Consumer:
Capacitive load
Residential
Consumer:
Resistive Δ- load
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Generator
The generator is our first sub-system to discuss. This is the source of the entire energy supplied
to the rest of the system and is therefore an important part. Figure 3 shows the part of the circuit
from Figure 2 which is of interest for the generator.
The major source of energy in the US are the fossil fuels -
consisting of natural gas (33%), petroleum (28%), and coal
(17%). Combined, they account for 78% of the nation’s energy
production. Other energy sources include renewable sources
like wind and solar (12%) and nuclear power (10%).
A typical generator output voltage is 20-22kV. For our project,
we used a value of 22kV. The generator outputs a 3-phase
voltage at 60 Hz frequency.
Figure 4 shows the PSCAD plot for the generator voltage (Ea1). We can see the existence of
the 3-phases which are 120 degrees out-of-phase to each other.
The peak value can be calculated as follows:
𝑉𝑝 𝐿𝑁 = 22 𝑘𝑉 √2
√3 = 17.96 𝑘𝑉
When we compare this with the plot, we can confirm the above calculated peak-value.
Figure 3: Generator Circuit
Figure 4: Generator Voltage Plot
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Step-Up Transformation to High-Voltage
Before energy is transmitted over long distances, voltage
levels are up-scaled by many magnitudes in order to keep
losses during the transportation low.
Depending on the distance of the transmission lines, different
voltage levels are used. Voltages in the US typically range
from 765 kV to 13 kV.
For our project, we used a voltage level of 230 kV. Figure 5
shows the step-up substation from the schematics.
Figure 6 shows the PSCAD plot for the transformer output voltage (Ea2). The peak value can be
calculated as follows:
𝑉𝑝 𝐿𝑁 = 230 𝑘𝑉 √2
√3 = 187.79 𝑘𝑉
When we compare this with the plot, we can confirm the above calculated peak-value.
Figure 5: Step-Up Transformer
Figure 6: Step-Up Transformer Voltage Plot
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Transmission Lines
Transmission lines come in different lengths and
towers. Tower size and shape generally depend
on the voltage levels and transmission distance.
The size of the towers usually increases with
voltage levels and transmission distance. Figure
7 shows a comparison between different
transmission towers and pertaining voltage
levels.
Step-Down Transformation to Medium-Voltage (Substation 2)
After the transportation over a long distance, voltage levels are reduced
for further distribution. In our project, voltage levels are reduced from
230 kV to 69 kV. Energy is usually distributed to multiple major
population regions (cities or factories) from here. Each major region has
its own substation that steps-down the 230 kV to the required 69 kV.
After the down-scaling of the voltage, transmission distances are
usually shorter than previously.
Figure 8 shows the part of interest from the schematics.
Figure 9 shows the PSCAD plot for the transformer output voltage
(Ea4). The peak value can be calculated as follows:
𝑉𝑝 𝐿𝑁 = 69 𝑘𝑉 √2
√3 = 56.34 𝑘𝑉
When we compare this with the plot, we can confirm the above calculated peak-value.
Figure 7: Transmission Towers
Figure 8: Step-Down
Transformer
Figure 9: Step-Down Transformer Voltage Plot
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Step-Down Transformation to Local Distribution (Substations 3 & 4)
Before energy is distributed within cities, voltage levels are again
down-scaled. In our project, voltages arriving at the local substations
are at 69 kV. The substations then generate 13 kV. This is a standard
voltage level for local distribution within cities.
Large factory buildings mostly have their own substation due to their
high energy consumptions. We incorporated this into our project as
well.
Figure 10 shows the part of interest from the schematics.
Figure 11 shows the PSCAD plot for the transformer output voltage
(Ea6). The peak value can be calculated as follows:
𝑉𝑝 𝐿𝑁 = 13 𝑘𝑉 √2
√3 = 10.6 𝑘𝑉
When we compare this with the plot, we can confirm the above calculated peak-value.
Figure 11: Step-Down Transformer Voltage Plot
Figure 10: Step-
Down Transformers
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Local Step-Down-Transformation (Substations 5 - 7)
Step-down transformation to residential voltage levels happens
with transformers located right on the transmission towers before
entering the consumers building. Those transformers step-down
the 13kV distribution-level voltage to the typical 110V used in
residential homes.
Figure 12 shows the part of interest from the schematics.
Figure 13 show typical transformer located right at the
transmission tower. Such transformers can be seen all around the
transmission towers within a city.
Figure 14 shows the PSCAD plot for the transformer output
voltage (Ea4). The peak value can be calculated as follows:
𝑉𝑝 𝐿𝑁 = 110 𝑉 √2
√3 = 89.8 𝑉
When we compare this with the plot, we can confirm the above
calculated peak-value.
Figure 12: Local Step-
Down Transformers
Figure 13: Local
Transformers Figure 14: Residential Voltage Plot
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Load Scenario 1 – Factory with Inductive Load
This load was designed to be an inductive load with a 0.6 PF
lagging. We chose this load as large factories usually have a lot of
motors which act as inductive loads. Initially, we run the simulation
without the capacitor connected. The capacitor was later used to
perform a power-factor correction to obtain a power-factor of 1.
Based on the PF, we could calculate the phase angle as follows:
𝜃 = 𝑐𝑜𝑠−1(𝑃𝐹) = 𝑐𝑜𝑠−1(0.6) = 53.13°
The resistor was chosen to be 100 Ohms. With this information we
could calculate the inductive reactance and its equivalent inductance in Henry.
𝑋𝐿 = 𝑅 ∗ tan(𝜃) = 100 ∗ tan(53.13) = 133.3 𝑂ℎ𝑚
𝐿 = 𝑋𝐿 𝜔
= 133.3
377 = 353.6 𝑚𝐻
In the PSCAD simulation, we generated plot for the power-factor and the reactive power. The
plot for the power-factor can be seen in figure 16. The plot was created using a phase difference
element and a cosine element. The reactive power is calculated as follows:
𝑄𝐿 = | 𝑉
𝑅 + 𝑗𝑋𝐿 | 2
∗ 𝑋𝐿 = | 13000
100 + 𝑗133.3 |
2
∗ 133.3 = 811.2 𝑘𝑉𝐴𝑅
From figure 17, we can confirm the value of the reactive power.
Figure 15: Inductive load
for factory
Figure 16: PF for inductive load Figure 17: Reactive Power
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We then repeated the above measurements with a capacitor connected in parallel to the
inductive load. The goal was to increase the power-factor to 1, which should result in zero
reactive power.
The value of the capacitor was calculated as follows:
𝑋𝐶 = 𝑉 2
𝑄𝐿 =
130002
811.2𝑥103 = 208.3 𝑂ℎ𝑚
𝐶 = 1
𝜔𝑋𝐶 =
1
377 ∗ 208.3 = 12.73 𝑢𝐹
Figure 18 and 19 show the results of the power factor correction. We achieved a power-factor of
1 and the reactive power decreased to zero.
Figure 18: PF for inductive load
with PF-correction
Figure 19: Reactive Power with PF-
correction
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Load Scenario 2 – Pure Resistive Load
Our second load consisted of a pure resistive load.
Consumer devices like heaters and lamps belong to
the resistive loads. Such loads have a power-factor
of 1, which means that voltage and current are in
phase.
For this load, we choose resistor values of 20 Ohm,
which are connected in a wye-configuration.
Figure 20 shows the part of interest from the
schematics.
In the PSCAD simulation, we generated a plot of the active power. It can be seen in figure 21.
To verify the reading, we calculated the theoretical value of the active power.
𝑃 = 𝑉 2
𝑅 =
1102
20 = 605 𝑊
As we can see in the plot, experimental and
theoretical values are consistent.
In load scenario 4, we constructed a similar resistive load, but used a delta-configuration instead
of a wye-configuration. Appropriate wye-to-delta transformation have been conducted on the
load resistors and total transformer currents have been compared between the 2 different
configurations.
Figure 20: Pure Resistive Load
Figure 21: Active Power
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Load Scenario 3 – Capacitive Load
Next load is a capacitive load with a power-
factor of 0.8 leading. Such loads occur with
large office buildings with a lot of computers
and data storage centers.
Figure 22 shows the part of interest from the
schematics.
Based on the PF, we could calculate the phase angle as follows:
𝜃 = 𝑐𝑜𝑠−1(𝑃𝐹) = 𝑐𝑜𝑠−1(0.8) = 36.87°
The resistor was chosen to be 10 Ohms. With this information we could calculate the capacitive
reactance and its equivalent capacitance in Farad.
𝑋𝐶 = 𝑅 ∗ tan(𝜃) = 10 ∗ tan(36.87) = 7.5 𝑂ℎ𝑚
𝐶 = 1
𝜔𝑋𝐶 =
1
377 ∗ 7.5 = 353.6 𝑢𝐹
To verify the power factor of this load, we
generated a plot in PSCAD which can be seen in
figure 23. Again, we used a phase difference
element and a cosine element to obtain the plot of
the power factor based on the loads current and
voltage readings obtained from the multimeter.
Figure 22: Capacitive Load
Figure 23: PF for capacitive load
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Load Scenario 4 – Resistive Delta Load
This load was included in the project for direct comparison with load scenario 2, the purely
resistive load connected in a wye-configuration.
Figure 24 shows the part of interest from the schematics.
The goal of this simulation run was to assemble a delta-load which will be equivalent to the wye-
load that was previously discussed.
The load from scenario 2 was transformed to a delta-load with the following calculation:
𝑅∆ = 3 ∗ 𝑅𝑌 = 3 ∗ 20 = 60 𝑂ℎ𝑚
In order to verify if both circuits (the wye-configuration and the delta-configuration) are
equivalent, we generated plots for the transformer output current, so we could verify their
amplitude. The two plots are shown in figure 25:
From the plots above, we can verify that both circuits have the same input current and we can
therefore conclude that both circuits are equivalent.
Figure 24: Resistive Delta Load
Figure 25: Load Current for wye-load (left) and delta-load (right)
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Influence of Transmission Line Length
The previous simulations have been performed by omitting the transmission line lengths. In this
last part of the project, we will include both transmission lines (long distance and short distance)
to see how they influence the voltage levels at the substations.
The first transmission line is a long line of 250 km and the second transmission line is of short
10 km length.
We again plotted the voltage levels at each side of the substation to compare them with the
previous measurements we did with neglected transmission line lengths.
Figure 26 shows the voltage levels before and after the transmission line of 250 km length. The
voltage levels are rated at 230 kV at this point.
Voltage levels before the transmission line are at around 200 kV and at around 205 kV after the
line. For comparison, when neglecting the length of the transmission line, we obtained peak
values of around 187 kV. This is an interesting observation. Rather than obtaining lower voltage
levels, we obtained overall higher voltage levels. This is due to the inductive parameters of the
transmission lines. Transmission lines do not consist of purely resistive loads but contain
inductive and capacitive characteristics.
Figure 27 shows the voltage levels before and after the transmission line of 10 km length. The
voltage levels are rated at 69 kV at this point. This time the line is so short that we cannot see a
difference in voltage levels before and after the transmission line.
Figure 26: Voltage levels before (left) and after (right) the 250 km line
Figure 27: Voltage levels before (left) and after (right) the 10 km line
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Conclusion
In this final lab project, we were successfully able to experiment with the simulation of a
potential real-world transmission grid system consisting of voltage generation, transmission
lines, multiple substations, all the way to the end consumer. We incorporated the knowledge
obtained in the previous labs and included some new topics on our own.
The PSCAD simulation software helped us to generate various graphs of voltages, currents,
powers, and power factors for verification of experimental and theoretical calculations.
Different load configurations helped us to see their difference in phase, power factor, and
reactive powers. We even performed a power factor correction of an inductive load and verified
the equivalence of a wye and delta load configuration.
In this lab report we went over each subsystem in detail and explained their background and
included helpful information with regard to the real world.
