Title:
Electrical Power And Machines Coursework Report
Author:
William Staal (Student Number: 29022927)
Session:
2022/2023
Module:
55-601323
Electrical Systems and Sustainable Energy
Module Leader:
Muhammad Akmal
Deadline for submission:
Thursday, 23/03/2023 15:00
Deadline for return of feedback:
27/04/2023
Table of Contents
Introduction ........................................................................................................................................ 1
Lab 1&2: Connection and Starting of Synchronous Generator .......................................................... 2
Part 1a: Varying Excitation on generator voltage at constant speed ............................................. 2
Part 1b: Varying Speed on generator voltage at constant excitation ............................................. 3
Part 1c: Load Characteristics at constant speed and excitation ..................................................... 3
Part 1d: Effect of Excitation and Torque changes on power feed .................................................. 6
Lab 3 Load Flow and Stability Analysis using DIgSILENT Power Factory ........................................... 10
Part 2a: Modelling a Network in DIgSILENT Power Factory and debug to describe parameters. 10
Part 2b: Describing the Load Flow results in detail....................................................................... 15
Part 2c: Creating switch events, faults at different points and running stability for dynamic
simulation of a power system. ...................................................................................................... 18
Part 2d: Describing potential applications and scenarios where this type of simulation is
required for power systems. ......................................................................................................... 19
Conclusions ....................................................................................................................................... 20
References ........................................................................................................................................ 20
Introduction
The following report outlines three practical labs carried out in semester one of the ELECTRICAL
SYSTEMS AND SUSTAINABLE ENERGY module, regarding Synchronous Machines through altering
specific elements and discussing results of the system in a controlled, professional laboratory
environment, and through simulation using DIgSILENT Power Factory. The purpose of these
investigations is to gain an understanding of the properties and fundamentals of Synchronous
Machines, including digital design and simulation, the characteristics of synchronous generators, and
building the skills to synchronise a generator the mains and power feed. The practical labs were
conducted under the supervision by Dr Muhammad Akmal.
Lab 1&2: Connection and Starting of Synchronous Generator
Part 1a: Varying Excitation on generator voltage at constant speed
The first alteration element regards varying excitation current on a constant speed synchronous
generator, to observe the impact on generator voltage. The results are shown in figure 1 and 2
below:
Figure 1: Table of results testing Induced Generator Voltage as excitation current increases.
Induced Voltage vs I excitation
400
350
Vind-G(V)
300
250
200
150
100
50
0
0.2
0.7
1.2
1.7
2.2
Iexc (A)
Figure 2: graph produced from the table of results in figure 1 showing the relationship between Induced Generator Voltage
and Excitation Current.
Figure 2 shows a non-linear positive relationship between excitation current and induced generator
voltage, concluding that as an increase in excitation occurs, an induced generator voltage also
increases at a decelerating rate. This occurs due to the strength of the magnetic field being adjusted
by the excitation system, creating an electromagnetic field in the rotor, generating electrical power
and by extension the induced generator voltage.
Part 1b: Varying Speed on generator voltage at constant excitation
The next element alteration the speed of a constant excitation generator, observing the impact on
generator voltage. In conclusion, as the generator speed increases, the induced generator voltage
also increases. This is proven as shown in figure 3 and 4 as below:
Figure 3: Table of results testing Induced Generator Voltage as generator speed increases.
Speed Vs Induced Voltage
400
350
Vind-G(V)
300
250
200
150
100
50
0
250
450
650
850
1050
1250
1450
1650
Speed(Rpm)
Figure 4: graph produced from the table of results in figure 3 showing the relationship between Induced Generator Voltage
and generator speed.
In conclusion, as excitation current increases, the induced generator voltage increases as well. This is
due to the forces that keep the rotor locked in synchronous speed with the frequency of the grid.
Part 1c: Load Characteristics at constant speed and excitation
The next investigation deals with varying the load characteristics when both speed and excitation of
the generator remain constant. The results are as shown in the figures below:
Figure 5- A table showing the load characteristics with constant speed and excitation.
Constant Speed is kept at 1500rpm, and constant excitation is kept at around 2A.
Load Characteristics
200
150
100
50
0
1000
1200
1400
1600
1800
2000
Resistance(ohms)
V(V)
I(A)
P(W)
Q(VAR)
Figure 6 - Showing a combined graph of all parameters to show load characteristics with individual graphs being shown
below.
190
185
V(V)
180
175
170
165
160
1000
1200
1400
1600
R(ohms)
1800
2000
Load characteristics of R vs I
0.4
I(A)
0.3
0.2
0.1
0
1000
1200
1400
1600
1800
2000
R(Ohms)
Q(VAR)
Q(VAR)
20
18
16
14
1000
1200
1400
1600
1800
2000
2200
R(Ohms)
P(W)
50
P(W)
40
30
20
10
0
1000
1200
1400
1600
1800
2000
R(Ohms)
Conclusions from the graphs:


The load characteristics has little to no effect on the output generator voltage(V) and
reactive power (Q) (ignoring anomalies in the table and graph).
The load characteristics has a negative relationship on the output current(I) and output
Power. So as load increases, the output power and current decrease as a result.
Part 1d: Effect of Excitation and Torque changes on power feed
Lab 2 investigates the impact of excitation and torque on the power feed of a synchronous machine:
The effect of excitation on power feed can be shown as below:
Figure 7 - Table of results showing the impact of excitation on power feed.
P (W)
20
P(W)
15
10
5
0
0.5
1
1.5
2
2.5
3
3.5
4
Iexc (A)
Figure 8 - Graph representing the impact on Power when changing excitation
Q (VA)
100
Q (VA)
80
60
40
20
0
0.5
1
1.5
2
2.5
3
3.5
4
Iexc (A)
Figure 9- Graph representing the impact on Active Power when changing excitation.
Power Factor (CosΦ)
Power Factor
1
0.8
0.6
0.4
0.2
0
0.5
1
1.5
2
2.5
3
3.5
4
Iexc (A)
Figure 10 - Graph representing the impact on Power factor when changing excitation.
From observing the table and produced graphs, we can make the following conclusions:

As excitation increases at a constant speed, the real power decreases in a decelerating curve
relationship. Increasing excitation causes the generators armature current to decrease,
reducing the terminal voltage and by extension a decreasing power.

As excitation increases at a constant speed, reactive power Q decreases and then increases
after a 2.5A excitation. The generator runs at a low power factor at lower excitation levels,
resulting in a high level of reactive power. As excitation increases, the power factor
increases, leading to a decrease in reactive power. However, as the excitation is further
increased, the generator experiences over-excitation, decreasing reactive power.

As excitation increases at a constant speed, the power factor has an inverse relationship
compared to reactive power, providing an accelerating increase curve to a peak of about
0.84 at 2.5A excitation, then a sudden decelerating decrease curve as excitation continues.
This occurs due to a leading to lagging power factor relationship, where the breaking point
for this sudden decrease is 2.5A excitation or the point over-excitation.
The effect of change in torque on power feed can be shown as below:
Figure 11 - Table showing the impact on power feed and efficiency, when changing the torque
Pmech = M ω
400
350
300
Pmech
250
200
150
100
50
0
-2.5
-2
-1.5
-1
-0.5
Torque(Nm)
Figure 12 - Graph representing the impact on Mechanical Power when changing torque.
0
Pexcitation
61.3
61.2
PExcitation
61.1
61
60.9
60.8
60.7
60.6
-2.5
-2
-1.5
-1
-0.5
0
Torque(Nm)
Figure 13 - Graph representing the impact on excitation power when changing torque.
Calculated Efficiency
25
20
Efficiency
15
10
5
0
-2.5
-2
-1.5
-1
-0.5
0
Torque(Nm)
Figure 14 - Graph representing the impact on efficiency when changing torque.
Therefore, from observing the table and produced graphs, we can make the following conclusions:

For this synchronous generator, the torque is being applied in the opposite direction to the
rotation of the rotor, producing a negative torque.

As torque negatively increases, the mechanical power increases in a linear relationship. An
increase in torque increases in the force applied to the rotor, leading to an increase in the
mechanical power output of the generator.

As torque negatively increases, the excitation power decreases in a stair linear relationship,
linearly decreasing until about -0.8Nm, then flatlining until about -1.6Nm, and then
continuing to linearly decrease until -2Nm, and then linearly decreasing at a different rate.
This occurs because torque may impact the excitation power via impacting the power factor
of the generator.

As torque negatively increases, the overall calculated efficiency increases in a backwards
accelerating curve made up of linear relationship lines, changing where the efficiency
accelerating rate changes at torque values -0.8Nm, -1.2Nm, and -2Nm. The torque is
negative due to the direction it is being applied to in relation to the generator.
Lab 3 Load Flow and Stability Analysis using DIgSILENT Power Factory
Part 2a: Modelling a Network in DIgSILENT Power Factory and debug to describe parameters.
To model a network in DIgSILENT Power Factory, the necessary data, and parameters, such as bus
locations and types, transmission lines, transformers, and loads, must be inputted into the software.
The system requires 3 terminal buses, 2 asynchronous machines, 2 transformers and a connection to
the national grid, or as shown below:
Figure 15 - Showing the drawn simulation diagram without parameters inputted.
The parameters for these components are shown in the table below:
Name
Busbar Type
1(station 1)
Type
Nominal Voltage
Station 1/B1
Line-Line Voltage
Busbar Type
2(station 2)
Nominal Voltage
Station 2/B1
Line-Line Voltage
Busbar Type
3(station 3)
Nominal Voltage
Value
Station 3/B1
Line-Line Voltage
Transformer
1
Rated Power,
Rated Voltages
Transformer
2
Rated Power,
Rated Voltages
Asynchronous
Machine 1
Rated Voltage,
Rated Apparent
Power
Asynchronous
Machine 1
Load Flow: Active
Power
Asynchronous
Machine 2
Rated Voltage,
Rated Apparent
Power
Asynchronous
Machine 2
Load Flow: Active
Power
After these parameters are inputted and the load flow is executed:
Figure 16 - Showing the drawn simulation diagram with parameters inputted.
For debugging we would refer to the bottom console detailing any warnings, errors or other that
could be interfering with the load flow. Or also to double check any connections, blocks and
parameters for the system.
Figure 17 - An image showing the bottom console for debugging purposes.
Part 2b: Describing the Load Flow results in detail.
Load Flow results:
Figure 18 - Simulation Diagram showing load flow results.
Figure 19 - Debugger showing load flow process.
Figure 20 - System summary page showing in detail load flow results.
Changing Asynchronous Machine 1’s Active Power from 4MW to 2MW:
Figure 21 - Altered parameters Simulation diagram showing load flow results.
Figure 22 - System summary showing results before alteration.
Figure 23 - System summary showing results after alteration.
From observing the prior screenshots, we can conclude that by decreasing the active power of
Asynchronous Machine 1, the power, active power and current from Station 2 to the external grid
also decreases, where power across external grid decreases from 5MW to 3MW. This can further be
seen by observing the detail results from the load flow in the console, we can observe various
changes such as a decrease from 0.92 Load to 0.85, where the motor load was originally 2.15Mvar &
5.44MVA and the decreases to 1.88Mvar & 3.54MVA.
Part 2c: Creating switch events, faults at different points and running stability for dynamic
simulation of a power system.
To perform a stability analysis in DIgSILENT Power Factory, switch events and faults must be created
at different points in the network and a dynamic simulation must be run, as shown below:
Figure 24 - Showing results for dynamic simulation of power system.
Referring to figure above, we can make various conclusions. For the top wave form:
-
All 3 stations are somewhat impacted, where station 1 is minimally impacted, and station 2
and 3 follow a similar pattern, where station 3 is affected the most.
There is an open circuit at 1 second and therefore voltage is at its maximum.
The motor then activates after 3 seconds, forming a closed circuit and causing a small dip in
voltage or voltage drop, until regulating back up to max voltage.
After approximately 10 seconds, the voltage drops to zero as the fault is expected around
this point.
Following 15 seconds the fault is corrected/cleared, where the a sudden increase and then a
gradual increase in voltage occurs.
For the bottom waveform:
-
Upon observing the waveforms, only station 3 seems to be impacted during the load flow
process, with station 1 and 2 being minimally impacted.
A spike in frequency occurs for station 3 from when the motor starts up, where beforehand
the frequency is stable at 50Hz.
A smaller spike can be observed when the fault occurs, and a large spike is seen when the
fault is in the process of being cleared.
Part 2d: Describing potential applications and scenarios where this type of simulation is
required for power systems.
Stability analysis using DIgSILENT Power Factory can be applied to a variety of power systems
scenarios to evaluate the dynamic behaviour of the system under different operating conditions and
disturbances. Some potential applications and scenarios where this type of simulation may be useful
include:





Assessing the stability of a power system during normal and abnormal operating conditions,
such as changes in load or generation, equipment failures, or network reconfigurations.
Evaluating the performance of power system protection and control schemes, such as fault
detection and isolation, load shedding, and automatic generation control.
Investigating the transient stability of a power system following a disturbance, such as a
short circuit or loss of a major component.
Analysing the dynamic response of a power system to events such as load changes,
generator tripping, or switch operations.
Determining the impact of new generators, transmission lines, or loads on the stability and
reliability of a power system.
Conclusions



In conclusion for lab 1, the investigations done have helped build an understanding of the
different characteristics of altering excitation, speed, and applied load onto a synchronous
generator.
The investigations in Lab 2 has built a good understanding of the ability to synchronise a
generator the mains and power feed, and any characteristics for improving efficiency and
power by altering the systems excitation or torque.
The completion of Lab 3 has built new skills regarding the ability to use simulation tools to
accurately design a synchronous system and observe load flow measurements and view
simulated characteristics of creating switch events and faults within the system.
References
Saini, M. K. (2021, October 28). Effect of Changing Field Excitation on Synchronous Motor
at Constant Load. www.tutorialspoint.com. Retrieved 2021, from
https://www.tutorialspoint.com/effect-of-changing-field-excitation-on-synchronousmotor-at-constant-load
Øyvang, T., Hegglid, G. J., & Lie, B. (2018, March 16). Models of synchronous generators
with excitation system, for transient power system studies. sciencedirect.com. Retrieved
March 21, 2023, from
https://www.sciencedirect.com/science/article/pii/S2405896318300168
University, Ç. (2018). CHAPTER 5 – SYNCHRONOUS GENERATOR. ABS. Retrieved
March 21, 2023, from chromeextension://efaidnbmnnnibpcajpcglclefindmkaj/https://abs.cu.edu.tr/Dokumanlar/2017/
EEE318/271877548_2_synchronous_machines.pdf