Mindanao State University – Iligan Institute of Technology
Department of Electronics Engineering Technology
COLLEGE OF ENGINEERING
ADVANCED THEORETICAL AND EXPERIMENTAL
INSIGHTS INTO UNLOADED THREE-PHASE
TRANSFORMER PERFORMANCE
Laboratory Report
In partial fulfillment of the requirements for
EEE148.1 Electrical Machines II
Thru
Noel R. Estoperez, D. Eng​
​
​
Rivera, Mary Grez Darlin
Tacolao, Rachelle Marie P.
Tambolero, Kent D.
Tobias, Renz Miguel P.
Tugahan, Richard Jr. R.
BS Electrical Engineering – III/IV
February 2024
I.​
INTRODUCTION
A.​ Background of the Study
Electric power generation and distribution systems worldwide predominantly rely on
three-phase AC systems. These systems play a crucial role in modern infrastructure, making
it essential to understand the operation and applications of transformers within them.
A three-phase (3-phase) electrical system is widely used for generating and
transmitting electrical power over long distances, supplying energy to industries, commercial
establishments, and residential areas. Three-phase transformers are used to efficiently raise or
lower voltage levels within these systems. Unlike single-phase transformers, three-phase
transformers are designed to handle multiple alternating currents that are 120 degrees out of
phase with each other.
Three-phase power, often written as 3-phase or 3φ, offers several advantages over
single-phase systems. These advantages include higher efficiency, reduced conductor material
requirements, smoother power delivery, and improved performance in industrial applications.
As a result, three-phase power is the standard choice for most electrical power generation,
transmission, and distribution networks.
When working with three-phase transformers, it is essential to consider the
interactions of three individual alternating voltages and currents, which differ in phase by 120
degrees. A three-phase transformer (3φ transformer) can be constructed in two ways: By
connecting three single-phase transformers to form a three-phase transformer bank and By
using a single pre-assembled three-phase transformer, which consists of three sets of
single-phase windings mounted onto a common laminated core. The latter option is more
compact and efficient, making it preferable in most industrial settings.
This study is about understanding the theoretical concepts related to three-phase
transformers and applying them through laboratory experiments. By conducting practical
activities, this research seeks to validate and reinforce theoretical principles, ensuring a
comprehensive grasp of three-phase transformer operations and their real-world applications.
B.​ Objectives
This study aims to investigate and understand the basic principles and behaviour of a
three-phase (3-phase) transformer under no-load conditions, explicitly focusing on delta-delta
(Δ-Δ) and delta-wye (Δ-Y) connections.
Specifically, this study seeks to:
●​ Measure and determine the line and phase voltages on the secondary side of the
three-phase transformer, as well as the current on the primary side under different
connection configurations.
●​ Analyze and verify the fundamental principle in the delta-wye (Δ-Y) connection,
where the line voltage is equal to √3 times the phase voltage.
C.​ Significance of the Study
Understanding three-phase transformers is crucial for electrical engineers, as these
devices play a fundamental role in power distribution and industrial applications. This study
provides hands-on experience with transformer configurations, enabling students to analyze
their characteristics and operational efficiencies. The insights gained from this experiment
will be valuable in real-world applications, particularly in power system design,
troubleshooting, and maintenance.
D.​ Scope and Limitations
This study focuses on using three single-phase transformers to construct a three-phase
system. The primary scope includes analyzing different transformer connections (wye and
delta), measuring unloaded parameters, and understanding the core principles of three-phase
transformer operation. However, the study is limited to laboratory-scale transformers under
unloaded conditions, meaning experiments that thoroughly explore the operation of
three-phase transformers are not included.
II. REVIEW OF RELATED LITERATURE
Three-phase transformers are essential components in electrical power systems,
facilitating efficient energy transmission by converting voltages between high, medium, and
low levels. They typically consist of three windings on both the primary and secondary sides,
with their axes aligned to optimize magnetic coupling and minimize losses. Several winding
configurations exist, including Delta-Delta (Δ-Δ), Wye-Wye (Y-Y), Wye-Delta (Y-Δ), and
Delta-Wye (Δ-Y), with commonly used connections such as Yy0, Yd11, Dd0, and Dy5.
The choice of connection significantly impacts system performance, efficiency, and
reliability. (Thomas et al., 2019)
The selection of a transformer connection impacts energy distribution, system stability, and
efficiency. Delta (Δ) and Wye (Y) configurations are widely used in residential, commercial,
and industrial applications (Alkadhim, 2020). Advanced modeling techniques help optimize
their design by considering factors such as neutral grounding, magnetizing effects, and load
variations (Novais et al., 2019). Additionally, dynamic modeling accounts for magnetic flux
disturbances due to hysteresis and saturation under different loading conditions (Reva et al.,
2021).
A study comparing Δ-Δ and Y-Δ transformers under load conditions reveals key
performance differences. The Δ-Δ configuration demonstrates high efficiency, reaching up to
93.8%, while the Y-Δ configuration offers better voltage regulation at 0.9% (Sarwito et al.,
2017). Although Δ-Δ transformers require higher leakage inductance for power transfer, both
configurations exert similar stress on power semiconductors (Nunez et al., 2014). Grounding
methods play a crucial role in stabilizing voltages and enhancing reliability, particularly in
delta-connected systems (Chen & Liao, 2016).
The Δ-Δ transformer connection consists of both primary and secondary windings
connected in a closed delta loop. This configuration provides load balancing, making it
well-suited for industrial applications with heavy three-phase motor loads. Additionally, Δ-Δ
transformers can continue operating in an open-delta (V-V) arrangement if one winding fails,
albeit at reduced capacity (Sung, 2005).
However, Δ-Δ transformers have certain limitations. Unbalanced currents can lead to
circulating currents within the delta loop, increasing losses and heating, which reduces
overall efficiency (Saied, 1996). Proper grounding methods help improve voltage stability
and minimize performance issues under load (Chen & Liao, 2016). While Δ-Δ transformers
are reliable for balanced loads, careful design is required to mitigate issues related to
unbalanced conditions (Saied, 1996).
The Y-Δ transformer connection features a primary winding in a wye (Y) configuration
and a secondary winding in a delta (Δ) configuration. This setup is commonly used in
step-down applications, offering a neutral point for improved safety, grounding, and voltage
stability (Chengtao et al., 2017; Sinay, 2023). The Y-Δ connection also reduces current stress
on the transformer and enhances power transfer efficiency in applications requiring electrical
isolation and voltage conversion (Baars et al., 2016; Gu & Jin, 2016).
Despite these advantages, Y-Δ transformers can experience magnetic leakage and design
complexity, requiring more maintenance than Δ-Δ transformers (Chengtao et al., 2017).
Performance is optimal when operating between 50% and 80% of rated power, but
unbalanced loads may lead to increased power losses (Sinay, 2023; Baars et al., 2016).
III. METHODOLOGY
A.​ Research Design
​
This study employs an experimental research design to analyze the
performance of Delta-to-Delta and Delta-to-Wye connected three phase transformers
under unloaded conditions. The research involves setting up physical transformer
systems, applying input voltage without a connected load, and
measuring their
operational characteristics.
B.​ Materials and Equipment
​
The following materials and equipment will be used for the experiment:
1.​ Three-phase transformers (Delta-to-Delta and Delta-to-Wye connections):
Laboratory-grade transformers rated at 220V to 230V.
2.​ Power supply unit (three-phase): A controlled three-phase power source
providing a stable input voltage.
3.​ Experimental Panel: The laboratory setup includes a structured panel with
labeled connection terminals (H1, H2, X1, X2, etc.), ammeters, and circuit
protection mechanisms.
4.​ Measuring Equipments: Voltmeter and Ammeter to measure voltage and
current, respectively.
5.​ Safety Equipment: Circuit breakers and fuses, and emergency cutoff switch.
C.​ Experimental Setup
1.​ Transformer Configurations:
a.​ Delta-to-Delta Configuration:
The primary winding terminals are connected as follows: H2 of the
transformer T1 is connected to H1 of transformer T2 to form one
phase, H2 of transformer T2 is connected to H1 of transformer T3, and
H2 of transformer T3 is connected to H1 of transformer T1, forming a
closed-loop Delta connection.
The secondary winding follows the same Delta pattern: X2 of the
transformer T1 is connected to X1 of transformer T2 to form one
phase, X2 of transformer T2 is connected to X1 of transformer T3, and
X2 of transformer T3 is connected to H1 of transformer X1.
b.​ Delta-to-Wye Configuration:
The primary side remains in Delta as in the previous configuration,
with H1 and H2 of each transformer forming a phase.
The secondary winding is connected in Wye: X2 of each of the
transformers are joined together to form the neutral point, while X1 of
transformers T1, T2, and T3 serve as phases A, B, and C, respectively.
2.​ Unloaded Operation: The secondary windings will remain open-circuited (no
load connected), allowing the measurement of no-load characteristics.
3.​ Measurement Points:
a.​ Delta-to-Delta Configuration:
Primary no-load current using ammeter with one terminal connected to
L1, and one to H1 of the transformer T1.
Secondary phase voltage using a voltmeter with terminals 1 and 2
connected to X1 and X2 of the transformer T1.
b.​ Delta-to-Wye Configuration:
Primary no-load current using ammeter with one terminal connected to
L1, and one to H1 of the transformer T1.
Secondary phase voltage using a voltmeter with terminals 1 and 2
connected to X1 and X2 of the transformer T1.
Secondary line voltage using a voltmeter with terminals 1 and 2
connected to X1 of transformers T1 and T2, respectively.
​
a.​​
​
​
​
​
​
​
b.
Figure 1: Actual Circuit Diagram for (a) Delta-to-Delta, (b) Delta-to-Wye.
IV. RESULTS AND DISCUSSIONS
​
The analysis of an unloaded three-phase transformer provides valuable insights into
its core losses, magnetizing current, and overall performance under no-load conditions. This
study examines the key parameters affecting transformer behavior and compares theoretical
expectations with experimental results. The measured values for both transformer
configurations under unloaded conditions are as follows:
Delta-to-Delta Connection
Delta-to-Wye Connection
Primary Line Current
0.11 A
0.11 A
Secondary Phase Voltage
118 V
118 V
Secondary Line Voltage
not measured
203 V
​
In an unloaded state, it only requires enough current to maintain the magnetic field in the
core, which is typically quite small, that’s why it’s only leading to minimal current draw. The
primary objective of this experiment was to identify the presence of the 3 factor in
three-phase transformer operation. In the Delta-to-Delta configuration, the phase voltage and
line voltage are equal due to the closed-loop delta connection, although in this experiment,
line voltage was not measured. In the Delta-to-Wye configuration, the secondary line voltage
is higher than the phase voltage by a factor of 3. Mathematically, the theoretical line voltage
in a Delta-to-Wye system should be:
𝑉𝐿 = 𝑉 𝑝 𝑥 3
where 𝑉𝐿 is the line voltage, 𝑉𝑝 is the phase voltage, and 3 as the magnitude multiplier. To
solve for the voltage transformation ratio while treating 3 as an unknown, given the
measured values: 𝑉𝐿 = 203 V and 𝑉𝑝 = 118 V, solving for 3:
𝑉𝐿
𝑉𝑝
203 𝑉
118 𝑉
= 3
= 3
1. 720 = 3
The percentage error between the theoretical and measured values of 3 is calculated as:
𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝐸𝑟𝑟𝑜𝑟 = (
|1.732−1.720|
)𝑥100
1.732
= 0. 69%
The small error, 0.69%, confirms the accuracy of the experiment and the expected voltage
transformation ratio.
V. CONCLUSION AND RECOMMENDATIONS
The experiment successfully measured and determined the line and phase voltages on
the secondary side of the three-phase transformer, as well as the primary side current under
different connection configurations. The resulting Percent Error is 0.69%, which means that
the experiment was very accurate and the theoretical values were very close to our
experimental values. These findings reinforce the practical understanding of three-phase
transformer behavior and its application in electrical power systems.
To fully understand transformer performance, future research should test transformers
under various load conditions to identify inefficiencies and performance variations.
Measuring power losses and efficiency at different loads will provide practical insights,
helping optimize transformer design for better reliability and energy savings.
References
Thomas, K., Carsten, L., & Jürgen, P. (2019). Three-phase transformer.
Alkadhim, S. A. S. (2020). Three Phase Transformer: Connection and Configuration. Social
Science Research Network. https://doi.org/10.2139/SSRN.3647143
Novais, I. F., Junior, A. P., & Silva, S. F. P. (2019). Modeling Three-Phase Transformers.
Renewable
Energy
&
Power
Quality
Journal,
17,
103–108.
https://doi.org/10.24084/REPQJ17.233
Reva, I., Bialobrzheskyi, O., Todorov, O., & Bezzub, M. (2021). Three-phase core-type
transformer model investigation taking into account hysteresis phenomena in asymmetric
load mode. https://doi.org/10.1109/KHPIWEEK53812.2021.9570085
Sarwito, S., & Al Hanif, M. I. (2017). Analysis of unbalanced load effect of three phase
transformer feedback 61-103 performance on the various connection windings.
https://doi.org/10.1109/ICAMIMIA.2017.8387575
Nunez, R. O., Oggier, G. G., Botteron, F., & Garcia, G. O. (2014). Convertidor CC-CC con
puentes duales activos trifásicos: Comparación transformador YY y ΔΔ. IEEE Biennial
Congress of Argentina, 332–337. https://doi.org/10.1109/ARGENCON.2014.6868515
Saied, M. M. (1996). Effect of the load and short-circuit impedance unbalance on the
operation of /spl Delta/-/spl Delta/ transformer banks. IEEE Industry Applications Society
Annual Meeting, 4, 2431–2435. https://doi.org/10.1109/IAS.1996.563911
Chen, T.-H., & Liao, R.-N. (2016). Investigation of transformer banks with delta-connected
secondary windings and various grounding methods for delta service. Iet Generation
Transmission & Distribution, 10(7), 1527–1535. https://doi.org/10.1049/IET-GTD.2015.0325
Kim, K. S. (2005). Three-phase four-line delta connected transformer with improved stability
in harmonic wave and reduced ground faults.
Chengtao, T., Zhengxun, X., Weidong, F., Lili, Y., Zhenhua, S., Fuming, R., Hanchang, C.,
Xuran, Z., & Yingjie, L. (2017). Y-shaped connection transformer.
Gu, L., & Jin, K. (2016). A Three-Phase Bidirectional AC/DC Converter With Y–Δ
Connected Transformers. IEEE Transactions on Power Electronics, 31(12), 1.
https://doi.org/10.1109/TPEL.2016.2517647
Sinay, P. (2023). Performance study of unbalanced load on open delta transformers.
https://doi.org/10.56127/ijml.v2i3.1252