In recent years, power quality has deteriorated due to the widespread use of modern electronic devices. Office buildings employ a variety of devices, such as computers and LCD monitors, contributing to a decrease in power factor and an increase in harmonic distortion. These commonly used devices, typically based on power electronic components, draw distorted current from the grid containing higher-order harmonics. This distorted current impacts the voltage at the point of connection, further degrading power quality. This article examines the impact of total harmonic distortion of voltage on the power consumption parameters and thermal performance of common office equipment. The study focuses on two types of computer power supplies and LCD monitors, evaluating how distorted voltage affects reactive power, power factor, and device temperature. Experimental measurements were conducted under varying levels of voltage distortion to assess changes in electrical parameters and thermal behavior. The results indicate that increased voltage distortion results in higher reactive power consumption, a decrease in power factor, and a significant increase in device temperature. These findings highlight the impact of power quality on the performance and durability of office equipment, underscoring the importance of managing voltage distortion in low-voltage networks.
Hinweise
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1 Introduction
Electricity constitutes a fundamental aspect of human existence, serving essential roles in meeting living requirements, ensuring public health, and significantly influencing economic and national security considerations. Presently, it is an important commodity, with considerable emphasis placed on ensuring its quality [1, 2]. However, a disadvantage of electricity is its inability to be stored on a large scale, necessitating immediate consumption [3]. The energy transmission involves multiple elements sensitive to external influences, each influencing the overall quality of the energy. Ensuring power quality at the point of consumption proves to be a complex task due to the variability in perspectives between consumers and suppliers. Consequently, a collaborative compromise becomes essential [4].
The power quality is generally evaluated based on compliance with specific parameters, including amplitude, frequency, pure sine waveform, and voltage asymmetry. Deviations from these parameters serve as indicators of a decline in power quality [5].
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The article analyzes the electricity consumption of electrical devices utilized in office buildings under degraded power quality. Power quality is defined by EN 50160, which describes the voltage characteristics of electricity supplied from the public electricity network [6]. This standard delineates key parameters of supply voltage at the user's point of connection in public AC electrical networks across various voltage levels under normal operating conditions. It specifically addresses the frequency, amplitude, waveform, and asymmetry of the voltage.
While EN 50160 focuses on these voltage-related parameters, it is equally important to monitor adverse phenomena associated with the current drawn by loads, aspects not provided by this standard. This encompasses reactive power and the power factor of the load [7]. Reactive power, a component of AC transmission, is created due to the inductive or capacitive nature of transmission elements and loads within the electricity network [8]. Despite not performing useful work, reactive power is essential for elements with inductive or capacitive nature that require the creation of magnetic or electric fields. The flow of reactive power increases the load of transmission elements, subsequently leading to higher power losses [9, 10].
Appliances in office buildings are typically connected to the low-voltage (LV) level; therefore, all measurements in this study were conducted at this voltage level. The investigation involved measurements on computers’ (PC) power supply unit (PSU) and LCD monitors. In a laboratory environment within the Department of Power Systems and Electric Drives, eight distinct voltage conditions were applied using the Applied Precision power supply, which provided power to each measured device. The impact of these varied voltages on the measured devices was evaluated using a power quality analyzer and a thermal imaging camera. Its various consumptions parameters, including consumed powers, power factors, total harmonic distortion of current, and the thermal response (warming up) of the electrical devices, were recorded.
The rest of this article is organized as follows: Sect. 2 discusses the appliances and measurement methods used in this study. Section 3 presents the measurement results, and Sect. 4 provides the conclusions of the study.
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2 Measurement of selected devices
A total of six appliances were measured, consisting of three types of PSUs and three types of LCD monitors. Figure 1 shows the block diagram of the measurement setup, with the PSU represented as the measured device. The block diagram for monitors is identical, with only the measured device changing.
The devices were tested under supply voltage conditions set according to the limit values specified in the EN 50160 standard. The supply voltage parameters, as detailed in Table 1, remain unchanged for both PSUs and LCD monitors.
Table 1
Description of supply voltage parameters
Measurement
Fundamental harmonic
Higher-order harmonics (%)
Number
Describe
V (V)
f (Hz)
3
5
7
11
13
1
Basic state
230
50
–
–
–
–
–
2
Harmonics 50% of standard
230
50
3
3
3
2
2
3
Harmonics 100% of standard
230
50
5
6
5
4
3
4
Harmonics 150% of standard
230
50
7
9
7
5
3
5
Lower voltage
210
50
–
–
–
–
–
6
Higher voltage
250
50
–
–
–
–
–
7
Lower frequency
230
49
–
–
–
–
–
8
Higher frequency
230
51
–
–
–
–
–
2.1 Measurement of PC PSUs
The PSU operates as a switching power supply, converting alternating network voltage into the direct voltage levels required by computer components. This conversion uses transistors with short switching times operating at frequencies in the tens to hundreds of kilohertz range. Due to the use of semiconductor components, the volt-ampere characteristic of a switching power supply is nonlinear, resulting in a distorted drawn current [11]. Each PSU incorporates a power factor correction (PFC) filter to mitigate this distortion and reduce its negative impact on the network [12]. The power factor is defined as the ratio of active power to apparent power serves as a metric for efficiency and varies with load [13]. PC power supplies typically achieve efficiencies ranging from 81 to 96% under optimal conditions, with efficiency levels categorized by the 80 Plus certification system. Higher efficiency often correlates with increased PSU costs.
In the measurements, loads were connected to the + 5 V and + 12 V output terminals on the DC side of the PSU, per the recommended operating conditions. The PSU utilized feedback mechanisms to maintain a stable DC output voltage, ensuring a constant current draw of 2 A on both voltage levels. Due to the differing characteristics of the tested PSUs, their operational losses varied, resulting in differences in active power consumption on the AC side. Modifying the DC-side load could increase active power draw on the AC side, potentially leading to improvements in THDI and power factor. This change would have a minimal impact on Q. However, due to time constraints, the DC load was not altered during this phase of the experiment. All measurements were conducted with the enclosures removed to allow thermal monitoring of components using a FLIR T620 thermal imaging camera. Power quality parameters were assessed using an ENA 330 network analyzer. All evaluated power consumption parameters were either measured or calculated using the ENA 330 network analyzer, which performs measurements and calculations in accordance with the IEC 61000-4-30 standard [14]. The network analyzer calculates individual power components according to the following equations:
Total active power is calculated from the voltage and current values obtained using the Fourier transform.
where \(U_{h}\) is RMS value of the voltage with frequency \(50 \cdot h\) Hz, \(I_{h}\) is RMS value of the current with frequency \(50 \cdot h\) Hz, and \(\varphi_{h}\) is phase shift between voltage and current for frequency \(50 \cdot h\) Hz. The active power of the fundamental harmonic is then calculated by considering the harmonic order h = 1. Apparent power is determined from RMS values of voltage and current, encompassing all harmonic components present in the signal.
$$ S = U \cdot I $$
(2)
where U is the RMS value of the voltage including all harmonic components, and I is the RMS value of the current including all harmonic components. Total reactive power and the total reactive power are then calculated as follows.
The reactive power of the fundamental harmonic is then calculated by considering the harmonic order h = 1. The total power factor is calculated from the obtained power values as follows:
$$ \lambda = \frac{\left| P \right|}{S} $$
(4)
The initial phase of the study involved determining the baseline states of the PC power sources. Each power supply was in a 5-min operation under conditions of a pure sine wave with an effective value of voltage 230 V and a frequency of 50 Hz. Subsequent variations in the supply voltage parameters on the Applied Precision power supply simulated degraded power quality. The steady-state condition was defined as one where the device temperature exhibited no change exceeding 0.2 °C in 30 s, as observed through the thermal imaging camera. This scenario served as the reference point for evaluating the effects observed in the subsequent test scenarios.
The first measurement involved setting higher-order voltage harmonics at half of the limit level according to EN 50160, reaching threshold values, and 1.5 times higher values. The second measurement entailed varying the magnitude of the supply voltage, with two levels representing ± 10% of 230 V (210 V and 250 V). The final measurement varied the frequency of the voltage, maintaining an effective value of 230 V with frequency values of 49 Hz and 51 Hz.
2.2 Measurements of LCD monitors
LCD monitors, similar to PC power source, utilize switching power supplies characterized by multiple voltage levels. However, the voltages are not exactly defined. Each producer uses its own. Within the structure of an LCD monitor, two primary circuit boards are typically present: the power supply board, encompassing the backlight power supply, and the logic board, which accommodates inputs for video and, in certain instances, audio. Over time, video connectors have evolved from VGA (Video Graphics Array) to DVI (Digital Visual Interface), and presently HDMI (High-Definition Multimedia Interface), which facilitates the simultaneous transmission of video and audio. Monitors employ software buttons for activation, allowing them to work in standby or operational modes. Complete shutdown necessitates disconnection from the power supply. Measurements for monitors were similar to those employed for PC sources, involving the removal of enclosures to enable temperature monitoring with a thermal imaging camera.
During measurements, monitors were initially supplied with a sinusoidal voltage of 230 V at a frequency of 50 Hz, displaying a white background at maximum brightness by VGA inputs. This configuration established a constant load throughout the measurement. Subsequent testing involved the application of a power supply with a spectrum of higher-order voltage harmonics, followed by alterations in voltage magnitude and, lastly, changes in frequency. The supply voltage parameters aligned with those applied to PC power supplies, as delineated in Table 1.
3 PC Power sources results
Owing to the extensive volume of collected data, outcomes are selectively presented only for the PC power supply Premier LC-B300ATX. This particular unit represented the worst-case device. A comprehensive evaluation of all measured power supplies is provided in the conclusion. The selection of a single unit for detailed presentation was made due to space limitations within the scope of the article.
3.1 PSU premier—basic state
Figures 2 and 3 illustrate the waveforms of the supply voltage and current and the magnitudes of current harmonics for the PC PSU Premier under basic state. The voltage waveform is pure sinusoid. However, the drawn current, influenced by the nonlinear characteristics of the connected PC PSU, is deformed. Subsequently, Fig. 4 depicts the temperature profiles of individual source components under the condition of a pure sinusoidal supply voltage. This state served as a reference for comparison with instances where power quality conditions were intentionally degraded.
The maximum temperature observed in the PC PSU, as indicated in Fig. 4, is 57.4 °C. Additionally, Table 2 provides an overview of the higher-order current components up to the 13th harmonics. Table 2 outlines the recorded consumed powers and power factors.
Table 2
Consumption parameters of PC source premier for all scenarios
P (W)
Q (var)
S (VA)
P1 (W)
Q1 (var)
cos φ
λ
THDU (%)
THDI (%)
1 Base state
55.4
− 110
115.2
55.5
− 15.5
0.96
0.48
0.191
172.8
2 Harmonics 50% of standard
57.2
− 141.1
152.3
51.48
− 10.8
0.98
0.38
5.615
271.2
3 Harmonics 100% of standard
58.6
− 146.2
157.5
48.79
− 10.2
0.98
0.37
10.04
296.9
4 Harmonics 150% of standard
59.1
− 145.7
157.2
45.72
− 9.89
0.98
0.38
14.45
313.8
5 Lower voltage
55.37
− 97.4
112
55.5
− 14.5
0.97
0.49
0.202
168
6 Higher voltage
59.9
− 105.5
119.9
57
− 16.9
0.96
0.47
0.117
174.9
7 Lower frequency
54.86
− 96.5
111
55
− 15.2
0.96
0.49
0.18
167
8 Higher frequency
55.1
− 97.3
111.8
55.2
− 15.4
0.96
0.49
0.18
167.8
The drawn current exhibits a substantial harmonic distortion, reaching 172.8%. Consequently, notable disparities emerge between the fundamental harmonic (Q1) and the total reactive power (Q), leading to distinctions between the fundamental power factor (cos φ) and the total power factor (λ).
3.2 PSU premier—harmonics 100% of standard
Figure 5 represents the waveforms of the supply voltage and current for the Premier PC PSU. The magnitude of harmonic components in the voltage spectrum, up to the 13th harmonic, reaches threshold values in accordance with the EN 50160 standard [6]. Figure 6 provides a temperature profile observed in individual source components under these specified conditions.
Under conditions of distorted voltage, the maximum temperature increased by 13.7 °C compared to the basic state. This temperature increase is caused by the increased presence of current harmonics and associated distortion, as presented in Tables 2 and 4.
Due to the influence of an increase in voltage distortion, there is a subsequent surge of 124.1% in current distortion. This escalation contributes to an increase in the magnitude of total reactive power. Simultaneously, the fundamental current harmonic experiences decrease compared to the basic state, resulting in reduced active power (P1) and reactive power of fundamental harmonic. These alterations contribute to a significant decrease in the total power factor, reaching a value of 0.37. Additionally, the negative values of reactive powers indicate a capacitive nature in the consumption of the Premier PC PSU in both scenarios.
3.3 PSU Premier—remaining measured scenarios
The results encompassing consumption parameters, temperatures, and current harmonic components for all remaining measured scenarios are presented in Tables 2, 3 and 4.
Table 3
Temperatures of PC sources premier
Measurement
1
2
3
4
5
6
7
8
Temperature (°C)
57.4
65.1
71.1
75.5
57.3
66.7
55
60.2
Table 4
Current harmonics of PC sources premier for all scenarios
Measurement
I1 (A)
I3 (A)
I5 (A)
I7 (A)
I11 (A)
I13 (A)
1
0.253
0.229
0.212
0.187
0.126
0.094
2
0.230
0.218
0.214
0.209
0.193
0.183
3
0.218
0.208
0.205
0.201
0.190
0.182
4
0.206
0.196
0.195
0.191
0.182
0.176
5
0.272
0.249
0.227
0.198
0.125
0.089
6
0.240
0.218
0.202
0.180
0.124
0.095
7
0.247
0.227
0.207
0.180
0.115
0.081
8
0.248
0.226
0.207
0.181
0.117
0.084
The identical type of results to those for the previously mentioned PSU Premier was recorded for the remaining two PSU, Dell and Fortron. However, for brevity, the outcomes of these sources will be discussed solely in the ensuing text. The subsequent section of the paper provides a comparative analysis of the results obtained for all measured PC PSUs.
3.4 Evaluation of measurements on PC PSU
Three types of PSUs were measured in total. During the measurements, constant active power consumption was maintained. The consumed active power for each PSU was approximately 45 W for Dell, 55 W for Premier, and 50 W for Fortron. All examined PSUs exhibited non-compliance with the amplitude law in the generation of current harmonics during measurements. The voltage and current waveforms exhibit substantial distortion in the current compared to the voltage. The observed current waveform represents the summation of all harmonic components. When the PSUs were supplied with a voltage containing harmonic distortion, the drawn current exhibited significantly higher distortion levels compared to the base state, where a pure sinusoidal voltage was applied. The distortion in the drawn current is quantified by the THDI, which is presented in Fig. 7 for all measured scenarios (Table 1).
Figure 7 identifies which power quality parameters have the most negative impact on power consumption parameters. In the base state (measurement 1), the recorded THDI values were 96.31% for Dell, 172.8% for Premier, and 94.67% for Fortron. When the supply voltage included harmonic components, the THDI increased proportionally to the magnitude of the individual higher-order voltage harmonics. However, in measurements 5–8, where the supply voltage was a pure sine wave and only its RMS value and frequency were varied, the impact on THDI was negligible compared to the base state for all tested PSU types.
The active and fundamental harmonic reactive power values for the PSUs showed minimal variation, regardless of supply voltage distortion. Consequently, these parameters are not graphically evaluated. In contrast, the total reactive power, as depicted in Fig. 8, demonstrates a distinct dependency on THDI. Its magnitude increases with the THDU, while variations in the RMS value and frequency of the supply voltage have a negligible impact. Two PSU types (Dell and Fortron) exhibit positive total reactive power values, indicating power consumption, whereas one type (Premier) shows negative values, suggesting reactive power supply to the network. Only a small part of the reactive power is associated with the fundamental harmonic component, resulting in a fundamental harmonic power factor (cos φ) close to 1. However, the total power factor (λ) ranges between 0.37 and 0.73 (Fig. 9).
Fig. 8
Total reactive power of LCD monitors for all measured scenarios
Thermal imaging analysis revealed a correlation between increased harmonic values and a significant rise in the maximum temperature (Fig. 10) of the power sources. The imaging data indicate that any deviation from the nominal supply voltage values, except for instances of lower voltage and lower frequency, contributes to an elevation in the PSUs' temperature. Such temperature increases are undesirable as they adversely impact the lifespan of individual components.
Fortron PC PSU was automatically shut down two times when supplied with reduced voltage, indicating the presence of an undervoltage fuse. Modern power supplies often incorporate thermal fuses designed to automatically disconnect the power supply, preventing damage. However, such disconnections may lead to potential data loss or damage to computer components.
4 LCD monitors results
Due to the substantial volume of recorded data, results are presented only for the LCD monitor HP L1908w, which represented the worst-case scenario. A comprehensive evaluation of all measured monitors is provided in the conclusion. The selection of a single unit for detailed presentation was made due to the limited scope of the article.
4.1 LCD monitor HP
The monitors were also tested according to the scenarios outlined in Table 1. Figure 11 illustrates the supply voltage waveform and LCD monitor HP's drawn current in the base state, where the voltage is a pure sinusoid. Additionally, Fig. 12 presents the LCD monitor's temperature profile under this baseline condition. This state served as a reference for comparison with scenarios where power quality conditions were intentionally degraded.
The waveform of the drawn current, shown in Fig. 11, is significantly distorted, exhibiting a THDI of 185.3% and containing higher-order harmonic components. The magnitudes of these harmonic components are presented in Figure 13 and Table 7. According to Fig. 12, the maximum temperature of the LCD monitor in the baseline state reaches 54.7 °C.
Fig. 13
The magnitudes of current harmonics for the base state
Tables 5, 6 and 7 provide a comprehensive summary of the results for all measured scenarios (Table 1) for the LCD monitor HP.
Table 5
Consumption parameters of LCD monitor HP for all scenarios
P [W]
Q (var)
S (VA)
P1 (W)
Q1 (var)
cos φ
λ
THDU (%)
THDI (%)
1 Base state
35.41
− 66
74.9
35.5
− 2.8
1
0.47
0.16
185.3
2 Harmonics 50% of standard
34.9
− 88.2
94.8
31.1
− 0.96
1
0.37
6.19
286.3
3 Harmonics 100% of standard
34.9
− 89.5
96.1
29.1
− 0.8
1
0.36
10.05
310.3
4 Harmonics 150% of standard
34.9
− 88.6
95.2
27.1
− 0.7
1
0.37
15.46
327.1
5 Lower voltage
34.5
− 63.9
72.6
34.5
− 2.8
1
0.47
0.16
184.1
6 Higher voltage
34.2
− 66.1
74.4
34.2
− 2.6
1
0.46
0.14
192.3
7 Lower frequency
33.6
− 63.9
72.2
33.6
− 2.7
1
0.46
0.15
189.1
8 Higher frequency
33.5
− 63.5
71.8
33.5
− 2.6
1
0.47
0.15
188.8
Table 6
Temperatures of LCD monitor HP for all scenarios
Measurement
1
2
3
4
5
6
7
8
Temperature (°C)
54.7
61.3
62.1
64.2
64.1
67.2
63.5
66.4
Table 7
Current harmonics of LCD monitor HP for all scenarios
Measurement
I1 (A)
I3 (A)
I5 (A)
I7 (A)
I11 (A)
I13 (A)
1
0.155
0.145
0.135
0.122
0.088
0.069
2
0.136
0.130
0.128
0.125
0.117
0.112
3
0.128
0.122
0.12
0.118
0.113
0.109
4
0.119
0.114
0.113
0.112
0.108
0.105
5
0.165
0.155
0.144
0.130
0.092
0.072
6
0.138
0.128
0.121
0.111
0.084
0.069
7
0.147
0.137
0.129
0.117
0.087
0.070
8
0.147
0.137
0.128
0.117
0.086
0.069
Figures 14 and 15 illustrate the supply voltage waveform, drawn current waveform, and thermal imaging of the LCD monitor HP under the third measurement scenario for improved comparison. In this scenario, higher-order harmonics in the supply voltage reach 100% of the limit value.
The lower voltage quality resulted in a more deformed drawn current waveform in Fig. 14 compared to the baseline state shown in Fig. 11. This is reflected in an increase in THDI from 185.3 to 310.3%. Thermal imaging recorded a rise in the maximum temperature of the LCD monitor HP by 7.4 °C. This temperature increase is likely due to the rise in the amplitude of the drawn current, which increased from approximately 1.2–2.5 A. Similar trends were observed for the other measured LCD monitors; however, for conciseness, the outcomes for these monitors will be addressed in later sections. The next part of the paper provides a comparative analysis of the results obtained for all measured LCD monitors.
4.2 Evaluation of measurements on LCD monitors
5. Three types of LCD monitors with varying screen sizes were measured. Like the PSUs, constant active power consumption was maintained during the measurements by displaying a static white screen. The consumed active power for each LCD monitor was approximately 33 W for Acer, 35 W for HP, and 15 W for Philips Consumption parameters which were analyzed, and one of them was the current harmonics in the drawn current. The analysis revealed non-compliance with the amplitude law in generating current harmonics.
The active power showed minimal variation across the measurements, with the majority of it being transmitted by the fundamental frequency component. A similar pattern was observed for the fundamental harmonic reactive power, which remained consistent across all measurement scenarios. However, the majority of the total reactive power, shown in Fig. 16, was associated with higher-order harmonic components.
Figure 16 shows that the same power quality parameters negatively impact the THDI of LCD monitors as in the case of PSUs. Specifically, only an increased THDU of the supply voltage leads to an increase in the THDI of the drawn current. For a pure sine wave supply voltage conditions (measurement 1), the THDI values of the individual monitors were recorded as 190.5% for Acer, 185.3% for HP, and 164.3% for Philips, higher than the corresponding values observed for PSUs. The THDI had the most significant impact on total reactive power for PSUs, a similar relationship for monitors is depicted in Fig. 17.
Fig. 17
Total reactive power of LCD monitors for all measured scenarios
Figure 17 indicates that the power consumption of LCD monitors exhibits a capacitive nature across all scenarios, resulting in negative values of reactive power. The total reactive power increases with rising THDI, while the degradation of other examined power quality parameters in measurements 5–8 was negligible. Like PSUs, the active power and fundamental harmonic reactive power values for monitors showed minimal variation regardless of supply voltage distortion; thus, these parameters are not graphically presented. The values of reactive power directly correspond to the power factor values. The total power factor is affected by THDI in the same way as total reactive power, decreasing as THDI increases. Its values range from 0.35 to 0.47, capacitive in nature (Fig. 18). In contrast, the fundamental harmonic power factor remained capacitive and independent of THDI. For the Acer and HP monitors, the fundamental harmonic power factor was consistently close to 1 across all measured scenarios. However, the Philips monitor exhibited a lower fundamental harmonic power factor, with values close to 0.9.
Fig. 18
Total power factors of LCD monitors for all scenarios
Thermal imaging revealed that under full load conditions, both the switching transformers and switching transistors in LCD monitors experienced significant heating, with changes in voltage quality contributing to this effect. The maximum temperature values of the monitors across all scenarios are presented in Fig. 19.
Fig. 19
Maximal temperature of LCD monitors for all scenarios
For PSUs, the most significant negative impact on temperature is caused by an increase in the THDU of the supply voltage. In contrast, for monitors, all examined degradations in power quality parameters have approximately the same impact on temperature. The difference in temperature between the base and other scenarios is smaller for monitors compared to PSUs.
5 Discussion
The primary objective of this article was to evaluate and compare the impact of different supply voltage conditions on the consumption and heating of two commonly used office appliances: LCD monitors and PC PSUs. Eight distinct voltage conditions, as outlined in Table 1, were employed. Initially, each appliance was supplied with a pure sine wave voltage. Subsequently, other voltage conditions were applied per the EN 50160 standard [6], including increased THDU levels (50%, 100%, and 150% of the limit value), variations in the RMS voltage, and frequency. For each voltage condition, selected consumption parameters and the maximum temperatures of the appliances were analyzed.
The measured data indicate that degraded voltage quality caused the most substantial variations in THDI, total reactive power, and total power factor during scenarios with increased THDU in the supply voltage. As a result, only these consumption parameters were graphically evaluated for each measured scenario and appliance. A common characteristic of these parameters is their dependence on higher-order harmonics. Percentual changes in these parameters compared to the base scenario (measurement 1) are summarized in Table 8. The percentual changes were calculated using the following formula:
where ∆M is a percentage change of consumption parameter, i is number of measured scenario (2–8), Mi is absolute value of the consumption parameter in i-th scenario, and M1 is absolute value of the consumption parameter in the base scenario (measurement 1).
Table 8
Percentual changes for all measured appliances and scenarios
Measurement
ΔTHD1 (%)
ΔQ (%)
Δλ (%)
Δt (%)
Dell
2
16.5
11.4
− 5.6
11.1
3
26.7
18.3
− 8.3
18.3
4
37.0
24.0
− 8.3
24.5
5
− 4.5
− 3.6
1.4
21.8
6
3.5
3.5
− 1.4
26.4
7
0.4
1.7
− 1.4
6.7
8
− 0.7
1.1
0.0
15.4
Premier
2
56.9
39.7
− 20.8
13.4
3
71.8
44.8
− 22.9
23.9
4
81.6
44.3
− 20.8
31.5
5
− 2.8
− 3.6
2.1
− 0.2
6
1.2
4.5
− 2.1
16.2
7
− 3.4
− 4.5
2.1
− 4.2
8
− 2.9
− 3.7
2.1
4.9
Fortron
2
15.5
9.8
− 4.2
8.3
3
23.7
9.7
− 5.6
10.6
4
40.4
11.5
− 5.6
13.1
5
− 2.8
− 10.2
− 1.4
0.0
6
7.3
3.0
− 2.8
6.2
7
4.3
0.7
− 1.4
0.5
8
− 0.1
− 7.5
0.0
2.1
Acer
2
46.5
2.81
− 20.0
8.6
3
58.0
29.1
− 20.0
10.2
4
65.1
27.5
− 17.8
12.3
5
− 1.3
− 5.7
2.2
4.7
6
2.2
1.2
− 2.2
− 0.4
7
0.9
− 2.2
0.0
8.4
8
0.7
− 2.9
0.0
8.8
HP
2
54.5
33.6
− 21.3
12.1
3
67.5
35.7
− 23.4
13.5
4
76.5
34.3
− 21.3
17.4
5
− 0.6
− 1.6
0.0
17.2
6
3.8
0.1
− 2.1
22.9
7
2.1
− 3.2
− 2.1
16.1
8
1.9
− 3.7
0.0
21.4
Philips
2
56.1
38.5
− 23.4
19.7
3
69.5
41.4
− 25.5
21.4
4
76.4
40.6
− 25.5
24.8
5
1.6
− 17.7
− 2.1
13.5
6
− 0.9
− 9.6
− 6.4
20.4
7
1.7
− 14.0
− 4.3
19.9
8
1.2
− 13.5
− 6.4
21.4
Table 8 highlights the highest percentage changes in bold and the lowest in italics for all measured appliances. This visual marking allows for identifying which deteriorations in power quality parameters had the most significant and minimal impacts on the appliances' consumption parameters and temperatures. The highest percentage changes were observed in scenarios with increased THDU in the supply voltage (measurements 2–4). Conversely, the lowest changes occurred under pure sine wave supply voltage conditions, where only the RMS value and frequency were varied (measurements 5–8).
All measured appliances drew distorted current even under ideal power quality conditions (measurement 1), where the supply voltage was a pure sine wave. The presence of higher-order harmonics in the supply voltage caused an increase in THDI and Q, leading to a corresponding decrease in λ. The degradation of these consumption parameters negatively impacts the network, causing additional losses, as discussed in [15, 16]. In public distribution networks, where power quality is often not ideal, variations in THDU can adversely affect the Q and λ of these appliances. Four of the measured appliances exhibited a capacitive nature, contributing to reverse reactive power flow (from lower voltage levels to higher voltage levels). Low-voltage networks, particularly in office buildings and households, contain a high density of such appliances. The cumulative negative effects of these appliances can lead to low-voltage networks becoming sources of reactive power, potentially impacting the stability and efficiency of the electrical system.
Degraded power quality also contributes to elevated maximum temperatures in appliances, which significantly impacts critical components such as electrolytic capacitors and switching transformers. For electrolytic capacitors, increased temperatures accelerate the drying out of electrolytes, leading to a reduction in capacitance over time. In the case of switching transformers, deviations from optimal operating conditions necessitate adjustments, such as changes in the switching frequency, to sustain the required output power. These frequency modulations further increase the temperature rise. As the temperature increases, the insulation of the transformer winding deteriorates, increasing the risk of insulation failure and potential transformer damage.
This study did not include a detailed analysis of the internal power circuits of the tested devices. Only external measurements and thermal imaging were employed. However, the results indicate changes in power consumption parameters and increased thermal stress under degraded power quality conditions. Specifically, when the supply voltage was distorted, the current drawn by the devices exhibited higher THDI, which, in turn, led to an increase in the RMS value of current. This higher RMS value of current is identified as the primary cause of increased heat generation. Although the exact internal behavior of each component was not analyzed, a correlation between increased THDI and temperature rise was consistently observed across multiple test scenarios. These trends are documented through both graphical and tabular data. While the findings are specific to the tested models of LCD monitors and PSUs, the observed behavior suggests that similar effects may occur in other devices based on comparable power electronic designs. Nevertheless, further research, including an analysis of internal circuitry and a broader set of device types, is required to confirm the general applicability of the results.
6 Conclusion
The measured data reveal that supply voltages characterized by degraded quality exerted adverse effects on all the examined devices. The drawn current, already significantly distorted under normal operation, exhibited alterations, as did the temperature, apparent power, and λ. Among all the measured devices, the Premier PC PSU and the HP LCD monitor demonstrated the most pronounced deviations due to the supply voltage. In the comparative assessment of PSUs and monitors, it is evident that degraded supply voltage has a more impact on monitors. Analysis of the measured values indicates that the increase in voltage and the presence of higher-order harmonics have the most substantial influence on the devices' operation. Under these conditions, the measured devices reached their highest temperatures. Irrespective of the specific condition, an elevation in temperature negatively affects the devices' operational lifespan.
As per the specifications indicated on the device labels, only the Fortron PSU is rated for operation at 250 V, while all other devices have a maximum voltage tolerance of up to 240 V. However, the supply voltage within the low-voltage network can fluctuate within a standard permissible range of ± 10%, corresponding to ranging from 207 to 253 V. During measurements conducted at reduced voltage, the Fortron PC PSU experienced two instances of automatic shutdown. Such interruptions in the power supply to the computer pose a substantial risk of data loss or potential damage to its components.
THDI exhibited high values for all measured devices under ideal voltage conditions. The significant disparity between cos φ and λ ensued from the elevated THDI, also leading to differences between Q1 and Q. The reactive power for the Dell and Fortron PC PSUs has an inductive nature, while for other measured devices, it exhibited a capacitive nature. These devices have the potential to cause undesirable reactive power flow, thereby posing challenges to voltage stability [9].
The increase in supply voltage distortion led to increased distortion in the drawn current, resulting in an increase in the total reactive power (Q). These findings show the negative impact of THDU in the network on reactive power flow.
Further research is required to gain a deeper understanding of these effects. A comprehensive analysis of load variation and its impact on power quality parameters is planned as part of future work.
Declarations
Conflict of interest
The authors declare no competing interests.
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