Neutral-to-Earth Voltage (NTEV) in distribution systems is a critical concern affecting safety and reliability. Elevated NTEV often results from unbalanced loads, harmonic distortions, and poor grounding, causing voltage differences between the neutral point and earth. This can lead to stray voltage, compromising both human safety and equipment performance. Harmonic currents from nonlinear loads exacerbate the issue by generating triple harmonics that do not cancel out in the neutral conductor. Key factors contributing to elevated NTEV include unbalanced loading, system asymmetries, earth resistivity, and feeder length. By referring to IEE1159 (IEEE Recommended Practice for Monitoring Electric Power Quality), the acceptable thresholds for NTEV or stray voltage is 10 V [1]. Table 1 shows the summary table for NTEV level.

Table 1. Summary table for NTEV level.

Shafie etal. (2010) examine the use of isolation transformers to mitigate harmonic voltages and Neutral-to-Earth Voltage (NTEV) in distribution systems, focusing on their effectiveness at Universiti Teknologi MARA in Penang. NTEV, or common-mode voltage, represents the potential difference between the neutral conductor and safety ground, which can cause operational issues, equipment failure, and higher losses for linear loads [2]. The results show that the isolation transformer significantly reduced both NTEV and Total Harmonic Distortion (THD). For example, Figure 1 and Figure 2 show the maximum NTEV in Computer Lab 1 decreased from 1.464 V to 0.977 V, and the THD for phase voltage dropped from 1.927% to 1.501%. These improvements are in line with IEEE 519-2014 standards on harmonic distortion [3].

Figure 1. NTEV profile with Isolation Transformer at Lab 1.

Research on Neutral-to-Earth Voltage (NTEV) in government buildings is of paramount importance, as these structures are subject to stringent safety regulations, possess intricate electrical systems, and have a significant public impact. Conducting such research enables the identification of potential electrical hazards, interference with communication systems, and issues related to legal compliance. A key objective of this research is to evaluate the relationship between Neutral-to-Earth Voltage and Total Harmonic Distortion (THD) in identifying the cause and effect of Neutral-to-Earth Voltage at government buildings. Thereby it aligns the government’s standards with international benchmarks.

1.2.1. Type of System in This Research

Recent studies from M.A Shafie highlight the increase in the use of nonlinear loads (like computers, printers, UPS, and electronic lighting) in distribution systems cause harmonic distortion and elevated neutral-to-ground voltages, which can lead to equipment malfunction, higher losses, and reliability issues. This study focuses on Low Voltage system with varies of load that contribute to the NTEV level which is distribution system at government buildings.

Figure 2. NTEV profile without Isolation Transformer at Lab 1.

1.2.2. Parameter

1) Frequency Stability

Referring to Malaysia Distribution Code, under clause 5.4.3 system frequency are required to be continuously maintained ±1% from 50 Hz within the range 49.5 Hz to 50.5 Hz this is to make sure the active power output does not decrease by more than 5% [4].

2) Harmonic Distortion

Harmonic distortion is defined as departure of a waveform from sinusoidal shape that is caused by the addition of one or more harmonics to the fundamental waveform. In Malaysian Distribution Code, clause 5.4.6.9 it is stated that Total Harmonic Distortion is to be maintained below 5% from the magnitude of the fundamental wave form [4]. In principle total harmonic distortion is equal to I harmonic divide by I fundamental [THD = Iн/Iı].

The site selection and site visit, as well as discussions with the building owner regarding the building’s function and the categories of loads present, are the initial steps of the process.

OverviewofTHD

Changes in frequency on each wave whether voltage or current, it can cause the existence of harmonic distortion. This includes neutral voltage and current components [5]. In a power system, the issue of power quality is very important because it can disrupt the entire system. Among the main components in this determination are harmonics. Therefore, all harmonics is very important for any operation or planning studies.

According to David from Okanagan College in Kelowna, BC, Canada states that Total Harmonic Distortion (THD) is the ratio for V_rms of all the harmonic frequency starting from the 2nd harmonic on, over the V_rms fundamental frequency. He also provided the equation to determine the THD value

were,

V_{n_rms} is the RMS voltage of the nth harmonic;

V_{fund_rms} is the RMS voltage of the fundamental frequency.

Scope

Standard and Regulation

In Malaysia, Total Harmonic Distortion (THD) limits are prescribed through national grid codes and utility-specific technical requirements to ensure power quality and the secure operation of electrical infrastructure. These regulations are primarily documented in the Malaysian Grid Code, the Distribution Code for Peninsular Malaysia, and technical publications by Tenaga Nasional Berhad (TNB), the country’s principal utility provider.

Voltage THD limits differ based on system voltage levels. According to the Malaysian Grid Code and corroborated by technical analyses, the allowable THD values are as follows:

High Voltage (HV) Systems (500 kV, 275 kV, 132 kV): Maximum THD is limited to 3.0% [6].Medium Voltage (MV) Systems (33 kV, 22 kV, 11 kV, 6.6 kV): THD must not exceed 6.5% [7].Low Voltage (LV) Systems (400 V and below): A THD threshold of 5.0% is applied [7].

Maintaining THD within these limits is critical to minimizing harmonic distortion, which can lead to overheating, equipment malfunction, and increased system losses.

Two types of analysis are used, which are Descriptive Analysis and Correlation Analysis.

Descriptive statistical analysis was applied to summarize the fundamental characteristics of the measured variables, including central tendency, variability, and data distribution. This preliminary analysis provides an essential basis for understanding the behavior of Neutral-to-Earth Voltage (NTEV) and Total Harmonic Distortion (THD) prior to inferential evaluation. Pearson correlation analysis was selected because both NTEV and THD are continuous variables, and this method is appropriate for examining the strength and direction of their linear relationship. Consequently, Pearson correlation offers a suitable statistical approach for assessing the association between harmonic distortion and variations in neutral-to-earth voltage.

The study conducted by Suziyani from the School of Electrical Engineering, College of Engineering, Universiti Teknologi MARA Dungun, Terengganu, demonstrated that the correlation coefficient method is an effective tool for analyzing the relationships between variables [8].

Referring to the research by Gabrijela Dimić and colleagues demonstrates the effectiveness of descriptive statistical analysis in educational data mining. By providing detailed insights into data distribution, identifying skewness, and applying histogram discretization, the method improved prediction model accuracy, particularly with the Random Forest classifier, which achieved 91.49% accuracy. The analysis also facilitated the transformation of continuous features into discrete intervals, enhancing algorithm efficiency and model performance. Overall, the study underscores the critical role of descriptive statistics in preprocessing, leading to more accurate and efficient data mining outcomes [9]. Table 2presents the judgement table for the descriptive analysis.

Table 2. Judgement table for descriptive analysis.

Table 3. Pearson correlation coefficient guide table.

Table 3 shows a guide to interpreting the Pearson Correlation Coefficient, which measures the strength and direction of the linear relationship between two continuous variables. In practice, the closer the coefficient is to either +1 or −1, the stronger the linear relationship. Values closer to 0 indicate weaker relationships, and the direction of the relationship (positive or negative) is indicated by the sign of the coefficient [10].

In this phase, several measurement locations have been identified for the purpose of acquiring raw data prior to analysis. Figure 4 below illustrates the point diagram, where a Fluke 435 PQ as shows in Figure 5 meter will be installed on the distribution network to collect data according to the desired parameters. Each location will be installed within a period of four days.

Figure 4. Point of connection.

Figure 5. PQ data logger fluke 435.

This research will utilize statistical methods, such as the Pearson correlation coefficient, to analyze the relationship between frequency, THD, and Voltage variation with NTEV levels. These analyses confirm that as frequency changes, especially with harmonic distortion, there is a significant correlation with fluctuations in NTEV levels. Consequently, Minitab software as shown in Figure 6 was selected as the optimal tool due to its user-friendly interface and extensive statistical capabilities. Within Minitab, two distinct types of analytical methods were employed:

1) Descriptive Statistical Analysis

2) Pearson Correlation Analysis

Figure 6. Power log software interface

A visual observation for Neutral-to-Earth Voltage (NTEV) graft and Total Harmonic Distortion (THD) graft typically involves comparing two separate graphical representations to assess their respective trends and relationships.

By comparing these graphs, one can observe if there’s a correlation between NTEV variations and spikes in THD. For instance, an increase in NTEV may coincide with a rise in THD, suggesting that grounding issues could contribute to higher harmonic distortion in the system.

This type of analysis helps to diagnose power quality problems and take corrective actions to improve the overall stability and performance of the electrical system.

Observation

From the result obtained in Figure 7, sine wave view, it can be seen that the NTEV pattern is directly proportional to the current value in each phase. High values occur during peak hours while low voltage values occur outside of peak hours.

Figure 7. Neutral to earth voltage at MSB1.

Table 4. Minimum and maximum NTEV for MSB1.

The Neutral to Earth Voltage’s minimum and maximum values are displayed in Table 4. During the recorded measurement period November 22nd to 25th 2022 at the first site, the minimal NTEV value of 0.32 V occurred every day during off-peak hours. The maximum value of 1.34 V happened on November 23, 2022, at 10 am, during peak hour.

Figure 8. THD for MSB1.

The percentage THD value at the first location is shown in Figure 8. The measurement began on November 22, 2022, at 10.40 a.m. and ended on November 25, 2022, at 9.16 a.m. Throughout the measurement record, the THD value remains within the specification range of less than 5%. When compared to the current in each phase, the pattern is nearly same, with high value at peak time and low value at non-peak. This is because VTHD and total current are depended on each other.

Table 5. THD at MSB1.

According to Table 5 above, for the Red phase, the lowest value is 1.38% and occurs on November 24, 2022, at 12.51 am, while the highest value occurs at peak time on November 25, 2022, at 9.15 am. On November 24, 2022, at 1.10 am, the yellow phase recorded a lowest value of 1.2%, and at 10.13 am the same day, a maximum value of 2.95%. One of the lowest VTHD values ever recorded was in the blue phase on November 23, 2022, at 7.12 am, while the highest value was at peak time on November 24, 2022, at 10.02 am.

Table 6. Statistic of MSB1.

NTEV

Referring to the Table 6 Statistic of MSB1, NTEV std deviation is 0.31, and mean 0.67. By this two information, the value of standard deviation provides evidence that Neutral to Earth voltage across neutral to ground line deviates very closely to the mean value. While skewness with the value of 0.46 and median of 0.54 provide informative evidence on how the measured data was distributed during measurement period and in this case is skewed to the right. As a result, the data might be interpreted as NTEV voltages tend to be greater than the average value.

VTHD RYB

Overall, the VTHD value on each phase is in the range of 1.19% to 2.95%. By this information, the value of standard deviation provides evidence that VTHD each phase deviates very closely to the mean value. While skewness with the value of 0.08, 0.23 and 0.17, provide informative evidence on how the measured data was distributed during measurement period. The data measured in this case is positively skewed. As a result, the data might be interpreted as VTHD each phase tend to be greater than the average value.

Table 7. NTEV and VTHD correlation MSB1.

Interpretation:

NTEVandVTHDcorrelatetoeachother. ReferringtoTable7,theanalysisofPearsoncorrelationcoefficientbetweenNTEVtoVTHDRed, VTHDYellowandVTHDBlueare 0.845, 0.919 and 0.905. AccordingtothePearsoncorrelationguideline, acoefficientwith 0.7 to 0.9 canbeinterpretedashighlypositivecorrelation. InthiscasetheNTEVisslightlydependentonVTHDRedcomparedwithVTHDYellowandBlue.

While the size of correlation is more than 0.9, the interpretation is very high correlation. Hence the result can be interpreted as NTEV is dependent to VTHD Red, Yellow and Blue, as VTHD value increase the voltage at Neutral increase. This is due to the effects of harmonics in which it changes the base frequency of the voltage hence changes the voltage magnitude. While within spec value of THD impose limited problem to line stability, severe THD beyond the specification imposes potent risk to the system stability.