**4.1. Harmonic measurements at grid station B**

Grid station B consists of two 220/132 kV parallel transformers (TX1 and TX2). Each transformer is 500 MVA capacity. The grid station B is located close to two power generation facilities. The maximum short circuit level on 132 kV side at the time of measurements is 17.96 kA. The grid station is supplying electricity to large industrial customers via 132 kV feeders as well as smaller industrial customers via two 132/33 kV transformers. Ten-minute average values were recoded using Hioki 3196 Power Quality Analyzer Meter [8]. The current clamps of the analyzer were connected to a 132 kV feeder supplying a steel smelter. Measurements were recoded over a period of 1 week starting from 28 January 2012. A summary of measurements is presented in **Figure 7**.

For the voltage signals, **Figure 7** shows that the average THD at the high-voltage side is between 0.97 and 0.90%, the maximum THD is between 0.97 and 0.90%, and the minimum THD level is between 0.28 and 0.32%. For the current signals, the THD at the high-voltage side (132 kV) ranges between 33.09 and 2.28%. Despite the high-current distortion, the voltage THD is small due to the high short circuit capacity.

The current waveform at grid station B is highly distorted as shown in **Figures 7**–**9**.

It is worth noting that the dominant harmonic components are the 5th, the 7th, the 11th, the 13th and the 17th orders. In addition, there is a clear content of the 2nd, the 3rd, and other harmonic orders.

Histograms of voltage THD and current TDD at station B are presented in **Figure 10**. Using the voltage THD histograms, the 95th percentiles are calculated for different phases. A comparison between the 95th percentile of voltage THD and IEEE Std 519 limit is presented in **Table 7**.


**Figure 7.** Summary of THD measurements at grid station B. (a) Voltage THD and (b) current THD.

**Figure 9.** Grid station B current spectrum.

**Figure 10.** Histograms of THD measurements at grid station B. (a) Voltage THD and (b) current TDD.

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**Figure 8.** Current waveform of the 132 kV feeder at grid station B.

Using measurements, the maximum demand load current is 208 A. The short circuit level at grid station B is obtained from OETC capability statement. The TDD limit based on *I SC*/*I <sup>L</sup>* = 91 is 6%. A comparison between the 95th and 99th percentiles of current TDD and IEEE Std 519 limits is presented in **Table 8**.

**Figure 9.** Grid station B current spectrum.

Using measurements, the maximum demand load current is 208 A. The short circuit level at

is 6%. A comparison between the 95th and 99th percentiles of current TDD and IEEE Std 519

*SC*/*I*

*<sup>L</sup>* = 91

grid station B is obtained from OETC capability statement. The TDD limit based on *I*

**Figure 7.** Summary of THD measurements at grid station B. (a) Voltage THD and (b) current THD.

44 Power System Harmonics - Analysis, Effects and Mitigation Solutions for Power Quality Improvement

limits is presented in **Table 8**.

**Figure 8.** Current waveform of the 132 kV feeder at grid station B.

**Figure 10.** Histograms of THD measurements at grid station B. (a) Voltage THD and (b) current TDD.


**Table 7.** Voltage THD 95th percentile vs. IEEE Std 519-2014 at station B.


**Figure 11.** Voltage temporal profile at grid station B.

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**Figure 12.** Fluctuating load current at grid station B.

**Figure 13.** Voltage harmonics temporal profile at grid station B.

**Table 8.** Current TDD 95th and 99th percentiles vs. IEEE Std 519-2014 at station B.

### **4.2. Voltage harmonics temporal profile at grid station B**

The voltage profile measured at grid station B is presented in **Figure 11** below. The daily diurnal profile is not clear due to high variability caused by load operations. These voltage fluctuations are attributed to fluctuation load current as seen in **Figure 12**.

**Figure 13** presents the voltage THD as well as evident individual harmonics temporal profiles. It is worth nothing that no clear diurnal profile exists. Moreover, the dominant harmonic components are the 11th, the 13th, the 7th and the 5th. There is a small trace of the 3th and 9th harmonics. There is a very small trace of the 2nd harmonic as seen in **Figure 14**.

A similar observation can be seen in the 2nd location, where individual harmonic distortion is related to specific harmonic-producing loads. Station B is a grid station that supplies with proximity close to the largest industrial area in Oman. There are many non-linear loads fed from this station such as steel factories and aluminum smelters. The arc-furnaces loads, either induction furnaces or DC arc furnaces, along with static var compensators (SVCs) contribute significantly to the harmonic components of 11th, 13th, 7th, and 5th order.

### **4.3. Current harmonics temporal profile at grid station B**

**Figure 15** presents the current THD and individual harmonics profile at grid station B. It is worth noting that these profiles are highly fluctuating similar to measured current profile shown in **Figure 12**. It is worth mentioning that the dominant harmonic components are the 5th, the 11th, the 7th, and the 13th. In addition, there is a clear content of the 2nd, the 3rd, and other harmonic orders.

#### **4.4. Reasons for temporal variations at grid station B**

Comparing voltage temporal profile at grid station A with grid station B, it can be concluded that this variation depends on the type of loads available. While in grid station A, the variation

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**Figure 11.** Voltage temporal profile at grid station B.

**4.2. Voltage harmonics temporal profile at grid station B**

**Table 8.** Current TDD 95th and 99th percentiles vs. IEEE Std 519-2014 at station B.

**Phase THD P95 THD IEEE limits**

46 Power System Harmonics - Analysis, Effects and Mitigation Solutions for Power Quality Improvement

**Table 7.** Voltage THD 95th percentile vs. IEEE Std 519-2014 at station B.

A 4.92 5.16 6 B 5.02 5.31 6 C 4.84 5.13 6

**Phase TDD P95 TDD P99 TDD IEEE limits**

A 0.58 2.5 B 0.621 2.5 C 0.641 2.5

fluctuations are attributed to fluctuation load current as seen in **Figure 12**.

harmonics. There is a very small trace of the 2nd harmonic as seen in **Figure 14**.

significantly to the harmonic components of 11th, 13th, 7th, and 5th order.

**4.3. Current harmonics temporal profile at grid station B**

**4.4. Reasons for temporal variations at grid station B**

other harmonic orders.

The voltage profile measured at grid station B is presented in **Figure 11** below. The daily diurnal profile is not clear due to high variability caused by load operations. These voltage

**Figure 13** presents the voltage THD as well as evident individual harmonics temporal profiles. It is worth nothing that no clear diurnal profile exists. Moreover, the dominant harmonic components are the 11th, the 13th, the 7th and the 5th. There is a small trace of the 3th and 9th

A similar observation can be seen in the 2nd location, where individual harmonic distortion is related to specific harmonic-producing loads. Station B is a grid station that supplies with proximity close to the largest industrial area in Oman. There are many non-linear loads fed from this station such as steel factories and aluminum smelters. The arc-furnaces loads, either induction furnaces or DC arc furnaces, along with static var compensators (SVCs) contribute

**Figure 15** presents the current THD and individual harmonics profile at grid station B. It is worth noting that these profiles are highly fluctuating similar to measured current profile shown in **Figure 12**. It is worth mentioning that the dominant harmonic components are the 5th, the 11th, the 7th, and the 13th. In addition, there is a clear content of the 2nd, the 3rd, and

Comparing voltage temporal profile at grid station A with grid station B, it can be concluded that this variation depends on the type of loads available. While in grid station A, the variation

**Figure 12.** Fluctuating load current at grid station B.

**Figure 13.** Voltage harmonics temporal profile at grid station B.

reflects almost the daily load profile but in grid station B the variation is completely different owing to the existing of steel industries. Furthermore, although there is high current distor-

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Harmonics were measured and analyzed for two grid stations in the main interconnected system of Oman. The first grid station is feeding both industrial and residential customers, while the second grid station is dedicated to large industrial customers including arc furnaces and rolling mills. A clear temporal variation of harmonics similar to that of aggregate load and local voltage profiles was observed at the grid station feeding both residential and industrial customers. However, this correlation between the system load and harmonics profiles dimin-

Mohammed H. Albadi\*, Rashid S. Al Abri, Amer S. Al Hinai and Abdullah H. Al-Badi

[1] Khan S, Khan S, Ahmed G. Industrial Power Systems. USA: CRC Press; 2007

[6] MJEC, MZEC, and MEDC. "The Distribution Code, Version 1.000," ed; 2005

[7] OETC. "Five-Year Annual Transmission Capability Statement (2016-2020)"; 2016

[8] HIOKI. HIOKI E.E. CORPORATION. Hioki 3196 Power Quality Analyzer Meter. http://

[2] Baggini A. Handbook of power quality, John Wiley & Sons; 2008. DOI: 10.1002/9780

[3] I. S. Association. 519-2014-IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems. New York: IEEE; 2014. DOI: 10.1109/IEEESTD.

[4] IEC. "IEC 61000-3-6: Assessment of Emission Limits of Distorting Loads in MV and HV

tion in grid station B, the voltage THD is small due to the high short circuit capacity.

ishes at the grid station dedicated for heavy industrial loads.

\*Address all correspondence to: mbadi@squ.edu.om

Sultan Qaboos University, Muscat, Oman

**5. Conclusions**

**Author details**

**References**

470754245

2014.6826459

Power Systems," ed; 2008

[5] OETC. "The Grid Code, Version 2," ed; 2010

www.hioki.com/product/3196/3196v.html; 2014

**Figure 14.** Harmonics bar graph at grid station B.

**Figure 15.** Current harmonics temporal profile at grid station B. (a) 7th and lower orders (b) 8th and higher orders.

reflects almost the daily load profile but in grid station B the variation is completely different owing to the existing of steel industries. Furthermore, although there is high current distortion in grid station B, the voltage THD is small due to the high short circuit capacity.
