A Power Quality Survey on a 22 kv Electrical Distribution System of a Technical Institution as per Standards

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1 Indian Journal of Science and Technology, Vol 9(30), DOI: /ijst/2016/v9i30/99034, August 2016 ISSN (Print) : ISSN (Online) : A Power Quality Survey on a 22 kv Electrical Distribution System of a Technical Institution as per Standards Nikita Rajan and Anu G. Kumar Department of Electrical and Electronics Engineering, Amrita School of Engineering, Coimbatore Amrita Vishwa Vidyapeetham, Amrita University, Coimbatore , Tamil Nadu, India; nikitarajan100@gmail.com, gk_anu@cb.amrita.edu Abstract Objective: Electrical power delivered to a load must be of sufficient quality to allow the load to function properly. Source side voltages and currents must be distortion free and of the proper magnitudes and frequencies. Critical equipment may undergo failure if quality power is not provided. So, the electrical voltages and currents flowing through our distribution system has to be monitored and analyzed to ensure quality power and thus proper working of the machineries in a technical institute. This paper presents a Power Quality Survey in a technical institute as per Standards. Methods: A Power Quality Survey has been conducted and the measured parameters are compared against Standards. Simulation study of the complete system is conducted using ETAP software, so as to understand the existing load flow and harmonic profile. Findings: Current and voltage harmonics was found to be within the limits at PCC. Improvement: Harmonic profile of UPS-Academic block improved, when the old UPS was replaced with a modern numeric UPS. Keywords: Point of Common Coupling, Power Quality, Total Harmonic Current Distortion, Total Harmonic Voltage Distortion 1. Introduction There are a number of sensitive and advanced equipment in any Engineering/academic institute, that are quite sensitive to Power Quality (PQ) disturbances in the supply network. These equipments require distortion-less supply to ensure proper working conditions. A Power Quality Survey is essential in any institute to monitor the quality of the power being supplied, for efficient operating of laboratory equipment 1 and to design a compensation technique for the problems identified, if any. In this paper, a detailed Power Quality Survey of the campus (Amrita 22 kv Electrical Distribution System) has been conducted, with an objective of identifying the Power Quality issues and to select suitable compensation techniques for the major problems being identified. As a part of the Power Quality survey, harmonic analysis of the Amrita 22 kv Electrical distribution system has also been conducted, to verify whether the THD limits at the point of common coupling are within the IEEE Standards. The single line diagram of the Amrita 22 kv distribution system, consisting of two Power houses are simulated in ETAP and its load flow analysis and harmonic analysis were performed under different operating conditions, namely With supply from Electricity board. With supply from DG sets. *Author for correspondence

2 A Power Quality Survey on a 22 kv Electrical Distribution System of a Technical Institution as per Standards 2. Power Quality Power Quality has become an inevitable term in electrical power industry. The reason for this increased concern about Power Quality is mainly due to the use of modern equipments like power electronic devices, office and IT equipments, motor drives etc. All Technical institutions use these equipments; these equipments require quality and distortion less supply to operate properly 2. The major Power Quality issues include voltage variations (under voltage/over-voltage), transients, harmonics, flickers, frequency unbalance etc 3. These problems have to be taken care of to ensure Power Quality. By definition, power is the rate of energy consumption in an electric circuit and is equal to the product of voltage and current 2. So, quantitatively, Power Quality is directly proportional to the quality of voltage, as it is possible only to control the quality of voltage and not the quality of current that will be drawn by specific loads. Power Quality has been an existing issue ever since the invention of electric power, but it has gained importance in the recent years, due to the usage of more sensitive and critical equipments in domestic, commercial and industrial fields. The major Power Quality problems are: Sags/swells: Under-voltages and over-voltages on the power system. It can be corrected using power sources such as UPSs, generators or similar voltage restoration technologies. Surges: Voltage spikes caused mainly due to switching off of heavy electrical equipment(s). Harmonics: Distortion of current and voltage waveforms from sinusoidal shape. It is caused due to non-linear loads connected to the power system, often corrected using filtering equipments 4. Continuous Power Quality monitoring detects the presence of Power Quality problems and hence leads to the prevention of the same Power Quality Standards The current distortion and voltage distortion are measured and verified against IEEE Standards. 4. System Overview The 22 kv electrical distribution system of Amrita campus consists of two power houses, viz. Power House-1 (PH-1) and Power House-2 (PH-2), as shown in Figure 1. Figure 1. Overview of the system under consideration. Power House-1 consists of 2 transformers of 500 kva each and three diesel generators of different ratings. The system parameters of Power House-1 are shown in Table 1. Table 1. System parameters of Power House-1 Sl. No. EQUIPMENT RATING 1 Power Grid 22 kv 2 Generator (G1) 0.2 MW 3 Generator (G2) 0.2 MW 4 Generator (G3) MW 5 Transformer (T1) 500 kva 6 Transformer (T2) 500 kva 7 Loads 57.4 MVA 2 Indian Journal of Science and Technology

3 Nikita Rajan and Anu G. Kumar Figure 2. Single line diagram of Power House-1. The single line diagram of Power House-1 is shown in Figure 2. Power House-2 consists of 2 transformers of 500 kva each and two diesel generators. The system parameters of Power House-1 are shown in Table 2. The single line diagram of Power House-1 is shown in Figure 3. Table 2. System parameters of Power House-2 Sl. No. EQUIPMENT RATING 1 Power Grid 22 kv 2 Generator (G1) 500 kva 3 Generator (G2) 500 kva 4 Transformer (T6) 500 kva 5 Transformer (T8) 500 kva 6 Loads 49.8 MVA Figure 3. Single line diagram of Power House Power Quality Survey The survey was done with an objective to understand the load flow of the entire distribution system and also to measure the harmonics and to verify whether it is within the limits as per the IEEE Standards. The on-site readings were taken with Power Quality Indian Journal of Science and Technology 3

4 A Power Quality Survey on a 22 kv Electrical Distribution System of a Technical Institution as per Standards analyzer (Fluke 435). Data samples were recorded at critical points. 5.1 Power Quality at PCC Power House-1 The readings obtained at PH-1 are shown in Table Performance Evaluation of UPS IT Block Figure 4 shows the data samples of the neutral current of the UPS in IT block measured in Fluke 435. The data was recorded for duration of 24 hours. Table 3. PCC readings of Power House-1 Voltage V rms ph-ph (V) RMS Current (A) Real power (kw) Apparent power (kva) Reactive power (kvar) PF V 249 A Power House-2 The readings obtained at PH-2 are shown in Table 4. Table 4. PCC readings of Power House-2 Voltage V rms ph-ph (V) RMS Current (A) Real power (kw) Apparent power (kva) Reactive power (kvar) PF V 420 A From the data collected from Power Quality analyzer (Fluke 435), a comparison has been done with the IEEE limits and it is shown in Table 5. Table 5. Comparison with IEEE limits location I sc /I L Current THD (limit) Current THD (actual) PH % 5-7 % PH % % 4 Indian Journal of Science and Technology

5 Nikita Rajan and Anu G. Kumar Figure 4. Neutral current of old UPS-IT block. Figure 6. Current THD of electrical machines laboratory. From the recorded data, it could be observed that the neutral varies between 18 A to 36 A, which is a large variation and it is not a permissible condition. Figure 5 shows the fluke data of the current THD of the UPS in IT block. The data was recorded for a duration of 24 hours. From the recorded data, the current THD is found to be 64%, which is high. Hence, compensation was required with immediate effect. Due to the these abnormalities, the old UPS in IT block is now replaced with a new numeric modular UPS. 5.4 Power Systems Laboratory Figure 7 shows the data samples of the current THD at the incoming of the machines lab, while the lab was working on power systems laboratory experiments. From the recorded data, it could be observed that the third and fifth Harmonics are more dominant. Figure 7. Current THD of machines lab (AC machines lab). Figure 5. Current THD of UPS-IT block. 5.3 Electrical Machines Laboratory Figure 6 shows the data samples of the current THD at the incoming of the machines lab, while the lab was working on AC machines laboratory experiments. The data was recorded continuously for 2 hours. From the recorded data, it could be observed that the third and fifth Harmonics are more dominant. 6. ETAP Simulation Study The single line diagram of PH-1 and PH-2 are simulated in ETAP Power House-1 (PH-1): Load Flow Analysis (with supply from EB) The ETAP simulation result of load flow analysis of PH-1 under EB supply is shown in Figure 8. Indian Journal of Science and Technology 5

6 A Power Quality Survey on a 22 kv Electrical Distribution System of a Technical Institution as per Standards Figure 8. from EB). ETAP simulation result-load flow analysis result of power house-1 (with supply From the load flow analysis of PH-1 with supply from EB, it is observed that transformer (T2) is underutilized (0.114 MVA, i.e. 22.7%). Hence, it is recommended that the load can be supplied from transformer (T1) alone, except at the time of peak load demand. 6.2 Power House-1 (PH-1): Harmonic Analysis (with supply from EB) The ETAP simulation result of harmonic analysis of PH-1 under EB supply is shown in Figure 9. From the harmonic analysis of PH-1 with supply from EB, it could be observed that the harmonic distortion (THD and IHD) exceeds the limits. 6.3 Power House-1 (PH-1): Load Flow Analysis (with supply from DG) The ETAP simulation result of load flow analysis of PH-1 under DG supply is shown in Figure 10. From the load flow analysis of PH-1, it is observed that a major portion of the demand is shared by the losses; total demand MW, total losses MW). Figure 9. ETAP simulation result-harmonic analysis result of Power House-1 (with supply from EB). 6 Indian Journal of Science and Technology

7 Nikita Rajan and Anu G. Kumar Figure 10. from DG). ETAP simulation result-load flow analysis result of Power House-1 (with supply 6.4 Power House-1 (PH-1): Harmonic Analysis (with supply from DG) The ETAP simulation result of harmonic analysis of PH-1 under DG supply is shown in Figure 11. From the harmonic analysis of PH-1 with supply from DG sets, it could be observed that the harmonic distortion (THD and IHD) exceeds the limits. 6.5 Power House-2 (PH-2): Load Flow Analysis (with supply from EB) The ETAP simulation result of load flow analysis of PH-2 under EB supply is shown in Figure 12. From the load flow analysis of PH-2, it is observed that both transformers are slightly overloaded (by MVA). Figure 11. from DG). ETAP simulation result-load flow analysis result of Power House-1 (with supply Indian Journal of Science and Technology 7

8 A Power Quality Survey on a 22 kv Electrical Distribution System of a Technical Institution as per Standards Figure 12. from EB). ETAP simulation result-load flow analysis result of Power House-2 (with supply 6.6 Power House-2 (PH-2): Harmonic Analysis (with supply from EB) The ETAP simulation result of the harmonic analysis of PH-2 under EB supply is shown in Figure Power House-2 (PH-2): Load Flow Analysis (with supply from DG sets) The ETAP simulation result of load flow analysis of PH-2 under DG supply is shown in Figure 14. Figure 13. ETAP simulation result-harmonic analysis result of Power House-2 (with supply from EB). 8 Indian Journal of Science and Technology

9 Nikita Rajan and Anu G. Kumar Figure 14. ETAP simulation result-load flow analysis result of Power House-2 (with supply from DG sets). 6.8 Power House-2 (PH-2): Harmonic Analysis (with supply from DG sets) The ETAP simulation result of harmonic analysis of PH-2 under DG supply is shown in Figure 15. From the harmonic analysis of Power House-2, it could be observed that THD is within the limit (as per IEEE Std.). Figure 15. ETAP simulation result-harmonic analysis result of Power House-2 (with supply from DG sets). Indian Journal of Science and Technology 9

10 A Power Quality Survey on a 22 kv Electrical Distribution System of a Technical Institution as per Standards 3. Recommendations and Improvements PCC: The transformer (T2) is found to be underutilized. The power can be supplied from transformer (T1) alone, except at the time of peak loads. UPS IT block: Due to the the abnormalities of the UPS in IT block and being an old UPS, the old UPS in IT block can be replaced with a modern numeric modular UPS. Electrical Machines Laboratory: The current THD was found to be approximately 25%, which violates the limit. Hence, small scale compensation is required, which can be achieved by implementing a suitable filter at the rectifier input of the laboratory. Power systems laboratory: The THD was found to be approximately 28%, which violates the limit. Hence, small scale compensation is required, which can be achieved by implementing a suitable filter at the rectifier input of the laboratory. Figure 16. Neutral current of new UPS-IT block. Figure 17. Current THD of new UPS-IT block. 10 Indian Journal of Science and Technology

11 Nikita Rajan and Anu G. Kumar Figure 16 shows the data samples of the neutral current of the new UPS in IT block recorded in Power Quality analyzer (Fluke 435) From the Fluke 435 recorded data, the neutral current was found to be less than 1A - Permissible. Figure 16 the fluke data of the current THD of the new UPS in IT block. The data was recorded for duration of 24 hours. From the Fluke 435 recorded data, the neutral current was found to be less than 1A - Permissible. Figure 17 the fluke data of the current THD of the new UPS in IT block. The data was recorded for duration of 24 hours. From the Fluke 435 recorded data, the current THD is found to be reduced from 64% to 6%. The harmonic profile was found to be improved to a large extent. 8. Conclusion A Power Quality Survey in a 22 kv electrical distribution system of a technical institute was conducted with an objective to understand the existing harmonic profile and the load flow. Various inferences were drawn from the load flow analysis and harmonic analysis done in ETAP software. It is observed that significant distortion in the current waveforms exist due to the use of electronic switching equipments. The UPS in the IT block was identified as a major harmonic causing load. Increasing use of these equipments can result in serious problems in the near future. As a result of the survey conducted, the old UPS was replaced with a modern UPS, which led to a noticeable improvement in the harmonic profile. The issues related to Power Quality are mainly contributed by voltage fluctuations in the supply. Voltage quality issues are the prime cause of other Power Quality issues. So, a control of the voltage fluctuations will greatly reduce the impact of other related issues 6. Hence, similar Power Quality surveys are essential in any technical or commercial institute prior to any new electrical installations, so as to understand the existing electrical profile and thereby to adjust the new installations accordingly. This will lead to the availability of quality power and consequently result in less damage of the sensitive equipments. 9. Acknowledgment Authors would like to thank Amrita Vishwa Vidyapeetham University and Department of Science and Technology for the financial support for carrying out this work. 10. References 1. Jain S, Agarwal P, Gupta HO. A survey of harmonics: Indian scenario. Proceedings of the IEEE INDICON; 2004 Dec. p Prabaakaran K, Chitra N, Senthil Kumar A. Power Quality enhancement in microgrid - A survey. IEEE International Conference on Circuits, Power and Computing Technologies (ICCPCT); 2013 Mar. p Ignatova V, Villard D, Hypolite JM. Simple indicators for an effective Power Quality monitoring and analysis. IEEE 15th International Conference on Environment and Electrical Engineering (EEEIC)); 2015 Jun. p Mack GW, Santoso S. Understanding power system harmonics. IEEE Power Engineering Review Dec; 21(11): Gosbell VJ, Perera S, Barr R, Baitch A. Primary and secondary indices for Power Quality (PQ) survey reporting. IEEE 11th International Conference on Harmonics and Quality of Power; 2004 Sep. p Ribeiro PF. Common misapplications of the IEEE 519 harmonic standard: Voltage or current limits. Power and Energy Society General Meeting-Conversion and Delivery of Electrical Energy in the 21st Century; Jul. p Indian Journal of Science and Technology 11