Design and Simulation software of Power System Equipment

Abstract

This paper gives a thorough insight of Design and Simulation software of Power System Equipment – Distribution Underground Cables through different papers. Distribution underground cables are the cables that are buried under the ground. The function of these cables is to distribute electrical power from Distribution Substation to Residential Consumers and Commercial & Industrial Business Consumers. Medium voltage is normally chosen for distribution underground cable. In Hong Kong, the distribution voltage [1] is 11, 22kV for HK Electric (HEC) and 11, 33kV for China Light and Power Company Limited (CLP).

The cables [1] used in Hong Kong for distribution underground cable are Cross-Linked Polyethylene (XLPE) and corrugated aluminum mental sheath/steel wire armour and PVC/MDPE outer-jacket cable. The literatures chosen will be focusing on 11 to 33kV and XLPE cable.

Introduction

Water Treeing is a phenomenon always occurred in underground cable. It will be happening once the cable contacted with water no matter the state of water is liquid or gas. Water tree will reduce the effectiveness of the insulation thickness and cause failure of the cable [7].

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The parameters affecting water tree growth are voltage, temperature, impurities, frequency, insulation materials and manufacturing process [2]. Water Treeing are different with electrical treeing.

Water Treeing:

• Invisible
• Tree discharging recognition extremely slow
• At low field strength
• Electrical Treeing
• Visible
• Tree grows very fast in XLPE insulation
• At high local strength
• Ampacity and Temperature

Monitoring the ampacity and temperature of underground cable is very important to power distribution. The ampacity is too high will cause overheating of the cable. Underground cable overheating will cause the failure of the cable and even will cause roadway breakage.

Methods

Water Tree - Materials

To prevent or slow down water treeing, the best way is to isolate the water away from the cable [6]. XLPE cable is the most common cable used for underground cable. However, XLPE cables are easy be treed and degraded its dielectric performance under humid environment. Therefore, a new martial of insulation for cables is needed. With mixing XLPE and other materials will be a method to slowdown water treeing [4]. With testing XLPE, XLPE/OMMT, XLPE/SiO2 and XLPE/EVA by analyzing the results of mechanical properties, melting and crystallization processes, the effect of water tree in XLPE were investigated.

Mechanical Properties

For the mechanical properties, the performance of XLPE composites are better than XLPE. With refer to [4, Table.1], it shows the results of Elastic Modulus, Tensile Strength, Elongation at Break and Fracture Energy. The higher the fracture energy of the materials is, the higher toughness is. XLPE/SiO2 has the highest fracture energy. However, with comparing to XLPE/OMMT, the performance of XLPE/OMMT in elastic modulus, tensile strength and elongation at break are better than XLPE/SiO2 and the fracture energy is not bad. Therefore, XLPE/OMMT perform the best in its mechanical properties.

Methods for Mitigating Water Treeing and Monitoring Ampacity & Temperature

Water Tree Mitigation Techniques:

1. Material Innovations: The integration of Cross-Linked Polyethylene (XLPE) with novel materials such as OMMT, SiO2, and EVA has shown promising results in enhancing mechanical properties and reducing water tree growth. Table 1 outlines the mechanical properties of XLPE composites, indicating improved performance over standard XLPE.
2. DSC Analysis: Differential Scanning Calorimetry (DSC) provides insights into the melting and crystallization processes of XLPE composites. The analysis suggests that composites exhibit better thermal behavior than pure XLPE, contributing to slower water tree growth.
3. Water Tree Growth Analysis: Studies comparing the growth of water trees in various XLPE composites highlight the effectiveness of XLPE/EVA in mitigating water tree development, making it a preferable insulation material for underground cables.

Ampacity and Temperature Monitoring Techniques

1. FBG Sensors: Fiber Bragg Grating (FBG) sensors offer a novel approach to temperature monitoring, exploiting the wavelength shifts in optical fibers to accurately measure temperature changes along the cable length.
2. Computational Analysis: Advanced simulation techniques employing the superposition principle of thermal fields enable precise calculation of temperature rise and ampacity in multi-circuit cable systems under varied operational conditions.

Using Fiber Bragg Grating (FBG) Sensor is one of the common ways to monitor the temperature of the underground distribution cable. The working principle is to detect the changes of the center wavelength in order to calculate the temperature as the FBG is only affected by temperature. With using the formula:

λB=2nⅇffΛ(1)

KT=ΔλBλBΔT=α+ξ(2)

ΔλBλB=(1-pe)Δε+(α+ξ)Δ(3)

To protect the FBG, both ends of FBG’s optical fiber are fixed which is dealing with temperature sensitization. However, in the actual operation of FBG and the cable, there are about 90% faults will be occurred in the cable joints. The temperature of the cable joint is increased greatly from the most obvious signal. Therefore, the connection of the cable is needed to connect carefully with arranging the sensor.

Conclusion

The relentless pursuit of enhanced materials and innovative monitoring methods signifies a significant leap towards improving the reliability and efficiency of underground power cables. The amalgamation of material science advancements and sophisticated monitoring techniques promises a future where power distribution systems are more resilient, efficient, and capable of meeting the increasing demands of modern infrastructure.

References

1. HK Electric., “Transmission & Distribution System,” [online document], 2014.[Accessed: 23-Sep-2019]
2. G. Platbrood, B. Hennuy, Y. Tits, and S. J. Sutton, “Water trees in medium voltage XLPE cables: Comparison of different polyethylene insulation using short time accelerated ageing tests,” 18-Oct-2009. [Online]. Available: https://ieeexplore-ieee-org.ezproxy.lib.rmit.edu.au/document/5377730. [Accessed: 23-Sep-2019].
3. A. Duvernay, “Overheated underground cable causes roadway breakage in Wilmington,” delawareonline, 29-Jun-2017. [Online]. Available: https://www.delawareonline.com/story/news/2017/06/29/piece-wilmington-roadway-crumbles-around-manhole/439741001/. [Accessed: 30-Sep-2019].
4. Q. Yu, X. Li, P. Zhang, P. Yang, and Y. Chen, “Properties of Water Tree Growing in XLPE and composites,” 07-Apr-2019. [Online]. Available: https://ieeexplore-ieee-org.ezproxy.lib.rmit.edu.au/document/8727376. [Accessed: 30-Sep-2019].
5. IMPACT ANALYTICAL, “DSC Analysis.” [online document]. Available: https://www.impactanalytical.com/services.aspx?id=33. [Accessed: 01-Oct-2019].
6. N. Promvichai, T. Supanarapan, K. Minja, B. Marungsri, and T. Boonraksa, “Effect of NaCl Solution and Temperatures on Water Treeing Propagation in XLPE Underground Cable for Medium Voltage,” 07-Mar-2018. [Online]. Available: https://ieeexplore-ieee-org.ezproxy.lib.rmit.edu.au/document/8712333. [Accessed: 23-Sep-2019].
7. Z. A. A. Zarim and A. B. A. Ghani, “The effect of water tree and partial discharge defects in XLPE cables to the dielectric absorption ratio,” 28-Nov-2016. [Online]. Available: https://ieeexplore-ieee-org.ezproxy.lib.rmit.edu.au/document/7951632. [Accessed: 24-Sep-2019].
8. Welltech Instrument Company Ltd., “FBG Sensor,”[online document], [Accessed: 3-Oct-2019]
9. X. Jie, Z. Li, Q. Huang, and C. Liu, “A new packaged FBG sensor for underground cable temperature monitoring,” 25-Mar-2017. [Online]. Available: https://ieeexplore-ieee-org.ezproxy.lib.rmit.edu.au/document/8054321. [Accessed: 04-Oct-2019].