TY - JOUR
T1 - Grid capacity and efficiency enhancement by operating medium voltage AC cables as DC links with modular multilevel converters
AU - Shekhar, Aditya
AU - Kontos, Epameinondas
AU - Ramírez-Elizondo, Laura
AU - Rodrigo-Mor, Armando
AU - Bauer, Pavol
PY - 2017
Y1 - 2017
N2 - It is anticipated that with the thrust towards use of clean energy resources such as electric vehicles, future distribution grids will face a steep increase in power demand, forcing the utility operators to invest in enhancing the power delivering capacity of the grid infrastructure. It is identified that the critical 5–20 km medium voltage (MV) underground ac distribution cable link, responsible for bulk power delivery to the inner urban city substation, can benefit the most with capacity and efficiency enhancement, if the existing infrastructure is reused and operated under dc. Quantification of the same is offered in this paper by incorporating all influencing factors like voltage regulation, dc voltage rating enhancement, capacitive leakage currents, skin and magnetic proximity effect, thermal proximity effect and load power factor. Results are presented for three different ac and dc system topologies for varying cable lengths and conductor cross-sections. The computed system efficiency is enhanced with use of modular multilevel converters that have lower losses due to lower switching frequency. A justified expectation of 50–60% capacity gains is proved along with a generalized insight on its variations that can be extrapolated for different network parameters and configurations. Conditions for achieving payback time of 5 years or lower due to energy savings are identified, while the socio-economic benefits of avoiding digging and installing new cable infrastructure are highlighted. The technical implications of refurbishing cables designed for ac to operate under dc conditions is discussed in terms of imposed electric fields, thermal profile and lifetime. A novel opportunity of temperature dependent dynamic dc voltage rating to achieve additional capacity and efficiency gains is presented.
AB - It is anticipated that with the thrust towards use of clean energy resources such as electric vehicles, future distribution grids will face a steep increase in power demand, forcing the utility operators to invest in enhancing the power delivering capacity of the grid infrastructure. It is identified that the critical 5–20 km medium voltage (MV) underground ac distribution cable link, responsible for bulk power delivery to the inner urban city substation, can benefit the most with capacity and efficiency enhancement, if the existing infrastructure is reused and operated under dc. Quantification of the same is offered in this paper by incorporating all influencing factors like voltage regulation, dc voltage rating enhancement, capacitive leakage currents, skin and magnetic proximity effect, thermal proximity effect and load power factor. Results are presented for three different ac and dc system topologies for varying cable lengths and conductor cross-sections. The computed system efficiency is enhanced with use of modular multilevel converters that have lower losses due to lower switching frequency. A justified expectation of 50–60% capacity gains is proved along with a generalized insight on its variations that can be extrapolated for different network parameters and configurations. Conditions for achieving payback time of 5 years or lower due to energy savings are identified, while the socio-economic benefits of avoiding digging and installing new cable infrastructure are highlighted. The technical implications of refurbishing cables designed for ac to operate under dc conditions is discussed in terms of imposed electric fields, thermal profile and lifetime. A novel opportunity of temperature dependent dynamic dc voltage rating to achieve additional capacity and efficiency gains is presented.
KW - Capacity
KW - Dc links
KW - Cables
KW - Dynamic rating
KW - Efficiency
KW - Electric fields
KW - Grid
KW - Medium voltage
KW - MMC
KW - Payback
UR - http://resolver.tudelft.nl/uuid:919be950-af26-43f0-863b-7dd3b11def49
U2 - 10.1016/j.ijepes.2017.06.012
DO - 10.1016/j.ijepes.2017.06.012
M3 - Article
SN - 0142-0615
VL - 93
SP - 479
EP - 493
JO - International Journal of Electrical Power & Energy Systems
JF - International Journal of Electrical Power & Energy Systems
ER -