Muhammad Faheem Meer
Business & Management Consultant
Worldwide Cables (Pvt.) Ltd.-Pakistan and Brugg Kabel AG-Switzerland
About the Author
Muhammad Faheem Meer is a veteran cable industry professional with over 35 years of experience. An Electrical Engineering graduate from UET Lahore with an MBA in Marketing, he began his career at NESPAK in 1988. He has held key roles at Saudi Cable Company and Siemens in Saudi Arabia and the UAE, and has also contributed to leading local manufacturers such as Newage and GM Cables. He served as Regional Sales Manager at Brugg Cables in Dubai, one of the most reputed Swiss manufacturers of extra high voltage underground cables. Currently, he works as a freelance management consultant, supporting Worldwide Cables (Pvt) Limited, supported Pakistan Solar Association, and other organizations in various capacities.
In my previous article, I explained the differences between DC (solar) cables and conventional AC cables and briefly introduced the Space Charge Effect. Since this phenomenon plays an important role in the performance and longevity of DC cables, it deserves a closer look.
What is Space Charge Effect?
The Space Charge Effect is the accumulation of electrical charges within a cable’s insulation when it is subjected to a high DC electric field for an extended period. Instead of moving freely, these charges become trapped at impurities, material defects, interfaces, or within the molecular structure of the insulation.
This phenomenon is particularly significant in High Voltage DC (HVDC) cables and, to a lesser extent, in solar DC cables, where the electric field is continuously applied in one direction.
How Does Space Charge Form?
When DC voltage is applied to cables:
- Electrical charges are injected from the conductor into the insulation.
- Some of these charges become trapped within the insulating material.
- Over time, the trapped charges accumulate and generate their own internal electric field.
- This additional field distorts the original electric field distribution within the insulation.
In AC cables, the voltage polarity reverses 50 or 60 times per second, preventing significant charge accumulation. As a result, the Space Charge Effect is far less pronounced in AC systems.
Effects of Space Charge on Cable Performance
1. Electric Field Distortion
The trapped charges distort the electric field within the insulation, creating localized regions of high electrical stress. These stress concentrations increase the risk of dielectric breakdown.
2. Reduced Insulation Life
Elevated electrical stress accelerates insulation ageing and chemical degradation, leading to microscopic defects that shorten cable service life and increase maintenance and replacement costs.
3. Partial Discharge (PD)
Localized electric field enhancement may exceed the insulation’s dielectric strength, initiating partial discharges. Over time, PD erodes the insulation and can ultimately lead to cable failure, particularly in high-voltage applications.
4. Reduced Reliability of HVDC Cables
Space charge is one of the primary design challenges in HVDC cable systems. It limits voltage ratings, affects long-term reliability, and often requires thicker insulation or specially engineered insulating materials.
5. Thermal-Electrical Interaction
Temperature significantly influences charge mobility and trapping. Higher operating temperatures promote charge migration, further altering the electric field and accelerating insulation ageing. This is especially important in solar farms, HVDC transmission systems, and industrial DC installations operating in hot environments.
How Manufacturers Minimize Space Charge?
Modern DC cable manufacturers employ several techniques to reduce space charge accumulation, including:
- Ultra-clean, high-purity insulation compounds
- Specially formulated XLPE and XLPO insulation
- Charge-suppressing additives
- Advanced manufacturing processes to eliminate contaminants and voids
Semiconductive conductor and insulation screens (for medium and high-voltage cables)
These measures improve electric field uniformity and enhance long-term cable reliability.
Why It Matters for Solar Cables?
Although low-voltage solar cables (600 V to 1.5 kV DC) experience much lower electric stress than HVDC transmission cables, they operate continuously under DC voltage while being exposed to elevated temperatures and UV radiation. Consequently, high-quality solar cables are designed with insulation materials that resist space charge accumulation and slow insulation ageing.
The Space Charge Effect is a fundamental characteristic of DC cable insulation and one of the key challenges in DC cable design. While its impact is most pronounced in HVDC systems, it is also an important consideration for solar DC cables operating continuously under demanding environmental conditions. By using advanced insulation materials and precision manufacturing techniques, modern cable manufacturers effectively minimize space charge accumulation, ensuring greater reliability, longer service life, and improved electrical performance.
