Why harmonics affect the service life of cable splices
Today’s power grids are changing faster than ever before. Decentralized generation and energy storage are no longer exceptions but are increasingly influencing the operation of medium-voltage networks. As a result, not only capacity and loading conditions are changing, but also voltage and current quality. This makes the central question increasingly relevant: does your existing infrastructure still operate reliably under these new grid conditions?
The new reality of the grid
For many years, medium-voltage networks were characterized by a relatively stable, sinusoidal 50 Hz voltage. Today, a fundamentally different picture is emerging.
- Power is generated locally (solar, wind)
- Voltage fluctuations are increasing
- Power converters operate at higher switching frequencies
The result: voltage and current waveforms are no longer purely sinusoidal but are distorted by higher-order harmonics. These harmonics enter the network and affect components that were originally designed for previous operating conditions.
Where things start to go wrong: insulation under stress
Failure analyses in medium-voltage networks often point to one recurring failure mechanism: degradation of the insulation medium. The reliability of medium-voltage assets is largely determined by the performance of the insulation system. As a result, the service life of cable systems is directly linked to the quality, dimensioning, and actual electrical loading of the insulation.
The issue is not that these systems are inherently underdesigned. The issue is that many designs, qualifications, and testing methods are based on assumptions that no longer fully correspond to today’s grid reality. Harmonic distortion played only a minor role in the past.
What harmonics physically do
Harmonics are not an abstract phenomenon. They have a direct and measurable impact on the electrical, thermal, and dielectric behavior of cable accessories. Three primary mechanisms are involved:
- Increased Electrical Stress on the Insulation– Higher frequencies affect electric field distribution, particularly around critical zones such as the interface between different insulation materials, the end of the semiconductive layer, and the stress control area.
- Increased Dielectric Losses– Energy dissipation within insulation materials increases as a result of:
- Frequency
- Voltage
- Dielectric losses (tan δ)
- Local Temperature Rise– Higher dielectric losses generate additional heat, often concentrated in critical areas. It is precisely the combination of increased electrical stress and localized heating that accelerates electrical and thermal ageing.
Not every cable termination or splice responds in the same way
A crucial factor is the method used to control electric field distribution within a cable accessory. In general, two field control principles can be distinguished:
Geometric Field Control
- Field distribution is primarily determined by the geometry of the stress cone
- Behavior remains relatively stable at higher frequency components
- Hardly affected by harmonics
Resistive Field Control
- Field distribution strongly depends on material properties and conductivity
- Behavior is clearly frequency dependent
- Greater sensitivity to harmonics
The differences are not only theoretical but can also be demonstrated in practice. Simulations and measurements show that:
- The local electric field can increase by up to four times at higher frequencies
- Temperature rise can increase from approximately 3 K to nearly 20 K without current loading
Additional project results confirm this picture:
- Local electric field strength up to 250% higher in resistive solutions
- Temperature differences of up to 50°C between configurations
In practical cases, for example at or near wind and solar energy projects, these effects may coincide with increased failure rates in these applications. The conclusion is clear: not every type of cable accessory exhibits sufficiently robust performance in medium-voltage networks with significant harmonic loading.
Would you like deeper insight into the impact of harmonics on cable accessories, field control, and dielectric behavior?
What does this mean for DNOs? s
For asset managers, this represents a shift in the way component behavior must be assessed, monitored, and managed. Accelerated insulation ageing, less predictable remaining service life, and the occurrence of failures in critical sections of the network mean that component behavior increasingly deviates from traditional design and lifetime models.
Pressure on maintenance and investment decisions is increasing, as replacement timing becomes less predictable and both condition monitoring and risk assessment become more complex. This does not require more of the same approach, but different starting points.
The Blind Spot in Testing and Standards
An important challenge lies in the way cable systems and accessories are qualified. Most standards, type tests, and qualification tests are based on:
- Fixed frequency
- Sinusoidal voltage
- Separated stress factors
Practical experience shows that:
- Frequencies vary
- Multiple harmonic components are combined
- Thermal and electrical stress influence each other
The reality of the grid is evolving faster than existing testing methodologies and qualification frameworks.
Looking ahead: What does this mean for design and asset management
For asset managers, this represents a shift in the way component behavior must be assessed, monitored, and managed. Accelerated insulation ageing, less predictable remaining service life, and the occurrence of failures in critical sections of the network mean that component behavior increasingly deviates from traditional design and lifetime models.
Pressure on maintenance and investment decisions is increasing, as replacement timing becomes less predictable and both condition monitoring and risk assessment become more complex. This does not require more of the same approach, but different starting points.
The Blind Spot in Testing and Standards An important challenge lies in the way cable systems and accessories are qualified. Most standards, type tests, and qualification tests are based on:
- Fixed frequency
- Sinusoidal voltage
- Separated stress factors
Practical experience shows that:
- Frequencies vary
- Multiple harmonic components are combined
- Thermal and electrical stress influence each other
The reality of the grid is evolving faster than existing testing methodologies and qualification frameworks.
Looking ahead: What does this mean for design and asset management?
The trend is clear: harmonics can no longer be ignored. On the contrary, the continued growth of power electronics, frequency converters, battery storage, and AC/DC conversion will further increase their influence on medium-voltage networks.
This means that design and asset management decisions must take into account:
- Frequency-dependent material behavior
- Combined thermal and electrical stress
- Location-specific effects within the network
Not as a theoretical scenario, but as daily operational reality.
From insight to robust solutions
The energy transition is changing not only how electricity is generated, but also how the network is electrically loaded. Cable splices play a silent yet critical role in this development. Because they often remain out of sight, their behavior under changing grid conditions is easily underestimated.
Those designing or managing networks today must consider how the grid will behave electrically tomorrow. A network with increasing harmonic loading requires cable accessories that continue to perform predictably, even beyond traditional design and testing conditions.
Lovink develops and tests cable splices based on exactly this principle: robust and predictable performance under changing grid conditions, founded on an understanding of field distribution, material behavior, dielectric stress, and long-term performance.
Discover how Lovink cable splices contribute to the reliable, robust, and predictable operation of your medium-voltage network.
