Difference Between Primary and Secondary Transmission

The movement of electrical energy from its point of generation to end-user consumption involves a sophisticated journey through multiple phases, collectively known as the power transmission and distribution system. Central to this system are the concepts of primary and secondary transmission, each playing a crucial role in ensuring the safe, efficient, and reliable delivery of electricity. The key differences between these two stages are rooted in their scope, voltage levels, and specific functionalities.

This article offers an in-depth exploration of these distinctions, focusing on the essential equipment used in each phase, particularly switchgear, and the cutting-edge solutions offered by Leistung Energie to support and enhance modern grids.

Primary Transmission

Primary transmission marks the first phase of transporting electricity from power generation stations to regional substations. At the generation stage, electricity is typically produced at relatively low voltages, often in the range of 11 kV to 33 kV. To enable the efficient transport of this energy over long distances, step-up transformers increase the voltage to levels between 100 kV and 700 kV, depending on the region and system requirements.

High-voltage levels are crucial for minimizing energy losses during transmission. Electrical power loss, often represented as I²R losses (where I is the current and R is the resistance), is directly proportional to the current flowing through the transmission lines. By increasing the voltage, the current is significantly reduced, which in turn minimizes resistive losses and enhances the overall efficiency of the power system.

The infrastructure supporting primary transmission comprises a network of overhead transmission lines, large substations, and underground cables in specific cases, such as in urban areas or regions with challenging terrains. Central to this network is primary switchgear, a collection of equipment designed to manage, control, and protect the high-voltage transmission lines.

Primary switchgear includes essential components such as circuit breakers, disconnectors, isolators, and protection relays. Circuit breakers are pivotal in interrupting fault currents, ensuring that power system components are safeguarded from potential damage. Disconnectors and isolators allow sections of the grid to be de-energized for maintenance or during fault conditions, ensuring the safety of personnel and equipment. Protection relays monitor the grid for abnormal conditions and trigger corrective actions to maintain stability and safety.

Leistung Energie’s AMS series air-insulated switchgear stands as a testament to innovation and reliability in this field. Designed to handle high fault currents and demanding operational conditions, these systems provide unparalleled performance. They are built to meet and exceed global standards, ensuring that utilities worldwide can rely on them for their primary transmission needs. The robust construction and advanced technology integrated into these systems make them ideal for use in harsh environments, such as in mining operations, large-scale industrial plants, and national grid systems.

Secondary Transmission

Secondary transmission, also referred to as sub-transmission, serves as the critical intermediary between primary transmission and local distribution systems. After electricity is transmitted to regional substations through primary lines, step-down transformers reduce the voltage to levels suitable for medium-range transport. These voltages typically range from 33 kV to 66 kV, making the energy manageable for distribution to urban centers, smaller substations, or industrial zones.

The secondary transmission phase ensures that power is efficiently delivered to points closer to end-users, where further voltage reductions prepare it for final consumption. The infrastructure involved includes medium-voltage lines, compact substations, and secondary switchgear, which plays a vital role in maintaining the stability and reliability of the network.

Secondary switchgear differs from its primary counterpart in that it operates at medium voltage and is often more compact and flexible in design. It includes gas-insulated and air-insulated configurations, offering options for different applications and environments. These systems perform crucial functions, such as isolating faults, rerouting power during maintenance, and managing load distribution across the network.

Leistung Energie’s portfolio of secondary switchgear products includes Ring Main Units (RMUs) and innovative SF6-free systems. These products are specifically designed for urban grids, renewable energy systems, and industrial facilities where space, safety, and environmental impact are critical factors. The RMUs are known for their compact design, high reliability, and advanced fault detection capabilities, ensuring that secondary transmission networks operate smoothly and efficiently.

Sub-Transmission: The Crucial In‑Between

Sub-transmission often overlaps with secondary transmission but serves a unique role in certain power systems. It involves voltages typically ranging from 69 kV to 138 kV and acts as a bridge between the primary transmission grid and the distribution network. Sub-transmission is particularly relevant in densely populated urban areas or industrial regions, where additional steps are required to balance efficiency with cost.

This phase delivers power to medium-scale substations that feed smaller distribution transformers or localized grids. By handling voltages that are lower than primary transmission but higher than typical secondary levels, sub-transmission ensures the efficient transfer of electricity to areas closer to the point of use.

Switchgear Safety & Standards

Safety is a paramount consideration in both primary and secondary transmission systems, and switchgear plays a critical role in ensuring this. Switchgear equipment is rigorously tested for internal arc resistance, fault interruption capabilities, and compliance with international standards such as IEC 62271, ANSI, GB, and GOST. These standards ensure that switchgear products can operate safely and reliably in diverse environments and under varying operational conditions.

Leistung Energie’s switchgear solutions are designed with these stringent standards in mind. From their high-voltage GIS products to their medium-voltage RMUs, every product is engineered to provide maximum safety, reliability, and performance. This focus on quality and compliance has made Leistung Energie a trusted name in the power industry, known for delivering solutions that meet the demands of modern grids.

SF6 Alternatives in Secondary Grids

Sulfur hexafluoride (SF6) has long been a standard insulating gas in switchgear due to its excellent dielectric properties. However, its high global warming potential has prompted the industry to seek more sustainable alternatives. Leistung Energie is at the forefront of this transition, offering SF6-free solutions such as the Airing and solid-insulated RMUs.

These innovative products maintain the reliability and safety of traditional systems while significantly reducing their environmental impact. By adopting SF6-free switchgear, utilities can align with global climate goals and reduce the carbon footprint of their transmission and distribution networks.

The power transmission and distribution system is a complex network that relies on the seamless integration of primary and secondary transmission stages. Primary transmission handles the bulk movement of electricity over long distances at high voltages, supported by robust primary switchgear. Secondary transmission, in contrast, bridges the gap to local distribution networks, utilizing compact and efficient secondary switchgear to deliver power to end-users.

Leistung Energie stands out as a leader in providing advanced solutions for both primary and secondary transmission. With a commitment to innovation, sustainability, and quality, their products are designed to meet the demands of modern power systems. From high-voltage GIS to eco-friendly RMUs, Leistung Energie offers the tools needed to power the future. Visit Leistung Energie to explore their comprehensive product range and discover how they can help optimize your power systems for reliability, safety, and sustainability.