Understanding the Shift to Transformerless UPS

At Legrand, our transformerless UPS systems have become a cornerstone of mission-critical infrastructure design, trusted across global data centers, healthcare, and industrial applications. As power demands grow and data center operators seek more efficient, scalable, and cost-effective uninterruptible power supply (UPS) solutions, the transformerless approach delivers on key performance metrics, without compromising reliability or capacity.

At their core, transformerless UPS systems eliminate the bulky internal isolation transformer found in older designs. Instead, they rely on high-frequency technology, advanced power electronics, and intelligent charging circuits to provide clean, stable voltage to connected loads. This shift enables a more compact footprint, greater energy efficiency, and lower operational costs - all essential benefits in today’s high-density environments.

Key Components and System Architecture

Transformerless UPS units share core similarities with transformer based systems—such as rectifiers, inverters, batteries, and bypass circuits but their internal layout and energy flow differ significantly.

Major components include:

• Input Rectifier and Power Factor Correction (PFC): Converts incoming AC voltage to DC and ensures optimal current draw from the utility grid.

• DC Link: Acts as the central node between rectifier and inverter stages.

• Inverter: Converts DC back to a precise AC output to supply the critical load.

• Battery Charger and Batteries: Manages charging and discharging cycles for backup power support.

• Static Bypass: Offers immediate transfer to utility in case of UPS fault or overload conditions.

By removing the transformer, these systems significantly reduce impedance and improve response times to load changes, an essential requirement for sensitive IT, medical, and industrial applications.

Comparing Transformerless vs. Transformer Based UPS Designs
 

Benefits of Transformerless UPS Systems

Transformerless UPS technology offers more than just reduced physical size. Its benefits are directly aligned with the operational priorities of today’s mission-critical environments:

1. Higher Efficiency and Lower Operating Costs

Legrand’s transformerless UPS solutions consistently deliver superior energy efficiency compared to traditional transformer-based systems, helping customers reduce operating expenses without compromising reliability. Many models operate above 96% efficiency at full load, and support ECO and Smart Active modes that push efficiency even higher (up to 98–99%). Thanks to the integration of new technologies and advanced power components such as silicon carbide (SiC) semiconductors, efficiencies exceeding 98% are now becoming more achievable and widespread. These performance gains translate to real-world savings, each 1% increase in efficiency can reduce annual electricity and cooling costs by thousands of dollars in medium to large-scale facilities.

The Legrand  Keor HPE series exemplifies this benefit, offering 96% double-conversion efficiency in a compact, high-reliability monolithic design ideal for critical loads.

2. Improved Power Quality and Fast Response

With advanced digital signal processors and high-speed switching, these systems can respond to power disturbances in microseconds. They ensure voltage stability, maintain frequency regulation, and support nonlinear loads without degradation of output quality.

KEOR MOD is ideal for edge environments where fast inverter response prevents cascading failures during voltage dips or transient disturbances.

3. Scalability and Design Flexibility

As digital infrastructure expands across hybrid and edge environments, Legrand’s transformerless UPS systems offer modular scalability that reduces upfront investment while enabling seamless power expansion. 

Products like the KEOR MOD and Trimod HE feature hot-swappable power modules, allowing facilities to start small and scale up to 250kVA or more without service interruption. Ideal for growing colocation sites or distributed IT architectures.

4. Reduced Total Cost of Ownership

Lower initial costs, reduced energy consumption, and minimized maintenance requirements combine to deliver a compelling long-term financial case. Additionally, simpler installation procedures and free air cooling in some models further lower overall costs.

5. Enhanced Battery Management

Transformerless UPS systems use digital battery management and temperature-compensated charging to optimize charging cycles, extend battery service life, and reduce strain during float conditions. Legrand UPS solutions support both VRLA and lithium-ion battery technologies—offering up to 60% longer lifespan, faster recharge times, and reduced cooling requirements compared to legacy chemistries.

Our integrated battery monitoring tools provide real-time runtime forecasting, failure detection, and intelligent alerts through DCIM and SNMP interfaces, empowering facilities to prevent downtime and optimize replacement cycles.

Limitations and Design Considerations

While transformerless UPS designs offer numerous benefits, they are not without limitations. Proper system design and understanding of the use case is essential:

• Susceptibility to Dirty Power: In environments with high harmonics, voltage distortion, or electrical noise, transformerless UPS units may be more vulnerable to instability. Additional filtering or conditioning equipment may be required.

• No Built-In Galvanic Isolation: Without an internal transformer, isolation from the utility or faults is absent. In some applications, external isolation transformers may be required—adding cost, complexity, and footprint.

• Lower Short-Circuit Current Capability: Transformer based systems can deliver higher phase-neutral fault currents, which is advantageous for downstream protection coordination.

• External Transformer Design Risks: Relying on external isolation increases the number of components that must be monitored and maintained, introducing potential single points of failure if not managed correctly.

Applications Across Critical Industries

Transformerless UPS systems are well-suited for a broad range of applications where high availability and power protection are non-negotiable.

• Data Centers : Optimal for rack-based deployments and colocation sites needing flexible, high-density power supplies.

• Healthcare Facilities: Supports diagnostic equipment, surgical suites, and life-sustaining systems where voltage fluctuations are unacceptable.

• Industrial and Manufacturing: Transformer based UPS may be preferred in heavy-duty applications with complex fault management and higher power levels.

• Telecom Networks: Ensures uptime across distributed infrastructure and remote installations, especially in edge or 5G deployments.

• Financial Institutions: Maintains system integrity for trading floors, transaction servers, and compliance infrastructure.

Real-World Design Considerations

When selecting and deploying a transformerless UPS, technical decision-makers should evaluate several key parameters to ensure alignment with facility needs:

• Load Profile and Capacity: Determine the kVA rating required for peak and average loads, accounting for potential growth.

• Battery Runtime: Assess backup requirements and choose battery capacity and chemistry accordingly.

• Voltage Compatibility: Ensure output voltage matches downstream equipment and regional standards.

• Redundancy and Bypass Design: Consider N+1 or 2N redundancy for critical applications.

• Environmental Conditions: Confirm that ambient temperature, airflow, and humidity are within operating specs for optimal performance.

• Need for Isolation: Evaluate whether external galvanic isolation is needed and its impact on cost and layout.

Future Outlook and Standards Alignment

Transformerless UPS systems are increasingly becoming the default architecture for modern installations, particularly as energy efficiency regulations tighten and rack densities continue to rise. Industry standards such as IEC 62040, which governs UPS performance and safety, and IEEE 446, offering best practices for standby power systems, continue to evolve to keep pace with these technological advancements. With innovations in silicon carbide (SiC) switching, lithium-ion batteries, and intelligent energy management platforms, transformerless UPS designs are poised to become even more efficient, compact, and capable. The focus on software integration for predictive maintenance and real-time diagnostics is also expanding the role of the UPS as an active component in facility-wide infrastructure management.

Making the Case for Transformerless UPS

For organizations seeking reliable, scalable, and energy-efficient uninterruptible power, transformerless UPS systems deliver clear, measurable advantages. From lower costs and smaller footprints to improved efficiency and better battery management, the benefits of this technology are aligned with the needs of modern, digitally driven operations.

However, decision-makers should also consider specific site conditions, load sensitivity, and required protection levels. In rugged industrial environments or applications demanding galvanic isolation and fault resilience, transformer based UPS systems may still be preferable.

Whether you're building a new facility or retrofitting legacy infrastructure, transformerless systems offer a future-proof solution that supports evolving workloads and operational demands. 

Our KEOR FLEX, KEOR HPE, Trimod HE, and Daker DK series UPS platforms provide scalable, efficient power protection for even the most demanding environments.