Medium-voltage uninterruptible power supply

Medium-voltage uninterruptible power supply

A large data center needs a power protection scheme that can supply a sizeable amount of power in a very reliable and efficient way. A power protection and distribution approach at the medium-voltage (MV) level provides the perfect solution.

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Domagoj Talapko ABB Smart Power Napier, New Zealand, domagoj.talapko@hr.abb.com

Continuous growth of the data center industry, particularly in the hyperscale space, is resulting in a dramatic increase in data center facility power needs. This trend is driving new strategies to fulfill customer ideals pertaining to higher efficiency, higher availability and minimal maintenance – in parallel with the insatiable need for reduction in capital investments. With all things considered, the natural next step for power protection for large critical power facilities is an MV-based system.

ABB’s PCS120 MV uninterruptible power supply (UPS) – based on the revolutionary impedance (Z) isolated static converter (ZISC) architecture – is the most recent addition to ABB’s MV product portfolio and represents the next generation of MV UPS intended for multi-MW power protection →01.

01 The PCS120 MV UPS.
01 The PCS120 MV UPS.

The UPS’s high-performance inverters – designed using ABB proprietary power electronics technology – combine with the ZISC architecture to ensure that the output voltage is regulated no matter what input supply disturbances are present. The PCS120 MV UPS provides continuously regulated, filtered power.

To maximize scalability and minimize spare parts, the PCS120 MV UPS system is built using UPS blocks, each with a rated power of 2,250 kVA. Up to 10 of these blocks can be paralleled in a so-called hard-parallel configuration to give 22.5 MVA or 20 can be arranged in a ring-bus configuration to give 45 MVA.

The PCS120 MV UPS was designed to meet the typical requirements of a large data center:

Maximum availability
The PCS120 MV UPS offers a high uptime that is driven by a robust MV design approach that delivers high power levels from single blocks, a lower switchgear count and a modular design that allows the loss of up to two converters without automatic transfer to bypass mode. Other internal redundancies for fans and switched-mode power supplies further increase system availability.

For large parallel or ring-bus systems, if the system designer includes a redundant module in the system, module maintenance is possible while keeping the system online and the load fully protected, thus yet further increasing system availability.

High performance
The PCS120 MV UPS delivers a clean output voltage in accordance with IEC62040-3 class 1 and can also supply high fault currents for downstream protection and fault clearing of up to five times nominal current.

Efficiency
The PCS120 MV UPS has a class-leading efficiency of 98 percent for the load spectrum from 50 percent up to full rated load and better than 96 percent for 25 to 50 percent load. Low no-load losses and modular design ensure a near-flat efficiency curve, allowing maximum foreseen capacity to be installed on day one, whilst minimizing energy wastage if the initial loading is low.

Operating cost-effectiveness
Because the power protection is at the MV level, facility build and operation costs are reduced as currents and electrical losses are lower at this higher voltage and cables can be thinner →02. An MV UPS can be placed on less expensive real estate – for example, in an electrical room or substation – distant from the loads. Furthermore, because MV requires less infrastructure, reliability is inherently improved.

02 Operating at MV levels allows the PCS120 MV to supply power protection to large data centers – at lower overall cost.
02 Operating at MV levels allows the PCS120 MV to supply power protection to large data centers – at lower overall cost.

Flexibility and scalability in large power applications
The PCS120 MV UPS’s flexibility allows it to accommodate several common data center architectures, such as “distributed redundant,” or “shared redundant” or “catcher.” These are in addition to the hard-parallel and ring-bus configurations mentioned above. Utilizing groups of 22.5 MVA configurations in hard-parallel mode gives a new perspective on using known architectures – and on a significantly higher power level as large backup systems such as diesel or gas generators are supported by the architecture.

Indoor and outdoor PCS120 MV solutions are possible as are versatile energy storage options with autonomies that range from a few seconds up to several minutes.

Grid support functions
With the rise of renewable energy generation comes a potential for UPS equipment to provide grid support functions in addition to their primary task of load protection.

Large data centers have a significant stranded power generation capacity due to their redundant design and battery systems. This infrastructure can generate an income stream through grid support services such as demand management and frequency regulation, as well as increase engagement in corporate social responsibility by helping out local community power schemes.

In addition to its core purpose as a load protection system, the ABB PCS120 MV UPS ZISC topology is also ideal for injecting real power into – or absorbing it from – the electrical network on request from an external power plant controller when network stability is threatened. On request, the PCS120 MV UPS will step in to supply power to the site critical load, thus reducing the drain on the grid, allowing it to recover. If the power relief requested would leave the critical load short, the UPS will support the full load and inject just any excess capacity into the grid – ie, the maximum available power to be injected into the grid is the PCS120 MV UPS system rating minus the required load power →03.

  • 03a Power flow in normal mode of operation.
  • 03b Power flow with grid support functionality.

03 Power support for the grid.

The PCS120’s modular approach allows unparalleled serviceability and redundancy while maximizing uptime. The PCS120 MV UPS is the ideal solution for large data centers that need power protection in the multi-MW range and the UPS covers every aspect the data center needs over the 20 years’ lifetime of the product with minimized maintenance and maximized efficiency, leading to an optimal total cost of ownership. 

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