ELECTRICAL RESILIENCE
which a UPS is positioned. The scope of back-up power equipment available presents its own pitfalls. There is perhaps too much commercial and technical choice, which is often pushed by manufacturers championing their own technical preferences. This makes the selection process even more confusing. Historically, transformer-based, standalone UPS systems were considered the most resilient solution, and were the only UPS type addressed in HTM 06-01. However, the most recent amendments to the HTM now include all UPS topologies. This has sparked huge industry debate as to whether modular UPS technologies should be included – can modular UPS be used as a substitute for traditional parallel, and can they really claim true redundancy, which in a modular set up, would require two in parallel?
Modular or standalone solution? Looking firstly at the core advantages and considerations to choose a modular UPS solution over a standalone one; modular systems offer greater vertical scalability. For example, a 125 kW frame can start with one 25 kW module, and be scaled up gradually to five modules to 125 kW or 100 kW N+1. This delivers a flexible, cost- effective solution for users and designers to scale resilience with actual business growth, which ultimately improves power efficiency. There are also technical and running cost advantages, as a single module failure will not affect the load, and redundancy is realised within the frame from the other modules. With many of the critical components housed in ‘hot-swappable’ modules, availability is at its greatest, and MTTR (mean time to repair) is also significantly decreased. When comparing a modular UPS solution directly against a traditional, standalone parallel UPS set-up, it is important to note that a modular UPS system does not provide true N+1 redundancy in the same way. By the nature of their design, modular UPS systems have single points of failure – single supply sources, batteries, and single outputs, whereas true N+1 systems can be split across locations to increase resilience against environmental factors such as water ingress and fire.
Scalability and footprint
Different modular technologies also need to be taken into account. For example, centralised modular UPS solutions are ideal for future scalability, deliver a small footprint, and are easy to maintain. The key element to be aware of is that within a centralised modular solution, the risk of failure is higher, as there are more single points of failure. Some manufacturers, such as Legrand and Borri Spa, have
70 Health Estate Journal October 2020
Left: The Borri Spa Ingenio Plus compact transformer-free UPS system; 30-160 kVA. Right: The CertaUPS C400 and C500 single-phase UPS systems.
developed modular solutions to include a decentralised bypass, which effectively reduces the points of failure, but does require more floor space. A decentralised UPS system is also likely to cost a bit more. There is an important balance to strike between cost vs resilience, whilst still complying with HTM 06-01. While modular UPS solutions can be used within healthcare applications, upgrading to a standalone system will provide true N+1 resilience.
When it comes to selecting the right UPS solution, creating a priority list of system criteria can be beneficial. There is no ‘one system fits all’ answer. The application being supported, and the environment in which the UPS will be positioned, are two primary influences. For example, while loss of power to medical imaging equipment does not necessarily directly risk patient safety, it can cause costly damage and disruption to the overall procedure. Due to the highly sensitive nature of imaging equipment, it requires an electrical supply with very low impedance, and a UPS solution that is able to manage high inrush currents. One of the most robust solutions available is an isolated transformer output UPS from Borri Spa. As a specialist manufacturer of UPS systems, Borri Spa has adapted and perfected its technologies specifically for sensitive applications, addressing all aspects of HTM06-01, and other industry standards such as BS EN 60896 and EN 50171.
Observing ‘a multitude of functional criteria’
The Legrand Trimod three-phase modular UPS; 10-80 kVA.
These industry standards observe a multitude of functional criteria, which include four pole switching, loss of neutral, bypass, and dual supply. Although loss of neutral is not a common occurrence, it does need to be factored into the selection process, especially when considering modular options, which are less tolerant to loss of neutral. The output neutral of a supply is referenced to the input neutral, so in normal operation, the downstream supply is fully grounded. Problems can occur when the input neutral is switched or broken. In this instance the UPS has no neutral reference point, which may result in neutral to ground or line to ground over voltages. The phase and neutral conductors could then be at different potentials than normally expected or required by the
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