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Understanding the HTM: UPS design requirements
Rapidly advancing healthcare technology is transforming the way patients are being diagnosed and treated. From sensitive medical imaging equipment to connected devices, data monitoring and lab tests, the future of healthcare lies in working hand-in–hand with technology and with that, comes a greater need for 24/7 regulated power.
Without the convergence of a secondary and tertiary backup power supply – generator and UPS system, this level of power continuity would not be possible. After determining the required medical groups and locations needing tertiary UPS backup, consideration must then be focussed on the design and resilience of the backup systems.
UPS Ratings
UPS systems must not only be rated to support the design load but thought should also be given to the type of load and fault clearance design.
Design loads may have a nominal rating, however, some medical loads such as an MRI, PET, CAT and X-Ray can all present a peak load during capture or image acquisition. Important consultation is required between the UPS and equipment design teams to ensure high peak inrush currents and line impedances are met by the UPS and infrastructure design.
Additionally, section 11.43 of the HTM references that UPS should be capable of clearing downstream circuit faults similarly to other distribution boards. This means designers should consider the effect of overloads and short circuit fault conditions.
Short circuits in the UPS load are isolated either by a downstream protective device, via the UPS static switch, or by the UPS inverter. Following BS 7671, where a UPS is used as a ‘life safety system’, it must clear the protective devices when on battery power.
When the mains power is unavailable, the UPS inverter output has limited overload capabilities at 120%. Some UPS will allow a maximum of 150% and up to 200% for a short period.
With this in mind, the UPS inverter electronics are more sensitive than the mains or static switch so careful calculations are required to ensure the inverter can clear protective devices. Actual overload characteristics vary from UPS to UPS so designers should verify the coordination of fault conditions when selecting the UPS type.
Redundancy and Resilience
Monolithic (standalone) UPS systems can be configured using a single unit (N) or multiple units working concurrently in parallel (N+1) to provide varying levels of redundancy and mitigate single points of failure. Modular UPS also provide redundancy and due to their modular architecture, this redundancy is achievable within the UPS system. Multiple modular units would eliminate additional points of failure but are often not cost–effective for healthcare facilities.
If the UPS are installed as multiple units in redundant UPS arrangements, each UPS should be sized to fully support the entire load.
Both UPS topologies can be installed into a variety of electrical design arrangements shown in section 11 of the HTM. The design configuration can be, single, N+1 and N+N, serving the critical medical locations via dual UPS output board and/or changeover devices within the Isolated Power System (IPS) or distribution boards.
The configuration should be selected based on the application it’s supporting and the medical locations. In many cases, it may be desirable to have redundancy within the UPS configuration, having distribution configuration via changeover switches, or having dual feeds into the medical location.
The HTM examples are for guidance only and state that the designer should demonstrate that any solution provided is the optimum solution to maintain both patient safety and their associated systems where the loss of power will affect the normal operation of the healthcare facility.
Consultation is therefore needed between the designers and UPS specialists at early stages.
Batteries
The configuration of battery strings in a UPS installation is critical to eliminating single points of failure. Batteries can be arranged in a single string or dual parallel strings. For simplicity, and to keep costs to a minimum, UPS battery subsystems are typically configured as single strings. However, during a mains failure, this leaves the system vulnerable due to multiple single points of failure.
In line with section 11.9 of the HTM, the use of parallel or split battery banks should instead be specified. This configuration allows the UPS to remain online even while half the battery system is being serviced.
Transformer Arrangements
Advice in the HTM stipulates that designers may wish to consider the use of zigzag transformers on the input, bypass line and output. In most cases, this is to provide a grounded neutral supply for the UPS and load. Additionally, such transformers provide a local earth and installation point. This provides a grounded neutral and adequate grounding for fault currents.
Under BS 7671 where a UPS is used as an electrical source for life safety systems, it should be able to operate distribution circuit protective devices.
Due to the added complexity, cost and space requirements, consultation between the designers and UPS specialists is required at the early stages of a project.
Dual UPS Supplies
UPS can be fed from a single mains supply. This single supply is usually from the LV (low voltage) distribution board within a hospital. This LV distribution may be supplied from the hospital’s primary electrical and secondary power supply from either an alternative energy plant, combined heat and power (CHP) or standby power system like a diesel genset.
Additionally, many UPS can be fed from a dual supply. Both feeds can come from the same LV distribution arrangement but via separate circuits or separate LV sources.
Firstly, the advantage of dual supplies and the UPS selects between them. When a UPS is supplied from a single supply inside the UPS, it’s split into one that feeds the rectifier (charger) and the other feeding the bypass line. When the UPS transfers to its internal bypass line (manually or failsafe) the load is fed from the mains supply via the UPS internal bypass, not from the UPS output inverter.
With a dual supply, the UPS bypass line can be fed from the secondary supply. The advantage of this is that once the UPS has depleted its batteries, it won’t switch off. Instead, it has the potential to transfer the load to the service line if this is available. Therefore, if a main supply protective device fails or trips, the UPS will have the better source and reverse supply.
Secondly, if the UPS faults and trips the incoming protective device, the load can be automatically transferred to the reserve supply with minimal interruption.
Careful thought is needed if supplies are fed via separate LV sources. Why? Because if the hospital has two primary supplies from separate building transformers, then each supply has its own earthing and neutral arrangements. In most cases, it’s critical for the designer to keep the two sources separate and not to bond or create multiple neutral paths.
The problem is that while many UPS can take dual inputs, there’s only one UPS output, resulting in most UPS systems internally bonding both neutrals together. While this UPS type is generally OK with dual supplies from the same source, they’re not compatible with sources from separate neutrals because they connect both paths.
For separate sourced dual supplies, compatible UPS are required that won’t bond the neutral internally. These UPS usually have an internal inverter transformer. Whilst taking dual supplies, they will use a single point as a reference and therefore provide further resilience without affecting the electrical earth and neutral design arrangements.
Consultation between the designers and UPS specialist is again required at the early stages of a project.
Power Control has been specifying, installing, and maintaining tertiary power systems in healthcare estates for over 27 years. Every UPS system, both monolithic and modular, suitable for healthcare applications are available with either VRLA or lithium-ion batteries and meet all relevant medical regulations including the IEC 60601, HTM 06-01, BS 7671 and BS 6290-4. Contact us to find out more, 01246 431 431, [email protected]
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Why lithium-ion based UPS are ideal for sensitive healthcare applications
Lithium-ion has been one of the most talked about developments in the UPS industry this year, revolutionising the way that UPS systems are used. Where they were once only installed to support sensitive loads in the event of a power failure, lithium-ion innovations have meant that UPS systems can diversify into facilitating energy storage, managing peak shaving, and maintaining levels of impedance.
The healthcare industry represents one of the most varied applications for critical power systems. These systems must support intensive care units, diagnostic systems, onsite data centres, life safety systems such as emergency lights, emergency rooms and medical imaging devices. With such an array of demanding applications and design considerations, it is more important than ever to work closely with consultants and facility managers and implement new critical power technologies.
Medical imaging can be one of the most sensitive applications, requiring levels of power at both extremes. Whilst idle, the medical imaging device requires only a small amount of electricity. However, whilst a patient is being scanned, a large amount of electricity is required to power the device for a short amount of time.
It is often the case that the supply of mains power to older hospital infrastructure is too small to support these temporary spikes that advanced medical technology creates, and so alternative sources are required.
By using lithium-ion UPS systems to store energy, more advanced medical technology can be used in existing older hospital buildings. There are a number of benefits to be had by choosing lithium-ion based UPS over the traditional VRLA (valve regulated lead acid) battery. Firstly, by drawing on the battery chemistry’s ability to store large amounts of electricity and the fact that they can be charged/discharged many times in their lifetime a necessary energy storage solution is created to enable peak shaving.
In the energy industry peak shaving refers to the levelling out of peaks in electricity used by energy storage systems. This is most commonly used to take advantage of storing energy during times where electricity from the grid is cheap and using the stored electricity during peak times of the day. However, it also branches into load control whereby the UPS provides shorts burst of additional power above what is available from a mains supply, as and when required.
For example, if the maximum input of a hospital is 100KW, where a lithium-ion UPS is installed, the input supply can be limited to the maximum 100KW and any additional power needed to support the medical imaging device will be drawn from energy stored in the batteries of the UPS system.
In this scenario, the UPS is being used both as an energy storage system and a tertiary supply of power, in line with relevant regulation relating to medical applications and backup power. Power failure or spikes could disrupt the medical imaging process and put patients at risk.
Whilst using a typical VRLA based UPS for this application is possible, a larger quantity of batteries would be required to provide the same amount of storage capability, requiring more space, and making the solution up to 5x heavier.
Secondly, a lithium-ion battery has a higher depth of discharge. This refers to the amount of overall capacity that can be used before recharging the battery, every battery chemistry has a recommended level. A VRLA battery should not be discharged past 50%, whereas a lithium-ion can handle a depth of 80% or more. This means that when using the UPS as an energy storage device, more energy can be utilised before charging is required and fewer batteries are necessary to achieve the same output power.
In addition to this, the charge rate of lithium-ion is faster than that of VRLA. Lead acid batteries are limited in how much charge current they can handle, mainly because they would overheat, whereas lithium-ion can handle a higher amperage from the charger. In some cases, the batteries can charge up to 2x more quickly, making them the ideal battery for applications that require constant use.
Another benefit to healthcare applications is the number of cycles (number of times a battery can be charged and discharged before the battery starts to degrade) a lithium-ion battery can cope with. Where a VRLA battery handles on average 300 cycles, a lithium-ion battery handles 5000, 10x the amount. This is critical for an application that requires many charges and discharges for example, a UPS being used for energy storage to power a medical imaging device in regular use.
It is not only the energy storage capabilities of lithium-ion that make them an ideal choice for powering sensitive applications. With a longer design life, the technology also improves the reliability, efficiency and flexibility of the facility’s overall backup power infrastructure. The HTM 06-01 recommends that batteries used for tertiary power supplies, such as those for a UPS, should have a design life of 10 years. Whilst specialist VRLA batteries do meet these guidelines, a standard lithium-ion battery has an average lifespan of 15 years, with no battery replacement necessary.
Until recently, lead acid batteries (VRLA) have been the go-to battery technology for providing stored energy for UPS applications. The high prices and lack of knowledge meant the superior lithium-ion chemistries seemed out of reach for the budget constrained healthcare sector. However, with demand going up and prices coming down, the availability of lithium-ion based UPS systems is on the rise and have become a viable alternative source of stored energy.
Power Control specialise in providing the right UPS solution for the healthcare market and has done so for nearly 30 years. Every UPS system, both static and modular, suitable for healthcare applications are available with either VRLA or lithium-ion batteries and meet all relevant medical regulations including the IEC 60601, HTM 06-01, BS 7671 and BS 6290-4. Contact us to find out more, 01246 431 431, [email protected]
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Building Resilience into Healthcare Facilities
Electrical demand in the healthcare sector is typically growing at a rate of between 3% and 6% year on year. With the continued developments in the world of technology and innovation it’s easy to see why. Electricity powers the equipment that keeps our families healthy; helping to diagnose and cure conditions, find new forms of treatment, or when required to provide the medical intervention that keeps us alive. It supports the administrative and communications network, connecting devices and applications, cloud-based systems etc, fuels heating, lighting, security systems …. the list goes on.
The sustained growth in demand highlights just how much we continue to rely on this particular power source. Yet it is more than purely the energy that we need. To support the growing requirement, we also need a robust electrical infrastructure - one that is capable of supporting the increasing forms of technology and innovation whilst still being able to meet the rising demands and expectations of patients.
Unfortunately, the UK’s hospitals and healthcare facilities are not immune to power issues, such as supply failures and anomalies. Nor are they exempt from power disturbances within the electrical distribution system. It is a concerning statistic that 80% of power quality issues actually originate onsite, largely from the electrical equipment itself, with only the other 20% arising through the energy provider.
These issues normally arise due to a distortion of electrical signal, the components within the equipment having loads which are non-linear current and voltage changes, such as variable speed drives or semiconductor technology. They will manifest as flickering lights, network communication issues, loss of data, humming transformers, tripping circuit breakers or in some instances, the unexpected shutdown of equipment.
The resulting disruption to services can cause extensive problems to the daily operation of departments. Add to this the risk of potential cyber-attacks, data breaches and malfunction of critical equipment, that can be caused through external power anomalies and outages, and the need for additional levels of resilience in the electrical infrastructure becomes very evident.
With the correct power protection strategy in place however, it is possible to overcome these areas of weakness to create a robust and reliable electrical infrastructure capable of protecting staff, patients, the general public and facility alike.
Power Quality Issues within Healthcare Facilities
Harmonics are the result of nonlinear loads that convert AC line voltage to DC. Due to the larger electrical current that is being drawn, they will often cause electrical systems to overheat, increasing the potential risk of fire, whilst also affecting the lifetime of the equipment the load is supplying.
Within a hospital setting, harmonics can usually be traced to active electrical equipment that contains variable speed drives and/or semiconductor technology; such as X-ray machines or MRI scanners.
The installation of power quality correction units will help to take care of many internal electrical disturbance issues however additional harmonic resilience can also be provided through a UPS.
Whilst it is accepted the UPS solution will typically add harmonics to the wider system, it will protect specific loads from excessive harmonics. The small filters on the input and output of the UPS can be used to create a virtual neutral allowing common-mode harmonics to pass through to the inverter, which are then cancelled by the inverter’s output.
The UPS’s primary function however, is obviously to provide a ‘no-break’ instantaneous supply of electricity that will safeguard vital equipment and applications throughout the healthcare facility. In areas where this is critical to patient care or safety, additional levels of resilience can also be built in through the design and configuration of the UPS system.
Building resilience through UPS system configuration
The selection of any particular UPS configuration for the emergency protection of final outlets, circuits and equipment will be dependent on the specific factors of each individual design. This should be based on a risk analysis to determine the appropriate level of resilience required.
According to the Health Technical Memorandum, HTM 06-01, a UPS system should be to, but not limited to, the following design and manufacturing standards:
- BS EN 620040-1
- BS EN 60146-1-1
- BS EN 61439-6
- The Energy Networks Association’s G5/4-1
UPS system ratings range from 250 VA up to several hundred kVA; the smaller units may be single-phase units used to support a single circuit, with the larger UPS systems either single-phase or three-phase capable of supporting an entire department.
A central UPS system may be considered where the need covers several smaller areas however designers should be aware that providing a central UPS system may increase the risk of single points of failure that will then ultimately affect a larger area or potentially more departments. Risks for consideration include the routing, location and segregation of UPS distribution cabling and switchboard configuration designed to avoid a single fire or fault affecting the whole system.
There are several recognised UPS system configurations; all of which will depend on the application they are supporting. Any design must be able to demonstrate that it is the optimum solution to maintain both patient safety and the associated systems, where loss of power will have an effect on normal operation of the healthcare facility.
UPS Arrangements – What’s the Difference Between Parallel Capacity (N) and Parallel Redundancy (N+1)
Parallel Capacity (N)
UPS units that are operating in parallel capacity (N) refers to where the total load demand is met by a number of UPS units. In this configuration there is no provision for redundancy (ie spare capacity). As a result, this design will not increase system resilience.
Carrying out maintenance on a parallel capacity UPS installation will therefore mean bypassing the entire UPS system, so that one or more modules can be powered down for service. At this point the load will be left unprotected as it is then powered directly by the mains supply, leaving it vulnerable to power anomalies or complete outages.
Dual UPS (N+N)
An N+N UPS configuration allows for redundancy due to the ‘two of everything’ approach and should be considered for medical locations in Group 2 or where support systems are considered high risk.
Each UPS will be rated for 50% of the load required through two systems. For greater resilience each UPS may be rated at 100% load with interleaved auto changeover provided to support the full load to all medical IT requirements in the event of total power failure.
Parallel Redundancy (N+1)
Introducing redundancy into the power supply, where two or more UPS units are capable of powering the load, provides a further level of resilience. This is often expressed through the term N+1.
The Health Technical Memorandum (HTM) considers N+1 to mean the normal total requirement plus one resilient unit, each individual unit being able to fully support the load. Under normal operating conditions each of the UPS will share the load equally. Should a power failure occur, both units will instantaneously switch to battery mode and the load continue to be shared. If either of the UPS fails it will automatically disconnect from the output AC busbar leaving the remaining unit to fully power the load.
For example, where the electrical demand is 600 kVA, two UPS systems at 600 kVA carrying 50% of the load would satisfy the N+1 definition.
The configuration is often used to protect critical or sensitive equipment or applications as it creates a level of fault tolerance that cannot be achieved otherwise. In the event that one of the UPS units fail, the additional unit (or units) will seamlessly take over the full operation of supplying power to the critical load, ensuring that devices remain functioning regardless of the circumstances. The solution is suitable for supporting inter-process communications and information technology areas. It can also be used in areas where space is at a premium or conversely, where further growth is possible.
The N+1 configuration enables UPS maintenance and servicing to be conducted without any interruption to the load, one module being allowed to power down whilst the remaining unit continues to support the load.
N+2 Redundancy would refer to the next level up, where the system functionality would have two separate backups. This further increases the redundancy of the system, providing an additional level of resilience for users due to the configuration of having two separate backups. Should one of the backups become corrupted, there are still two further units to guarantee supply to the load.
If you are looking to build additional levels of power resilience to safeguard your healthcare facility, it is crucial you seek the advice of a specialist UPS provider.
Power Control has nearly three decades of experience working in the healthcare sector and maintains UPS systems for a plethora of NHS and private healthcare sites across the country. The UK’s largest privately owned and independent UPS and power protection specialist, the company has an extensive portfolio of systems to suit a wide range of needs. For more information, please visit powercontrol.co.uk, email [email protected] or call the office on 01246 431431.
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Blackouts and fuel rationing to start in December, is your business prepared?
On the 29th of May 2022, the government released a stark outlook for the winter after officials drew up a ‘reasonable’ worst-case scenario following the knock-on effects as the energy crisis continues in the UK. riven by geopolitical tensions and the ‘perfect storm’ of market forces, this statement has exposed the fragility of the current state of fuel supplies and the significant impacts it will have on businesses across all sectors.
The ‘worst-case’ scenario outlines what will happen if Norwegian imports of gas are limited to more than half and if there is no support from interconnectors such as Belgium and the Netherlands as they face their own supply crisis and if Russia cuts off gas entirely to the EU.
‘Businesses and residential properties could all see energy blackouts starting from December and lasting for three months with blackouts both on weekdays and weekends.’1 The government would be forced to in effect ration electricity, suggesting it would be turned off on weekdays at peak times in the morning between 7 am and 10 am, and in the evenings between 4 pm and 9 pm.
To add to the already dismal outlook, at the time of writing this blog post, the wholesale price of natural gas is escalating drastically. It stands between 400% - 800% higher than this time last year and places an additional strain on businesses across the country. Sectors such as data centres, manufacturing and facilities are already feeling the pinch with reports that the NHS could see their energy bills soaring past £1 billion in the next ERIC reports.
With industries facing a double whammy, prices going up and instability of energy supplies, businesses are being urged to scrutinise their existing critical power infrastructure and bolster their backup power strategy for what is likely to be increasingly turbulent times in the very near future.
Preparing your infrastructure for energy supply blackouts
For businesses with mission critical equipment, an uninterruptible power supply (UPS) solution is a vital asset. These systems provide instantaneous power in the event of a mains failure and will keep equipment running either until the mains power is resumed, a generator kicks in or until a safe shutdown procedure has been performed.
Depending on the industry, many facilities and premises will likely already have a critical power infrastructure in place with some level of power resilience either through an uninterruptible power supply (UPS), central power supply (CPSS), diesel generator or a combination of the three. Whilst this may tick a box, it is important to ensure they are still in good working order and will support the electrical load during a mains blackout. The following things should be considered:
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How old are the existing UPS?
The first thing to check is the age of the existing UPS and whether the backup power system/s has had regular maintenance intervals over its life. A UPS has a typical lifespan of 10-14 years, after which the internal parts may start to degrade rendering the UPS unfit for purpose. Those without a full-service history may incur problems and be unreliable earlier in their lifespan. If a UPS older than this is installed, it may be time to request a site survey and look at a new UPS solution.
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Is the UPS still sized correctly?
what happens if the business has expanded since installing a UPS causing the new load to exceed the capacity of the UPS? If this happens, the UPS will flag up a warning that it is overloaded.
How the UPS reacts to the overload depends on how much it is overloaded by. Many UPS can operate at up to 125% overload for 10minutes, 125%-150% for 30 seconds and around 150% for 100 milliseconds. Over these overload figures, the UPS is likely to go to static bypass (so the load still will not be dropped), meaning the UPS will be supported by raw mains until the load drops to within the capacity of the UPS. If the overload condition continues, some UPS models automatically shut down.
An efficiency audit will asses whether the existing UPS is sized to correctly support the current infrastructure and take into account any future plans of expansion.
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Has the environment around the UPS changed?
Like other electrical equipment, the UPS and batteries must be installed and kept in an environment that is conducive to the manufacturer's guidelines. Typically, this should be in a climate controlled room with the temperature kept between 0 – 25C, no moisture and free from dust or abrasive materials. Failure to do so is likely to affect the internal components of the UPS and impact the battery performance.
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Prevention is better than cure (preventative maintenance)
With businesses becoming more reliant on their power supplies, a power failure is an unmitigated disaster. A preventative UPS maintenance programme ensures maintenance is carried out at regular intervals and will include a full inspection of UPS components, identifying risks before they affect the health of a UPS.
It is recommended that all consumable parts such as capacitors, fans, batteries, etc are replaced once during the life span of the UPS.
All of these considerations are key to ensuring the UPS and backup power infrastructure is working at its optimum and will support the critical architecture during a mains failure. The energy crisis is one that remains at the top of the government's agenda and with no end in sight for the near future, it is important to have peace of mind that the backup power infrastructure will work when needed.
Power Control has nearly three decades of experience in the critical power industry and operates across a plethora of sectors. Our UPS manufacturing partners provide up to the minute training on their UPS systems and our engineers are trained across multivendor systems.
For more information please visit www.powercontrol.co.uk, email [email protected] or call the office on 01246 431431
Alternatively please visit https://powercontrol.co.uk/product-category/ups-systems/ for specific product information or email Power Control’s solutions director direct [email protected]
1. https://www.thetimes.co.uk/article/millions-warned-of-power-cuts-this-winter-b7gl2ckx9
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Understanding the HTM: Section 11.4 UPS Batteries
Understanding the HTM: Section 11.4 UPS Batteries