ELECTRICAL SYSTEMS
HV or LV system. In fact, it is not necessarily more resilient, as both supplies may still be lost in the event of a transmission network fault. Another cost- effective solution with equal resilience can be provided by two supplies from
different busbars of the same primary sub- station. The AE can
An example of compliant electrical system signage.
advise on the optimum option. Struggle to upgrade
As demand for electricity continues to increase, many DNOs are struggling to upgrade their networks to meet the increased capacity. As an alternative to a firm supply, DNOs are increasingly offering ‘flexible’ connections, whereby the customer can draw an agreed capacity under normal running of the DNO’s network, but agrees to reduce demand (load shed) under certain conditions. These conditions might include the loss of a DNO grid transformer or an HV cable fault. For these events a signal is sent to the customer, who then has a pre-agreed time to reduce demand to a pre-agreed level. Such Active Network Management (ANM) schemes are still in their infancy, and don’t particularly lend themselves to the requirements of a healthcare institution. A bespoke scheme was successfully installed at a major London hospital which already had in place a shedding strategy. In the event of a loss of normal mains supplies to a hospital, back-up standby generation is installed to be able to supply the site load. Standby generation is generally sized to support the full load. However, where cost and space constraints apply, generation capacity is sometimes reduced to meet the essential load only, i.e., risk category ‘A’ & ‘B’ medical areas.
‘Bridging the gap’
To bridge the gap between mains failure and generation coming online, an Uninterruptible Power Supply (UPS) is installed to support risk category A medical areas. UPS and generator maintenance is an essential requirement, and the AE is required to audit and report on this activity, and on occasion give guidance on the generators’ operation and installation.
Generators should be load tested monthly to ensure that they will be available and capable of supporting the site in the event of the failure of the mains supplies. A question that is often asked of the AE is: ‘How can generators be load tested without causing disruption to the
42 Health Estate Journal January 2022
site?’ This can be achieved by operating standby generation in Short Term Parallel (STP) mode with the ‘mains’ supplies. The generator can be started and
synchronised (voltage and frequency matched) with the healthy mains supply, allowing the generator to take the load of the site and the mains
supply to be disconnected. Thus there is no interruption in the power supply to the site. This test should not be regarded as a replacement for the annual “black start’ test, which is required to test the integrity of an integrated system and the operational knowledge of the Estates and medical staff. STP is limited to a maximum of 60 seconds of parallel operation between the mains and generator supplies. An added advantage to STP is that the site can be returned seamlessly to the mains supply following an outage by reverse synchronising the generator with the mains when it becomes re-available. A word of caution – some DNOs will require the site to call them before synchronisation between generators and mains supplies. Early engagement with the DNO before installing any generation is always advisable.
Operation in parallel
Some healthcare organisations enter a Long-Term Parallel (LTP) agreement with the DNO. This allows their generation to operate in parallel with the mains supplies to the site for extended periods of time. There are several advantages to LTP, including being able to leave the mains supplies connected during generator testing for increased security during the test, being able to export surplus power back to the grid, and participation in incentives such as Short-Term Operating Reserve (STOR), switching to generator supply to avoid paying high tariffs during peak network demand (TRIAD), and Enhanced Frequency Response (EFR). However, the requirements for operating in LTP are far more onerous than those for STP, and must satisfy the requirements of the ENA Engineering Recommendation G99.
By their nature, generation systems such as CHPs and PV operate in LTP. Another common question is ‘Can we use our CHP as an additional standby generator?’ In principle this can be achieved, but generally in practice often causes problems when gas-powered CHPs attempt to synchronise with diesel- powered standby generators. The two types of generation often find it hard to
share the load, which can result in long- term damage to their prime movers. If a CHP is being used to support load in the event of a mains outage, it is best utilised in isolation from diesel-driven standby generators.
UPS service and maintenance Servicing and maintaining UPS systems are essential requirements. However, there is sometimes confusion regarding the requirement for live working. Working on batteries is the only form of live working permitted. A supporting document often missed is the Live Functional testing checklist. The self-certification checklist must be completed by a Competent Person to determine whether live working is required and can be undertaken safely. If completion of the checklist indicates that live working is required, then a Certificate of Authorisation for Live Working form must be issued by the Authorised Person to a suitably competent Person (CP). Note: The Authorising Engineer must be informed when any authorisation is given to live working. Remember, Regulation 14 of the Electricity at Work Regulation (EWR) 1989 stipulates that ‘no work shall be undertaken on or near live conductors’.
Incident investigation
Incident investigation is probably the most interesting part of an Authorising Engineer’s duties. We are regularly called in to investigate issues related to a healthcare facility’s electrical network, which can include anything from electrical incidents such as electric shocks, to electrical flashovers, fires, and inadvertent loss of electrical supply etc. The work of an AE is varied, and it is always interesting to see how healthcare institutions, Government, and private organisations, manage their electrical systems. The AE must be able to quickly understand sometimes complex systems to issue an accurate and meaningful audit report. Finally, it is always very heartening as an AE when it is obvious that a healthcare provider organisation is making great efforts to achieve compliance with the HTMs. Most hospitals now employ dedicated compliance officers to liaise with the AEs and APs to ensure that the requirements of the HTMs are being met. The AE role often extends to investigative work, which demands experience, expertise, ‘eagle eyes’, and an absolute open mind approach, as so often the initial picture does not tell the full story – as recent cases studies reveal.
Incident case study
The AE responsibility extends to more exciting duties, especially in an investigative role where an electrical incident occurs on a central UPS system. In one recent instance, a battery failure occurred on a central UPS system at a
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