Andrew Keith, product development director at power resistor manufacturer Cressall Resistors, explains why load bank testing for hospital generators is a crucial industry requirement.
In August 2019, Ipswich Hospital plunged into darkness after it was hit during a 15-minute UK-wide power outage. The trust revealed that the disruption caused the unit’s circuit breaker to fail, briefly cutting the electrical supply to outpatients and the x-ray department. Luckily, the hospital’s back-up generators took over and prevented risk to both patients and life-saving medical equipment.
The failure of an electrical supply network is disastrous for any industry. But keeping the power on in healthcare facilities can be a matter of life and death. While power backup failure is extremely rare, especially in developed countries, there have been incidents that have resulted in surgeons operating by torchlight and staff having to manually remove fluid from the lungs of intensive care patients. With lives at stake, even one power failure is too many.
Putting a plan in place
Having a standby power supply plan in place is essential. These normally come in the form of batteries, generating-sets or a combination of the two.
A battery-powered uninterruptible power supply can instantaneously take over if the regular power supply fails. There would also normally be a diesel generator that runs for as long as there is a fuel source. Its purpose is to take over as medium-term supply once the battery has managed the immediate problem.
Supplying sufficient fuel for the generator to run for an extended period is the first and most basic requirement. And that’s not all. Maintenance tasks such as visual inspections and regular generator testing are also critical.
It is obviously not acceptable to interrupt the power supply to a hospital once a month to connect the generator and run a test. However, simply turning on the generator occasionally is not sufficient, it must be run under load to ensure it will perform as required in the event of a mains failure. In addition, diesel engines that regularly run on very low loads — or even no load at all — become increasingly unreliable, and effects such as smoky exhausts and carbon build-up further impact their dependability.
Installing a fixed load bank to the backup generator does not only justify a saving in the maintenance cost of the generator’s life, but also greatly improves the likelihood of it running efficiently in the event of a power emergency.
Remember the Memoranda
The Health Technical Memoranda (HTM) gives advice and guidance on the design, installation and operation of specialised building and engineering technology used in the healthcare industry from supply to point of use.
Memoranda HTM06-01 provides guidance for all works on the fixed wiring and integral electrical equipment used for electrical services in healthcare premises. It should be applied to all forms of electrical design work, from greenfield sites to modifying an existing final sub circuit.
Crucially, it also addresses the operational management and maintenance of the electrical service supply and distribution within any healthcare facility.
The memoranda stipulates that all standby generators should be tested every month, for a duration of at least one hour. The generator being tested should operate at greater than 70 per cent full load. Where the backup generators do not have grid synchronisation connection the only way to test the generator is with a load bank.
Additionally, maintenance programmes should include a longer test to establish the generator engine’s mechanical performance as well as a test to prove the generator’s condition up to 110 per cent full load. These tests should be carried out annually for a test period of no less than three hours. The optimal test would be performed at a representative power factor such as 0.8, which requires a load bank with both resistive and reactive sections. This will ensure the generators alternator is tested to full load current.
In a healthcare application, using building loads alone to test a generator is not desirable because the load is uncontrollable, unlike load banks which have precise load steps, making it problematic to sustain the load above the required level for the duration of the test.
However, the biggest mistake is to assume you can sufficiently check a generator by simply turning it on with no load or a low building load. Low loading would not comply with maintenance standards and often can lead to generator ‘wet stacking’ — a condition in which unburned fuel passes into the exhaust system in diesel engine exhaust systems. This low loading impacts the integrity and service life for any generator.
Using load banks for generator testing and maintenance provides certainty when streamlining compliance testing with reliable performance monitoring.
For any standby generator, routine testing that includes on-load running to bring the equipment up to normal working temperatures means a much higher certainty that it will perform as expected during a real power outage. With effective load bank testing in place, healthcare facilities can continue to save lives — minus the torches.