POWER INFRASTRUCTURE


battery systems typically 24volts and the 110volt VT supply should not be used for emergency tripping.


6. Emergency standby generators The hospital emergency standby generator forms the key secondary power source in the increasingly common case of interruptions on the DNO local area network. However, in many cases they either inadvertently start, fail to start and/or fail during a short period of operation. n Key issues: Inadvertent operation or failure to operate for many reasons, such as: a) Lack of solid star point earthing leading to equipment failures during testing/operation.


b) Starter battery failure. c) Failure of fuel lines and/or fuel contamination. d) Failure of phase failure relay and/or incorrect selection-commissioning.


e) Lack of/or Inadequate testing regimes. f) Failure Automatic Transfer Switches (ATYS). g) Inadvertent operation of protective devices. h) Lack of load bank testing points. i) Lack of resilience/redundancy should the generator fail for any reason.


Other issues include incorrect earthing, poor LV switchgear control interface. One of the most common causes of power interruptions is related to malfunction of the conventional reliance on outdated phase-failure relays. Note. This is variable voltage only with no time domain selection. Modern practice includes using digital


generator controllers with graphical HMI, event logging, and BMS integration. n Recommendation: Confirm G99 compliance if operating in long-time operation, ensure correct rating, specify digital (phase failure) controllers with HMI, and test under load conditions. If using traditional phase failure relays, ensure they are voltage/time variable.


7. Automatic Transfer Switches (ATYS) – Key considerations in hospital power resilience


Automatic Transfer Switches (ATYS) are a critical component in virtually all hospital secondary backup systems, enabling seamless transfer between normal and emergency power supplies. However, their reliability is only guaranteed when properly designed, configured, and tested in alignment with site-specific conditions. n Key issues: Factory default settings applied leading to nuisance inadvertent operation – particularly if voltage sensing thresholds set too sensitive.


These parameters must be adjusted to reflect the actual site voltage characteristics, accounting for expected tolerances and the behaviour of the local distribution network. Ultimately, correct ATYS configuration is not a one-size-fits-all approach. It requires coordination with electrical design engineers and commissioning specialists to ensure the system supports safe, reliable, and resilient healthcare operations. n Recommendations: The switch’s timing logic is equally important. Both transfer and retransfer delays must be programmed


January 2026 Health Estate Journal 61


Modern practice includes


using digital generator


controllers with graphical HMI, event logging, and BMS


integration.


with suitable time lags to accommodate voltage sags, transients, or momentary outages. This prevents nuisance switching and ensures system stability during supply restoration. We suggest 3-5 seconds typically.


8. Uninterruptible power supplies (UPS) UPS systems provide critical backup power to Group 2 Medical Areas and key services such as IT, medical records, and security systems. Their reliability directly impacts patient safety and operational continuity. n Key issues: n No Wraparound Bypass: Limits ability to maintain


This waveform capture displays both the voltage & current waveform which indicates a significant presence of 5th & 7th harmonic distortion typically found on electrical systems with significant element of frequency-controlled motors.


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