Stabilising MV Circuit & Enhancing LV Network Performance For A UK Hospital
A UK hospital faced significant challenges due to an unstable Medium Voltage (MV) circuit, further complicated by the integration of a gas turbine in sync with the Low Voltage (LV) network. The instability in the MV circuit not only affected critical hospital operations but also contributed to voltage disturbances, increased negative sequence currents, and nuisance tripping of the gas turbine. Johnson & Phillips was engaged by the hospital, in collaboration with a UK Distribution Network Operator (DNO), to deliver a comprehensive solution aimed at stabilising the MV circuit, supporting the LV network, and ensuring reliable gas turbine operation.
Challenges
- Unstable MV Circuit: The hospital experienced frequent fluctuations in voltage, resulting in operational disruptions and increased maintenance needs.
- Gas Turbine Integration Issues: Syncing the gas turbine with the LV network caused disturbances, leading to negative sequence currents and unreliable performance.
- LV Network Support: The existing LV network lacked sufficient support to handle the added stress from the gas turbine connection, increasing the risk of nuisance tripping.
Solution
Johnson & Phillips approached the problem by performing a thorough power quality analysis and designing a targeted rectification solution. The project involved:
- Design and Assembly of a 1250KVA DYN11 Transformer:
- The team custom-designed a DYN11 11-433V, 1250KVA transformer equipped with a 9-position MR EcoTap On-Load Tap Changer (OLTC). This was pivotal in maintaining stable voltage levels on the MV circuit despite load fluctuations.
- The OLTC allowed for automatic adjustments to the transformer output, minimising voltage variances and ensuring the hospital’s MV supply remained within the desired parameters.
- Accusine Active Filters for Disturbance Mitigation:
- To counteract the disturbances caused by negative sequence currents and harmonic distortions, Johnson & Phillips installed two 300A Accusine Active Filters:
- One filter was placed parallel to the laden LV switchboard to enhance LV network stability.
- The second filter was installed in parallel with the gas turbine alternator, minimising harmonic interference and improving turbine synchronisation.
- Enhanced Reactive and Active Power Support:
- With the newly installed transformer we manufactured along with the active filters, the system was able to provide additional reactive power support. This reduced the overall strain on the network and supported the efficient operation of both the MV and LV systems.
Outcomes
The project’s outcomes yielded significant and lasting benefits for the hospital:
- Stable Voltage Levels: The DYN11 transformer with the MR EcoTap OLTC significantly improved voltage stability on the MV circuit, ensuring reliable power delivery throughout the hospital.
- Reduced Nuisance Tripping: The active filters prevented disturbances from interfering with the gas turbine’s operation, virtually eliminating nuisance tripping events. This led to smoother turbine performance and enhanced operational reliability.
- Cost Savings: By stabilising the power supply and reducing the need for reactive power compensation, the hospital realised considerable cost savings. These savings came from a reduction in maintenance costs, fewer interruptions, and a more efficient power usage profile.
- Enhanced Network Support: The improvements in voltage stability and network support also minimised strain on the hospital’s equipment, prolonging its lifespan and reducing the likelihood of future issues.
Conclusion
Johnson & Phillips’ work with the UK DNO exemplifies a successful implementation of specialised power quality solutions in a critical healthcare environment. By addressing the specific challenges posed by an unstable MV circuit and supporting the LV network in sync with a gas turbine, Johnson & Phillips delivered a solution that significantly improved operational resilience and reduced costs. This project highlights the company’s commitment to delivering customised, high-quality solutions that ensure reliable power for essential facilities like hospitals.
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