MV electrical supply gets hospital pass

Reliable, secure and flexible electrical supplies are critical to healthcare. As hospitals continuously increase in size it is important to minimise low-voltage distribution losses. Thus, the trend is to run the 10kV supply deeper into the building.

The Dutch installation consortium ICI (Installatie Combinatie Isala) selected a design that uses two 10kV ring circuits and allows the supply to come from either mains or emergency power generators as required. One ring circuit supplies the preferential power supply system, and the other the non-preferential one, with any power outages in the preferential system being absorbed by emergency power generators.

The advantage of using open ring circuits is that faulty sections can be isolated, allowing other sections to remain functional and bottlenecks or Single Points of Failure (SPOF) to be eliminated. The two incoming 10 kV cables are also set a distance apart to avoid potential problems from excavation work.

At the heart of the installation is Eaton’s Power Xpert FMX switchgear panel, an IEC single busbar, and solid- and air-insulated (SF6-free) MV switchgear for voltages up to 24 kV. The FMX units are set up to provide a non-preferential and a preferential part for each room and are connected using a specially made wall bushing with a coupling at the centre.

Vacuum technology

"We chose the FMX because of its innovative vacuum technology which allows for frequent and high levels of switching," explains Gert Jan van Tolij, specialist engineer from ICI. "Even more important was the high power level it offers and the extremely compact design with slim panels.”

In case of a power outage, four emergency power generators are available to supply 1MVA each to the preferential busbar of the Power Xpert FMX. These generators are connected with a step-up dry transformer monitored by positive temperature coefficient (PTC) elements with a PTC relay. The design of the installation distinguishes between three levels: the operation of two, three or all four emergency power generators. If a power failure lasts longer than 0.5s, the emergency power generators kick in and emergency power is supplied within 15s. Brief dips of less than 0.5s are picked up at a local level by Uninterruptible Power Supplies (UPSs).

The Central Control Panel (CCP) is the brain of the whole electrical installation. The CCP is part of Eaton’s Power System Automation Services. Redundancy has also been implemented within the control unit, which is equipped with two PLCs that communicate directly with each other and monitor each other’s functions. The PSA comprises a Central Control Unit (CCU) that efficiently manages all necessary steps should a power failure occur anywhere in the system. There are double feeds for the CCU that come from two 110 V DC Eaton units in each of the rooms in the power building. These units ensure that all the control, protection and switching actions are and remain available.

The power distribution system also includes equipment installed on the roof of the building with eight Magnefix Ring Main Units (RMU) and transformers supplied by Eaton have been fitted in a dedicated 10kV room (the Eaton Magnefix switchgear does not require a raised floor, but allows for the cable panels to be reversed and for the supply to feed from the top). The RMUs are set up in pairs in each wing of the building - one unit for the preferential and one for the non-preferential system. The power that is supplied from either the mains or the emergency power system via the Power Xpert FMX to the Magnefix is then transformed from 10kV to 400V.