Testing medical equipment for immunity at Amphia Hospital
Amphia Hospital is one of the Netherlands’ larger general hospitals, with 550 beds, over 300 medical specialists and 4500 employees. Like all hospitals, Amphia utilizes equipment that must comply with strict requirements. This requires a very high quality of mains power, to ensure safe and reliable operation. After all, interruption, failure, or a shortened life span of critical medical equipment, for example due to poor Power Quality, can pose a risk to patient safety.
Challenge
“We asked HyTEPS to investigate what level of harmonics and voltage dips some of our medical devices are immune to,” states Egon Scheepers, Clinical Physician, Amphia. “We also wanted to know whether the harmonics that devices inject back into the installation (emission) comply with the international IEC 60601 standard for medical devices.”
Amphia wanted to be sure that the Total Harmonic Distortion – THDu – in the installation would be contained. This high distortion can affect all devices connected to the installation. Devices may fail, work improperly, or have a reduced lifespan. Voltage dips were also tested. These can be caused by starting up larger machines, or by short circuits in the installation. Voltage dips that exceed a prescribed ‘safe’ standard can lead to equipment failure.
Purpose
- Simulate Power Quality phenomena
- Understanding Power Quality aspects, such as harmonic distortion and THDu
- Check compliance with IEC 60601 standard for medical equipment
- Advise on implementing a suitable solution
Solution
“To simulate the different PQ phenomena, a programmable 1.5 kVA voltage source was used,” says Mark Kurvers, Student Engineer, HyTEPS. “This can inject any possible type of waveform into the circuit. Voltage dips were tested using the test levels defined in IEC 60601. The harmonic emission was tested by injecting a perfect 230 V, 50 Hz sine wave and then measuring the harmonic current. This was compared to the limits specified in medical standard. Harmonic immunity with respect to hospital pollution was measured by measuring the THDu for a week and then injecting it. The injected THDu contains the actual spectrum of THDu present in the hospital.
Results
In a controlled environment, it was confirmed that certain devices were not immune to a certain THDu level or did not properly meet the medical standard for voltage dips. The THDu level of the equipment confirmed that the relatively high harmonic distortion in the hospital actually causes problems. The hospital is therefore looking into the possibility of also strengthening the grid in terms of Power Quality by installing a third DRUPS – a dynamic UPS with integrated emergency power generator.
“Generally speaking, hospitals are advised to permanently monitor Power Quality in their facilities, which allows any problems to be spotted and investigated at a very early stage,” concludes Mark. For this purpose, a HyTEPS MFED (Multifunctional Energy Device) has been installed at Amphia. This allows continuous monitoring of the status of new equipment, as well as other grid-connected devices. The HyTEPS Power Competence Centre can watch at any time and offer advice if required.
Generally speaking, hospitals are advised to permanently monitor Power Quality in their facilities, which allows any problems to be spotted and investigated at a very early stage.
