Clinics and hospitals use a variety of highly sensitive medical equipment for diagnosis or patient monitoring. Some of these medical devices provide important information, for example for planned operations, or help to provide the patient with the best possible treatment. Many of these medical devices are costly to manufacture, purchase and maintain, and often place high demands on the quality of the voltage and power supply. This is what happened with a state-of-the-art medical equipment purchased by a hospital for radiation treatment, which frequently experienced uncontrolled shutdowns, forcing treatment to be interrupted.
Voltage dip (reduction of the effective value)
Transient voltage change (dip)
The medical equipment purchased for radiation treatment was relatively sensitive to electrical grid fluctuations. According to the manufacturer’s specifications, only minor deviations in the mains voltage to be supplied were permitted, “only” +/- 5% from the formal nominal value (UN = 400 V).
To ensure trouble-free operation of the medical equipment, a system was sought that would respond quickly and effectively to power fluctuations, provide continuous availability, with low power loss, and have low maintenance requirements.
The customer’s requirements were met in full. A system was installed to ensure safe and trouble-free operation, consisting of an OSKαR® dynamic line voltage regulator and a passive high-pass filter (HP). The combination of dynamic line voltage regulator OSKαR® and passive high-pass filter (HP) significantly counteracts both “slow” rms voltage changes (lowering of amplitude) and transient (short-time) voltage events (dips/peaks). OSKαR® is a three-phase active line voltage regulator for highly dynamic correction of symmetrical and unbalanced voltage dips and/or phase unbalances in the electrical power supply. Voltage dips of up to 30 %, e.g. caused by faults in the power supply network, or by large load switching, are completely corrected by the use of OSKαR®.
The installed HP filter is a passive, voltage-guided filter system, which has a reciprocal impedance characteristic – which means that the filter impedance becomes steadily lower with increasing frequency (order) (“1/n” characteristic). This makes it possible to selectively influence the complex network impedance (higher-level network, feed-in transformers, cables, etc.) with the aid of the filter over a broad band (especially in the higher frequency range) and to effectively combat any harmonic voltage levels (disturbance variables) that may be present over a wide frequency range.
RMS voltage curve at the input (mains side) and at the output (load side) of OSKαR®:
Impedance-frequency characteristic (“I-F-C” curve) of the resulting
Impedance of the hospital network:
(the mains impedance is shown without and with the HP filter switched on).
Network conditions before the measure was connected:
Network conditions after connection of the measure:
Curve of the voltage before switching on the measure:
Curve of the voltage with the measure switched on: