Case Study 2

Hospital’s MRI & CT Imaging Systems & Patient Flow Interrupted by Voltage Transients Caused by Malfunctioning Switching Cubicle on the Utility Power Distribution System

A hospital in the South started experiencing malfunctions & failures of their magnetic resonance imaging (MRI) & computed tomography (CT) modalities. These problems caused patients to miss their imaging appointments. This included in-patients to miss their appointments as well as emergency room (ER) patients. Because both sets of patients missed their appointments, their care was delayed.

MRI & CT machines are very sensitive electronic systems. They are sensitive to certain changes (i.e., electrical disturbances) in the AC input voltage that powers them, vibrations in the imaging suite & changes in the electromagnetic environment (i.e., electrical & magnetic fields) among other influences.  These machines use 1,000’s of digital electronic systems for capturing & processing images. They also used dynamic electrical current (i.e., large changes in current when images are being taken).

Interruptions in patients schedules & care was not only a major problem for the patients, but it also created a financial impact on the operation of the imaging center & hospital. The average cost of an MRI is $3,500 per patient, and the average cost of a CT scan is $5,000. This problem occurred for over six weeks before PBE Engineers were contacted. Moreover, this problem caused the medical staff to have to schedule imaging services for these patients at a hospital down the street. This was a severe inconvenience for these patients.

The account manager from the local power company contacted PBE Engineers to find some expert professional help for their hospital customer. When PBE Engineers was contacted, a power quality engineer from PBE visited the hospital to discuss the problems with the hospital’s electrician, the director of the imaging center & one of the hospital’s biomedical engineers. The PBE engineer provided some background on their professional services & explained to the hospital that PBE has over 25 years of experience in helping hospitals & imaging centers resolve electrical problems with imaging systems.

PBE learned more about the MRI & CT problems during this visit. The account manager at the utility company turned the job over to PBE Engineers. During the meeting, the imaging director requested that PBE prepare a proposal to determine the cause of the problems & how to resolve & prevent them. PBE prepared a proposal describing the professional power quality engineering services proposed for the hospital.

After PBE received notification to proceed with the work, PBE prepared for the power quality evaluation & traveled to the hospital. Once the PBE engineer arrived at the hospital, a power quality monitor was installed at the main switchgear that delivered power to the power distribution panel in the imaging suite. A second monitor was installed on this panel. The purpose of the monitors was to characterize the power quality at the switchgear (where the power came into the hospital from the utility service transformer) & at the panel that delivered the power to the MRI & CT machines. Both monitors were connected to the local cellular network, so the PBE engineer could access the monitors (securely) to begin reviewing the monitoring data.

After the monitors were installed, the PBE engineer conducted a thorough electrical system evaluation starting at the switchgear & continuing to the panel that powered the imaging systems. PBE uncovered some problems in the switchgear as well as in the panel powering the imaging systems. PBE documented these problems in detail, so they could be presented & discussed with the hospital’s electrician & the imaging suite director. PBE specified the monitoring period to be one month to help ensure common everyday electrical disturbances were captured. PBE asked the imaging suite director to keep a detailed log of when the imaging systems malfunctioned & failed.

Once the evaluation was complete, the PBE engineer conducted a detailed analysis of the data retrieved from both monitors. PBE determined that some voltage transients were occurring at the main switchgear & at the panel powering the imaging systems. The transients occurred randomly sometimes once a week & at other times twice a week. PBE’s expert analysis of the monitoring data revealed that the transients were related to some type of switching activities. The PBE engineer’s evaluation of the BES in the hospital documented all types of switching activities occurring on the BES. This included evaluating the automatic transfer switches (ATSs) that were part of the hospital’s emergency power system as well as the use of certain contactors used to control some of the HVAC motors & other electrical loads in the hospital. PBE also documented the type, location & use of several variable frequency drives (VFDs). (VFDs can sometimes cause voltage transients that can be reflected onto the circuits upstream of the loads they were specified to control.)

PBE determined that the ATSs in the hospital as well as the operation of certain VFDs were not causing the voltage transients to occur. Further evaluation of the situation by PBE determined that the transients might be generated when the utility’s automatic switching cubicle operated to switch the hospital from one utility feeder to another. Most hospitals are fed by at least two feeders derived from different utility substations. This approach typically increases the reliability of the distribution circuits powering the hospital. After further data analysis by PBE & discussing the analyzed data with the utility account manager & one of their distribution engineers, PBE determined that the transients were likely caused by operation of a medium voltage switching cubicle that switched between utility feeders coming into the hospital from the local utility’s substation.

After meeting with the utility account manager & distribution engineer for the area where the hospital is located, a decision was made to evaluate the switching cubicle to determine its working order & if it was operating normally or had some type of electrical or mechanical problem. Upon visiting the cubicle, the team evaluated the condition & operation of the cubicle. The team determined that arcing had been occurring inside the cubicle. Also, the team determined that the cubicle was experiencing some intermittent switching when the quality of the voltage on both feeders was within the utility’s specifications.

At this point, the PBE engineer decided to install a third monitor inside the switching cubicle to characterize the quality of the voltage & current on the primary feeder to the cubicle & one of the circuits from the cubicle that was powering the hospital.

After conducting monitoring for about two weeks, the PBE determined that the cubicle was indeed malfunctioning, causing voltage transients to occur at random. The PBE engineer & the utility team met again to discuss the data analysis & identify next steps.

To expedite the process, PBE recommended that the utility company proceed to replace the cubicle as soon as possible. Because this situation was urgent in that the imaging systems were continuing to experience malfunctions & failure, the utility company decided to replace the control module inside the cubicle as well as recondition & clean the exposed bus bars inside the cubicle.

Once the control module was replaced & the bus bars thoroughly cleaned & insulated, the monitors at the cubicle & large panel powering were left in place another two weeks after the control module was replaced & bus bars cleaned & insulated.

Once the repairs were made to the switching cubicle, the PBE engineer analyzed the additional monitoring data. The voltage transients that caused the imaging system problems were no longer occurring.

Because these disturbances caused so much interruption of patient flow & financial impact to the hospital, the hospital decided to enter into a second agreement with PBE to install a permanent monitor at the main switchgear & one at the power distribution panel powering the imaging systems.

The imaging suite director reported no additional problems with the imaging systems after 30 days had passed after the cubicle was repaired. The utility account executive & the hospital’s electrician & imaging suite director were happy with PBE’s results. Regular patient flow in the imaging department returned to normal.