VFD INSTALLATION IN OLD HOSPITAL

[telasin13]

HELLO
I AM AN OPERATION ENGINEER IN A HOSPITAL IN BRONX NY.THE HOSPITAL IS ABOUT 40 YEARS OLD AND IT'S PRIMARY SERVICE IS 208V 3PHASE 60hz. IT IS SITUATED IN AN INDUSTRIAL AREA WITH FACTORIES AS WELL AS OTHER MEDICAL FACILITIES.ALL OF WHICH SHARE A COMMON POWER GRID WITH US.
ALL OF MY MOTOR CONTROLES AT THIS TIME ARE CONTACTOR TYPE.
IMINANT RENOVATIONS TO MUCH OF OUR MACHANICAL SPACES CALL FOR THE INSTALLATION OF SOME (16) 6 PULSE VFD'S,RANGING IN SIZE FROM 20-60 HP.
IN MY TEN YEARS HERE I HAVE SEEN THE INTRODUCTION OF ALOT OF SENSITIVE ELECTRONICS ,MOSTLY IN OUR OR WINGS.MANY OF THESE DEVICES HAVE SUFFURED PROBLEMS DUE TO POWER QUALITY(AS PER THEIR MANUFACTURERS).UPS AND OTHER TYPES OF LINE FILTERS HAVE BEEN USED TO CORRECT THESE PROBLEMS.
WHAT INFORMATION I HAVE BEEN ABLE TO FIND INDICATES THE 6 PULSE DRIVES HAVE A POTENTIAL TO ADD TO WHAT I BELIEVE TO BE AN HARMONICS PROBLEM IN THE HOSPITAL.
THE VENDERS HAVE DISMISED MY CONCERNS TO THE HIGHER UPS.AND SUBSEQUENTLY MY REQUESTS FOR AN HARMONICS STUDY PRIOR TO THE VFD INSTALLATIONS.
IF IM SPINNING MY WHEELS ABOUT NOTHING FEEL FREE TO TELL ME SO. NOT LOOKING FOR ANYONE TO DUE MY WORK FOR ME ,JUST GIVE ME A PIONT IN THE RIGHT DIRECTION. THOUGH I HAVE BEEN AN ELECTRICIAN FOR OVER 18 YEARS IM FEELING A LITTLE OVER MY HEAD ON THIS ONE.
THANKS IN ADVANCE TO ALL

 

[DanDel]

Typically, 6 pulse drives will introduce 5th amd 7th harmonics into the system. Some newer drive manufacturers may have some harmonic canceling or filtering circuitry already 'inside the box'.
The only way to determine if there will be a problem is to either perform a study or install the drives and do some harmonic surveying.
The first step in a study will be to request the harmonic operating signature from the drive manufacturer, anyway, so you may be able to see what the typical output would look like and get an idea how it would affect your system.

 

[jraef]

I think your concerns are valid, and vendors who dismiss them out-of-hand like that should, in my opinion, be disqualified. Harmonics are ALWAYS a concern with VFDs, even 12 pulse or 18 pulse. How much of a concern is the operative difference, but certainly the issue should never be ignored, especially in a hospital for crying out load! If I am hooked up to a machine that is keeping me alive, I would not want a VFD running next to it!

That said, if you have already solved ALL of your power quality problems with UPS systems and power conditioners, it may be true that the VFD harmonics effects will not get through to the places where they would have life-safety consequences. However I agree with DanDel, your "higher ups" should commission a study at the very least).

"Venditori de oleum-vipera non vigere excordis populi"

 

[hbendillo]

How much renovation has been done to the hospital in the past 40 years and how recent? Harmonics were a big problem back in the 80's primarily because the power supplies for computers and other electronic equipment were not nearly as well made as today and produced undesireable harmonics. Other culprits were electronic ballasts for lighting fixtures and of course VFD's. Today, manufacturer's have greatly reduced the amount of harmonic content in these devices. I have done a lot of work in hospitals and we have had no problems adding VFD's. Does this mean you are guaranteed no problems? Certainly not. But I would attack the problem by looking at critical equipment installations such as operating rooms, CT Scan Rooms, etc., and make sure power conditioning is built into the feeders and circuits for sensitive equipment. Also, consider replacing older electronic based equipment with new equipment.

 

[jrhaus]

VFD's are a major source of harmonics. IEEE 519 requires that harmonics be limited to 5% at the point of common coupling (ie. the service entrance). Recently my firm has insisted that a harmonic study be performed or a harmonic mitgation, passive filter be installed to limit harmonics to 5% at the drive input. We do a lot of healthcare work and we also require filtering at the input of UPS's and power conditioners.

 

[alehman]

I agree with the previous posts. Better quality drives have improved over the years, but can still cause problems. For six-pulse, harmonic filters may be advisable but study is needed. At the very least I would want to make some pre-installation harmonic measurements for comparison purposes. You can put a performance clause in the specification to make the contractor or supplier responsible for assuring the line harmonic distortion is limited.

If the equipment being applied on the VFD's is critical in nature, your engineer should carefully evaluate those motors. Many old motors have failed quickly when connected to a new drives. New motors should be specified for VFD application. Motor lead length should be limited per the drive mfg's recommendation.