POWER QUALITY FOR MEDICAL APPLICATIONS A Simplified Approach to Understanding Power Quality Problems and How to Solve Them.

Why is Power So Important? Modern technology is a tool for achieving productivity and profit. It’s designed to run on clean electrical power. Clean power for technology is like clean fuel for cars.

Where Do Power Quality Problems Start? Disturbances can be generated external to a facility. Disturbances can be generated internal to a facility.

External Origins Lightning Grid Switching Power Factor Correction Inductive Load Switching Utility Fault Clearing

What Must The Utility Provide? Constant Voltage All the current needed (breaker limited) Protection for people and traditional loads (lights and motors) through grounding procedures.

Utility Power Profile The shaded area is the RMS 170 volts peak 340 volts p-p 170 volts peak The shaded area is the RMS voltage value that we refer to when we speak of 120 volts.

Nominal Voltage Definition According to ANSI C84.1-1977, “Voltage Ratings For Electric Power Systems and Equipment (60 Hz)”, . . . . . “The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.”

Internal Origins Internal disturbances are typically more numerous and destructive. They are created by all the various electrical loads in your facility. The disturbance sources are also closer to sensitive devices which limits the damping effect of wiring.

Hospital Noise Sources Refrigerators Fluorescent Lights Dimmer Switches Copy Machines Computers Large UPS Systems MRI-CAT Scan Centrifuges Motors Heating Elements Generator Sets

Grounding Ground exists primarily for safety. Safety ground comes from the point in the power distribution where transformer neutral is bonded to ground. This is the only code legal ground in a facility.

Grounding Use of alternate, supplementary, or secondary grounds is a code violation and creates a personnel safety and fire hazard. Such grounding methods may allow significant touch potential to exist on the conductive surfaces of “faulted” equipment.

Grounding Proper grounding is also required to assure consistently high power quality. Supplementary grounding methods create ground loops which allow disturbance currents to flow in unpredictable pathways. Safety ground must be clean. It is the logic reference for the microprocessor.

Patient Safety Issues UL544 (to be replaced in 2005 by UL2601.1) addresses patient safety. The standard for medical and dental equipment. Specifies the allowable amount of leakage current to ground for both patient connected and patient vicinity applications.

Technology’s Evolution In the beginning, society’s information processing needs were simple and could be accomplished with relatively simple electro-mechanical systems.

Evolution (contd.) As information needs increased, more automation of the process became necessary. In 1939, the world’s first electronic computer was invented and built in Ames, Iowa. Atanasoff-Berry Calculator, Courtesy Iowa State University

Evolution (contd.) ENIAC EDVAC UNIVAC Mainframes Super Mini’s LAN’s WAN’s Foreground - 1 meg dram Background - 1500 bit memory drum from first digital computer.

Evolution (contd.) Migration from vacuum tube to integrated circuit was driven by the need to increase speed and reduce physical size. Changing voltage and current requirements precipitated the introduction of switch mode power supplies as a means of further reducing size and cost and increasing power supply efficiency.

Linear Power Supplies Inefficient 60 Hz. front end transformer Large and expensive Provided electrical isolation for the system electronics Narrow regulation range required compliance with tight input voltage specifications.

Switch Mode Power Supplies High current capability Reduced size, weight, and cost PWM circuitry improves efficiency and provides immunity to voltage variations Size reduction accomplished in part by elimination of 60 Hz. transformer. Loss of isolation negatively impacts performance.

Linear vs. SMPS Good Isolation Low Efficiency Poor Isolation Susceptible to Voltage regulation issues Large Heavy Expensive Poor Isolation High Efficiency Immune to Voltage regulation issues Small and Compact Lightweight Inexpensive

GENERIC POWER PROBLEMS Blackouts Brownouts Sags Surges Impulses Frequency Changes Noise Harmonics Power Factor Problems

THE BLACKOUT A total loss of power for an extended period of time. Blackouts are easy to identify for most of us since we find ourselves completely in the dark.

THE BROWNOUT Brownouts are a reduction in overall line voltage that may last for minutes or hours. They often occur when demand exceeds the power company’s generating capacity.

THE SAG Sags occur when line voltage decreases momentarily and then returns to normal. Sags generally last fractions of a second.

Swells Swells occur when the line voltage increases momentarily and then returns to normal. Swells usually last fractions of a second.

IMPULSES (surges) Short Duration High energy Often called spikes, transients, and voltage surges They can be destructive

NOISE Noise is typically described as a low voltage but high frequency event. It can readily couple throughout logic circuits and be misread as legitimate logic signals.

FREQUENCY CHANGES Frequency changes occur on generators, but under some conditions can result from utility operation. They represent cycle to cycle changes from the fundamental 60 or 50 Hz. supply.

HARMONICS Harmonics are of two types: voltage harmonics and current harmonics They occur most often as a result of large numbers of non-linear loads such as computer power supplies, etc. Harmonics are primarily a concern because they cause overheating of transformers and in cases have been known to melt wiring.

POWER FACTOR PROBLEMS Power Factor ( PF) is an expression of the phase angle between voltage and current. In facilities with large numbers of inductive and non-linear loads, the power factor may be very low (.65) The utility company prefers higher PF to make their system more efficient and cost effective. PF penalties may be levied.

FINDING SOLUTIONS Electrical disturbances are nothing more than electrical power in an unusable or undesirable form. All electrical power, both usable and the unusable kind, obeys certain physical laws. These laws were defined by physicists Ohm, Kirchoff, and others.

NON-PHYSICAL LAWS Certain non-physical laws also govern the process of eliminating power disturbances. They are known as Common Sense Laws Together with the physical laws, they form the basis for successfully dealing with a complete range of power problems.

Common Sense Law #1 You Can’t Change the Laws of Physics Solving power problems requires an acceptance of physical laws and how they affect the behavior of power disturbances. To solve a power problem, you must use a device that is capable of affecting the behavior of the power disturbance in the desired way.

Corollary #1 You can’t stop a charging elephant by taking away his credit card !!!!!

COMMON SENSE RULE #2 Solving power problems is a process that requires attention to both results and investment. It is usually not possible to get a lot and spend a little.

Corollary #2 The Result of Poor Planning It’s very easy to spend a lot and end up with nothing !!

COMMON SENSE RULE #3 That which is not done right the first time will almost certainly have to be done again.

Corollary #3 It’s usually far less stressful to do something right than to be screamed at later when someone finds out you did it wrong!!

Effects of Power Problems Destructive disturbances are powerful enough to destroy electronic components.

Effects of Power Problems Degrading electrical disturbances do not cause outright destruction. They damage systems in a way that is invisible. Many times you will not learn of the damage until it is too late.

Effects of Power Problems Disruptive electrical disturbances are low energy events that cause data loss, system lockups, and aborted tests. Disruptive power problems can make systems very user “unfriendly”.

What Devices Are Used To Solve Power Problems What Devices Are Used To Solve Power Problems. How Do I Decide Which Device Is The Appropriate One To Use?

The ABC’s of POWER Conditioning® Input AC Output Surge Low Noise Voltage Battery Frequency Ground Diverter Impedance Filter Regulator Backup Regulator Loop Isolation System Control Transformer A B C D E F G

A - THE SURGE DIVERTER Surge diverters may be metal oxide varistors (MOV’s), silicon avalanche diodes (SAD’s) or gas tubes. These devices have a thresh-hold above which they conduct and limit the rising amplitude of an impulse. They reduce destructive disturbances to degrading and disruptive ones.

SURGE DIVERTERS Good for control of catastrophic events Most will either degrade or be destroyed by repeated exposure to high energy power disturbances. Surge diverters are generally inexpensive, but remember they are only one small part of the power protection plan.

B - THE ISOLATION TRANSFORMER Isolation transformers provide a “code legal” point for bonding electrical system neutral to ground. This N-G bond is the focal point of what FIPS Pub. 94 refers to as a “newly derived power source”. In plain language, isolation transformers eliminate common mode voltage.

ISOLATON TRANSFORMERS (contd.) This capability is a very important one for today’s systems. Modern systems require ultra-quiet ground references to function properly. Noisy ground references are the most common disruptive power problem. Isolation transformers are expensive, so many manufacturers leave them out.

THE ELEGANCE OF A TRANSFORMER In addition to creating a clean ground reference, transformers have an often overlooked benefit. The transformer isolates or electrically separates the system from any other electrical device in the facility. This permits better control of the power flowing to a system.

C - THE POWERLINE FILTER Powerline filters are needed to address the high frequency, low voltage disturbances that may be missed by the surge diverter. These disturbances are often referred to as conducted disturbances, EMI, RFI, etc. Powerline filters address degrading disturbances by diverting them to ground.

FILTER INADEQUACIES This action turns a degrading disturbance into a disruptive one. The electrical characteristics of filters can often interact with the characteristics of electrical wiring producing results that are undesirable as well as unpredictable.

D - THE VOLTAGE REGULATOR Voltage regulators, as their name implies, are designed to maintain voltage levels within specifications. They may take one of several different forms. All voltage regulators maintain voltage levels by controlling the flow of current in a circuit - a possible drawback for SMPS.

VOLTAGE REGULATOR TYPES Dedicated electrical circuits Ferro-resonant isolation transformers (CVT) Tap-switching isolation transformers Tap-switching autoformers Electronic PWM regulators Magnetic synthesizers

D - VOLTAGE REGULATORS Voltage regulators were often used with older generation systems where steady voltage was mandatory. Modern systems with switch mode power supplies are very tolerant of voltage variations. As a result, voltage regulators are generally no longer necessary.

E - THE BATTERY (UPS) The battery or UPS is used to provide continuity of power. UPS systems are the most misunderstood power protection device. They come in a variety of designs.

STANDBY UPS The battery or reserve power section does not activate until after utility power is lost. Transfer from utility to battery occurs in a few thousandths of a second. Most standby UPS systems provide only surge diversion and noise filtration. Isolation is seldom provided.

LINE INTERACTIVE UPS Line interactive UPS systems function similar to standby UPS. Their design includes a voltage regulating transformer that functions to permit a wider operating range without depleting batteries. Most include surge diverters and filters but no isolation transformer.

ON-LINE UPS On-line UPS systems are those in which the inverter is the primary power supply. There is no transfer time involved when utility power is lost. The design provides natural surge diversion and noise filtration, but many on-line systems may still lack an isolation transformer.

HYBRID UPS Numerous hybrid designs also exist. They may provide varying levels of protection depending on the components they include.

E - THE BATTERY (contd.) Inverter design also varies tremendously. Inverter designs include sine wave, modified sine wave, square wave, and modified square wave (the last three often resulting in waves of nausea, waves of despair, and ultimately the opportunity to wave goodbye to your expensive system!)

E - THE BATTERY (contd.) The UPS is the most misunderstood power protection technology available today. Correctly selected, the UPS can provide total and complete power protection. Improperly selected, hundreds or thousands of dollars may be spent for little more protection than that gotten from a surge diverter.

F - THE FREQUENCY REGULATOR In the United States, the frequency of utility power is 60 Hz. In much of the rest of the world it’s 50 Hz. Frequency regulators make certain that utility power stays at the right frequency. This is important for things like motors and transformers.

G – GROUND LOOP CONTROL Ground loops exist anytime components are networked together and powered from separate sources (i.e. branch circuits, panels, transformers, etc.) Differences in the circuit characteristics cause “loop currents” to flow through the interconnecting data cabling, which leads to system disruption

G – GROUND LOOP CONTROL Networked systems in the medical environment are as susceptible to the problems caused by ground loops as any other networked system When used as part of the total protection formula, special power conditioning elements called Ground Guard™ can prevent ground loops from forming. Ground Guard eliminates the requirement for dedicated/isolated electrical wiring

What Solutions Are Appropriate For Today’s Sophisticated Technology?

What Symptoms Are Signs That Our Systems Are Being Affected By Power Quality Problems?

Today every system needs: A - A Surge Diverter B - An Isolation Transformer C - A Powerline Noise Filter These are the minimum requirements. If data, software, or memory contents are volatile a UPS may be required as well.

What About UPS’s? UPS systems may be either standby, line interactive, or on-line. Systems with modern power supplies (SMPS) don’t really care which one you use. UPS Systems should provide a SINEWAVE output from the inverter. UPS Systems MUST INCLUDE a surge diverter, filter, and isolation transformer.

What are the Symptoms? Damaged hardware Erratic operation Halted tests Communication errors Unreliable test data Unexplainable problems Slow system operation Numerous service calls System lockups Damaged or lost data or software Problems that cannot be duplicated

What Are The Costs? Power disturbances account for 14-21% of total service costs. BMI Study LAN’s function properly 94% of the time. The other 6% of the time, they cost corporations an average of $3.48 million in losses per year. Infonectics, Inc. Power problems are the number one cause of computer damage. David Johnson, CEO, Safeware, Inc.

What Can Proper Power Conditioning Provide? Better system performance Fewer communication errors More reliable data Fewer service calls Increased production time Lower cost of ownership Higher revenue generation

Properly specified and installed, power quality solutions will increase productivity, improve patient care, and pay for themselves through reduced operating and maintenance costs.