By Rob Morris, UK Country Manager, POWERVAR Ltd
Electrical power is an enormous power for good in today’s health environment. It is behind so many of the wonders of modern medical technology, in fact life without it is unimaginable.
While it is true that almost every piece of clinical equipment depends on electricity for life, there is a hidden and dangerous downside – invisible side effects that can damage costly and life preserving equipment – an effect that is frequently ignored. Power problems often have a cumulative detrimental, sometime disastrous impact, and at the very least can shorten the life of vital systems leading to sudden failure and the high cost of repair or replacement.
Our society is so used to depending on the electrical infrastructure it is hard to believe that it is often not only inadequate to provide the quality and consistency of power that sophisticated and sensitive equipment demands, it can actually be damaging it.
While, on the face it, the conventional power supply is remarkably reliable – often available for 99.99% of the time – when power failure occurs it happens at the worst possible time. Healthcare institutions often take care to provide for those rare but crucial occasions when the mains supply is lost. They are less aware of the fact that even when it is available this power carries a great many impurities that may cause sudden damage to equipment and, even if they do not, are causing hidden wear that will ultimately result in the failure of critical components.
These problems with electricity quality can have many sources. Some may be to do with the utility providing the supply and take the form of brownouts and outages etc; others may be closer to home in the healthcare establishment such as overloaded transformers, circuits, blown circuit breakers, and other electrical loads that create disruptive electrical noise, surges, and voltage spikes.
The effects of these problems may not always be immediately visible. Often a vital piece of equipment fails without any obvious cause.
Healthcare establishments and clinical laboratories must take their own steps to ensure that the quality of power is adequate. As in healthcare itself the key is preventative action rather than costly reactive responses.
There are many pieces of equipment available which profess to remove or mitigate the effect of impurities in the supply, others that provide continuity of power in an emergency and some that claim to do both. However, in reality the choices are not always as clear cut as suppliers would claim and the performance of all products are by no means always equal.
Many people have the mistaken idea that an uninterruptible power supply (UPS) will automatically protect against these problems. As we shall see later in this article, this is a mistake. Most UPS systems are only designed to provide backup power in case of a failure.
Finding the culprit
Poor power quality may be the culprit in many cases and the reason that problems are escalating can be found in the equipment itself. Modern instrumentation, analysers and medical equipment rely extensively on the latest high performance microprocessor and semiconductor technology. These devices are extremely susceptible to damage from electrical power transients, noise, spikes and other problems on the incoming AC power line.
With so much of this microprocessor-based equipment running on non-isolated switch-mode power supplies, voltage fluctuations have little effect. Instead, electrical noise, voltage transients, common-mode voltages, and neutral-to-ground problems have become increasingly troublesome.
Electrical transients on the power line can actually punch a hole through a sensitive semiconductor substrate, leading to the immediate failure of a critical component, or they can erode microscopic bits of silicon.
Lightning causes the largest transients; if a spike caused by a nearby lightning strike reaches an instrument through the power or communication cable, it can literally fry the system.
Large value transients can also be generated by electric utility transformer switching, motors turning on and off in the building or even the photocopier in another room.
One of the biggest producers of noise on the power line is an uninterruptible power supply (UPS), such as might be protecting a nearby computer. Excessive powerline noise, of this sort, will have an erosive effect on semi-conductor components. The effect is similar to rust in a car – it may not be visible, have no effect on performance until the day it rusts right through and causes an immediate failure. Electrical equipment subjected to constant electric noise will be affected in the same way and, one day, just stop working.
This same erosion can cause sporadic data disturbances, such as incorrect or unrecognisable characters. And as the components get smaller their vulnerability increases.
Changes in computing power have made the equipment more susceptible to common mode problems. Even systems that are free of spikes and transients can experience common mode problems that corrupt data or prevent systems from communicating with each other.
The problem for medical and clinical applications is that the more sophisticated the technology, the more susceptible it is to power problems.
The cure for common-mode voltage problems
Most sophisticated electronic instrumentation is designed to run only on clean, transient-free, stable, and isolated voltage. Power plagued by electrical noise or branch electrical circuits with high levels of neutral to ground (common-mode voltage) can cause problems such as system lockups, incorrect or unreliable test results, communications errors and no trouble found service calls.
Of all problems, neutral to ground (common mode) noise is particularly troublesome because it is so easily disruptive to microprocessor function but as easily difficult to identify. Fortunately, it is very easy to mitigate with an isolation transformer, which eliminates all neutral to ground voltages and establishes a true zero volt logic reference on the safety ground. Isolation transformers are used in all power conditioners and some UPS systems.
Total protection – or not
A typical building will experience over 6,000 power disturbances a year but only 3-5% of these will be brownouts or power failures. The rest are sags, surges, transients, spikes, lightning strikes, common and normal mode voltage events, and low voltage impulses. All these can be more damaging than a power loss, often resulting in disruption and long term degradation, especially if equipment is not properly protected.
Paradoxically, laboratories, clinics and other institutions invest large amounts in money to reap the rewards of increasingly sophisticated electronic instruments and analysers but very few take steps to protect valuable equipment from damage, eliminate the source of long term erosion or eradicate common-mode voltages for more accurate data acquisition and communications.
The UPSs and downs of total protection
UPS’s are designed to provide backup power and it is important to be clear about what they can and cannot do to protect sensitive equipment. In an online UPS, AC power is constantly converted from AC to DC and back to AC, which ensures that output voltage is well regulated in terms of both frequency and voltage and that the voltage output is free of normal mode (phase to neutral) transients. However, only an online UPS with an isolation transformer will provide the kind of comprehensive protection that most people believe that all UPS systems provide.
Complete power protection includes the following six elements:
- Surge diverter
- Isolation transformer.
- Power line filter.
- Voltage regulator.
- Battery backup/UPS.
- Frequency regulator.
. This device protects equipment from spikes or transients in excess of 250V. These surges are caused by lightning, switching of heavy loads on power lines, or the turning on and off loads within a facility, such as air conditioning, lifts, switch mode power supplies and AC motors.
This protects against common mode noise voltage. It blocks disturbances by establishing the vital connection between neutral and ground, ensuring that there is no voltage disturbance at the output of the isolation transformer.
This attenuates low voltage impulses, providing a high degree of normal mode protection. It ensures that no disturbing voltages appear between hot and neutral at the output. A power line filter is the one piece of equipment that is missing from most power protection systems.
This adjusts voltage to meet the precise needs of electronic equipment. While most computers, with switch-mode power supplies, do not need voltage regulation, some instruments and analysers with linear power may need voltage regulation. If so, a tapswitching rather than ferroresonant regulator should be used to prevent new transients.
This equipment is specifically designed to provide continuing power in case of a power failure or brownout.
Typically found in an online UPS, this device provides constant power by regenerating the AC waveform from a DC device.
Different devices provide different degrees of protection. A power strip surge suppressor will not provide the common mode protection of an isolation transformer. These devices are designed to provide protection only against catastrophic voltage transients. Most are low cost devices that do not last long and often wear out in a few months. This is because they experience the same wear and tear as other electronic components. More expensive surge devices are not necessarily better performers.
A UPS, even an expensive one, may only provide protection outlined in 1 and 5 above. If it has an isolation transformer it will also cover 2, while a high end online UPS will cover all the bases.
It also needs to be remembered that the batteries in a UPS wear out and can need replacing ever three years and, as mentioned earlier, if protecting a computer can generate a considerable amount of electrical noise which in turn may affect nearby instrumentation.
Power conditioners offer 1,2 and 3 protection and if backup protection is not needed then a power conditioner could be a better, more cost effective solution than a UPS.
Powervar Article
Not all systems require every base to be covered. The key is to know exactly where the issues are and how to design solutions for each individual installation.
Ultimately the challenge for all is to avoid costly disruptions and failures that can delay or prevent a facility from going about its business. Power protection systems can deliver real return on investment once engineers understand what the issues are and can recognise some of the hidden negative effects that come from not protecting their systems effectively.