Powervar covers power supplies in medical settings

A great deal of critical clinical equipment requires a reliable power supply for its correct operation and hospitals are well aware of the need to provide for those rare but crucial occasions when the mains supply is lost.

They are often less aware of the fact that their regular power supply can carry many impurities that can both damage equipment and cause hidden wear, resulting in the sudden failure of critical components.

Power problems have many sources.

Some relate directly to the utility providing the supply in the form of brownouts and outages; others are closer to home, such as overloaded transformers, circuits, blown circuit breakers and other electrical loads that create disruptive electrical noise, surges and voltage spikes.

The effects are not always immediately visible.

Often a vital piece of equipment can fail without any obvious cause.

There is a common belief that an uninterruptible power supply (UPS) automatically protects against all power quality problems, but most UPS systems are only designed to provide backup power in case of a failure.

Modern medical equipment relies 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.

Since much of this microprocessor-based equipment runs 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.

Lightning causes the largest transients; if a voltage spike caused by a nearby strike reaches an instrument through the power or communication cable, it can literally fry the system.

Large-value transients can also be generated by transformer switching, electric motors or even photocopiers.

One of the biggest sources of power line noise can be the UPS installed to protect a nearby computer.

This type of noise can have an erosive effect on semiconductor components.

The effect is similar to rust in a car - it may not be visible and has no effect on performance until it causes failure.

Electrical equipment subjected to constant electric noise will be similarly affected and eventually just stops working.

Even systems that are free of spikes and transients can experience common-mode problems that corrupt data or prevent systems from communicating with one another.

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.

Neutral to ground noise is particularly troublesome because it is so disruptive to microprocessor function but 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.

A typical building will experience over 6,000 power disturbances a year, but only 3-5 per cent 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.

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 hospitals invest large amounts to reap the rewards of increasingly sophisticated electronic instruments and analysers, but few take steps to protect this crucial equipment from damage or faulty operation caused by a poor-quality power supply.

Not all UPSs are equal UPSs are designed to provide backup power, but it's important to understand 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 frequency and voltage, and is free of normal mode (phase to neutral) transients.

Only an online UPS with an isolation transformer actually provides the comprehensive protection that most people believe that all UPS systems provide.

In designing a complete power-protection solution, it is important to consider several specific elements.

A surge diverter protects equipment from spikes or transients in excess of 250V.

An isolation transformer protects against common mode noise voltage.

The power-line filter attenuates low-voltage impulses and is the one piece of equipment missing from most power-protection systems.

A voltage regulator adjusts voltage to meet the precise needs of electronic equipment.

A battery backup/UPS provides continuous power in case of a power failure or brownout.

Typically found in an online UPS, a frequency regulator provides constant power by regenerating the AC waveform from a DC device.

Different devices provide different degrees of protection.

But not all systems require every base to be covered.

Ultimately, the challenge is to avoid costly disruptions and failures.

Investment in hospital power-protection systems can only deliver a real return when the end user recognises the key issues and understands the often hidden negative effects that come from not protecting systems effectively.