Power quality - Inadequate protection damages business prospects


Kevin Beavan of PowerVar wonders why, despite the fact computers and other critical electronic systems can easily be damaged or destroyed by power fluctuations, UK businesses often choose ineffective solutions for limited cost savings

Many UK businesses will select surge protectors as their sole defence against power fluctuations without appreciating they can only provide rudimentary protection; without adequate protection there is a high likelihood of costly damage to computers and other sensitive electronic equipment. It is not just the damage to equipment that costs money, the more serious threat is the financial losses that can result from not being able to function normally.
There is one good reason surge protectors remain the prime choice; they are markedly cheaper than an effective solution. The savings in opting just for surge protectors are easily outweighed by the potentially massive costs resulting from any damage in terms of replacing or restoring any damaged components.
Part of the problem is a failure to understand the inherent limitations of the surge protector that make it so poor for protecting sensitive electronic equipment.
Technically even the term surge protector is misleading since it implies the device will protect against all surges. A more accurate term for these devices is surge diverters since they divert high voltage transients or impulses away from the electronic system they are supposed to protect.
surge diverters
Surge diverters work by utilising a threshold voltage, often called the clamping voltage, and may also have a clamping response or delay. When the clamping voltage is exceeded, any transient voltages are shunted to an alternative path and away from the protected equipment. Once the surge voltage drops below the threshold the diverter stops operating and the normal electrical conducting path is restored allowing current through to the equipment. The clamping time simply acts as a delay to the diverter so that relatively short surges are not diverted. Every surge diverter is designed to handle a maximum amount of energy without being destroyed.

Different technologies
To achieve their basic function, surge diverter products are manufactured with a variety of different electronic components including metal oxide varistors (MOVs), silicon avalanche diodes (SADs), and gas tubes. Each of these components functions differently and can affect the surge diverter’s performance. Yet it is rare for suppliers to actually state which technology is used in their surge diverter.
Characteristically MOVs have a high clamping voltage of between 300 and 500 volts and a slow response time. This means that voltage impulses of less than 500 volts will not be diverted and can enter the computer system unimpeded. The slow response time means that very fast, high voltages can pass through the MOV before it responds leading to additional damage. MOVs do have an advantage because they can handle significant amounts of energy yet they physically degrade each time they clamp which adversely affects future performance and ultimately leads to their failure.
To overcome these disadvantages, manufacturers turned to silicon avalanche diodes (SADs) that have a faster response time and improved long term performance compared with MOVs. However, SADs have a much lower energy handling capability and impulses that merely degrade an MOV may destroy a SAD. Surge diverter manufacturers will either use multiple SADs in parallel or use the components in conjunction with MOVs to improve the diverter’s energy handling capability.
The final type of component that can be found in surge diverters is the gas tube. These act like bouncers at a nightclub because they can handle almost unlimited amounts of energy although they are comparatively slow and have a high clamp voltage. This capability means they can protect all other surge diverter components during a catastrophic power disturbance.

Combining components
The limitations of the different component types means that some surge diverter manufacturers include all three technologies in an effort to improve performance by combining their relative strengths. Yet since MOVs and SADs are both electronic components, both are subject to failure from a high-energy impulse whether they are used singly or in combination with one another. The high probability of total failure is the reason why many surge diverters include an indicator light to show that the protective elements are no longer functioning. In most cases, surge diverter components operate ‘naked’ on the power line and it is almost certain that they will eventually fail.

The modern power supply
Another factor that limits the effectiveness of surge diverters as the sole line of defence is the characteristics of the modern power supply. Older generation computers used linear power supplies that required voltage regulation compared with modern systems which are powered by switch mode power supplies (SMPS). While SMPS are immune to voltage regulation problems they do require protection from impulses, power line noise, and, most importantly, common mode (neutral to ground) voltage.
A computer’s microprocessor makes logic decisions with reference to a clean, quiet ground that is destroyed by common mode voltage resulting in lockups, lost data, and unexplained system failures. Common mode voltage is very disruptive to a computer’s operation. Because surge diverters divert disturbing energy to ground they create common mode voltage. Effectively they convert a destructive disturbance into a disruptive one. And since surge diverters still allow substantial energy to pass through to the computer, damage may still occur.
To avoid these problems businesses need to move beyond simple reliance on power diverters and enhance their systems by fitting a power conditioner. A power conditioner is any device that provides all the power protection elements needed by the technology it’s protecting. Although the surge diverter remains a key element in the circuit’s protection for sensitive equipment its performance can be enhanced by the addition of an isolation transformer and a power line noise filter to provide a power conditioner.

Elegant power tools
Transformers are elegant power quality tools with unchanging secondary impedance. The benefit of using an isolation transformer is that bonding of neutral to ground on the transformer secondary is permitted and eliminates common mode voltages.
This enables the surge diverter to divert surge energy to ground without creating any common mode disturbances. Noise filters function in a similar manner by diverting EMI and RFI to ground and, when combined with an isolation transformer, their performance is enhanced.
This is of particular importance at the end of long-branch circuits where most computer equipment is installed. Wiring in buildings contains significant inductive and capacitive reactance giving rise to a unique frequency at which the system oscillates for every location in the building. This makes power line transients unpredictable.
Although a lot of research has been done by the IEEE to characterize a branch circuit impulse’s typical characteristics the reality varies greatly for every different location throughout the building. When a surge diverter is installed on a branch circuit it becomes part of the wiring system and the circuit impedance resulting from the wiring reactance affects the surge diverter’s performance.
This means the performance of surge diverters is often unpredictable since the varying electrical characteristics affect the frequency, wave form, and impulse’s rise time at different places throughout the building. This explains why a power diverter, when used as the sole form of protection, may reduce the frequency of hardware failures, while still making the system behave unreliably at times.
However, by fitting an isolation transformer and a noise filter, the surge diverter’s performance becomes predictable, controllable and repeatable.
On their own, surge diverters will limit transient impulses to hundreds of volts but by fitting an integrated power conditioner the same transient impulses are limited to typically ten volts or less. By fitting a transformer-based power conditioner far less of any disturbance is allowed to reach the critical electronic equipment ensuring improved functionality, greater reliability and enhanced longevity.