In recent years a massive rise in the number of
However, when voltage fluctuates outside equipment design specifications, that equipment has to work harder. In the case of the fridge-freezer, if the mains voltage goes below 220V, the circuit powering the compressor motor will run hotter, which reduces its effectiveness and life.
Even if the supply voltage is very stable at your electricity meter, it may vary throughout your building. These fluctuations are called ‘voltage events’. Voltage events are common and have various causes, but become a concern when they go beyond what a piece of equipment is designed to handle.
So, if voltage events happen all the time, why doesn’t equipment fail all the time? Electrical equipment is designed to work at nominal voltage. Equipment may not fail the first time an event occurs, but over time failure will occur because of the excessive stress caused by repeated voltage events. Voltage events are the cause of many intermittent problems that go undiagnosed - often problems which have existed for years are finally traced back to undetected voltage events.
Voltage events and their effects
Most power quality issues come from within your own building. Sources of voltage events include motors, photocopiers, arcing switches, water coolers, air conditioners and some routine utility operations. Some voltage events are the result of the power utility and some are a result of neighbouring facilities; but 85% of all voltage events originate from within your own facility.
Voltage event glossary:
Sag - A period of low voltage. Minor sags occur frequently, sometimes without affecting equipment performance.
Swell - A period of high voltage lasting for longer than one minute. Not as common as sags, both minor and major swells can have a serious impact on equipment function.
Impulse / spike - A short burst of energy ranging in magnitude from twice the normal voltage to several thousand volts.
Total harmonic distortion (THD) - A distorted waveform is made up of multiple frequencies known as harmonic distortion, and is measured as a percentage of distortion. A small level of distortion won’t affect equipment, but higher levels may cause problems.
Voltage events can be caused by an inadequate supply, under-sized wiring, overloaded circuits, and frequently by other equipment being turned on or off on the same circuit. Sometimes they can be caused by environmental changes such as lightening storms, high winds, flooding or physical damage.
The greater the voltage sag, the greater the likelihood of damage. Additionally, the greater the number of sags, the greater the chance of failure or damage. Sags occur for many reasons, including voltage drop caused by long cable runs or switching loads, poor wiring and overloaded circuits.
A voltage spike produces a temporary increase in current. In integrated circuits (IC’s) it might mean that the voltage exceeds the reverse breakdown potential of the semi-conductor junction, thus destroying or severely weakening the device.
Harmonics are a more frequent problem than they used to be because of the proliferation of equipment such as PC’s, printers etc. Technology in the workplace has resulted in many non-linear loads on the power supply - the cumulative effect of which is harmonic distortion. Rather than a single voltage event, this is a condition that can be present throughout your facilities power distribution system. Harmonics can cause equipment and circuits to overheat, which is a waste of energy and a potential fire risk.
Non-linear loads like PCs and copying machines create harmonic currents that distort the voltage. The more electronic devices there are on a circuit, the greater the likelihood of severe voltage distortion.
Standards
In Europe the primary standard that relates to voltage variations is EN50160. However, throughout the world standards vary depending on local markets and applications.
Combating voltage performance issues
The failure of electrical equipment costs companies time and money, so it is important to understand voltage event issues, and to monitor voltage performance. By doing this you can determine whether an equipment problem is related to voltage performance, or check that your circuit can support a new piece of sensitive equipment.
The key is first to understand what is happening throughout the power system in your building - then you know if problems are caused by faulty equipment, voltage events, or something else.
Installing advanced condition monitoring equipment throughout your building as a precaution would work, but would be very expensive, and somewhat excessive – a sledgehammer to crack a nut.
A low-cost, voltage quality monitor is a sound investment. Traditional test instruments do not have the sampling speed necessary to analyse voltage events, and the full-functioning power quality analysers are not designed to work at the wall outlet - the most important place to measure voltage because it is where it’s installed.
New, low cost single-phase monitoring systems are now available for as little as £275.00 excl. VAT. These allow simple monitoring and logging of voltage data on your different circuits. Quick and easy to use, they only record out-of-threshold events. The best models have the thresholds for the standards built-in so you can just select the voltage standard you want to use, or input your own.
Using voltage monitoring systems like these will prove invaluable for troubleshooting and maintenance problems, and can help you anticipate or prevent problems before they occur - saving your company time and money.
