On365

Much of the mystery surrounding downtime, device failure and software corruption can be attributed to a problematic supply of power. on365 can help you diagnose the most common symptoms and causes as well what they could do to your business critical equipment.

Introduction
A lot of power problems originate in the national power grid, which, with its thousands of miles of transmission lines, is subject to weather conditions such as heavy storms, lightning stikes, snow, ice, and flooding along with equipment failure, traffic accidents and major switching operations. Of course the problem can also materialise much closer to home with construction in the local area, heavy start up loads on power supplies as well as faulty distribution components or just simple background noise.

Agreeing on common terms is a first step in dealing with power disturbances. Power quality is an ever important feature in our domestic and commercial lives, everything from the household appliances to the largest industrial processes rely heavily on quality of power supply. Electricity at the wall socket is no less than an electromagnetic phenomenon and seeing what this energy is doing, in small slices of time, can provide an understanding of how important simple, smooth ac power is to reliable operation of our systems. In a perfect world, commercial ac power appears as a smooth, symmetrical sine wave, varying at either 50 or 60 cycles every second (Hertz – Hz) depending on which part of the world you’re in.

on365 understand the science of power, we can advise on the difference between an interruption, and an oscillatory transient, and how knowledge of these situations makes for qualified purchasing decisions when contemplating power correction devices. Incorrect provision against these threats can lead to downtime, lost profitability and equipment failure. We think there are seven important interruptions to power supply that should be focused upon:

1. Transients
2. Interruptions
3. Sag / Undervoltage
4. Swell / Overvoltage
5. Waveform distortion
6. Voltage fluctuations
7. Frequency variations

1. Transients
This form of power disturbance can be the most damaging, they can be split into two precise categories:
 i. Impulsive - sudden and extreme spikes that raise the voltage and/or current levels in either a positive or a negative direction. These types of events can be categorised further by the speed at which they occur (fast, medium, and slow).
ii. Oscillatory – occurs when there’s an unexpected change to the steady rate condition of voltages at both negative and positive ends of the signal limits. 

2. Interruptions
An interruption is a complete cut of current that can be, depending on duration, classed as instant, momentary, temporary, or sustained. The causes of interruptions can vary, but are usually the result of some type of electrical supply grid damage, such as lightning strikes, animals, trees, vehicle accidents, destructive weather (high winds, heavy snow or ice on lines, etc.)

3. Sag / Undervoltage Sag
A sag is a reduction of AC voltage at a given frequency for the duration of 0.5 cycles to 1 minute’s time. Sags are usually caused by system faults, and are also often the result of switching on loads with heavy startup currents. Common causes of sags include starting large loads (such as one might see when they first start up a large air conditioning unit) and remote fault clearing performed by utility equipment.
Undervoltages are the result of long-term problems that create sags. The term “brownout” has been commonly used to describe this problem, and has been superceded by the term undervoltage.

4. Swell / Overvoltage
A swell is the reverse form of a sag, having an increase in AC voltage for a duration of 0.5 cycles to 1 minute’s time. For swells, high-impedance neutral connections, sudden (especially large) load reductions, and a single-phase fault on a three-phase system are common sources.
Overvoltages can be the result of long-term problems that create swells. An overvoltage can be thought of as an extended swell.

5. Waveform Distortion
There are five primary types of waveform distortion:
1. DC offset
2. Harmonics
3. Interharmonics
4. Notching
5. Noise

6. Voltage Fluctuations
Since voltage fluctuations are fundamentally different from the rest of the waveform anomalies, they are placed in there own category. A Voltage fluctuation (Figure 17) is a systematic variation of the voltage waveform or a series of random voltage changes, of small dimensions, namely 95 to 105% of nominal at a low frequency, generally below 25 Hz.

7. Frequency Variations
Frequency variation (Figure 18) is extremely rare in stable utility power systems, especially systems interconnected via a power grid. Where sites have dedicated standby generators or poor power infrastructure, frequency variation is more common especially if the generator is heavily loaded. IT equipment is frequency tolerant, and generally not affected by minor shifts in local generator frequency.

Conclusions
The widespread use of electronics has raised the awareness of power quality and its affect on the critical
electrical equipment that businesses use. Our world is increasingly run by small microprocessors that are
sensitive to even small electrical fluctuations. These microprocessors can control blazingly fast automated
robotic assembly and packaging line systems that cannot afford downtime. Economical solutions are
available to limit, or eliminate, the affects of power quality disturbances. However, in order for the industry to
communicate and understand power disturbances and how to prevent them, common terms and definitions
are needed to describe the different phenomena. This article has attempted to define and illustrate power
quality disturbances as outlined in IEEE Standard 1159-1995, "IEEE Recommended Practice for Monitoring
Electrical Power Quality."

Reducing equipment downtime and production expense, therefore increasing profit, is the goal of any size business. Communicating by understanding the electrical environment, and equipment's susceptibility to power quality disturbances, will help in the discovery of better methods to achieve business goals and dreams.