You're almost finished with a full days worth of EQ adjustments on the DSP for a large sound installation. Unknown to you a huge thunderstorm is rolling in. Minutes later you hear a loud boom and the lights go out. When the power comes back on the DSP is dead and the file on your laptop, which you didn't back up, is hopelessly scrambled. It's time to get acquainted with the technology behind power quality.

The most frequently suggested reasons for electronic equipment failure are electrical power disturbances.  With more pieces of sensitive electronic equipment making their way into our homes and businesses, protection against power disturbances becomes a crucial issue.  Products like surge suppressors, line conditioners, and uninterruptible power supplies ( UPS ) provide protection against data loss, and can even extend the life of integral equipment by providing optimal operating conditions.  

Power disturbances can be broken down into groups such as sags, swells, transients and harmonics.  Voltage sags are caused by a sudden increase in load such as a short circuit or a motor starting, a voltage swell is typically caused by a sudden reduction in load or a damaged neutral connection, and a transient is a random high magnitude voltage and/or current that lasts for a short period of time.  A harmonic is a multiple of a fundamental; in this case a 120V/60Hz AC sine wave typically caused by nonlinear loads such as variable speed motor drives, switching power supplies, and electronic ballasts in fluorescent lights.  Each occurrence can be caused by a number of culprits, each having its own effect and solution. 

When protecting vital equipment from these phenomena there are three fundamental types of protection to choose from; surge suppression, line conditioning, and battery backup; each having its own capabilities to protect against a number of problems.  However, each alone will not protect against all power disturbances.  Choosing what type of protection you require should be based on the nature of the occurrence(s) you wish to protect against.  Some methods of protection can be costly, so analyzing your power systems performance is recommended when choosing what method of protection is required. 

The first concern when protecting against power disturbances should be to check the design of your electrical distribution system. This includes making sure the system is properly grounded (connected to earth), bonded (has a conductive path designed to carry fault current back to the system neutral), uses properly sized conductors, and has properly sized and installed overcurrent protection devices (circuit breakers or fuses). The requirements for these can be found in the NEC (National Electrical Code) or your local building code depending on your location. Improper design or installation of any of the above can pose serious safety risks in addition to being the root cause of power quality issues. Inspection and correction of the above issues should be handled by a qualified electrician.

Surge Suppression

About 80% of recorded transient voltage surges come from internal switching transients caused by turning on motors, transformers, photocopiers, or other loads on and off. Externally generated surges, on the other hand, come from induced lightning, grid switching, or other facilities on the same distribution node. (Chiste)  

Surge suppressors come in two types, each protecting against a limited number of fault conditions.  The first type uses metal oxide varistors or MOV’s; these surge suppressors are typically designed to provide a low impedance path from the hot conductor to ground when the line voltage exceeds a certain level.  Other common types of surge suppressors will filter and/or modulate the surge; in effect storing the energy of the surge and gradually releasing it over time into the line conductor. Some suppressors will not protect against line noise or distortion and will only safeguard transitory spikes.  The more advanced devices will provide filtering of line noise as well as control of transitory over voltages. 

Typically surge suppressors are rated by the amount of power they will dissipate expressed in Joules.

[Joule, Noun 1. A unit of electrical energy equal to the work done when a current of one ampere passes through a resistance of one ohm for one second.  2. English physicist who established the mechanical theory of heat and discovered the first law of thermodynamics (1818-1889)]. (Farlex) 

The higher the rating the more effective the surge suppressor will be at dissipating energy.  Surge Suppression will hinder transitory over voltages; however, it will not protect against power failure, under voltages, and non transitory over voltages.

Line Conditioners

Line conditioners are available in many formats.  Typically they offer voltage regulation and line filtering for noise/harmonics.  The basic types of line voltage regulators are the motor driven autotransformer with series transformer, the motor driven induction regulator, the saturable reactor, the electronic tap-switching autotransformer, and the ferroresonant transformer. (Giddings) 

The most common type of Line Conditioner used in audio, video and data applications is the electronic tap-switching autotransformer. These devices function by measuring the input voltage and then electronically selecting an output tap on the autotransformer to maintain a consistent output voltage independent of the input voltage. Each of these devices will differ in their reaction time and effectiveness. 

Isolation transformers, also considered a type of line conditioning are intended to protect against common mode transients, noise, and varying loads.  Also, in most cases where a dedicated service line would be ideal but not possible, an isolation transformer will provide an isolated ground.  The NEC has specific neutral-ground bonding and grounding requirements for isolation transformers (separately derived sources), consult a qualified electrician to ensure a safe and effective installation of these devices. Isolation transformers will not protect against over voltages or under voltages of significant duration, or non-common mode transients and noise.  Although isolation transformers offer many of the same options as line conditioners they cannot be considered true line conditioners because they do not offer voltage regulation.  It is important to choose an isolation transformer with the adequate voltage and current ratings for your application.

Continued >
page 1>2>3