Most engineers and users have a perception that once a Power Protection Device, like UPS or power conditioner, is installed, all their power irregularities will get solved. With this incorrect approach, they tend to ignore the very basic issues like grounding, wiring destination and also the bonding of the system. If the grounding, wiring and bonding of the facility are not done properly, UPS or even power conditioners may not function properly themselves, let alone provide protection to critical systems.

Power quality phenomena include all possible situations in which the waveform of the supply voltage (voltage quality) or load current (current quality) deviate from the sinusoidal waveform at rated frequency with amplitude corresponding to the rated RMS value for all three phases of a three-phase system. The wide range of power quality disturbances covers sudden, short-duration deviations, e.g. impulsive and oscillatory transients, voltage dips (or sags), short interruptions, as well as steady-state deviations, such as harmonics and flicker. One can also distinguish, based on the cause, between disturbances related to the quality of the supply voltage and those related to the quality of the current taken by the load.

The correct or True Power Quality Strategy should begin with the basic items in the strategy, as referred
in the above diagram. One should first review the Grounding, Bonding and Wiring Systems of the facility.

These systems must first be installed properly for the electrical system to operate safely. The next itemto look at should be to study the requirement for Pro-Active Protection Systems like Transient Suppression Systems or Filters. We call these systems pro-active because the types of power problems these systems tackle are more commonly encountered in most locations. These can be said as inherent problem in our electrical generation and distribution system. These protections should be employed in all critical installations.

To move to the next level of protections, we have to study the critical systems themselves as well as their operations. For example, it is necessary to install power conditioners or voltage stabilizers if the critical system is very sensitive to voltage variations, or if the site where the critical system is installed has a bad record on voltage fluctuations. If the result of the investigation on the system operation indicative that the equipment must never be switched off at all and it cannot tolerate any momentary power loss or the site has frequent and known power failures, an UPS system must be installed.

Power Electronics based solutions are widely used now a days for the mitigation of Power Quality aberrations. These devices for mitigation of interruptions and voltage dips (sags) and devices for compensation of unbalance, flicker and harmonics are treated. Static UPS Systems are one of the best power electronic based solutions used to mitigate outages. For flicker mitigation, a number of different methods are available, which differ in performance, feasibility and cost. Electrical methods for flicker reduction deal with the arc furnace current and can be grouped in direct and indirect methods. The direct methods include apparatus that alter the arc furnace current directly and are connected in series with the furnace. Indirect methods do not intervene on the arc furnace current, but tackle its effects indirectly with a mitigating device connected in parallel with the furnace by injecting compensating current.

In order to remove current harmonics from the grid, passive or active shunt-filters are used. Passive filters for harmonic reduction provide low impedance paths for current harmonics. A common active filtering method is based on using the instantaneous active and reactive power. This method detects all non-sinusoidal components and, when it is implemented with a hysteresis current controller, allows obtaining good filtering performance. |

Short-duration, shallow dips can be mitigated by improving equipment tolerance characteristics. Long- duration, deep dips and interruptions can be avoided by changing structure and/or operation of the power system. However, for industrial customers, who do not normally have access to system or equipment improvement, the installation of additional mitigation equipment is often the only option left to achieve the desired quality of supply at the system-load interface. Static Series Compensators, Static switches with dual feeders e.t.c are other electronic based mitigation devices.

Rather than devices, the strategies are quite vital. We can regard the top two levels of the protections to be more application related, while the lower two levels are pro-active strategy for protection. Before we closely study the various types of power solutions, we should first look at the proper approach to Power Quality Strategy.