FAQs

Power Line Conditioning -- FAQs
Question 1: Why do we need power line conditioning?
 
Answer 1:

Our supply of electricity cannot be taken for granted because it is far from clean, stable and continuous. Severe weather, interferences, accidents involving electric transmission lines, transmission equipment failure, thefts and vandalism can cause power disturbances. There are also disturbances resulting from sources within and around your premises such as on-off operation of air-conditioners, photostat machines, printers, switching power supplies, fluorescent lights, arc welders, elevators and so on.
 
All building electronic systems are designed to be operated from a uniform clean electric supply. If the electric supply becomes disturbed or distorted, the electronic systems may be unstable, sending false signals, even malfunction or suffer damage.
 
Therefore, just as we need treatment systems to purify contaminants from the tap water and a backup supply from water storage tanks, we also need  power line conditioning. Power line conditioner is the general term for UPS, AVR, surge suppressors, VSP (Voltage Sag Protectors) and so on.
 
For example, the UPS is analogous to the water storage tank in every household as it provides backup power supply in case of blackouts. Similarly, if water pressure is low, we use a water pump to increase its pressure. Therefore, the AVR is the equivalent of the water pump; if the utility voltage is low, it can regulate it to normal voltage. 
 
 
Question 2: What are the types of power disturbances, causes and effects?
Answer 2: 

The utility electric supply is subject to a variety of power disturbances such as:
 
                            
   Voltage fluctuations                                                                                 Spikes or surges      

                             
Sags                                                                                                                  Noise

                           
Power outages or blackouts                                                                           Over-voltage            

   
Under-voltage

 
 
DISTURBANCES
CAUSE
EFFECTS
VOLTAGE FLUCTUATIONS
Defined as a series of r.m.s. voltage changes or a cyclic variation of the voltage waveform envelope. Or a sudden and noticeable change in AC r.m.s. voltage level.
 
 
 
Typically caused by the use of large loads having rapidly fluctuating active and reactive power demand.
 
 
Reduce the service life of building electronic systems and also disrupt production processes. Flicker - one of the consequential effects can significantly impair our vision and cause general discomfort and fatigue.
 
SPIKES
Also referred to as an impulse, a spike is an instantaneous, dramatic increase in voltage. Akin to the force of a tidal wave, a spike can enter electronic equipment through utility electric supply, network, serial or phone lines and damage or completely destroy components.
 
 
Spikes are typically caused by a nearby lightning strike. Spikes always occur when utility electric supply resumes after blackouts.
 
Catastrophic damage to building electronic systems. Loss of data.
SURGES
A very short duration increase in voltage, typically lasting at least 1/120 of a second.
 
 
Surges result from presence of high-powered electrical motors, such as air conditioners, and household appliances in the vicinity. When this equipment is switched off, the extra voltage is dissipated through the power line.

 
 
Computers and similar sensitive electronic devices are designed to receive power within a certain voltage range. Anything outside of expected peak and r.m.s. levels will stress delicate components and cause premature failure.
 
NOISE
More technically referred to as Electro-Magnetic Interference (EMI) and Radio Frequency Interference (RFI), electrical noise disrupts the smooth sine wave one expects from utility electric supply.

 
 
Electrical noise is caused by many factors and phenomena, including lightning, load switching, generators, radio transmitters and industrial equipment. It may be intermittent or chronic.
 
Noise introduces glitches and errors into executable programs and data files.
SAGS
Also known as dips or brownouts. Sags are short duration (3 to 10 cycles) drop below 90 percent of the nominal voltage level. This is the most common power problem, accounting for 87% of all power disturbances according to a study by Bell Labs.
 
 
Sags are usually caused by the start-up power demands of many electrical devices (including motors, compressors, elevators, shop tools, etc.) Electric companies use sags to cope with extraordinary power demands. In a procedure known as rolling brownouts, the utility will systematically lower voltage levels in certain areas for hours or days at a time. Hot Summer days, when air conditioning requirements are at their peak, will often prompt rolling brownouts.
 
 
A sag can starve a computer of the power it needs to function, and cause frozen keyboards and unexpected system crashes which both result in lost or corrupted data. Sags also reduce the efficiency and life span of electrical equipment, particularly motors.
BLACKOUTS
Total loss of utility power.
 
 
Blackouts are caused by excessive demand on the power grid, lightning storms, ice on power lines, car accidents, backhoes, earthquakes and other catastrophes.

 
 
Current work in RAM or cache is lost. The hard drive File Allocation Table (FAT) may also be lost, which results in total loss of data stored on drive.
OVER/UNDERVOLTAGE
Technically speaking, an over/under voltage condition is reached when the voltage exceeds/lags the nominal voltage by 10% for more than 1 minute.  Both of these conditions result in voltage that falls outside the acceptable power envelope.
 
 
Over voltage typically caused by a massive reduction in power loads or heavy equipment being turned off around your premises. Under voltage typically caused by other heavy loads that exceed supply capacity, or intentional utility electric supply reduction to conserve power during peak demand periods.

 
 
Premature hardware failure. Data corruption, data loss and erratic behavior in some building electronic systems.
 


Question 3: What are the basic components of a power conditioning system?
Answer 3:

A power conditioning system can be either simple or sophisticated depending on its specifications and circuit designs. However, it usually consists of the following basic components; namely:
 

• Metal Oxide Varistors (MOV)
A MOV acts like a "sponge" to soak-up and absorb an incoming power surge. The more MOVs a surge protector contains, the higher the joule rating - a measurement of energy against power surges. MOVs pass current only when the voltage across them is above a set value, and they react very quickly in terms of microseconds. MOVs are only good  for a few uses and wear out; the bigger the spike, the more damage is done.


• Sidactors
A sidactor is a solid-state, over-voltage protection component. A sidactor will actually switch open when a surge occurs. When the power surge is over, the switch will close and be ready to protect against the next surge. Sidactors have the advantage of not wearing out  but they are designed to work on a low voltage line, such as telephone lines.
 

• Thermal Fuses
A thermal fuse is a component that will break the electrical circuit if and when too much heat is generated by melting MOV's.
 

• Suppression Inductors
An Inductor is used to oppose inrush surge current. It is a very good filtering component against electrical noise, EMI/RFI, etc. The inductance is measured in Henry (H).
 

• Transient Suppression Diodes
A diode works in reverse-biased to absorb transient energy.
 

• Resistors
A Resistor is used to limit current and voltage. It is present in electrical circuits because of their electrical resistance. The resistance is measured in Ohms (Ω).
 

• Film Capacitors
EMI/RFI is absorbed by film capacitors.
 

• Circuit Breakers
A circuit breaker stops the flow of electricity when a circuit is overloaded. However, it has limited surge protection capability as it reacts slowly --  in terms of tens of milliseconds.
 

 
 
Question 4: What are the types of power conditioning equipment?
Answer 4:

A wide range of such equipment is available that have claimed features such as joule rating, maximum spike current, clamping voltage, response time, EMI/RFI filtering, attenuation, lines protected and so on.  In fact, a simple surge/spike protector can be bought easily at electrical shops, hardware stores or even supermarkets. However, such gadgets are as good as nothing because they give the false sense of security that you are protected, when you are not.
 
Basically, two categories of power conditioning equipment are available for protecting your building electronic systems. They include:
 

• Power Enhancers - A power enhancer provides a way to improve the AC power quality and make it more suitable for building electronic systems. However, it provides no help for loss of power during a power outage.
 

• 
Power Synthesizers - A power synthesizer is capable of not only enhancing the incoming power, but also providing auxiliary power during power outages.
 
The rationale for choosing power synthesis over power enhancement may not be obvious. Severe power disturbances usually occur less frequently and the total cost of disruption is difficult to quantify. Power synthesizers are more complex and costly than power enhancers. In addition, power synthesizers are usually less efficient and require more maintenance.
 
In order to achieve positive results, power-conditioning equipment must be properly understood, installed and maintained. The availability of proper maintenance and unit cost are other factors to consider in the selection of power conditioning equipment.



Question 5: What are the different types of power enhancers?
 
Answer 5:
 

• Surge Suppressors
Surge and transient or spike suppressors are the simplest, least expensive way to condition power. They reduce the magnitude of spikes to levels that are safe for your building electronic systems. Three levels - high risk, medium risk and low risk -- are commonly classified to provide different protection areas along the power stream. High-energy surge suppressors based on varistors and encapsulated spark gaps are installed at the inputs of AC mains supply at highly exposed sites or main buildings for protection against direct lightning. Followed by medium-to-high energy surge protectors installed at Distribution Boards (DB) of secondary buildings. Next transient voltage surge suppressors (TVSS) are recommended at the AC input of all electronic systems to provide protection against lower energy spikes which occur very abruptly. Different types or levels of TVSS have their own performance specifications and prices.
 

• Automatic Voltage Regulators (AVR)
AVRs maintain voltage output within a desired limit despite wide fluctuations in the input. There are different types of AVRs and most of them respond best to slow changes in voltage. They might provide certain level of protection against spikes or noise, but limited or no protection from fast voltage changes depending upon their respond time.
 

• 
Isolation Transformers
Isolation transformers protect sensitive electronic systems by buffering electrical noise. They effectively reject common mode line-to-ground noise, but are limited in their rejection of normal mode line-to-line or line-to-neutral noise. Isolation transformers do provide a “separately derived” power source and permit single point grounding.
 
 

 

Question 6: What are the different types of Power Synthesizers?
 
Answer 6:

Basically, they can be divided into Motor Generators, Rotary Uninterruptible Power Supplies (UPS) and Static Uninterruptible Power Supplies (UPS)
 

• Motor Generators
Motor Generators consist of an electric motor driving a generator. They convert incoming electrical energy into mechanical energy and back into electrical energy. The mechanical shaft isolates the electrical load from incoming disturbances such as voltage impulses, surges and sags. The motor generator rides through many short “momentary interruptions” but will not protect against sustained outages.
 

• Rotary Uninterruptible Power Supplies (UPS)
A rotary UPS uses some form of a motor generator and batteries as the energy source so as to provide uninterruptible power during blackouts.
 

• 
Static Uninterruptible Power Supplies (UPS)
A static UPS has no moving parts and typically uses power semiconductors. It basically includes a rectifier/charger, a battery bank and a static inverter. Progress in the development of semiconductor power device has resulted in static UPS availability in power ratings from 300VA to 1000KVA.
 
Static UPSs generally come in three configurations namely on-line, off-line and hybrid shown in figures (1), (2) and (3) below:
 
 
 


In on-line configuration, the load is continuously fed by the inverter and the battery is constantly float-charged. On AC mains failure the inverter then draws its energy from the battery. There is no discontinuity in the changeover from AC mains to battery operation. The on-line UPS not only exhibits zero transfer time but also acts as an ideal isolation between its input and output.
 
In off-line (or line-interactive) configuration, the load is supplied by the AC mains and the inverter is kept off-line. Upon loss of AC mains power, the load is then transferred to the inverter and draws energy from the battery. Some off-line designs include a transfer during certain power disturbances such as over-voltage and under-voltage. The off-line UPS is effective only when the electronic system being protected can withstand the transfer time, usually in terms of milliseconds. Off-line UPSs are typically available only in lower capacities, i.e. 300VA to 3KVA.
 
In hybrid configuration, the load is also connected directly to the inverter of the UPS without a break, just like its on-line counterpart. This is a hot standby technique and exhibiting zero transfer time with proper circuit design.
 
 

Question 7: What is the obvious conclusion from this discussion?
Answer 7: 

An unpredictable power disturbance can cause disaster for any building electronic systems whose operation depends merely on the AC mains supply. The loss of valuable data and down time mean loss of productivity, loss of sales and disruption of all work.
 
Solutions to power disturbance problems must include an economic evaluation plus intangible considerations. Sometimes, engaging power conditioning equipment alone might not be sufficient. Many power quality problems must also be resolved with practical and basic solutions. These solutions include preventive maintenance, relocation and electrical rewiring for building electronic systems.
 



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