protection against surges & transients

8/12/2019 Protection Against Surges & Transients

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PROTECTION AGAINST SURGES & TRANSIENTS

GUJRAT TECHNOLOGICAL UNIVERSITY Page 1

CHAPTER-1

INTRODUCTION

1.1 SURGES

A power surge is one form of electrical power disturbance. There are four main

types of power disturbances:

Fig.1 Storm lightning

Power surges are generally considered to be the most destructive of the four types

of electrical power disturbances. Power surges are spikes in voltage.

They are very brief, usually lasting millionths of a second. Power surges can vary in

duration and magnitude, varying from a few hundred volts to several thousand volts.

No matter where you live, your home experiences power surges. How Does a Power

Surge Cause Damage? In the United States, most homes use electrical power in the form

of 120-volt, 60 Hz, single phase, alternating current. However, the voltage is not

delivered at constant 120-volts. With alternating current the voltage rises and falls in a

predetermined rhythm. The voltage oscillates from 0 to a peak voltage of 169 volts. Most

appliances and electrical devices in your home used in the United States are designed to

be powered by this form of generated electricity. During a power surge, the voltage

exceeds the peak voltage of 169 volts.
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A spike in voltage can be harmful to appliances and electrical devices in your

home. An increase in voltage above an appliance's normal operating voltage can cause an

arc of electrical current within the appliance. The heat generated in the arc causes damage

to the electronic circuit boards and other electrical components.

Smaller, repeated power surges may slowly damage your electronic equipment.

Your computer or stereo may continue to function after small surges occur until the

integrity of the electronic components finally erode and your satellite system, cordless

phone, or answering machine mysteriously stops working. Repeated, small power surges

shorten the life of appliances and electronics.

When you put together a computer system, one piece of standard equipmentyou'll probably buy is a surge protector. Most designs serve one immediately obvious

function -- they let you plug multiple components into one power outlet. With all of the

different components that make up a computer system, this is definitely a useful device.

But the other function of a surge protector power strip -- protecting the

electronics in your computer from surges in power -- is far more important. In this article,

we'll look at surge protectors, also called surge suppressors, to find out what they do,

when you need them, and how well they work. We'll also find out what levels of

protection are available and see why you might not have all the protection you need, even

if you do use a quality surge protector.

The main job of a surge protector system is to protect electronic devices from

"surges." So if you're wondering what a surge protector does, the first question is,

"What are surges?" And then, "Why do electronics need to be protected from them?"

A power surge, or transient voltage, is an increase in voltage significantly above

the designated level in a flow of electricity. In normal household and office wiring in the

United States, the standard voltage is 120 volts. If the voltage rises above 120 volts, there

is a problem, and a surge protector helps to prevent that problem from destroying your

computer.
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To understand the problem, it is helpful to understand something about voltage.

Voltage is a measure of a difference in electric potential energy. Electric current travels

from point to point because there is a greater electric potential energy on one end of the

wire than there is on the other end. This is the same sort of principle that makes water

under pressure flow out of a hose -- higher pressure on one end of the hose pushes water

toward an area of lower pressure. You can think of voltage as a measure of electrical

pressure.

As we'll see later on, various factors can cause a brief increase in voltage.

When the increase lasts three nanoseconds (billionths of a second) or more, it'scalled a surge.

When it only lasts for one or two nanoseconds, it's called a spike.

If the surge or spike is high enough, it can inflict some heavy damage on a

machine. The effect is very similar to applying too much water pressure to a hose. If there

is too much water pressure, a hose will burst. Approximately the same thing happens

when too much electrical pressure runs through a wire -- the wire "bursts." Actually, it

heats up like the filament in a light bulb and burns, but it's the same idea. Even if

increased voltage doesn't immediately break your machine, it may put extra strain on thecomponents, wearing them down over time. In the next section, we'll look at what surge

protectors do to prevent this from happening.
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1.2 TRANSIENTS

Transient surges are defined as momentary bursts of energy that are induced upon

power, data, or communication lines. They are characterized by extremely high voltages

that can drive tremendous amounts of current into an electrical circuit for a few

millionths, up to a few thousandths of a second.

Surge activity is often assumed to be an outside engendered anomaly. Lightning

induced electrical energy bursts, for example, typically come to mind as the primary

source of surge activity. However, while lightning induced surges represent are the most

formidable transient related equipment menace, most surges are originate from internal

sources within a facility. Internal transient generators range from copiers to coffee

makers, from vacuum cleaners to variable speed drives, and from fluorescent light

ballasts to furnace igniters. Studies have verified that approximately 80% of transient

activity at a given facility is internally generated. Copiers and laser printers, for example,

are notorious transient generatorsas are heating and air conditioning systems. Any time

an inductive load, whether it is a vacuum cleaner or a heavy duty variable speed drive, is

either powered on or off it generates a low magnitude surge impulse that propagates

back through the electrical distribution. While internally generated transient activity can

weaken equipment over time, the threat posed from lightning activity is particularly

disconcerting due to its capability of delivering vast amounts of energy into unsuspecting

electronic equipment loads. According to an article on Nationwide Insurance website,

The average claim for lightning-related damage is well over $10,000. Nationwide

deduces in that same article that surge suppressors, specifically, rapidly pay for

themselves. That article can be referenced at In any event, todays electronic equipment

is particularly vulnerable to the voltage component of the transient energy. Thats

because modern computer chips are comprised of literally millions of active components,

all of which are positioned upon a silicon wafer whose surface area measures no more

than a square inch. For example, Intels Core i7 920 (D0 stepping) microprocessor

employs 781 million transistors. With that in mind, it becomes obvious that there isnt

much physical space separating the microprocessors individual components.


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It doesnt take much of an overvoltage, lightning induced or otherwise, to cause

arcing between the ICs internal components and damaging todays microprocessor based

electronic components. Stateof theart surge suppressors, now more than ever, are

required to protect modern day state of the art electronic equipment. Transient

overvoltage surges measuring as low as a few hundred volts/peak pack enough punch to

damage sensitive electronic equipment beyond repair. General Electric reported in their

in-house magazine, Current Scene, the observation of transient surges of several

thousand volts occurring regularly on 120 V power circuits within facilities ranging from

family homes to large industrial manufacturing plants. The voltage element of a transient

surge is received like a slap in the face by modern integrated circuits (ICs), i.e. computer

chips. In the same manner that we would feel a rush of facial pain should someone slap

us across the cheek, the computer chip will suffer, albeit metaphorically, in a similar

sense. And while a series of quickly reoccurring and repeated slaps across our face would

result with our feeling intense bodily pain, multiple back to back to back transient surges

occurring in quick succession will cause an otherwise healthy computer chip to fail

catastrophically. It becomes prudent to mitigate the damage causing potential that is

associated with the transient threat. And, that task is accomplished with Surge Protection

Devices (SPDs). The quality SPD has a very basic purpose. And, that is to protect critical

electronic equipment loads by diverting intense levels of transient current away fromthem while limiting the corresponding voltage amplitudes to safe levels. In other words,

an SPD serves as an electronic shock absorber that attracts transient surge energy and

safely soaks it up before it gets to its protected equipment loads. With that said, SPD

safety standards have been revised in recent years; calling for testing that stresses the

SPD to failure while ensuring that it does so safely. The fact is SPD failures were, and

still are, typically caused by temporary over voltage (TOV) events, rather than surge

activity.


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While most surge suppressors have always easily withstood momentary voltage

bursts, they could and would fail catastrophically when subjected to a sustained

overvoltage high enough to drive them into continuous conduction. SPD safety testing,

beginning in February 2007 when ANSI/UL 1449 2nd edition was revised to include

extended abnormal over current test parameters, required SPDs to be subjected to a full

gamut of abnormal fault current scenarios; necessitating them to conduct various amounts

of fault current until they failed in a safe and orderly fashion. SPD products of yesteryear,

without redesign or augmentation, could not meet the new enhanced safety requirements.

While ANSI/UL 1449 was again revised in September 2009, with the advent of its 3rd

edition, the over current testing implemented in its previous iteration remains to be a key

significance. A strong argument can be made that SPDs still in service and manufactured

before February 2007 before todays accepted safety standards adapted more robust

testing requirements, are not completely safe for use. They should be replaced based

solely on safety concerns. However, since most SPDs employ suppression components

that wear out over time, it is not a bad idea to replace older SPDs as a preventative

measure, as well.


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CHAPTER-2

TRANSEINT VOLTAGE SUPRESSOR

2.1 TRANSIENT VOLTAGE SURGE SUPRESSOR (TVSS)

Transient Voltage Surge Suppressor (TVSS) is a device that every data center or

mission critical facility should have. Why should every data center have one and what

does it do you ask? The purpose of a TVSS is to eliminate or reduce damage to data

processing equipment and other critical equipment by limiting transient (surge) voltages

and currents (surges) on electrical circuits. These transients or surges may come from

inside a facility, or may be injected into a facility from the outside. What is a transient? Atransient surge is a short blast or pulse of high energy that can either come in its natural

form such as lightning or produced by other equipment. Transients caused by other

equipment are usually caused by the discharge of stored energy in inductive and

capacitive components. Some examples are Electric motors, such as those used in

elevators, heating, air conditioning, refrigeration or other inductive loads. Two other

sources are arc welders and furnace igniters. These transients are capable of causing

significant damage to equipment and electronics.

The transient causes damage to a device when the transient voltage exceeds the

weakest exposed component's ability to withstand that voltage. Transients normally flow

into equipment via electrical conductors, but other paths are common. These paths

include: telephone lines, data-com lines, measurement and control lines, DC power buses

and neutral and ground lines. To protect against these surges designers recommend the

installation of a TVSS devices that connects to all points of potential voltage threat and

limit this voltage to a level below the equipment "withstand" voltage. The TVSS device

absorbs or diverts all the energy present in the surge and clamping or holding the "let

through" over voltage down to a level safe for exposed circuitry.

TVSS protection is typically applied at several points throughout a facility. These

locations include the service entrance point, distribution panels, branch panels and the

individual circuit.


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As you can see a TVSS device is important to a mission critical electrical system

and its benefits are great. A TVSS is a low cost protection device that will help to reduce

downtime or production losses. It helps to extend lighting lamp and ballast life

expectancy. The TVSS will help in reducing motor stress and overheating and is a

constant protection of data processing and digital equipment. If your mission critical

facility does not already have TVSS devices installed we highly recommend it. If you are

not sure if your system has them installed we suggest asking your engineer or electrician

to verify. It is a small price for additional peace of mind.

A transient voltage suppressor or TVS is a general classification of an array of

devices that are designed to react to sudden or momentary overvoltage conditions. Onesuch common device used for this purpose is known as thetransient voltage suppression

diode that is simply a Zener diode designed to protect electronics device against over

voltages.Another design alternative applies a family of products that are known asmetal-

oxide varistors (MOV) that protect electronic circuits and electrical equipment.

The characteristic of a TVS requires that it respond to overvoltage faster than

other common overvoltage protection components such as varistors or gas discharge

tubes.This makes TVS devices or components useful for protection against very fast and

often damaging voltage spikes. These fast overvoltage spikes are present on all

distribution networks and can be caused by either internal or external events, such as

lightning or motor arcing. Applications of transient voltage suppression diodes are used

for unidirectional or bidirectional electrostatic discharge protection of transmission or

data lines in electronic circuits. MOV based TVSs are utilized to protect home

electronics, distribution systems and may accommodate industrial level power

distribution disturbances saving downtime and damage to equipment. The level of energyin a transient overvoltage can be equated to energy measured in joules or related to

electric current when devices are rated for various applications. These bursts of

overvoltage can be measured with specialized electronic meters that can show power

disturbances of thousands of volts amplitude that last for a few microseconds or less.
http://en.wikipedia.org/wiki/Transient_voltage_suppression_diodehttp://en.wikipedia.org/wiki/Transient_voltage_suppression_diodehttp://en.wikipedia.org/wiki/Zener_diodehttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Overvoltagehttp://en.wikipedia.org/wiki/Overvoltagehttp://en.wikipedia.org/wiki/Varistor#Metal_oxide_varistorhttp://en.wikipedia.org/wiki/Varistor#Metal_oxide_varistorhttp://en.wikipedia.org/wiki/Varistorhttp://en.wikipedia.org/wiki/Gas_discharge_tubehttp://en.wikipedia.org/wiki/Gas_discharge_tubehttp://en.wikipedia.org/wiki/Voltage_spikehttp://en.wikipedia.org/wiki/Electrostatic_dischargehttp://en.wikipedia.org/wiki/Joulehttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Joulehttp://en.wikipedia.org/wiki/Electrostatic_dischargehttp://en.wikipedia.org/wiki/Voltage_spikehttp://en.wikipedia.org/wiki/Gas_discharge_tubehttp://en.wikipedia.org/wiki/Gas_discharge_tubehttp://en.wikipedia.org/wiki/Varistorhttp://en.wikipedia.org/wiki/Varistor#Metal_oxide_varistorhttp://en.wikipedia.org/wiki/Varistor#Metal_oxide_varistorhttp://en.wikipedia.org/wiki/Overvoltagehttp://en.wikipedia.org/wiki/Overvoltagehttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Zener_diodehttp://en.wikipedia.org/wiki/Transient_voltage_suppression_diodehttp://en.wikipedia.org/wiki/Transient_voltage_suppression_diode


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2.2 TRANSIENT VOLTAG SUPRRESSION DIODE

Transient-voltag-suppression diode

Fig.2 Schematic symbols used to denote a bidirectional transient-voltage-suppression

diode.

Fig.3 STMicroelectronics Transit devices. These devices are 1.5KE series, able to handle

1.5 kW of peak power for a short period .

A transient-voltage-suppression (TVS) diode is an electronic component used to

protect sensitive electronics from voltage spikes induced on connected wires.[1]

The

device operates by shunting excess current when the induced voltage exceeds the

avalanche breakdown potential. It is a clamping device, suppressing all overvoltage

above its breakdown voltage. Like all clamping devices, it automatically resets when the

overvoltage goes away, but absorbs much more of the transient energy internally than a

similarly ratedcrowbar device.
http://en.wikipedia.org/wiki/Circuit_diagramhttp://en.wikipedia.org/wiki/Electronic_componenthttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Voltage_spikehttp://en.wikipedia.org/wiki/Transient-voltage-suppression_diode#cite_note-1http://en.wikipedia.org/wiki/Transient-voltage-suppression_diode#cite_note-1http://en.wikipedia.org/wiki/Transient-voltage-suppression_diode#cite_note-1http://en.wikipedia.org/wiki/Avalanche_breakdownhttp://en.wikipedia.org/wiki/Clamp_%28circuit%29http://en.wikipedia.org/wiki/Crowbar_%28circuit%29http://en.wikipedia.org/wiki/File:Transils-01.jpeghttp://en.wikipedia.org/wiki/File:Transient_voltage_suppression_diode_symbol.svghttp://en.wikipedia.org/wiki/File:Transils-01.jpeghttp://en.wikipedia.org/wiki/File:Transient_voltage_suppression_diode_symbol.svghttp://en.wikipedia.org/wiki/Crowbar_%28circuit%29http://en.wikipedia.org/wiki/Clamp_%28circuit%29http://en.wikipedia.org/wiki/Avalanche_breakdownhttp://en.wikipedia.org/wiki/Transient-voltage-suppression_diode#cite_note-1http://en.wikipedia.org/wiki/Voltage_spikehttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Electronic_componenthttp://en.wikipedia.org/wiki/Circuit_diagram


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A transient-voltage-suppression diode may be either unidirectional or

bidirectional. A unidirectional device operates as a rectifier in the forward direction like

any otheravalanche diode,but is made and tested to handle very large peak currents. The

popular 41.5KE series allows 1500 W of peak power, for a short time. A bidirectional

transient-voltage-suppression diode can be represented by two mutually opposing

avalanche diodes in series with one another and connected in parallel with the circuit to

be protected. While this representation is schematically accurate, physically the devices

are now manufactured as a single component.

A transient-voltage-suppression diode can respond to over-voltages faster than

other common over-voltage protection components such as varistors or gas discharge

tubes.The actual clamping occurs in roughly onepicosecond,but in a practical circuit the

inductance of the wires leading to the device imposes a higher limit. This makes

transient-voltage-suppression diodes useful for protection against very fast and often

damaging voltage transients. These fast over-voltage transients are present on all

distribution networks and can be caused by either internal or external events, such as

lightning or motor arcing. Transient-voltage suppressors will fail if they are subjected to

voltages or conditions beyond those that the particular product was designed to

accommodate. There are three key modes in which the TVS will fail: short, open, and

degraded device.
http://en.wikipedia.org/wiki/Rectifierhttp://en.wikipedia.org/wiki/Avalanche_diodehttp://en.wikipedia.org/wiki/Avalanche_diodehttp://en.wikipedia.org/wiki/Varistorhttp://en.wikipedia.org/wiki/Gas_discharge_tubehttp://en.wikipedia.org/wiki/Gas_discharge_tubehttp://en.wikipedia.org/wiki/Picosecondhttp://en.wikipedia.org/wiki/Inductancehttp://en.wikipedia.org/wiki/Inductancehttp://en.wikipedia.org/wiki/Picosecondhttp://en.wikipedia.org/wiki/Gas_discharge_tubehttp://en.wikipedia.org/wiki/Gas_discharge_tubehttp://en.wikipedia.org/wiki/Varistorhttp://en.wikipedia.org/wiki/Avalanche_diodehttp://en.wikipedia.org/wiki/Avalanche_diodehttp://en.wikipedia.org/wiki/Rectifier


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3.2 A HYBRID SURGE PROTECTION DEVICES

Hybrid surge protection devices combine at least two types of surge components

typically MOVs and SADs. An effective hybrid design limits the amount of surge

current through the SAD module to an acceptable level and diverts the remaining surge

current through the MOV modulesharing the surge. When properly designed, a hybrid

SPD will outperform an SPD that uses only MOVs. However, an effective hybrid SPD

requires significant engineering.

SOME OF THE PITFALLS OF A HYBRID APPROACH INCLUDE:

Designs with all components on-line at all times can result in component failure during

surge or overvoltage events.

Some components may not be appropriate for the application of the end unit.

Some manufacturers may claim a capacitor constitutes a hybrid design, but this may not

be the case.

The key to a successful hybrid design is to maximize each individual components

strengths and transition awayfrom the weaknesses.


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FIG.4 POORLY DESIGNED HYBRID SPD

FIG.5 PROPERLY DESIGNED HYBRID SPD


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3.3 THYRISTOR SURGE PROTECTION DEVICES

Thyristors are crowbar devices. Thyristors are based on a pair of intertwined

bipolartransistors created by a 4 layer stack of n and p doped silicon regions as shown in

Figure16. The n doped region N1, p doped region P1, and n doped region N2 form the

emitter,base and collector of an npn transistor while p doped region P2, n doped region

N2, and pdoped region P1 form the emitter, base and collector of a pnp transistor. With

thisarrangement the collector of each transistor provides the base of the other transistor.

In this way any emitter to collector current of one transistor provides the base current for

theother transistor. For a positive Anode to Cathode voltage, both emitter-base junctions,

J1and J3, are forward biased. Only the reverse biased junction J2 prevents current flow.

Ifthe Anode to Cathode voltage is increased to the breakdown voltage of the J2 junction

Currents will begin to flow directly into the bases of the two bipolar transistors. Thisturns

both transistors on. With both transistors on the Thyristors resistance drops, andthe

voltage across the Thyristor also drops. The resulting I-V curve for forcing a

positivecurrent from the Anode to the Cathode of a Thyristor is shown in Figure 17. A

protection. Element with this form of I-V curve can provide excellent protection; when

triggered the Voltage drops well below the trigger condition and considerable current canbe carriedwith very little power dissipation in the protection element. A caution is that the

currentor voltage must fall below the Holding Point, as shown in Figure 17, to return the

Thyristor to its high resistance state.

FIG.6 THYRISTOR PHYSICAL STRUCTURE AND CIRCUIT


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FIG.7 I-VCURVE FOR A THYRISTOR BIASED ANODE TO CATHODE

Under a negative Anode to Cathode voltage there is no regenerative feature and

the I-V curve looks like a reverse bias diode breakdown. The protection properties of a

simple Thyristor are very asymmetric. To provide symmetrical crowbar behavior it is

necessary to use two anti parallelThyristors. This can be done with a pair of discrete

Thyristors, as, or it can be done with an integrated structure on a single piece of silicon

including

5 doping levels, as illustrated in Figure 18b. The integrated device is usually called a

Thyristor Surge Protection Device (TSPD) and its I-V characteristic is shown in figure.

Most TSPDs are of the symmetrical behavior but there are other options.


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Referenceswww.wikipedia.com

www.rosemount.com

www.emersonelectric.com

www.onsemi.com
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