7/28/2019 1.2 Terminology...

1/41

E l e c t r i c a l S t a n d a r d P r o d u c t s

S w i t c h g e a r T r a i n i n g C e n t r e , C o o n o o r

7/28/2019 1.2 Terminology...

2/41

UNDERSTANDING SWITCHGEAR TERMINOLOGY

S w i t c h g e a r T r a i n i n g C e n t r e , C o o n o o r

E l e c t r i c a l S t a n d a r d P r o d u c t s

7/28/2019 1.2 Terminology...

3/41

W h a t i s S w i t c h g e a r ?

S w i t c h g e a r T r a i n i n g C e n t r e , C o o n o o r

UNDERSTANDING SWITCHGEAR TERMINOLOGY

7/28/2019 1.2 Terminology...

4/41

A device or a combination of devices,

primarily intended for the purpose of

making, carrying and breaking electriccurrents in circuits during normal circuit

conditions as well as under abnormal

(faulty) circuit conditions

S w i t c h g e a r T r a i n i n g C e n t r e , C o o n o o r

WhatisSwitchgear?

UNDERSTANDING SWITCHGEAR TERMINOLOGY

7/28/2019 1.2 Terminology...

5/41

L o w Vo l t a ge Sw it c hg e a r Terminology

WhataretheLVSwitchgearTerminologies?

TheLVSwitchgearTerminologiesaregenerallywithrespecttothefollowingparameters:

Voltages

Currents

BehaviorunderNormal&OverloadConditions

Behaviorunder

Short

Circuit

Conditions

Utilisationcategories

S w i t c h g e a r T r a i n i n g C e n t r e , C o o n o o r

7/28/2019 1.2 Terminology...

6/41

RATEDOPERATIONAL

VOLTAGE

(Ue)

RATEDINSULATION

VOLTAGE

(Ui)

RATEDIMPULSEVOLTAGE(Uimp)

L O W V O L T A G E S W I T C H G E A R

T E R M I N O L O G Y V O L T A G E S

S w i t c h g e a r T r a i n i n g C e n t r e , C o o n o o r

7/28/2019 1.2 Terminology...

7/41

Rated Operational Voltage (Ue): This is the voltagethat would normally be available continuously

across the terminals of different phases of the

switchgear. Unless otherwise specified, this ratingwill be 415V for LV Switchgear. This implies that

even while 415V @50Hz is present between the

terminals, there will not be any flashover (i.e.) the

insulation between phases is sufficient to tolerate a

potential difference of 415V continuously.

LOW VOLTAGE SWITCHGEAR TERMINOLOGY

V O L T A G E S

7/28/2019 1.2 Terminology...

8/41

Rated Insulation Withstand Voltage (Ui): Then, one

might ask, at what voltage the interphase

insulation would fail, if it would not fail for 415V.

What is be the probability of such a happening,that the system voltage can go beyond 415V?

LOW VOLTAGE SWITCHGEAR TERMINOLOGY

V O L T A G E S

7/28/2019 1.2 Terminology...

9/41

There are two possibilities (viz.) transformer tap

changers & the system fluctuation on the upperside. One can go by the permissible fluctuationsin the supply voltage (+10%) and the worst

probable tap ratios in transformers (+/

12.5%).Considering that the worst condition of thetransformer tap in the maximum position and at

the same time, the system voltage too fluctuateson the plus side, there could be a net systemvoltage variation of +25% + +10% on the

switchgear.

LOW VOLTAGE SWITCHGEAR TERMINOLOGY

V O L T A G E S

7/28/2019 1.2 Terminology...

10/41

If the switchgear is exactly rated for 415V, then

under the above conditions, it would fail. So,

another rating called Ui is specified. Normallythis would be 690V for LV Switchgear. Even

under the worst condition as described above,

the 415V system voltage would not go beyond595V. So, a switchgear rated for an Ui of 690V

would very well withstand the above condition.

LOW VOLTAGE SWITCHGEAR TERMINOLOGY

V O L T A G E S

7/28/2019 1.2 Terminology...

11/41

Rated Impulse Withstand Voltage (Uimp): Therecould be impulse voltages striking the system either a Lightning Impulse (LI) or a SwitchingImpulse (SI). These are very high magnitude butvery short duration voltage waves. Typically, theyare high frequency. They can strike our system

and our switchgear might fail. So, this rating isalso given for switchgear.

LOW VOLTAGE SWITCHGEAR TERMINOLOGY

V O L T A G E S

7/28/2019 1.2 Terminology...

12/41

R a t e d I m p u l s e V o l t a g e ( U i m p )

Impulse voltage values are selected based on

Rated voltage range

Installation category

Parameters considered for selection

Internally generated Overvoltage

Ability to withstand externally applied

Overvoltage

Both to conform to values given in the table

Use of surge suppressors, if necessary

7/28/2019 1.2 Terminology...

13/41

7/28/2019 1.2 Terminology...

14/41

I n s t a l l a t i o n C a t e g o r y( O v e r v o l t a g e c a t e g o r y )

CategoryI Speciallyprotectedlevel

CategoryII Load(Appliancesor

Equipment

level)

CategoryIII DistributionCircuit

level

CategoryIV Originofinstallationi.e.serviceentrancelevel

7/28/2019 1.2 Terminology...

15/41

I m p u l s e v o l t a g e l e v e l sSystemVoltage

Vrms

Cat.IVimp

Cat.IIVimp

Cat.IIIVimp

Cat.IVVimp

50 330 500 800 1500

100 500 800 1500 2500

150 800 1500 2500 4000

300 1500 2500 4000 6000

600 2500 4000 6000 8000

1000 4000 6000 8000 12000

7/28/2019 1.2 Terminology...

16/41

CONVENTIONALFREEAIRTHERMALCURRENT

(Ith)

CONVENTIONALENCLOSEDTHERMAL

CURRENT(Ithe)

RATEDOPERATIONALCURRENT(Ie)

RATEDUNINTERRUPTED

CURRENT

(Iu)

RATEDCURRENT(In)

LOW VOLTAGE SWITCHGEAR TERMINOLOGY

C U R R E N T S

7/28/2019 1.2 Terminology...

17/41

Low Voltage Switchgear Terminology Currents

Rated Free Air Thermal Current (Ith): The current rating

for any equipment given based on the temperature riseonly. As such, the heating current is important.

This specification implies the maximum current thatthe switchgear can carry continuously for a period of 8

hours, without the temperature rise of any part

reaching beyond permissible limits. This test isconducted in openair conditions.

7/28/2019 1.2 Terminology...

18/41

Low Voltage Switchgear Terminology Currents

Rated Enclosed Thermal Current (Ithe): But no LVswitchgear is used in open air. Most of the LV switchgear is

used under enclosed conditions. The heat dissipation willbe poor. So, a more precise rating would be the Ithe.

This implies the maximum current that the switchgear cancarry continuously for a period of 8 hours, without thetemperature rise of any part reaching beyond permissiblelimits. This test is conducted in enclosed conditions.

7/28/2019 1.2 Terminology...

19/41

Low Voltage Switchgear Terminology Currents

Rated Uninterrupted Current (Iu): Again, electricalequipment are utilized, not in intermittent loading periods

of 8 hours each. Rather they are used and loadedcontinuously, much beyond 8 hours.

This rating obviously implies the maximum current theswitchgear can carry continuously for periods extending toeven hours, weeks & months, without the temperaturerise of any part reaching beyond permissible limits. Unless

otherwise specified, this will be equal to the ratedoperational current of the switchgear.

7/28/2019 1.2 Terminology...

20/41

Low Voltage Switchgear Terminology Currents

Rated Operational Current (Ie): All the above three currents

take into account only one function the carry function of the Switchgear. But, a switchgear must also make &break. The making and breaking capacities would varydepending upon the application of the switchgear and are

normally specified as a multiple of the rated continuouscurrent. So, the continuous current of a switchgear wouldalso vary depending upon the application and the making &

breaking capacities expected in that application. Such arating is the Ie rating.

7/28/2019 1.2 Terminology...

21/41

Low Voltage Switchgear Terminology Currents

Rated Current (In): This rating is similar to the Rated

Operational Current Rating, but is applied to Fuses & CircuitBreakers.

7/28/2019 1.2 Terminology...

22/41

C H A R A C T E R I S T I C Q U A N T I T I E S

NORMAL LOAD & OVERLOAD CHARACTERISTICSRATED BREAKING CAPACITY

RATED MAKING CAPACITY

7/28/2019 1.2 Terminology...

23/41

Low Voltage Switchgear Terminology Normal

C o n d i t i o n B e h a v i o r

Rated Normal Condition Making Current: Even during the

normal conditions, a switchgear may be expected toswitchon more than its rated current. For example, whileswitching on an induction motor. The switchgear shouldnot fail then.

This specification implies the maximum current told as amultiple of Ie, that the switchgear can safely make,

without causing any damage to itself or to the installationor to the operator.

7/28/2019 1.2 Terminology...

24/41

Rated Normal Condition Breaking Current: Even during the

normal conditions, a switchgear may be expected toswitchoff more than its rated current. For example, whilethe overload relay of an induction motor senses a overloadand trips the switchgear. The switchgear should not fail

then.

This specification implies the maximum current told as a

multiple of Ie, that the switchgear can safely break,without causing any damage to itself or to the installationor to the operator.

Low Voltage Switchgear Terminology Normal

C o n d i t i o n B e h a v i o r

7/28/2019 1.2 Terminology...

25/41

RATEDSHORTCIRCUITMAKINGCAPACITY(Icm

)

RATEDSHORTTIMEWITHSTANDCURRENT(Icw)

RATEDSHORTCIRCUITBREAKINGCAPACITY(Icn)

Low Voltage Switchgear Terminology Short

C i r c u i t C o n d i t i o n B e h a v i o r

7/28/2019 1.2 Terminology...

26/41

Low Voltage Switchgear Terminology Behavioru n d e r S h o r t C i r c u i t C o n d i t i o n

Rated Short Circuit Making Current: It might be possible thatthe switchgear might be closing on to a fault. (i.e.) theremight be an existing fault and unaware of the same, anattempt is made to close the switchgear. Quite a huge electro

dynamic force is developed under such conditions and theswitchgear shall not explode. It should withstand suchstresses too. This capacity of the switchgear is called the rated

short circuit making capacity. This will tell the maximumcurrent that the switchgear can safely make, under shortcircuit conditions, without causing any damage to itself or tothe installation or to the operator.

7/28/2019 1.2 Terminology...

27/41

Rated Short Circuit Breaking Current: Similarly, a

switchgear is also expected to break short circuit currents.

The capacity of the switchgear to break short circuit

currents is called the rated short circuit breaking capacity.This will tell the maximum current that the switchgear can

safely break, under short circuit conditions, without

causing any damage to itself or to the installation or to theoperator.

Low Voltage Switchgear Terminology Behavior

u n d e r S h o r t C i r c u i t C o n d i t i o n

7/28/2019 1.2 Terminology...

28/41

Rated Short time withstand Current (Icw): When there is ashort circuit, the nearest switchgear to the fault shall tripand isolate the fault. In case, it doesnt trip, the next

upstream breaker would trip after a time delay, and so on.This is called discrimination.

In the worst case of the uppermost stream breaker onlytripping on a down

most stream fault, all the breakers in

series, would have to carry the fault current for the entireduration, without any damage.

Low Voltage Switchgear Terminology Behavior

u n d e r S h o r t C i r c u i t C o n d i t i o n

7/28/2019 1.2 Terminology...

29/41

The ability of the switchgear to carry the short circuitcurrent for the coordinated short circuit time, is called

Icw. Obviously, the more Icw, that a switchgear has got,

the more coordination interval that one has got. This is

normally specified as, say, 50kA for 1 sec. Many switchgear

may have making and breaking capacities of, say, 50kA, but

their oneminute Icw will be lower at, say, 35kA only. So,

this specification must also be paid attention to, while

specifying switchgear.

Low Voltage Switchgear Terminology Behavior

u n d e r S h o r t C i r c u i t C o n d i t i o n

7/28/2019 1.2 Terminology...

30/41

Low Voltage Switchgear Terminology Utilisation

c a t e g o r y

Switchgear is a switching device. As such, it could beemployed for any kind of switching operation. But, its

characteristics like the operational current, the making &breaking currents will greatly depend on the application.Based on the applications, switchgear are categorizedunder different Utilization categories.

7/28/2019 1.2 Terminology...

31/41

N O R M A L S E R V I C E C O N D I T I O NAMBIENT TEMPERATURE

MAXIMUM 40C AVERAGE OVER 24 HRS NOT

MORE THAN 35C

MINIMUM 5C

ALTITUDE

DOES NOT EXCEED 2000m

7/28/2019 1.2 Terminology...

32/41

HUMIDITY

RELATIVE HUMIDITY DOES NOT

EXCEED 50% AT MAXIMUM

TEMPERATURE OF 40 C

POLLUTION DEGREE

POLLUTION DEGREE 3

N O R M A L S E R V I C E C O N D I T I O N

7/28/2019 1.2 Terminology...

33/41

P O L L U T I O N D E G R E E 1 ( L I G H T )

Areas without industries and with low density of houses

equipped with heating.

Areas with low density of industries or houses but

subjected to winds and/or rainfall.

Agricultural areas

Mountainous areas

These areas shall be situated at least 20 km from the sea

and thus not exposed to wind from the sea.

7/28/2019 1.2 Terminology...

34/41

P O L L U T I O N D E G R E E 2 ( M E D I U M )

Areas with industries not producing particularly

polluting smoke and / or with average density of housesequipped with heating.

Areas with high density of houses and / or industries butsubjected to frequent winds and / or rainfall.

Areas exposed to wind from the sea but not too close tothe coast.

7/28/2019 1.2 Terminology...

35/41

P O L L U T I O N D E G R E E 3 ( H E A V Y )

Areas with high density of industries and suburbs

of large cities with high density of heating plants

producing pollution.

Areas close to the sea or in any case exposed to

relatively strong winds from the sea.

7/28/2019 1.2 Terminology...

36/41

P O L L U T I O N D E G R E E 4( V E R Y H E A V Y )

Areas generally of moderate extent, subjected toconductive dusts and to industrial smoke producingparticularly thick conductive deposits.

Areas generally of moderate extent, very close tothe coast and exposed to sea-spray or very strongand polluting winds from the sea.

Desert areas, characterized by no rain for longperiods, exposed to strong winds carrying sand andsalt, and subject to regular condensation.

7/28/2019 1.2 Terminology...

37/41

POLLUTION DEGREEPollution Degree 1- No Pollution or only dry non-conductingpollution

Pollution Degree 2- Normally non-conductive pollution, butoccasionally temporary conductivity caused by condensationmust be expected

Pollution Degree 3- Conductive pollution or dry non-conductive pollution which becomes conducting due tocondensation

Pollution Degree 4- Pollution generates persistent conductivitycaused by conductive dust and/or rain or snow

7/28/2019 1.2 Terminology...

38/41

P o l l u t i o n d e g r e e

Guidelines:

A/c and/or drydustfree areas Degree 1

Household & similar areas Degree 2

Normal industrial

environment Degree 3

Outdoor Installation Degree 4

7/28/2019 1.2 Terminology...

39/41

P O L L U T I O N D E G R E E S

Pollutionlevel Minimumnominal

specificcreepage

distance(mm/kV)

I

Light 16

II Medium 20

III Heavy 25

IV

Very Heavy 31

7/28/2019 1.2 Terminology...

40/41

M a t e r i a l g r o u p

Classification of Insulating materials

Group I 600 < CTI

Group II 400 < CTI < 600

Group III a 175 < CTI < 400

Group III b 100 < CTI < 175

(CTI = Comparative Tracking Index)

7/28/2019 1.2 Terminology...

41/41

ThankYou

stccoonoor@LNTEBG.com

sivakumark@LNTEBG.com