Basics Electricity

8/2/2019 Basics Electricity

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Physical laws

Variables and units

Electrical definitions

Breaking techniques

Types of networks

Device functions

A

B

C

D

E

F

Understand the basics of electricity March 20071

UNDERSTAND THE BASICS OF ELECTRICITY

Understand the basic laws andvocabulary of electricity

Duration: 29 mn

Expert: P. GIVORD / D. FULCHIRONPedagogy: F. FINCHELSTEINProduction: M. ALLAGNAT / E. RODRIGUES


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Physical laws

Variables and units


Breaking techniques

Types of networks

Device functions

A

B

C

D

E

F


VARIABLES AND UNITS

Variables and units


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- multiples and sub-multiples of units

Multiples

103 106 109 1012k M G T

kilo mega giga tera

Sub-multiples

10-3 10-6 10-9 10-12m n p

milli micro nano pico


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- international system of measurement units

Base units

Dimensional equation: examples

Speed: LT-1 Acceleration: LT-2

Force: MLT-2 Electric charge:IT Voltage:ML2T-3 I-1

L length meter mM mass kilogram kg

T time second sI electric current ampere A

These variables form the base of all other units


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- particular measurement units

Length:

1 centimeter = 0.3937 inch

1 meter = 1.094 yards

1 kilometer = 0.6214 mile

Weight:

1 gram = 15.4 grains

1 kilogram = 2.2046 pounds

1 metric ton = 0.9842 ton


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- main variables and related units

rs

l

U = R I

R =

force N Newtonenergy J Joulepower W Wattacceleration m / s2pressure Pa Pascalmoment of inertia kg.m2

electric charge C Coulombvoltage V Voltelectric field V / mimpedance W ohmresistance Wreactance W

inductance H Henrycapacitance F Faradmagnetic induction T Teslamagnetic field A / mmagnetic flux Wb Weberpermeability m H / mpermittivity e F / m

conductance S Siemensresistivity W . mfrequency Hz Hertz (s-1)angular frequency rd / s


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- sun - earth power emission

10 TWhuman activity

180.103 TW1400 W / m received

200 TWphotosynthesis

35 TW

internal

180.103TWre-emitted

loss of

mass:

4.109kg /s

390.1012TWradiation

1000 nuclear reactors = 1 TW


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Physical laws

Variables and units


Breaking techniques

Types of networks

Device functions

A

B

C

D

E

F


ELECTRICAL DEFINITIONS



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- voltages

Equipment operating characteristics are defined by three voltagevalues:

rated voltage

service voltage

rated insulation level

overvoltage withstand at power frequency for one minute

standardized impulse withstand voltage

l


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- voltages

rated voltage

rated insulation level rated impulse withstandvoltage

STANDARD IEC VOLTAGES

t


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- currents

Equipment

rated normal current

rated short-time withstand current

The peak value of rated short-time withstand current is equal to2.5 times the rms value

Network

service current

short-circuit current (or Isc)

f


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- frequency

Two frequencies are commonly used in the world:

50 Hz in Europe

60 Hz in North America

Some countries use both frequencies:

Japan, Saudi Arabia...

PHYSICAL LAWS


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Physical laws

Variables and units


Breaking techniques

Types of networks

Device functions

A

B

C

D

E

F


PHYSICAL LAWS

Physical laws

how is electrical energy produced?


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- how is electrical energy produced?

A magnet rotating near a circuit containing turns generatesalternating voltage (Lenz's law)

e

= magnetic flux

e =dt

d

representation of an alternating variable


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- representation of an alternating variable

An alternating variable may be represented by a rotating vector anda sine wave

3p/2

q 02p

p/2

p0 p/2 p 3p/2 2p

y = a sin qy y

r

q

r

qq

rr

q

alternating current


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I rms = Isc / 2

- alternating current

Root mean square (rms) value: the value of direct current thatwould give off the same energy by the Joule effect in a resistor

0 q/w p/w 2p/w

I

t

IscI rms

i = Isc . sin wt

... The same thing applies to voltage

Ohm's law applied to direct current


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P in W

in . m

I in m

S in m

r

- Ohm s law applied to direct current

U = RI

Wire resistance: R = l / s

r = 1.8.10- .m copper

r = 2.9.10- .m aluminumr = 100.10- .m nickel - chromium (alloy for resistors)

I inA

U inV

R in

U

I R

P = U I = R I = U / R

Ohm's law applied to alternating current (AC)


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- Ohm s law applied to alternating current (AC)

z =impedanceof the AC curcuit with afrequency fw = 2 p f current angular frequency

RL

Ci

u

u = z . i in complex numbers

equivalent circuit

u

z

i

X Z

R

z is a complex number,the real part of which is resistance Rand the imaginary part reactance X

z = R + j.X z in Wwhere X = Lw - 1/ Cw X in WL: inductance in Henry f in HzC: capacitance in Farad

Ohm's law applied to alternating current (AC)


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- Ohm s law applied to alternating current (AC)

z

iu

z = R + j X

z = (Z , ) in polar formwhere Z2 = R2 + X2and tg = X / Rz = Z e j

i = I e j w t

u = z . i = Z.I ej

. ej w t

= Z.I e j(w t + ) = U e j(w t + )

z

i

u

U = ZIX

R

u = z . iin complex numbers

- active power and reactive power


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active power and reactive power

P(t) = U(t) . I(t) = U . I sin(wt) sin(wt)

P(t) = U . I cos (1 cos2 wt) + U . I sin sin (2 wt)

The integral cycle shows:

S = U.I apparent power in VA

Q = U.I.sin reactive power in VARP = U.I.cos active power in W

P Q

- line losses and voltage drops


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line losses and voltage drops

Source Load

Line

z = R + j X

V1 V2

I

The Joule effect depends only on R

P I Rline= .2

(in Watts)

Depend on R and X

D V = V1 - V2(in Volts)

Line losses Voltage drops

- law of impedance combination


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law of impedance combination

z1

z2

z = z1 + z2

The impedances add up

z1 z2

1 / z = 1 / z1 + 1 / z2

z = z1 . z2 / (z1 + z2)

The admittances add up

Series:

Parallel:

Admittance = reciprocal of impedance

- three-phase diagram


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V2 lagging behind V1

3

2p

three phase diagram

N

Ph3

Ph 2

Ph1

2V

V3

V1

U23

U12

3

2p

3

2p

3

p2

U31

V1, V2, V3: phase voltages

U12, U23, U31: phase-to-phase voltages

U12 = V2 - V1 in vectors

In balanced three-phase operatingconditions,U = V . 3

3 coils with phase

displacement of 120 (2 p / 3)

- why three-phase current?


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why three phase current?

The most economical way to transmit movement: minimum numberof coils to create a rotating magnetic field

AC generator motor

- three-phase power diagram


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Apparent power

S = U.I. in VA (= 3 VI)3

Active power

Pr = U.I. cos in W (= 3VI cos)3

Pa

Pr

RII

jXI

p p g

Reactive power

Pr = U.I. sin in VAR3

- Coulomb's law


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q M Er4p e r2

q

E =

Electric field created on M by a point charge q

Interaction between two electric point charges

q q' FdFq . q'

F =

4p e r2q in CE in Vr in md in me in F/m e0 = dielectric constant in a vacuum

er

= relative permittivity of ambient material

Dielectric constant e = e0 . e re0 = 10

-7 / 4 p c0 = 8.85 . 10-12 F / m

Two charges of the same sign repel each otherTwo charges of the opposite sign attract each other

- Kirchhoff's law


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On a node

S i = 0N

A

B

C D

E

Around a loop

S D u = 0

- Ampre's law


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p

A continuous straight conductor, through which a current (I) flows,creates magnetic induction B in the surrounding space

I

B

rMagnetic permeability m = m0.mrm0 = 4 p 10

-7 = 12.6 .10-7 0 in H/m

mr = 1 for vacuum, air, aluminum

mr= 600 800 for iron

e0. m0 . c02 = 1

B in T

I in A

R in m

m0 I

div B = 0

B =2pr

-Laplace's law of force


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Induction B exerts force F on a conductor through which a current(I) is flowing

F = i . dl . B . sin aF = i . dl L B

I

B

a

F

Right hand

Thumb

Middle finger

Index finger

- Lenz's law


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A conductive circuit forms a ring around a surface through whichthe induction varies. The circuit is subjected to an electromotiveforce E along the circuit.

B variable(increasing)

E

E = - d / dt

- Ampre's and Laplace's laws


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II

Force of repulsion---> loop effect

Proportional tothe product

of the currentsI I

Force of attraction

- Lenz's and Laplace's laws


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Circular currents induced in metal frames by a variation in magneticflux

Aluminumdisk

- calculation of voltage drop


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Voltage drop in vectors V1 - V2 = z . I = (R + j.X).I

As an absolute value, this is very close to AB = AH + HB

Hence DV = R I cos + X I sin PLEASE NOTE: voltage drop may be negative....

Source Load

line

z = R + jX

V2

Z , V1

I

D V

V2 R.I

A H B

V1

X.I

I DV

TYPES OF NETWORKS


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Physical laws

Variables and units


Breaking techniques

Types of networks

Device functions

A

B

C

D

E

F


Types of networks

- different types of MV networks


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Overhead or underground

Two types of configuration

Radial

Loop

- radial configuration


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Substation

Clusteredconnection

Direct connection

Substation

- open loop configuration


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substation substation substation

- networks


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- public network


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LVconsumer

MVconsumer(service sector,small industry)

HVconsumer(heavy industry)

EHVnational

MVlocal

LVlocal

HVregional

DEVICE FUNCTIONS


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Physical laws

Variables and units


Breaking techniques

Types of networks

Device functions

A

B

C

D

E

F


Device functions

- safety functions: isolation, earthing


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DESIGNATION FUNCTION Switching on/off Closing/breakingAND SYMBOL of service currents of fault current

DisconnectorIsolate NO NO

Earthing switch

Isolate NO NO(capable ofclosing on

short-circuit)

- control functions


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NO

DESIGNATION FUNCTION Switching Closing and breakingAND SYMBOL on/off of of fault currents

service currents

YESSwitch on / off

not isolate

SwitchNO

NOYESSwitch on / offnot isolate

DisconnectorNO

NOYESSwitch on / offnot isolate

NOContactor

- protection functions


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Protectnot isolate YES

(once)

NOFuse

Switch on / off

Protect - isolatein "disconnected"

position

DESIGNATION FUNCTION Switching on-off Closing and breaking

AND SYMBOL the service currents the faulted currents

Protectnot isolate

YES YESFixed circuit breaker

DESIGNATION FUNCTION Switching on/off Closing and breakingAND SYMBOL of service currents of fault currents

YESYESWithdrawable circuit-breaker

BREAKING TECHNIQUES


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Physical laws

Variables and units


Breaking techniques

Types of networks

Device functions

A

B

C

D

E

F


Breaking techniques

- the electric arc


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An arc is created when the voltage between two conductors isgreater than the maximum dielectric withstand of the mediumbetween the conductors

Irreversible deterioration in solid insulating materials

Ionization of the medium between the contacts air

SF6 gas

oil vacuum: vaporization of metal on the contacts

The ionized insulating medium becomes temporarily conductive

Presence of an arc voltage according to the ionized medium andthe type of electrodes

- the "puffer" technique


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Movingcontact

Fixed

contact

I

Flow ofcurrent

Separationof contacts &

arcing

Lengtheningof the arc &

blow-out

Extinction of the arcwhen the current

reaches zero

- the vacuum technique


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Movingcontact

Fixedcontact

I

Flow of

currentInitial

AMF

Diffuse

U net

RMF

Constricted

Control of the arc Interruption

- end of the module


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Thank you for your attentionAnd don't hesitate to discover:

Basics Electricity

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