Electrical fundamental assignment

Institute of Technology of Cambodia Electrical
Assignment P a g e | I
ContentsI. Introduction: ............................................................................................. 1
i. Purpose:.....................................................................................................1
ii. Apparatus: ..............................................................................................1
1. Ammeter:..........................................................................................1
2. Voltmeter:.........................................................................................5
II. Electrical system: ......................................................................................6
i. Line voltage:..............................................................................................7
ii. Phase voltage:.........................................................................................7
iii. Ohmmeter:..............................................................................................7
iv. Counter energy: ......................................................................................8
v. The connection: ......................................................................................8
III. Conclusion:................................................................................................9
IV. Reference................................................................................................. 10
V. Solution.................................................................................................... 11

Assignment P a g e | 1
Assignment of Electrical fundamental
I. Introduction:
i. Purpose:
The scope of electrical installation is to help and provide the designer and user
of electrical plants with the correct definition application of equipment, in numerous
practical installation situations. The dimensioning of an electrical plant requires
knowledge of different factors relating to, for example, installation utilities, the
electrical conductors and other components; this knowledge leads the design
engineer to consult numerous documents and technical catalogues.
ii. Apparatus:
There are two types of apparatus that are used in the installation:
1. Ammeter:
An ammeter (from Ampere Meter) is a
measuring instrument used to measure the current in
a circuit. Electric currents are measured in amperes
(A), hence the name. Instruments used to measure
smaller currents, in the milliampere or microampere
range, are designated as milliammeters or
microammeters. Early ammeters were laboratory
instruments which relied on the Earth's magnetic
field for operation. By the late 19th century,
improved instruments were designed which could
be mounted in any position and allowed accurate
measurements in electric power systems. It is
generally represented by letter 'A' in a circle.
There are eight differences type of ammeter:

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a) Moving-coil:
It is a moving coil
ammeter. It uses magnetic
deflection, where current
passing through a coil placed in
the magnetic field of a
permanent magnet causes the
coil to move.
These meters have linear
scales. Basic meter movements
can have full-scale deflection
for currents from about 25
microamperes to 10
milliamperes.
Because the magnetic field is polarized, the meter needle acts in opposite
directions for each direction of current. A DC ammeter is thus sensitive to which
way round it is connected; most are marked with a positive terminal, but some have
center-zero mechanisms and can display currents in either direction. A moving coil
meter indicates the average (mean) of a varying current through it, which is zero for
AC. For this reason, moving-coil meters are only usable directly for DC, not AC.
b) Moving magnet:
Moving magnet ammeters operate
on essentially the same principle as
moving coil, except that the coil is
mounted in the meter case, and a
permanent magnet moves the needle.
Moving magnet Ammeters are able to
carry larger currents than moving coil
instruments, often several tens of
Amperes, because the coil can be made
of thicker wire and the current does not
have to be carried by the hairsprings.
Indeed, some Ammeters of this type do
not have hairsprings at all, instead using
a fixed permanent magnet to provide the
restoring force.

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c) Moving-iron:
Moving iron ammeters use a piece of iron which moves when acted upon by
the electromagnetic force of a fixed coil of wire. This type of meter responds to both
direct and alternating currents (as opposed to
the moving-coil ammeter, which works on
direct current only). The iron element consists
of a moving vane attached to a pointer, and a
fixed vane, surrounded by a coil. As
alternating or direct current flows through the
coil and induces a magnetic field in both
vanes, the vanes repel each other and the
moving vane deflects against the restoring
force provided by fine helical springs. The
deflection of a moving iron meter is
proportional to the square of the current.
Moving iron ammeters are commonly used to
measure current in industrial frequency AC circuits.
d) Electrodynamic:
An electrodynamic
movement uses an
electromagnet instead of the
permanent magnet of the
d'Arsonval movement. This
instrument can respond to
both alternating and direct
current and also indicates
true RMS for AC. See
Wattmeter for an alternative
use for this instrument.
e) Hot-wire:
In a hot-wire ammeter, a
current pass through a wire which
expands as it heats. Although these
instruments have slow response
time and low accuracy, they were
sometimes used in measuring
radio-frequency current. These also
measure true RMS for an applied
AC.

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f) Digital:
In much the same way as the analogue ammeter formed the basis for a wide
variety of derived meters, including
voltmeters, the basic mechanism for
a digital meter is a digital voltmeter
mechanism, and other types of
meter are built around this.
Digital ammeter designs use a
shunt resistor to produce a calibrated
voltage proportional to the current
flowing. This voltage is then
measured by a digital voltmeter,
through use of an analog to digital
converter (ADC); the digital display
is calibrated to display the current
through the shunt.
g) Integrating:
There is also a range of
devices referred to as integrating
ammeters.[6][7] In these
ammeters the current is summed
over time, giving as a result the
product of current and time;
which is proportional to the
electrical charge transferred with
that current. These can be used for
metering energy (the charge
needs to be multiplied by the
voltage to give energy) or for estimating the charge of a battery or capacitor.
h) Picoammeter:
A picoammeter, or pico ammeter, measures very low electric current, usually
from the picoampere range at the
lower end to the milliampere
range at the upper end.
Picoammeters are used for
sensitive measurements where
the current being measured is
below the theoretical limits of
sensitivity of other devices, such
as Multimeters.
Most picoammeters use a "virtual short" technique and have several different
measurement ranges that must be switched between to cover multiple decades of
measurement. Other modern picoammeters use log compression and a "current sink"

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method that eliminates range switching and associated voltage spikes. Special design
and usage considerations must be observed in order to reduce leakage current which
may swamp measurements such as special insulators and driven shields. Triaxial
cable is often used for probe connections.
2. Voltmeter:
A voltmeter is an instrument used
for measuring electrical potential
difference between two points in an
electric circuit. Analog voltmeters move a
pointer across a scale in proportion to the
voltage of the circuit; digital voltmeters
give a numerical display of voltage by use
of an analog to digital converter.
A voltmeter in a circuit diagram is
represented by the letter V in a circle.
Voltmeters are made in a wide range
of styles. Instruments permanently
mounted in a panel are used to monitor
generators or other fixed apparatus.
Portable instruments, usually equipped to
also measure current and resistance in the
form of a multimeter, are standard test
instruments used in electrical and
electronics work. Any measurement that
can be converted to a voltage can be displayed on a meter that is suitably calibrated;
for example, pressure, temperature, flow or level in a chemical process plant.
i) Analog voltmeter:
A moving coil galvanometer can be used as a
voltmeter by inserting a resistor in series with the
instrument. The galvanometer has a coil of fine wire
suspended in a strong magnetic field. When an electric
current is applied, the interaction of the magnetic field
of the coil and of the stationary magnet creates a torque,
tending to make the coil rotate. The torque is
proportional to the current through the coil. The coil
rotates, compressing a spring that opposes the rotation.
The deflection of the coil is thus proportional to the
current, which in turn is proportional to the applied
voltage, which is indicated by a pointer on a scale.

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j) Digital voltmeter:
A digital voltmeter (DVM) measures an
unknown input voltage by converting the
voltage to a digital value and then displays the
voltage in numeric form. DVMs are usually
designed around a special type of analog-to-
digital converter called an integrating
converter.
DVM measurement accuracy is affected
by many factors, including temperature, input
impedance, and DVM power supply voltage
variations. Less expensive DVMs often have
input resistance on the order of 10 MΩ.
Precision DVMs can have input resistances of
1 GΩ or higher for the lower voltage ranges
II. Electrical system:
Three-phase electric power is a
common method of alternating current
electric power generation,
transmission, and distribution. It is a
type of polyphase system and is the
most common method used by
electrical grids worldwide to transfer
power. It is also used to power large
motors and other heavy loads.
A three-wire three-phase circuit
is usually more economical than an
equivalent two-wire single-phase
circuit at the same line to ground
voltage because it uses less conductor
material to transmit a given amount of
electrical power.

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i. Line voltage:
Line voltage is voltage
between any two line in
different phase in polyphase
system. Like in 3 phase system
voltage between R-Y or Y-B or
R-B is line voltage. While
voltage between any Phase and
neutral is Phase voltage say R phase to neutral is Phase voltage. In Three phase star
connection phase Voltage and Line voltage have different values Ratio of line to
phase voltage is √3. While in delta connection line and phase voltage is same.
Generally, line voltage is 400V and phase voltage is 230V (which we used for
residential purpose)
ii. Phase voltage:
The conductors between a voltage source and a load
are called lines, and the voltage between any two lines is
called line voltage. The voltage measured between any line
and neutral is called phase voltage. For example, for a
208Y/120volt service, the line voltage is 208 Volts, and
the phase voltage is 120 Volts.
iii. Ohmmeter:
An ohmmeter is an electrical
instrument that measures electrical
resistance, the opposition to an electric
current. Micro-ohmmeters (micrometer or
micro ohmmeter) make low resistance
measurements. Megohmmeters (also a
trademarked device Megger) measure
large values of resistance. The unit of
measurement for resistance is ohms (Ω).

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iv. Counter energy:
An electricity meter,
electric meter, electrical
meter, or energy meter is a
device that measures the
amount of electric energy
consumed by a residence, a
business, or an electrically
powered device.
Electric utilities use
electric meters installed at
customers' premises for
billing purposes. They are
typically calibrated in billing
units, the most common one
being the kilowatt hour
(kWh). They are usually read
once each billing period.
When energy savings
during certain periods are
desired, some meters may measure demand, the maximum use of power in some
interval. "Time of day" metering allows electric rates to be changed during a day, to
record usage during peak high-cost periods and off-peak, lower-cost, periods. Also,
in some areas meters have relays for demand response load shedding during peak
load periods.
v. The connection:
a) Single phase (2-wires connection phase):
If it is single-
phase connection, two
wires come into your
electrical service panel:
 a black or red 'live'
wire
 a blue 'neutral' wire
A voltage
difference of 230 V
separates these two
wires.

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b) Three phases (3/4-wires connection):
If it is three-phase connection, 3 or 4 wires come into your electrical service
panel, according to what your electrician was able to install with the available utility
network.
 three 'live' wires: black, red, brown or grey
 a blue 'neutral' wire
This will allow him to properly allocate your home's power cables depending
on the type of connection to maintain the balance of the electrical network.
Most of the time, a voltage difference of 230 V separates each live wire from
the neutral, while there is a voltage difference of 400 V between two live wires. This
makes it possible to supply both the domestic cables with 230 V and machines
requiring 400 V (a car charger for example).
Note that some homes are supplied with three-phase 3 x 230 V. A voltage of
230 V separates each live wire and there is no neutral wire.
III. Conclusion:
Electrical Installation is closely associated with other parts of the construction
industry, and electricians find themselves working in all manner of commercial,
residential, agricultural, and manufacturing environments.
In these various settings, they will plan and design, select and safely install a
reliable system. Also, the electrician will commission, test, program, maintain to
relevant standards, diagnose and report malfunctions, and repair systems.
Work organization and self-management, communication and interpersonal
skills, concentration and attention to details, problem solving, flexibility, and a deep
body of knowledge are the universal attributes of the outstanding electrician.

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IV. Reference
http://www.moyokonsult.com/index.php/electrical-installations-maintenance
https://en.wikipedia.org/wiki/Ammeter
https://en.wikipedia.org/wiki/Voltmeter

TTDD TTRRIIPPHHAASSEE
I. Exercice 1 :
Chaque élément chauffant d’un radiateur triphasé doit avoir 400 V à ses bornes. La puissance
absorbée par ce radiateur est de 3kW.
1) Quel type de couplage doit-on réaliser ?
2) Le dessiner sur la figure ci-contre et indiquer la
connexion au réseau EDF.
3) Déterminer la valeur efficace de l’intensité du courant
dans chacun des fils de ligne.
4) Déterminer la valeur de la résistance de chaque élément
chauffant.
5) Calculer la puissance réactive de ce radiateur.
II. Exercice 2 :
Sur la plaque signalétique d’un moteur triphasé on lit 400 V / 700 V.
On utilise un réseau 230 V / 400 V ; 50 Hz. On donne pour chaque enroulement du moteur
l’impédance Z = 46,5  et le déphasage  = 36 °.
Calculer :
1) Calculer le facteur de puissance du moteur
2) Quel doit être le couplage des enroulements du moteur sur le réseau.
3) La valeur efficace J des courants circulant dans les enroulements.
4) La valeur efficace I des courants circulant en ligne.
5) La puissance apparente S
6) La puissance active absorbée P.
7) La puissance réactive Q.
III. Exercice 3 :
Un récepteur triphasé équilibré est couplé en triangle et alimenté par un réseau 230/400 V, 50
Hz. On mesure la puissance P1 reçue pour une phase par ce récepteur
1) L’intensité efficace du courant dans une branche du triangle est égale à 2,78 A. quels
calibres d’intensités et de tension doit-on utiliser pour faire la mesure de P1 sachant que le
wattmètre possède les calibres suivants :
1 A ; 3 A ; 10 A pour le courant
480 V ; 240 V ; 120 V et 60 V pour la tension.
2) La déviation du wattmètre est de 20 divisions, il en comporte 120 au total. en déduire
la valeur de la puissance P1.
3) En déduire la puissance active consommée par ce récepteur.
4) Quel est le facteur de puissance de ce récepteur ?

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V. Solution
Exercice 1:
1. Le type de couplage on doiit réaliser est Couplage triangle.
2. Le dessiner sur la figure ci-contre et indiquer la connexion au réseau EDF.
3. Déterminer la valeur efficace de l’intensité du courant dans chacun des fils de
ligne
On a:      3 3 , 0 1P U J cos U I xcos cos        
3
3000
4.33
3 cos( ) 400 3
I J
P
then I A
U
 
  
   
4. Déterminer la valeur de la résistance de chaque élément chauffant.
On a:
400
92.3
4.33
U
R
I
   
5. Calculer la puissance réactive de ce radiateur
Puissance réactive de ce radiateur est nulle.
Exercice 2:
1. Calculer le facteur de puissance du moteur
On a:
700
3 cos( ) 3 cos( ); 15.05
46.5
U
P U J U I J A
Z
            
0
3 700 15.05 cos(36 ) 25568.98P W    
2. Quel doit être le couplage des enroulements du moteur sur le réseau. La tension
maximale supportée par un enroulement du stator du moteur correspond
exactement à la tension composée du réseau U = 400 V, On couple donc le stator
en triangle.
3. La valeur efficace J des courants circulant dans les enroulements.
On a: 0400
8.60 3.92
1
46.5
2
U
J
Z
j f
   

 
4. La valeur efficace I des courants circulant en ligne
On a: 0 0
I= 3 3 8.6 3.92 14.89 3.92J A     
5. La puissance apparente S
On a: 3 3 3 400 8.60 10320S UJ U I VA     

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6. La puissance active absorbée P
On a:      0
3 3 3 400 8.60 36 8349.05P UJcos UIcos cos W      
7. La puissance réactive Q
On a:      0
3 3 3 400 8.60 36 6065.94Q UJsin UIsin sin Var      
Exercice 3:
1. Quels calibres d’intensités et de tension doit-on utiliser pour faire la mesure de
P1 sachant que le wattmètre possède les calibres suivants:
1 A; 3 A; 10 A pour le courant
480 V; 240 V; 120 V et 60 V pour la tension
On a:    1 230 2.78 0 639.4P UxIxCos xcos W  
Par le courant donner on a
1A; 480V donc P1 = VxIcos(0)=480W
Alor d’intensité et tension que peuvant utiliser pour P1 est 3A; 240V.
2. La déviation du wattmètre est de 20 divisions, il en comporte 120 au total.
En déduire la valeur de la puissance P1.
Le wattmètre mesure
Déviation
P UI
nombre de déviation

On a:
20
240 3 120
120
P W   
3. En déduire la puissance active consommée par ce récepteur.
On a:    240 3 240 3 120P UIcos cos W      
4. Quel est le facteur de puissance de ce récepteur
On a:  
230 2.78
0.95
240 2.78
P
Cos
S

  


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