Generation of Three Phase balanced EMFs Flashcards
phase of 3 phase balanced system
and 3 phase load must be what is B,Y,R
what is polyphase
advantages and disadvantages of phase system
B,Y,R are names of each voltage which is 120 degrees btw each other; and I ,same magnitude of V same phase angle,
3 phase load must be star or delta
several single phase voltages having same magnitude
Advantages:
- total power delivered is constant if leads are balanced
- three phase apparatus is more efficient than single phase
- wear and tear are lesser
three phase motor produce a uniform torque whereas, the torque produced by single phase motor is pulsating - three phase motors except synchronous motors, there is no need of providing an auxiliary means of supply very IMP
ex: motor like fan needs starter to start the motor
three phase: required 3/4 weight of copper of that required to transmit same power at a given voltage over a given distance
rotating magnetic field can be set up by passing three phase currents through stationary coils
phase sequence
phase and line quantity
star and delta 3phase connection, what both are equal and formulas
power formulas
also is there anything called ZL
RYB(+), anticlockwise phase angles
BYR(-), clockwise phase angles
In 3 phase both load connections need to have same phase sequence, else magnitude will vary
phase voltage/current: Vph/Iph measured across single winding/load/phase
line voltage/current: V/I measure btw conductor/phase
P1*3=3phase power
Star: IL= IPH;
VL = √3 Vph
Each line voltage leads the corresponding phase voltage by 30
Delta: VL= VPh
IL=√3IPh
Each line current lags the corresponding phase current by 30
power
power=3VphIph
thus…
Active: P = 3VphIphcosθ
p=√3VLILcosθ
Reactive: P = 3VphIphsinθ
p=√3VLIL*sinθ
Apparent: P = 3VphIph
p=√3VL*IL
delta power = 3*star power
nothing called ZL!!!
Wattmeter ISA-2
Is a power measuring instrument,
consists of a fixed coil called current coil (CC)
c=common, v=voltage
moving coil called pressure coil(PC). Pressure coil is also called ‘Voltage coil’
wattmeter has point M and C on left side and L and V and right side
2 wattmeter’s with varying phase angles ISA-2 IMPPP
and formula for ϕ
phase angle: 0,30,60,>60
Load power factor cosϕ
1, 0.866 Lag, 0.5Lag, <0.5Lag
W1=VLI*Lcos(30+ϕ):
√3VlIL/2
VL*IL/2
0
negative(
wattmeter has point M and C on left side and L and V and right side, here Right and Left change), thus W value will became negative
W1=VLILcos(30-ϕ):
√3VlIL/2
VLIL
√3VLIL/2
positive
COMMENTS
W1=W2
W1=W1/2
W1=0;W2=P3 Phase
W1=-ve, W2=+ve
ϕ = tan^-1(√3*(W1-W2/W1+W2))
Energy Calculation
1KWHr=1Unit
KW*hrs = KWHr
there is fixed charges
Rs. 50/- for first KW
Rs. 60/- for every additional KW
ENERGY CONSUMPTION CHARGES:
Energy consumption
Charges
0 to 30 units @ Rs. 3.5 per unit
31 to 100 units @ Rs. 4.95 per unit
101 to 200 units @ Rs. 6.5 per unit
201 to 300 units @ Rs. 7.55 per unit
301 to 400 units @ Rs. 7.6 per unit
Above 400 units @ Rs. 7.65 per unit
Fuel Adjustment Charges @ 14paisa per unit consumed
.Overall Tax 9% on above charges
tariffs electrical bill
calculates units(KWHr)
add the total units*days of month
FIXED CHARGES FOR SANCTION LOAD = first KW70+rest KWHr80
=170+804
THESE DOESNT CHANGE
if units = 256.875
round off to 256, extra units added next month
then energy consumption prices: 0-30,31-100,101-200, above 200
calculate the cost by partition until u reach the specified units
than @8paise of total units => fuel adjustments
then @9percent tax on energy consumption
thus add total
fuses characteristics
Electronic device that protects the circuit from different electrical fault: over current and overload
a fuse scarifies itself and reliably opens the circuit when there is an excessive current
consists of a small conductive material with low R and placed in series
with the circuit. cross-section area of this allows a certain amount of I that is permitted to flow in the circuit.
excessive I will melt
the conductive element in and opens the circuit.
very simple and cheap devices
CLASSIFICATIONS OF RESISTORS
Current or Ampere Rating: max I before blowing
*Melting Time
*Voltage Rating:
Low V (LV) Fuses, (HV) (and even miniature fuses).
- Interrupting Rating/ Breaking capacity=>
InterruptingCharacteristics
max safe I that the fuse
can interrupt at a V less than the max rated V - I^2T value:
heat energy in the fuse, due to I flow and also the arc produced when the fuse is blown.
*Packaging
*Temperature
Current Rating and Melting Time=> thermal characteristics
If there are any inductive components then melting of the conductive element in the fuse is not enough for interrupting the current. though fuse melts, there is a chance of arc in the fuse before the current is completelydisconnected.
amount of I in the circuit increases, the melting time of the conducting element in the fuse decreases due to I2R increases and temp increases rapidly
TYPES OF FUSES
AC Fuses: HV >1000V , LV <1000V
LV types: Cartridge Fuses (Totally Enclosed Type), - -
- Rewirable Fuses, Kit kat type
- (Semi – Enclosed Type), - -
- Switch Fuses, Drop out
- Fuses and Striker Fuses.
HV types: Cartridge Type HRC (HighRupturing Capacity), Liquid Type HRC, Expulsion type
DIFF FUSES
DC FUSES
DC is constant value and is always above 0V
a chance of an electric arc btw the melted wires
electrodes of the DC Fuses are placed at larger distance
AC FUSES
50 or 60 times/s
At one point of
this oscillation, the AC V touches the 0V and hence the arc between the melted electrodes can be easily terminated.
AC Fuses can be much smaller
Cartridge Type
closed structure with the Fuse Links
helps keep the arc
within thecontainer
(LV), (HV) and miniature fuses.
further divided in to D Type,Link Type
Rewireable Fuses
LV fuses
used in house wiring, small industries and other small current
applications.
A Fuse Base: in
and out terminal, (Porcelain)
Fuse Carrier: holds the Fuse Element. (Tinned Cu) Al, Pb, etc.
Fuse Carrier can be easily plugged in or removed from the Fuse Base
DROP OUT FUSE
High-V drop-out fuse mounting plate is fixed in the middle of the support insulator.
insulator has the upper and lower terminals for connection, and also attached to the upper and lower static contact
The fuse tube both ends are equipped with upper and lower moving contact, the fuse penetrates the fuse tube, Move the contact so that the fuse remains closed.
When operating. Insert the lower moving contact of the fuse tube into the lower
terminal with the high V insulated rod and make it come into contact with the lower
stationary contact, then insert the pull hook of the high V insulated rod into the operating ring of the fuse tube to drive the fuse tube the upper moving contact pushed
into the terminal, contact with the static contact, the circuit connected.
fuse is blown: upper and lower movable contact of the fuse tube
loses the tension, the movable contact slides down under the action of the spring, the fuse tube falls by its own weight, the fuse is in the disconnected state,
The fault current =>fuse create an arc. Arc extinguishing tube produces a lot of gas under the action of the electric arc, so that the tube to form a great pressure, the gas jet out at high speed, this powerful
air flow, the arc quickly elongated and extinguished.
Switch Fuse and HRC Fuses, Cartridge Type HV
Liquid Type HV HRC Fuse
switches is used for low and medium voltages circuit,
as 3-pole and 4-pole unit
HRC FUSES
carries the short circuit or faults current for the specific interval of time
And if the fault removes in that specific period then the fuse element remains safe and it does not melt or breaks
fuses element is kept inside the airtight container.
HRC fuse has inverse time characteristic: if the mag of the fault I is high, then their rupturing t is low and for low mag fault I the rupturing t is high.
When the fault current passes through the fuse, the fuse element melt and break.
The enclosure in which the fuse element is placed is filled with the chemical powder.
The vapors of fuse element and the powder together form the high resistive substance
which extinguishes the arc.
used in power systems
Cartridge Type HV:
similar to the low V fuses
in shape of the ring
In some of the HRC two fuse elements are used.
are connected parallel. one element is used for the flows of the
normal current, the other is used for short circuit current where element melts. fuse element for heavy I=tungsten
Liquid Type HV HRC Fuse:
used in the high voltage circuit
has the glass tube which fills with CCl4. The fuse
element places inside the glass tube. The one end of the tube is sealed, and another fix
at the end of the glass tube by the help of the phosphorous bronze wire.
When fault occurs, the short circuit I passes through the fuse element which melts and breaks. ;small quantity of gas generated at
the time of fusion. The liquid uses in the fuse extinguish the arc
Miniature Circuit Breaker
in low V electrical network instead of fuse.
compared to fuse:
automatically switches off circuit in over load condition/faulty condition
MCB is more sensitive to over I than fuse and does it in more reliable way
switch operating knob comes at its off position during tripping, the faulty zone of the can easily be identified.
Quick restoration of supply
Handling MCB is more electrically safe than fuse.
THOUGH
more costly than fuse .
WORKING PRINCIPLE
2 arrangments:
thermal effect of over I => a bimetallic strip
strip is heated and
deflects by bending. which releases mechanical latch. which is attached with operating mechanism, causes to open the MCB contacts.
electromagnetic effect of over I. =>
In short circuit condition, sudden rising of I, causes
electromechanical displacement of plunger associated with tripping coil/ solenoid of
MCB. plunger strikes the trip lever causing release of latch mechanism opening the contacts of MCB
MCB CONSTRUCTION
simple, robust and maintenance
free.just replaced by new one when
required. A MCB has three main parts.These are:
Frame of Miniature Circuit Breaker:a molded case, rigid, strong,insulated housing
Operating
Mechanism of Miniature Circuit Breaker:
“ON,” “OFF,” and “TRIPPED”, manual opening and closing operation of MCB
Trip Unit of Miniature Circuit Breaker:
Two types: A bimetal =>over load current electromagnet =>
short circuit
Operation of MCB
Ratedt I not more than 100 A.
Trip characteristics normally not adjustable.
Thermal or thermal-magnetic operation
3 mechanisms in a single MCB to
make it switched off. mainly one bi - metallic strip, one trip coil and one hand operated on-off lever. First left-hand side power terminal - then bimetallic strip - then current coil or trip coil -then moving contact - then fixed contact and - lastly right had side power terminal. All
are arranged in series.
If circuit is overloaded for long time, bi - metallic strip becomes over heated and deformed. causes displacement of latch point. causes release of spring to open the MCB
The current coil or trip coil during short circuit fault the emf of that coil causes its plunger to hit the
same latch point and make the latch to open MCB in same manner. Again, when operating lever of the MCB is operated by
hand, the same latch point
is displaced as a result moving contact separated from fixed contact
So, whatever the operating mechanism, that means, may be due to deformation
of bi - metallic strip, due to increased emf of trip coil or may due to manual operation,
the same latch point is displaced and same deformed spring is released, responsible for movement of the moving contact.
When the moving contact
separated from fixed contact, there may be a high chance of arc. This arc then goes up
through the arc runner and enters into arc splitters and is finally quenched.
When we
switch on an MCB, we actually reset the displaced operating latch to its previous on
position and make the MCB ready for another switch off or trip operation.
ELCB(earth leakage
current breaker)
ELVB
Voltage Earth Leakage Circuit Breaker
Operating Time of ELCB:
The safest limit of Current which Human Body can withstand is 30ma sec.
Phase (line), Neutral and Earth wire connected through ELCB.
If any current leaks from any electrical installation, ELCB detects the earth leakage
I and makes the power supply off by opening the associated circuit breaker.
2 types ELCB for I and V
ELVB:
One terminal of the relay
coil is connected to the metal body of the equipment to be protected against earth
leakage and other terminal to the earth directly.
If any insulation failure occurs or live phase wire touches the metal body, of the
equipment, there must be a V diff appears across the terminal of the coil
connected to the equipment body and earth. This V diff produces a I
to flow the relay coil.
If the V difference crosses, a predetermined limit, the I in
relay becomes sufficient to actuate the relay for tripping the breaker to
used to detect and protect only that equipment /installation with which it isattached.
RCCB (Residual Current Circuit Breaker)
Phase (line) and Neutral both wires connected through RCD
It falls under the category of wide range of circuit breakers.
and trip the circuit within 30Miliseconed.
extremely effective form of shock protection the most widely used are 30
mA (milliamp) and 100 mA devices. A I flow of 30 mA (or 0.03 amps) is
sufficiently small that it makes it very difficult to receive a dangerous shock. Even 100 mA is a relatively small figure when compared to the current that may flow in an earth
fault without such protection (100s of amps
Function: a device which senses
current and disconnects any low voltage (unbalanced current) circuit whenever any fault occurs.
installed to prevent
human from shocks or death caused by shocks. prevents accidents by disconnecting
the main circuit within fraction of seconds.
based on Kirchhoff’s Current Law i.e. the incoming
current in a circuit must be equal to the outgoing current from that circuit. whenever a fault occur the current balance of line and neutral
did not matches (imbalance occurs, as the fault I finds another earthing path of I.every instance it compares the value of incoming
and outgoing current. Whenever =! equal, the residual current actuates the circuit to trip/switch off.
WORKING PRINCIPAL
There are two coils Primary (containing line I)
and Secondary (containing neutral I) which produces equal and opposite fluxes if
both I are equal. in the case of a fault and both the I
changes, it creates out of balance flux, which produces the differential I
which flows through the third coil (sensing coil) connected
to relay.
The Toroidal transformer, sensing coil and relay together is known as RCD -
Residual Current Device. Test Circuit: The test circuit is always included with the RCD
which basically connects between the line conductor on the load side and the supply
neutral. It helps to test the circuit when it is on or off the live supply.
Whenever the test
button is pushed I starts flowing through the test circuit depending upon the
resistance provided in this circuit. This current passes through the RCD line side coil
along with load current. But as this circuit bypasses neutral side coil of RCD, there will
be an unbalance between the line side and neutral side coil of the device and
consequently, the RCCB trips to disconnect the supply even in normal condition. This is
how the test circuit tests the reliability of RCCB.
MCCB(Molded Case Circuit Breakers)
Rated I up to 1000 A.
Trip current may be adjustable.
Thermal or thermal-magnetic operation.
electromechanical devices which protect a
circuit from Over current and Short Circuit.
primary functions are to provide a means to manually open a circuit and automatically open a circuit under overload or short circuit conditions.
The over current,
in an electrical circuit, may result from short circuit, overload or faulty design.
alternative to a fuse since it does not require replacement once an
overload is detected. Unlike fuse, a MCCB can be easily reset after a fault and offers
improved operational safety and convenience without incurring operating cost.
MCCB have a
* Thermal element for over current and
* Magnetic element for short circuit release which has to operate faster.
MCCBs are manufactured such that end user will not have access to internal workings of the over-current protection device. constructed of two pieces of heavy-duty
electrically insulated plastic, Inside is a series of thermal elements and a Spring-loaded trigger.
When the thermal element gets too warm, from an over current situation, the spring trips, which in turn will shut off the electrical circuit.
