Generation of Three Phase balanced EMFs Flashcards
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’
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
√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
#wattmeter interchanging = wattmeter negative
W2
√3VlIL/2
VLIL
√3VL*IL/2
positive
W1=VLILcos(30-ϕ):
W2=VLILcos(30+ϕ):
angle will be negative in I<-34, but postive in Z<34
take the positive angle
COMMENTS
W1=W2
W1=W1/2
W1=0;W2=P3 Phase
W1=-ve, W2=+ve
ϕ = tan^-1(√3*(W1-W2/W1+W2))
TOTAL WATTMETER POWER: W1+W2
P(active power)=W1+W2
Q=(√3)
Energy Calculation
tariffs electrical bill
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 #take it as 30-100 thus 70 units
101 to 200 units @ Rs. 6.5 per unit #take it as 100-200 => 100 units
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 #times number of energies
.Overall Tax 9% on above charges
only for energy consumption 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
an electric / electronic device=>protect circuits=> over current,
overload => protection of the circuit.
principle of a fuse is based on the heating effect of the electric current.
small conductive material with low R and placed in series =>certain I permitted to flow
excessive I will melt
conductive element => opens the circuit.
simple and cheap
Miniature Circuit Breaker
in low V electrical network instead of 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
Quick restoration of supply
more electrically safe than fuse.
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
simple, robust and maintenance
free.just replaced by new one when
required
RCCB (Residual Current Circuit Breaker)
RCCB
any
It detects the earth leakage current
Protects the humans and other living beings from Electric shock.
Protects the electrical appliances from are-over.
It consists of sensing coil, secondary coil, primary coil wherein the difference in current between line and neutral is sensed by sensing coil and the signal is sent to relay to trip the circuit.
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.
Electrical Wires and Cabels principal
and CLASSIFICATIONS OF CABLES
Wire is a single electrical conductor
cable is a group of wires swathed in sheathing
conducting materials made of Cu, Al ,Ag ,Fe
conduct power from the point where it is generated to the point where it is used.
Cu, Al wires without insulation are usually used for grounding
,high V transmission lines.
* Nichrome wire, constantan, manganin, used as resistance wires in electrical equipment and appliances
There is a limit to the degree of heat that various types of wire insulation and sizes can safely withstand
Electrical Code specifies the maximum current-carrying capacity in amperes
that is safe for wires of different with different insulations and under different
circumstances and conditions
TYPES of WIRES:
Vulcanised Indian Rubber wire (V.I.R)
❖ Tough Rubber Sheathed wire (T.R.S)
❖ Poly Vinyl Chloride wire (P.V.C.)
❖ Lead Alloy Sheathed wire
❖ Weather Proof wires
❖ Mineral Insulated Copper Covered wire
CLASSIFICATIONS OF CABLES
- Low tension cables: max V handling capacity 1000 V
- High tension cables:
11 kV. - Super tension cables: 33 kV.
- Extra high tension cables:
66 kV. - Extra super voltage
132 kV.
EARTHING/grounding
transferring immediate discharge of electricity directly to the earth plate, by means of low resistance
electrical cables or
wires.
In case of a short circuit due to leakages arising from weak insulation or damage,
safely removes excess electricity and passes it on to the ground
alternative path for dangerous currents to flow so that accidents
COMPONENTS
Earth Continuity Conductor / Earth Wire
interconnects the overall metallic parts of electrical installation where electrical devices, components are installed => earth wire or earth continuity conductor
The resistance of the earth continuity conductor is very low.
Earthing Lead or Earthing Joint
The point where earth continuity conductor and earth electrode meet is.
should be minimum joints in earthing lead
copper wire can be used as earthing lead or A hard drawn bare copper wire
as an earthing lead.
To increase safety: 2 copper wires are used as
earthing lead to connect the device metallic body to the earth electrode or earth plate.
thus there would be four earthing leads.
Earthing Electrode or Earth Plate
A metallic electrode or plate which is buried in the earth (underground)
final metallic (plate) part of the earthing system which is connected with earthing lead
A metallic plate, pipe or rode is used which has low resistance
