Why energy meter reads energy while wattmeter does not. An energy meter has a registration constant of 100rev/kwh if the meter is connected to a load

An energy meter is fitted with some type of registration mechanism whereby all the instantaneous reading of power are summed over a definite period of time.ENERGY = POWER X TIME So, an energy meter can read energy.Whereas, a wattmeter indicates the value of power at a particular instant when it is read and hence it can not read energy.
Registration constant= 100 rev/Kwh I = 20 A, V = 230 V, cos φ = 0.8
Energy in 5 hours = VI Cos φ x 5 / 1000
= 20 x 230 x 0.8 x 5 / 1000
= 18.4 Kwh
The number of revolution of the meter should make it is correct
= 18.4 x 100
= 1840 revolution.
Number of revolution actually made
= 1800 revolution
(% error = 1840 - 1800 x 100 )/ 1840
= 0.0217%
It would be better from the customer point of view % age error is very less.

A Note on PMMC Instruments

1. DEFLECTING TORQUE:- The deflecting torque is produced by making use of one of the magnetic, chemical, electrostatic and electromagnetic induction effects of current or voltage and causes the moving system of the instrument to move from its zero position when the instrument is connected in an electrical circuit to measure the electrical quantity. The method of producing this torque depend upon the type of instrument. In attracting the type of instrument, this torque to equal to Td = 1/2 I2 dL/dθWhereas in Pmmc instruments Td = Bilur Where B - magnetic density i - current flowing l - length of coil u - number of turn r - radius of coil 2. CONTROLLING TORQUE:- The magnitude of the movement to the moving system would be somewhat indefinite under the influence of deflecting torque unless some controlling torque exist. This torque opposes the deflecting torque and increases with increase in deflection of the moving system without controlling system the irrespective magnitude of current and moreover, once deflected it would not return to its zero position on removing the current. In attraction type instrument it is produced by spring control and in PMMC too it would be produced by spring control. 3. DAMPING TORQUE:- This torque is also necessary to avoid oscillation of the moving system about it's final deflected position owing to the inertia of the moving parts and to bring the moving system to rest in it's final deflected position quickly.

An energy meter revolves 10 revolutions of disc for unit of energy. Find the number of revolutions made by it during an hour when connected across whe

Energy consumed in one hour = VI cos φ / 1000
= 210 x 20 x 0.8 / 1000
= 3.360 kwh.

The number of revolution the meter should make it is correct
= 3.360 x registration const in revolution per kwh
= 3.360 x 100
= 336Number of revolution actually made
= 350
% error = (350-336) x 100 / 350
% error = 0.1466 %

Moving Iron Type Inbstruments

These instruments are widely used in laboratories and switch board at commercial frequencies because these are cheaper in cost, robust in construction and can be manufactured with required accuracy. These are generally of two types:- 1. The attraction type.2. The repulsion type.
The attraction type instrument operate on the principle of attraction of a single piece of soft iron into a magnetic field and repulsion type instrument operate on the principle of repulsion of two adjacent iron pieces magnified by the same magnetic field. Repulsion type instrument are more sensitive than attraction type instrument as in repulsion type instrument large separating torque is developed by having two iron element positional class together inside the field coil where the magnetizing effect is maximum.
In both type of these instruments, the current under measurement is passed through a coil of wire. This current carrying coil set up the necessary field depending on the magnitude of the current to be measured. The coil may be of a few turns of very heavy conductor or of many turns of fine wire. The instrument to be used as an ammeter is provided with a coil of few turns of thick wire in order to have low resistance and carry large current and that to be used as a voltameter is provided with a coil of large number of turns of wire in order to have high resistance and draw as small current as possible.
EXPRESSION FOR TORQUE
Let L be the self inductance corresponding to a total angular deflection of q radians and change in inductance be dL correponding to small change in deflection angel dq due to small change in current.
The change in energy of magnetic field,
dw = Td dθ
Since change in energy dE = workdone, dw
Td dθ = ½ I2dL
Td = ½ I2dL/dθ
where I is in amperes, L is in Henry and θ is in Radians.
Thus toruqe is proportional to the square of the instrument current and to the rate of change of inductance with deflection.

What are Soft starters?

Soft starters make are ABB, Siemens,power boss etc. Soft starters used to minimise the starting time of a motor and limit the current also. In starting time aalso we limit the input voltage of the motor. (Ramp Up Ramp Down Pedestal Step Down Supply Frequency Current Limit Time Current Limit Level Kick Start Time Kick Start Level Arc-less Switching)All theses parameters also we adjustable in soft starters.

Soft starters nothing but thyristor control starters,this different form VFD drives,All VFD drives are soft starters but All soft starters are not Drives,In VFD we can adjust the speed,Torque & master-slave operation,But in soft starters is used only to reduse starting current of motor and for soft starting of motors.

1)air cored reactor soft starters(hormonic effect free)
2)Iron core reactor soft starters(hormonic effect will be there)
2)flux compensating magnetic amplifier starters(FCMA)

Delta Primary & Star Secondary &
Delta Primary & Delta Secondary
This two arrangemetns are imposible....

there are various soft starters for both AC and DC machines...
for DC motor>>>>>
1.three point starter
2.four point starter
for AC motor>>>>>
1.star -delta starter.
2.auto transformer starter
3.rotor resistance starter
4.direct on line starter
soft starters are used.
to reduce the starting current
to reduce the starting voltage
simultaneously to increase the torque of motor as it gains speed
soft starters are not only used to give a soft start to the motor but also togive protections

1.in the absence of the starter the starting current will be too high so it would effect the parallel loads connected and may blow out the fuse
2.if the motor fails to start due to cogging then the circulating current may burn the armature winding of motor
3.as at start the starting current is 10-15 times high so starting torque also 10-15 times high so that torque may damage the motor getting if higher speed than rated.
so the soft starter's are used to start the motor in a safe way

Grounding

Advantages of neutral grounding

• Voltages of phases are limited to "phase to ground" voltage.


• High Voltages due to arcing grounds or or transient line to ground faults are eliminated.


• Sensitive protection relays against L-G faults can be used.


• Overvoltages due to lightening are discharged to ground.

Advantages of isolated neutral

• It is possible to maintain supply with fault on one line.


• Interference with communication lines is reduced because of no Z sequence currents.

Some "matching" problem on electrical machines

Interpoles-------------Commutation in DC machines
Three pt starter ..........D Shunt motor
Dummy coils..................Wave winding
Equalising Ring.............Lap Winding

Frequencies

Frequencies increase from VG to HP to TA.

Vibration Galvanometers (VG):- 5 - 1000 Hz
Head Phones ( HP) :- 200 - 2 KHz
Tuneable Amplifier Detecter( TA) :- 10 - 100 KHz output of this can be fed to pointer type instrument.

Q) Find out level calculation at 11 KV bus . ( % Z = 9.88 )

Fault level at 110 KV bus = 1517 MVA ( from utility's fault study )

Take base MVA as 100

System % Impedance = ( Base MVA x 100 )/ fault MVA

% source impedance = (100 x 100 ) /1517 = 6.59 %

% Impedance of T/F at Base MVA = (9.88 x 100)/12.5 = 79.04 %

Effective Impedance since T/F are in parallel = 79.02/2 = 39.52 %
Fault level at 11 KV Bus = ( base MVA x 100 )/% Z upto 11 KV bus
= (base MVAx100)/(6.59+39.52)
= 100x100/46.11

= 216.87 MVA

Fault current on 11 KV side = ( 216.87 x 10^6 )/ sq.root 3 x 11000 KA = 11.39 KA

Calculation for cross section of conductor

A = 11.1 x Is x sq.rt t

Is = SC Current , t= duration of fault in seconds.

Transmission Systems

Hybrid transmission systems ( HVDC+ FACTS) offer many technical and reliability advantages. There are now ways of transmitting 3-4 GW over large distances with only bipolar DC transmission system. This is usefull in offshore wind projects.
HVDC provides reduction in transmission costs due to less losses, and for sea cable transmission with distances over 80 km, DC is the only technically feasible solution.
Today's maximum rating of 6 GW ( at DC voltages of =/- 800 kv) - with UHV AC at voltages of 1000 KV, power transmission on one 3-phase circuit with 10 GW is feasible.
HVDC at present are limited to 600 KV, in order to enable bipolar ratings of 6 GW, we need 750 KV HVDC.

New Technologies in Power Generation

Gas Fired Power Plants

• Coke Oven Gas


• Blast Furnance Gas


• Linz Donawitz Gas ( LDG)

Cryogenic Plants

Electricity-------> O2 , N2 , Ar ---------> Steel Making.