ELECTRICAL NOTES

Heat produced by 1 kg Atomic material is equivalent to 2700 quintal coal.

In India: AC supply is 33Kv, 66Kv, 132Kv,220Kv, 400Kv

             : DC supply is 100Kv, 200Kv, 300Kv, 400Kv, 600Kv 800Kv.

Difference between Overhead line & underground line.

sn	Overhead line	Underground line
1	Cheap to install	Costly to install
2	Easy disconnection	Disconnection is not possible
3	When load increases, extra connection is to be given & connections can be changed.	Not possible
4	Line voltage can be increased	For increasing line voltage, cable to be replaced
5	In emergency excess load can be given	Possibility of cable break
6	Fault can be easily detected	Hard to detect the fault

Dielectric Strength: The point on which voltage can stand.

1.      Material thickness, 2. Temperature, 3. Size of electrode, moisture absorbent value.

1.      Air – 3.2 Kv/mm

2.             – 12 to 20Kv/mm

3.      Mica_ 20 to 60 Kv/mm

4.      Porcelene – 15 to 60 Kv/mm

5.      Trx oil – 20 kv/mm – 50 kv/2.5mm (IS 335)

Ø  Tungsten is used as a filament of lamp because the temperature coefficient of tungsten is high and melting point is also high.

Ø  Vacuum is a media in the lamp because filament should not burn.

Ø  Gas is filled in the lamp to increase the capacity of the lamp. Gas: ozone, Helium  etc(inert gasses)

Type of lamps and advantages:

1.      Fluorescent lamp: Household use & internal light of the bldg.

2.      Incandescent lamp: Household use & internal light of the bldg.

3.      Mercury vapor Lamp: Road & ground

4.      Sodium vapor lamp:  Road & ground

5.      Neon lamp: Advertisement

6.      Arc lamp: Search light & cinema projector

ü  To remove motor bearing permanently – use puller

ü  To fix motor bearing: Bearing to be heated up to 80⁰C & then it can be fixed easily

ü  Roller bearing is mostly provided to driving end side.

ü  Ball bearing can be provided to both the ends or non-driving end.

ü  Fuse is used in place of neutral link: If there is unbalance load, current will flow through fuse and it will blow and series ckt will form. Then low voltage will flow from excess load side & high voltage from lesser load side. 2 phase supply will flow if it is single phase and equipment will burn.

ü  3 ph loads should be balanced because in the balance load, current is same in each phase. If there is unbalance load, current will also unbalance. So there is a change to damage the equipment. Sometimes in the balance load, current flowing through neutral is zero. In the unbalance load, current flows through neutral & the phase on which load is excess, voltage will low and equipment will not work properly. If load of the phase is less, voltage will more and the equipments can get damaged. So balancing of load is necessary.

ü  Auto transformer starter is used in place of star delta starter to increase Starting torque as in starting, 80% voltage is getting to winding

ü  Star delta starter gives less starting torque because in starting 58% voltage is getting to winding.

ü  If motor trips while starting by star-delta starter, timer setting may low. Timer to be set on 80% speed of the motor.

ü  For heavy torque, DOL starter is used. 100% voltage is getting to the winding.

ü  Inductance: If supply is given to a coil, which opposes to the voltage is inductance.

ü  Impedance: Ckt consist of resistance, Inductance & capacitance, the total resistance is called impedance. Its unit is Ωmho. Z= √R²+(XL-XC)².

ü  Resistance = V x I

ü  Inductance =        L = X_L/2πF

ü  Capacitance = 1/2πFX_C

ü  Capacitive reactance   X_c = 1/2πFX_C

ü  Inductive reactance     X_L = 2πFX_L

ü  Capacitor50 mfd & 100 mfd =100 mfd Capacitor will take more current

ü  PF depend upon inductive reactance & capacitive reactance.

ü  PF on load: Resistive ckt – Unity

                   : Inductive ckt – Lagging

                   : Capacitive ckt- Leading

ü  No volt coil is connected in the series of field coil.

ü  Over load coil is connected in the series of supply and load

ü  3ph, 10HP motor installation: It will take mostly 15 amps current.

i.                    3½ core, 2.5sq mm Al conductor, PVC insulated armored cable

ii.                  32 Amps switch-fuse unit or isolator

iii.                16 swg copper conductor for earthing

iv.                 Over load relay: 10 – 25Amps.

v.                   Back up fuse: 35Amps HRC (2.5 times of full load current)

vi.                 Indication lamps On Off, 3 ph, trip : 6 Nos.

vii.               Ammeter & voltmeter selector switches

viii.             Motor insulation resistance

ix.                 Cable insulation resistance

                        Output 

ü  Efficiency of motor= ---------  x 100%

                                      Input

                                     Out put KWH

ü  All day efficiency  = ------------------- X 100%

                                    Input KWH

                                        No load Voltage – Load Voltage

ü  Voltage Regulation = -------------------------------------------

                                                    No load Voltage

ü  If the Gap between Stator & Rotor of induction motor is minimum, magnetizing current will less and power factor will increase.

Torque = Ir x Cos Φ = Rotor current x Rotor pf.

ü  Fault level : Switch yard – 1000 MVA

                      33 Kv busbar- 750 MVA

                      3.3 Kv busbar- 175 MVA

                      MV busbar     - 35 MVA

ü  Neutral displacement: On Earth fault, lightening, voltage increases. This increased voltage is controlled.

ü  Lightening arrestor: On system voltage it works as a insulator & on high voltage it works as conductor.

ü  Direct stroke: By direct earth wire, in earth or ground – 80% negative, 20% positive charge.

ü  Non direct stroke: Drop in overhead line & observe arrestor & goes to ground: -ve + positive.

ü  If DC supply is given to transformer, it will burn because there will no induction and it will become a resistive ckt and will take high current and will burnt transformer winding.

ü  DG AVR Fails: It means failure of excitation, hence DG will be continue running but no EMF will be generator.

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