Brief definition and measurement of voltage

In electrical circuit voltage play important role, it is act as an energy source caused current to flow. In other word voltage is pressure from an electrical circuits pushes the charged electrons through a conducting loop to enabling the charge to do work such as illuminating a light hear conducting loop means close circuits of conducting wire .The unit of voltage is volt denoted as (V) we can also called electromotive force (EMF), denoted as (E).The value of EMF is E=B L V sinӨ 10^-8 volts when conductor moves close circuit in magnetic field, where E-EMF,B-flux density, V-velocity of conductor  cm/sec, L-length of conductor. Voltage can be AC (alternating current) and DC (direct current).AC voltage pulsating nature in both directions and DC voltage constant nature in one direction only. AC voltage is either single phase or three phases. According to utility AC voltage categorize below;

·         Low tension (LT) voltage either single phase (110 Volts, 240 Volts) or three phases (440 Volts) up to 1000 volts used for domestic purpose.

·         M V (medium voltage) is three phases from 6.6 kilo volt to 33 kilo volt generally used for industrial purpose.

·         HT (High tension) voltage is three phases from 66 kilo volt to 132 kilo volt is transmission voltage.

·         E H T (Extra High tension) voltage is three phases from 220 kilo volt and above is also transmission voltage.

The DC voltage gets it from cell, battery or by converting AC voltage to DC voltage using converter. The DC voltages categorize below; 1.5 Volt from dry cell torch, 5 Volt cell phones other electronics circuits.12, 24 48 volt DC etc in auto mobile vehicles. In traction system locomotive converting ac voltages to dc voltage using converter 600 volt,12 kilo volt,15 kV,30 kV and 40 kV DC utilize by locomotive.

We can check the presence of voltage in a circuit by using test lamp, neon glow lamp tester and high voltage tester etc. In test lamp method two test lead of insulated wire one is against under test conductor other against ground when lamp glow between conductor and ground than the voltage is present. Neon glow lamp tester completes the circuit human body capacitance to earth and glow up. High voltage tester to check the presence of high voltage without touching the conductor can be detected by holding a tester in close proximity to the conductor.

Voltmeter is an instrument used to measured potential difference between two points in electrical circuits. Voltmeter is always connected to parallel with the circuits because its internal resistance is high if it is connected to series fault in readings because minimize the current in circuit due to presence of high resistance will change the potential difference. Usually analog and digital voltmeter used.

ANALOG VOLTMETER

                Analog voltmeter is MI (moving iron), MC (moving coil) and electrostatic type. Further we categorize moving iron voltmeter is  attraction, repulsion, induction and dynamo types and moving coil voltmeter is permanent magnet and dynamo types. In moving iron voltmeter consists of movable soft iron piece and other is fixed coil. The interaction of flux produce by these two elements produced deflecting torque pointer attached to the soft iron piece. In moving coil voltmeter the coil is movable which is wounded on soft piece placed in permanent magnet. When current start flowing through this coil rotates about its own axis in vertical position pointer connected in it. Electrostatic type voltmeter based on electrostatic principle in such type meter two charged plate one is fixed and other is movable repulsion between these two plate caused developed deflecting torque. Such type of meter high sensitive and used for high voltage measurements. Dynamo meter type voltmeter consists of a pair of coil that is fixed and other movable coil interaction between two coil produce a deflecting torque. Such types of meters used for DC voltage measurements.

DC analog meter

AC analog meter

DIGITAL METER

Clamp meter and multi meter given in image below  such type of meter convert analog to digital converter and show the readings in digital display ,used for low voltage measurements  three phase and single phase up to 1000 volts.In both the image shows the single phase AC voltage. We can also measure the DC voltages through these meters.Both have two test lead black and red used for measurement.

Clamp meter

Multi meter

HT VOLTMETER

We can not connect the voltmeter directly in high tension (HT) lines,potential transformer use to step down the voltage and this PT voltage given to analog or digital voltmeter for measuring HT voltage.In this image digital voltmeter with selector used for measuring HT (11kv) voltage. In selector switch 110 volts comes from 11kv over head line step down by PT (11KV/110Volts) and 220 volts aux. supply given to voltmeter.PT connected to parallel of the HT line and used for step down the HT voltage. 

HT digital voltmeter with selector switch

 The PT primary winding has large number of turn and secondary winding much small number of turns co-axial winding is used for reduced the leakage reactance. This is also called instrument transformer.