Session:09

Basics of Electrical Parameters- charge, current, voltage,

R-L-C parametersMeasurement of Electrical Parameters

DEPARTMENT OF BASIC ENGINEERING SCIENCES-1

2

STUDENT OUTCOMEAble to understand the parametersAble to define and represent with unitsUnderstand the conventional methods to

measure.Learn a specific instrument to measure.

Lecture -9

9.1 Basic of Voltage and current:

9.2 Measurement of voltage and current with moving iron instruments.

9.3 Measurement of voltage and current with digital millimeters

9.2.1 Types Moving Iron Instruments:

9.2.2 Construction of Moving Iron Instrument (attraction type)

9.2.4 MI instrument as Ammeter

9.2.5 MI instrument as voltmeter

9.2.3 Torque Expressions:

9.4 References

OutlinesBasic Electrical Parameters:Voltage CurrentResistance ,inductance and CapacitanceImpedancePower and EnergyPower factor.Electrical Meters and Applications(MC,MI and

EDM)

Electrical Circuit:The path through which an electrical current flows is called

a circuit.A current is the movement of electrons through an electrical

conductor. The complete electrical pathway from the power source through the load and back to the source is known as a closed circuit.

As long as electrical equipment is turned on and the circuit is completed or closed, there is a continuous flow of current.

If the electrical pathway is not complete the circuit is said to be an open circuit. For example, when electrical equipment is turned off, the circuit is opened and electron flow stops.

Circuit Elements

Current (I)Current is the quantity of electrons passing a given point. The unit of current is the Ampere.

One Ampere is 280,000,000,000,000,000 electrons passing a point in one second.

Electrical current flows from a region of high charge or potential to a region of low potential.

Conventional Current assumes that current flows out of the positive terminal, through the circuit and into the negative terminal of the source.

Voltage (V or E)Voltage is electrical pressure or force. Voltage

is sometimes referred to as Potential.Voltage Drop is the difference in Voltage

between the two ends of a conductor through which current is flowing.

Voltage types DC and AC( RMS ) voltage.

Voltage by CountryAC voltage supply may vary for each country.European countries use 230V while north America countries use 120V. 

Country Voltage[Volts] Frequency[Hertz]Australia 230V 50HzBrazil 110V 60HzCanada 120V 60HzChina 220V 50HzFrance 230V 50HzGermany 230V 50HzIndia 230V 50HzIreland 230V 50HzIsrael 230V 50HzItaly 230V 50HzJapan 100V 50/60HzNew Zealand 230V 50HzPhilippines 220V 60HzRussia 220V 50HzSouth Africa 220V 50HzThailand 220V 50HzUK 230V 50HzUSA 120V 60Hz

ResistanceResistance (R)Conductors are not perfect. They resist to

some degree the flow of current. The unitof resistance is the Ohm.

Electrical PowerElectric power is the rate at which electrical energy is

transferred by an electric circuit. The SI unit of power is the watt, one joule per second. 

Electric power is usually produced by electric generators, but can also be supplied by sources such as electric batteries.

The electric power P is equal to the energy consumption E divided by the consumption time t:

P is the electric power in watt (W).E is the energy consumption in joule (J).t is the time in seconds (s).

Electrical EnergyThe most common unit of measurement on the electricity

meter is the kilowatt hour [kWh], which is equal to the amount of energy used by a load of one kilowatt over a period of one hour, or 3,600,000 joules.

The formula that links energy and power is: Energy = Power x Time. The unit of energy is the joule, the unit of power is the watt,

and the unit of time is the second. If we know the power in watts of an appliance and how

many seconds it is used we can calculate the number of joules of electrical energy which have been converted to sortie other form.

The Kilowatt Hour (kWh) Because the joule is so small, electrical energy

supplied to consumers is bought by the UNIT. The UNIT is the kilowatt hour (kWh). One

kilowatt hour is the amount of energy that would be converted by a one thousand watt appliance when used for one hour.

Network Elements: R-L-CThe Series RLC Circuitwe have seen that the three basic passive

components, R, L and C have very different phase relationships to each other when connected to a sinusoidal AC supply.

In a pure ohmic resistor the voltage waveforms are “in-phase” with the current.

In a pure inductance the voltage waveform “leads” the current by 90o, giving us the expression of ELI.

In a pure capacitance the voltage waveform “lags” the current by 90o, giving us the expression of ICE.

Impedance triangle

Measurements Of Electrical ParametersThe three basic quantities in the electrical measurement

are voltage, current and power. The measurement of these quantities is important as it is used for obtaining measurement of some other quantity or used to test the performance of some electronics circuits.

The necessary requirements for any measuring instruments are :◦with the introduction of the instrument in the circuit,

the circuit conditions should not altered. ◦The power consumed by the instruments for their

operation should be as small as possible.

Electrical Instruments : Classifications based on calibration Absolute(primary),Secondary InstrumentsClassification Based on methods Direct measuring instrument Comparison type of instrumentsClassification based on the various effects:

Electromagnetic, Electro Static, Electro Thermal, Chemical etc

Classification based on the Kind of Current : DC and AC instruments

Types of InstrumentsAnalog instruments:Classification:

Indicating instruents Integrating instruments

Recoding instruments

Digital instruments:

Various forces/torques required in measuring instruments

Deflecting torque/force: The defection of any instrument is determined by the combined effect of the deflecting torque/force, control torque/force and damping torque/force.

Controlling torque/force: This torque/force must act in the opposite sense to the deflecting torque/force, and the movement will take up an equilibrium or definite position when the deflecting and controlling torque are equal in magnitude. Spiral springs or gravity usually provides the controlling torque.

Damping torque/force: A damping force is required to act in a direction opposite to the movement of the moving system. This brings the moving system to rest at the deflected position reasonably quickly without any oscillation or very small oscillation. This is provided by i) air friction ii) fluid friction iii) eddy current.

Measuring instruments are classified according to both the quantity measured by the instrument and the principle of operation.

Three general principles of operation are available:

(i) electromagnetic, which utilizes the magnetic effects of electric currents;

ii) electrostatic, which utilizes the forces between electrically-charged conductors;

(iii) electro-thermic, which utilizes the heating effect.

Control Systems

Damping Systems

Electrical Measuring Instrument:PMMC (Permanent Magnet Moving Coil)MI ( Moving Iron)EDM (Electro Dynamo Meter)ES ( Electro Static Meter)RF Ammeter

Fig 9.1 Attraction type moving iron instrument

Moving Iron Meter:

Fig 9.2 MI Ammeter

Fig 9.3 MI Voltmeter

Fig 9.4 the simple block diagram of a typical digital multi meter

Fig 9.5 Laboratory multi meter

9.4 Referenceshttps://learn.sparkfun.com/tutorials/voltage-current-resista

nce-and-ohms-law/voltage (9.1)

A Course in Electrical and electronic measurement by A. K. Sawhney page no 258 (9.2)

L-42(GDR) (ET) ((EE) NPTEL).pdf (9.2)https://www.engineersgarage.com/insight/how-digital-mult

imeter-works (9.3)

https://www.electrical4u.com/digital-multimeter/ . (9.3)https://vsagar.org/how-digital-multimeter-works/ (9.3)