Comprehensive Guide to Energy Metering Systems - Types, Advantages, and Errors

1. PERTEMUAN 14 PENGUKURAN ENERGI

2. Measurement of Energy • Energy is measured by means of the energy meter (watt-hour-meter) • Energy meter is an integrating instrument and takes into account both of the quantities • Three types of energy meter : • Electrolytic meters • Motor meters • Clock meters

3. Electrolytic Meters • Operates on the principle of electrolytic action and is purely a dc meter measuring ampere-hour • Used for measurement of energy when the supply voltage is constant • Advantages : • They are accurate even at very small loads • They are unaffected by stray magnetic fields • They are free from friction loads • Disadvantages : • There is a potential drop across their terminals • They require frequent inspection • The destruction of the old record of energy on re-set • It is not taking account the variations of circuit voltage

4. Reason Electrolytic Meters • It is generally used on d.c. supply systems • The range of the meter is extended by providing it with shunt • No appreciable error is introduced at low loads due to any departure from the correct division of current between meter ans shunt

5. Types of Motor Meters • Principle : small motor of d.c. or a.c. type whose instantaneous speed of rotation is proportional to the circuit current • Essential parts : • Operating torque system • Braking device • A device for registering the number of revolutions made by rotating elements • Mechanical construction : must be such that the functioning of the meter is not readily interfered with by tilting or any external means. • Errors in motor meters : friction errors and braking errors • With the increase in temperature, the resistance of eddy current path will increase and therefore the braking torque will decrease

6. Mercury Motor Meters • Ferranti mercury motor meter - • It is the most common used and best form of mercury ampere hour meter • Illustration of principle of Ferranti D.C. A-H meter ------------------- • There is a lack of strict proportionality between the flux in the magnet and the voltage creating it

7. Commutator Motor Meters • It is essentially small d.c. motor with a wound armature • Advantages : • Simple construction • Small voltage drop across the meter • The considerably large current carrying capacity without use of shunt • Small starting friction owing to the very small pressure on the bearings

8. Motor Meters for A.C. Circuits • The most commonly used meter is the induction type watthour meter • Advantage : higher torque/weight ratio and the absence of commutator -- more accurate than the commutator type on the light loads • Principle of operation : exactly the same as that of induction type wattmeter • The construction is also the same except that the spring control and pointer od wattmeter are replaced by a brake magnet

9. Induction Type Single Phase Watt-hour Meters • Errors and adjustments : • Phase and speed errors : bringing the shading band nearer to the disc, adjustment of the position of the brake magnet • Friction compensation : variation of the positions of the bands • Temperature and frequency errors: They can be adjusted to have a minimum error at declared supply frequency