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PERTEMUAN 14. PENGUKURAN ENERGI. 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.

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pertemuan 14



measurement of energy
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
electrolytic meters
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
reason electrolytic meters
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
types of motor meters
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
mercury motor meters
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
commutator motor meters
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
motor meters for a c circuits
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
induction type single phase watt hour meters
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