PERTEMUAN 14

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PERTEMUAN 14

• PENGUKURAN ENERGI

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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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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

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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

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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

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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

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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

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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

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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