Download lecture 9 - Openstorage Gunadarma

PERTEMUAN 14
PENGUKURAN ENERGI
Measurement of Energy
• Energy is measured by means of the energy meter (watt-hourmeter)
• 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
• 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 :
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–
–
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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
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•
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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
• 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
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•
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
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•
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
• 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
•
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