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Question
What is the major difference between P.T. & C.V.T ? Why CVT 
is used in HT Transmission line in place of P.T.?
 Question Submitted By :: Electrical-Engineering
I also faced this Question!!     Answer Posted By  
 
Answer
# 1
Potential Transformer is Inductive step down transformer
used for measurement of voltage and protection where as cvt
is capacitive voltage transformer consisting of stack of
series connected capacitor the voltage across the capacitor
is used to measure the voltage.
It also serves the purpose of power line carrier
communication
 
Is This Answer Correct ?    119 Yes 12 No
Shyam Majgaonkar
 
Answer
# 2
Hi Sharma,
Answer #2 is correct but let me add more to it. For
voltages like 11 and 33kV the voltage transformers may be
referred to as P.Ts unlike 132kV etc where CVTs are used.
For either 11 or 33kV the magnetic part with iron core is
not bulky hence are used directly to step down 11 or 33kV
to say 110V used for protection and metering.
In the case of CVTs series capacitors are used to drop down
(note, not stepping down) the voltage i.e.like a voltage
divider from 132kV to a manageable value that can be
transformed like the 11 or 33kV P.T. Take a careful look at
the CVT you will find out that the bottom part is the
transformer part. That part may be transforming say 13kV to
110V. If 132kV were to be transformed directly to 110V then
the voltage transformer or P.T as it were will be so bulky
that there may be little space for other devices. Both are
for the same purpose but the use of each depends on the
voltage level.
 
Is This Answer Correct ?    80 Yes 10 No
Engr. L. O. Osuji
 
 
 
Answer
# 3
Well PTs and CVTs are both used primarily to measure voltage.
Primarily is used coz in CVT, we use it for another equally important aspect , i.e. to filter out the PLCC carrier wave.
AS regarding what's PLCC, thats a diff. concept altogether, and doesnt need a mention here.
PT and CVT both can be used both for 11KV and above lyns...but in practicality for 132KV and above....the transformer w/g of PT becomes highly bulky...and hence losses are more.
Whereas in CVT instead of the usual "Transformer w/g" we use as already said...capacitor series...thats performs two notable functions:
1) gives a low impedance path to PLCC carrier wave freq. which is of order of 100-500KHZ...and hence its used for protection and relaying and telemtering purposes
2) it is as already said...the voltage drops across each cap. and hence its viable to measure the voltage by using low coiled transformer...

So both PT and CVT can be used for any lyn...that be 11KV or 220KV....but as the line voltage increases...the losses in PT increases...and CVT provides that other extremely imprtant function. which PT totally lacks.
So in terms of economy and advancement CVT have been steadily replacing PTs as CVTs rank much higher in terms of efficiency , usability, and longevity
 
Is This Answer Correct ?    24 Yes 5 No
Zeeshan
 
Answer
# 4
p.t is without capacitor and cvt is with capacitor.cvt is
used in HT transmission for communication purpose between
two sub sation or two power plant
 
Is This Answer Correct ?    50 Yes 34 No
Vijay Shinde
 
Answer
# 5
CVT means capacitive voltage transformer which consists of
stack of capacitor connected in series and is used where
PLCC is used so that no additional capacitor is required in
PLCC. Also during transient condition, voltage build up
process in capacitor is slow which limits fast steepness
fronted wave. The protective device operates within this
voltage build up process.
Whereas, PT means simply potential transformer and is used
where only measurement and protection is required.PT is
cheaper in comparision with CVT but in expense of cost, CVT
can be used.
 
Is This Answer Correct ?    8 Yes 4 No
Roshan Khadka
 
Answer
# 6
For voltages from 11 kV to 132kV electromagnetic voltage
transformers or P.Ts are used commonly.But above 132kV for
electromagnetic VTs/PTs the insulation is a problem and
uneconomical compared to CVTs .so for higher voltages CVTs
are used.Also for low voltages the Electromagnetic voltage
transformers are not bulky and hence are used directly to
step down to lower values,say 110V used for protection and
metering.
In the case of CVTs capacitors in series are used to drop
down the voltages( not stepping down) the voltage i.e.like
a voltage divider from higher voltages to a manageable
value that can be transformed using 11kV or 33kV
P.T.connected to the lower tapping of the capacitor of the
CVT. The lower part of the CVT you will find an
electrmagnetic transformer. That part is used to transform
say lower primary voltage to 110V. If 132kV or higher
voltages were to be transformed directly to 110V then
the voltage transformer or P.T will be so bulky
and costly. CVTs if connected with a wave trap and PLCC
equipments the same shall be used for carrie communications
also.
 
Is This Answer Correct ?    3 Yes 1 No
Ahamad Kutty K.v.
 
Answer
# 7
Hi Engr.L.O.Osuji,

You are said 132kV and above rating switchyard used CVT
but in my project we used 132kV PT ( Potential Transformer )
not used CVT..
So,can you reply me???
 
Is This Answer Correct ?    3 Yes 8 No
Karthik Ccel
 
Answer
# 8
hi
pottential transformers are in the one of the category of
induction trasformers.these are use to measure the voltage
at some particular level that is atmedium level.(see it is
exactly similar to the question why we use voltmeters
instaed of potentiometers)capacitor voltage transformer we
form series of capacitors that can stote(trasform)voltage
high levels.where pts are inductive type in nature
 
Is This Answer Correct ?    7 Yes 21 No
Anil Kumar
 
Answer
# 9
PT we are using at low voltgae and CVT we are using at EHV
line , CVT has more accuracy than PT
capacitor divider drop the voltage
 
Is This Answer Correct ?    8 Yes 27 No
Mrudang
 
Answer
# 10
CVT means capacitive voltage transformer which is connected
between the lightening arrester and CT,which is used to
measure the voltage in the line in higher ratings,PT is
connected at the end of the bus bar system which is also
used to measure the voltage.
 
Is This Answer Correct ?    5 Yes 26 No
Abhishek
 

 
 
 
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