10 % increase in voltage gives you 50 % increase in
excitation current is called knee point voltage.
To measure this first demagnetise the CT and apply
voltage gradually from secondary keeping primary
winding open circuited. while doing this above
phenomeneo will be obsesrved.
to calculate knee point voltage of current transformer by
formal
Vknee point = Isecandary(Rct+ Rcable+ Rburden)
where
Rct= resistenc of current transformer
Rcable =resistenc of cable =2Rcable
Rburden =burden of relay
IF Vknee point< manufacture voltage of current transformer
current transformer is good
IF Vknee point> manufacture voltage of current transformer
current transformer must be change
10 % increase in voltage gives you nearly 50 % increase in
excitation current is called knee point voltage or
breakdown voltage.
To measure this first demagnetise the CT and apply
voltage gradually(like 10% or 20% step) from secondary
keeping primary should be open circuited.
The knee-point voltage will depend on the size and class of
the CT, and it can be very high on some CTs (several
hundreds of volts) Be very cautious, you will be working on
live equipment during the test.
Now you can just plot the current and voltage values on a
graph. This is the mag-curve of the CT. IEC classify the
knee point voltage as the point where a 10% increase in
voltage results in a 50% increase in current.
I am not familiar with the term saturation test but it seems
from the above posts like an exciting current test to
obtain the knee-point of the CT. With this test you can also
obtain the exciting curve (mag-curve) of the CT.
You'll need a variable voltage, (easiest obtain from a
variac - must be able to obtain the suitable voltage) a
voltmeter, an ammeter, a pencil and paper.You'll have to
measure the voltage and the current while you do the test.
Apply the voltage to the secondary winding with the primary
and other windings being open-circuited. Increase the
voltage until you reach a point where a small increase in
voltage results in a big increase in current.
Now slowly decrease the voltage to a few measuring points,
while you measure the current. (write it down) Something like:
You have to decrease your voltage slowly to zero volt to
demagnetize the CT-core.
BEWARE The knee-point voltage will depend on the size and
class of the CT, and it can be very high on some CTs
(several hundreds of volts) Be very cautious, you will be
working on live equipment during the test.
Now you can just plot the current and voltage values on a
graph. This is the mag-curve of the CT. IEC classify the
knee point voltage as the point where a 10% increase in
voltage results in a 50% increase in current.
The knee-point voltage will depend on the size and class of
the CT, and it can be very high on some CTs Be very
cautious, you will be working on
live equipment during the test.
Now you can just plot the current and voltage values on a
graph. This is the mag-curve of the CT. IEC classify the
knee point voltage as the point where a 10% increase in
voltage results in a 50% increase in current.
Calculation:
1) Fault Current at Primary Side of CT (kA) = MVA/*100(%
Z*1.732*KLV) 7.55
2) Fault Current at Secondary Side of CT, If (A)=
6.29
3) Cable Lead Resistance, RL (Ohm)= 1.02
4) Knee Point Voltage Vk (Volt) = 2If(RCT+2RL)
101.2
REMARKS : -
Knee Point Voltage of CT provided by CGL for REF CT = 115V
and for Differental CT = 200V are in order.
why the Parameters : Base Voltage & Maximum Voltage can't be
equal in value in a VFD (Variable Frequency Drive) ?
How much the base voltage would be lower than the maximum
voltage ? If 400 V is the 3 phase output of a VFD ... then
what should be the base voltage ?
thanks a lot
In any Industry, Which voltage level either 3.3kV or 6.6KV
to be chosen? Then I would like to know ,Is there any cost
consideration or Rating of motor?
We have three 33kv substations. All of them energised by
same source.When i am checking the phase sequence between
one substation to other substation
(like R Phase to R Phase) by multimeter i am getting
some voltage.Near to LT panels UPS panels are there. Can u
explain whether any possible to happen
like that. In Phase SEquencemeter is showing correctly
in both substations. How is it happen. Explain me.Explain
me communication signal will produce
Phase difference on this case.
along with your userid / name. ThanQ
Site Map
