CT saturation is a term used to describe the state wherein
a CT is no longer able to reproduce an output current in
propotional to its primary current or as per its Ratio
The basic reason for CT saturation is due to the property
of the core which goes to magnetic sturation due to number
of reasons like large primary current or high burden at
the secondary or an open circuit in the secondary
The saturation can be found out in the following way
Apply voltage to the secondary windings of CT and gradually
increase the voltage noting down the current . initially
you will find that voltage and current are following a
leniear path and as you increase the voltage you will find
a point where 10% increase in voltage results in 50%
increase in current . This point is practically taken as
CT saturates if it is not correcly rated. its ratio has to
be matched to the maximum fault current that it has to
pass. normally the ratio of fault current to rated current
should be kept within 20.
it is very relevant that the fault current is calculated as
per the upstream network fault level. furthe the X/R ratio
of the connecting network needs to be known for calculating
the DC component and its time delay. if the time constant
is small, the saturation shall occur for the first few
cycles, and delaying the actuation will solve the initial
mis-read of current signal. but if the time constant is
large, say of the order of ten cycles, proper sampling
solutions have to be resorted to, that is the current must
be sampled before the onset of saturation.
Answer #6 is absolutely right I want to add one thing in it that when once a ct got saturated then it tends to built higher voltage on secondary side then normal due. as normally there is very less voltage on secondary side.
The CT saturates when we exceed load on CT greater than its VA burden capacity either in case of fault or during testing or normal operation. VA burden depends upon core material of CT used and depends upon B-H curve of the material. These ferromagnetic materials used have ability if they are over excited than they will loose their normal operation properties. in this why if we put more load than its VA capacity of CT than CT will saturate. means that it will not give you accurate results.
Ans 6 and 9 are combinely correct. Actually if we want to
check CT saturation that means ouput current must be
correct according to its rating.
And output current is nothing but a voltage across its
secondary which is calculated as its current(like 1V=10A)
i.e. if 1 V output vltg across secondary you find that
means instrument will read 10A current.
So if CT gets saturated then it will read more than 1V and
correspondingly we find false output current.
ct saturation is a condition when the secondary gets open
circuited & so there is no provision of counter balancing
the huge mmf produced due to enormous line current in
primary & so secondary must be connected to the coil of
metering element.& never left open..............
Sorry to say Mr Kiran Patil if CT is shorted ckted then it
will complete the ckt and save it from any further damage
and meter connected to that CT not able to read current
flowing from that CT.
There are two simple way to calculate the CT saturation
1. There is an instrument operates on 240v,50HZ known as RED
PHASE instrument it is an Australian instrument.
2. Primary injection method in this method we use an
instrument which can only provide current to both of the
primary position of the CT known as P1,P2 and secondary of
that CT are being short ckted so as to calculate the current
and with the help of tong tester we can calculate the
for example we are having CT ratio of 10/5 A and we are
providing primary current of 10 A and from secondary point
we are calculating 5 A current then CT are OK but if we are
getting lesser current than we must say that CT are saturated.