Answer / william lobo

Knee Point voltage is nothing but a point at which the CT
saturates. Thats why its always better to design the CTs
which can operate without saturation even at a voltage
appears in the CT during fault condition. Pls find below
the following formula for calculating the Knee point
voltage.

Vk=2If(Rct+2Rl).

where, If is the current refected to the CT secondary
during fault condition,

Rct is the resistance of the CT which can be adopted by
means of a thumb rule considering the CT ratio,

Rl is the lead resistance i.e. sum of the resistance of the
wire connected between the relay & CT and Impedance offered
by the internal circuitary of the relay

For PS class CT's designed considering the above,burden is
not applicable.

Answer / williamlobo

Restricted earth fault protection is a differential scheme,
with CTs on the transformer neutral and phase leads. The
phase CTs are connected together in parallel & then
paralleled with the neutral CT. The resticted earth fault
(REF) relay is connected across the paralled CT circuits.

The relay is either a voltage operated device (eg Alstom
MFAC14)or a current relay with an external setting resistor
(eg Alstom MCAG14). In either case, the scheme is set at a
voltage based on the maximum voltage that is developed at
the relay for an external fault. A practical setting is
50% of the CT knee point voltage, if full info is not
available.

Answer / william lobo

For PX class CTs , the burden is not normally mentioned .
There the CT is defiened based on the CT kneepoint
voltage , magnetising current etc . The burden is mentioned
in class P CTs

In PX class CTs the kneepoint voltage is normally based on
the max fault current and a diamensioning factor based on
system X/R ratio

1kva=how many kw & amps

4 Answers   Jakson,

---

how meger function

0 Answers  

---

instead of neutral can we use earth/ground to flow the current in the circuit

2 Answers   Infosys,

---

We have two parts in generator, electrical & mechanical. how it works?

0 Answers   TATA,

---

why transformer are rated in KVA not in watt?

7 Answers   DMRC, L&T, TCS,

---

Why we use RYB phase sequence?

3 Answers  

---

What is the drawback of class b amplifier? How is this minimized?

0 Answers  

---

Do anybody has a design software or tools for the selection and design of electromechanical components???

1 Answers  

---

Draw a circuit diagram in which if button is open we can use socket and bulb as a series test circit and if button is close than simple we can use socket as any load purpose.

0 Answers  

---

which is better VCB or ACB and why?

7 Answers  

---

Three phase star connected PT transformer primary side one phase fuse is blown what will be the output in secondary side(Secondary side also three phase star connected)

2 Answers   Sun Pharma,

---

Generator protection &generator test

1 Answers  

---