Answer / k.prakashchandra

Have you measured IR properly, as the values are very high
?The IR should not exceed 2 ohms for a 66 KV MUSS .I do not
know whether primary neutral is to be earthed in case of
star/star tr.It is stated that LV side IR is 130 ohms ,and
hence the maximum earth fault current will be 50A.For 7.5
MVA tr the rated LV line current is about 400 A and EFR is
likely to be set at 80A.It appears that the earth wire
melted due to continuous earth fault current.If there is
conductor to ground fault at a distance of 100 m from tr
earthing ,there will be a pd of 63.5 V /m along the line
between the fault point and the neutral earth. If anybody
stands barefooted with feet 1 m apart along this line, he is
likely to be electrocuted as the power line does not
trip.Further the ground around the earthing also may be at
nearly phase voltage during earth fault

Answer / gairhe

I think you are right.

for the LV even if the imbalance neutral current is 10 A,
the 130 ohm resistance will produce GPR ( Ground Potential
Rise ) of 10 X 130 = 1.3 kV.

Also at the site the transformer neutral earth conductor was
touching the 185 sq mm single core copper power cable and
control cable. May be because of this high GPR , sparking
occurred and heat was generated.

The neutral earthing conductor is of size 95 sq mm. so 10 A
current is not a big issue.

In my view 1.3 kV and sparking developed heating at the
group of XLPE power cable, control cable and fire started .
Then the XLPE power cable was damaged and because of the hig
earth fault from the damage of XLPE cable, the near by
neutral earthing conductor got melted.

how to calculate the KVAr for an motor for improving the PF

3 Answers  

---

What will happen if the rotor of an induction motor is fed from a 3 phase supply and the stator short circuited ?

4 Answers  

---

line vltage of three phase distribution transformer is 433v and phase voltage is 250v,but we required 230v for domestic distribution,then how we reduce phase voltage of transformer

5 Answers  

---

In a 11kv/433v transformer,at the LT side ie 433 V side why do we need to put 3.5 core Cable upto Panel.The full load rated Amps is 666 at LV side.What value of current will flow through the Nuetral Conductor.Why can't we use 4Core Cable instea of that?

2 Answers  

---

define the active power?

0 Answers  

---

Which type of arc protection devices used.

2 Answers   KSEB, L&T, Siemens,

---

In Plumbing services What are accessories we consider for a bathroom?

0 Answers  

---

What shall be the secondary output voltage if the primary winding of a 220/6V, 50 Hz transformer is energized by an 110V, 60 Hz supply?

0 Answers   HPCL,

---

Why the colour of insulator is always is chocolate in colour?

1 Answers   MRF,

---

We have 3 Gensets 1.500kva,2.380kva,3.250kva How can we connect in common busbar&we have variable load.

4 Answers  

---

what sort of general awareness questions are asked in o.n.g.c entrance exam?????????????????

0 Answers  

---

How can we calculate the capacitance of generator?

1 Answers  

---