Answer / raghavendran

Sensitive Earth fault protection: Normally used on systems
where the earth fault current is limited to a very low
value. Scheme consists out of a ring CT (Core Balance CT)
around the three phase conductors, and the relay connected
to the secondary side of the CT. A very low setting is
possible, even sometimes lower then 1% FLA. Need to
coordinate with similar relays downstream. This method is
based on primary current vector addition or flux summation.
The conductor
cables pass through the center hole of the core balance CT.
Secondary current is the system zero-sequence current
3I_0.This scheme provides increased sensitivity with no
false residual currents. However,
care must be taken to prevent false tripping from unbalanced
inrush currents that may
saturate the current transformer core.

residual Earth Fault Relay:Restricted Earth Fault Protection
Is a type of zone of protection, or a differential scheme.
You get two types, low impedance and high impedance. Low
impedance is normally current operated and high impedance
voltage operated. High impedance REF is the most commonly
used. Relay connected in parallel with three phase CTs and
one neutral CT. It will look just for faults inside the
transformer, and need not to coordinate with relays
downstream (can operate very fast). With this kind of
protection you can protect over 90% transformer windings.
Need to use special class CTs, previously called class X
CTs.low impedance REF, are incorporated into some the new
microprocessor relays.

Answer / raghavendran

A Restricted Earth Fault (R.E.F.) has nothing to do with the
magnitude of the current. It is in fact a normal earth fault
that is restricted to a 'zone'. That is, the R.E.F.
protection is only looking for earth faults occuring in a
given zone. Any earth fault outside the zone (restricted
area) is ignored by the R.E.F. protection. It is typically
used on power transformers, with the protected zone
typically being between the star-point current transformer
and the phase transformers of the star-wound winding.

Answer / surendar

Restricted earth fault function only protect the specified
zone .But sensitive earth fault function can protect all
earth faults(only applicaple for after start of ct point).
both protection analog inputs taking from neutral ct of
power transformer.but in ref taking ct reference for all
phases of ct for making protection of specified area .
setting of ref lesser then sef.sef also back up for ref.
both protection only applicable for star side for
transformer

Answer / sekuvara

thanks pa

how will you find out the fuse failure by remote operation?

1 Answers  

---

In my project i am layout cables under the Maintainance bay /Maintainance yard in the TG Building. Whether in this route i can lay the H.T.Cables??? i am taking all H.T cables from the H.T Transformer to the TG Building..

1 Answers  

---

how to check avr of dg set of 125kva

0 Answers  

---

how to find motor contactor rating and bimetalic relay rating? of 30kw motor which will operate on star-delta starter?

6 Answers   HCC, L&T,

---

what is the working principle/operation/theory of 3-phase rectifier power transformer used in cold rolling mills.

1 Answers   TATA,

---

What is the different between Insulator & Di-electrict?

2 Answers  

---

We operate a 10 Mw facility and we have been experiencing several trips due to fluctuations on the MVAR? We have checked all issues related to the AVR and we have found all OK? Can anyone help us? The grid voltage, internal voltage, all regular parameters look ok. MVAR fluctuate and there it goes the unit? What could be happening? Thanks!

5 Answers  

---

If an electrical component has a positive temperature coefficient, how come such components have high power losses due to heat if current decreases when resistance increases? assuming power given by I^2*R whereby the Resistance is infinite.

0 Answers  

---

What is the difference between RMS and average value

5 Answers   CEERI, HPCL,

---

what is phase and neutral.

16 Answers   HP, Voltech,

---

HOW DOES THE ELECTRONIC ENERGY METER WORKS?

0 Answers   Core Solutions,

---

WHAT IS VCB SAFETY

0 Answers  

---