Answer / tapas

* In REF scheme 4 nos of CTs are used. 3 for phase and 1 for Neutral.
* It operates in the principle of balance current between phase and neutral and only inside In-zones. i.e. it protects Transformer, Busduct, LV switchgear.
* In this protection phase CTs are connected in such a way that it forms a close path between phase CT secondaries and this close path is connected with neutral CT secondary.
* In between the close path connected to common terminals of phase CT secondary and Neutral CT secondary REF relay is connected.
* When a phase fault occurs there is also residual current in Neutral. So current between both paths oppose each other and hence there will be no current in REF relay. So it won't operate.

Suppose i Have an Ac motor of 25Hp 1500 Rpm 50 Hz Can i run a motor 2500 Rpm by AC drives by increasing a frequency either it safe or not ....

2 Answers  

---

what is b checks and m checks in diesel generator maintenance?

1 Answers  

---

which theorem is used to analyse fault a)thevinin b)Norton c)Superposition d)jordan

1 Answers   FFC, NTS,

---

how synchronous generator can be used as synchronous condenser?

3 Answers   Monnet, Wipro,

---

How can i modify the design of 3 phase induction motor to be as 3 phase synchronous motor??

2 Answers  

---

---

why the electrolyte level in lead acid battery is maintained 2.5 cms above electrodes?

0 Answers  

---

A 150KW 440V motor is need to replace in the field instead of faulty one. what are the main parameter should I need to check?

1 Answers  

---

V.c.b and a.c.b difference

4 Answers  

---

What is the permissible value of earth resistance!

11 Answers   Torrent Power,

---

how to caluclate cable size by Amps

2 Answers  

---

what is XLPE type cable

8 Answers   Areva,

---

Where r use in Dc motor in power plant?

2 Answers  

---