Answer / meenakshi

Differential relay is one that operates when the phasor
difference of two or more similar electrical quantities
exceed a predetermined value. Thus a current differential
relay is one that compares the current entering a section
of the system with current leaving the section.Under normal
operating conditions, the two currents are equal but as
soon as fault occurs, this condition no longer applies. The
difference between the incoming and outgoing currents is
arranged to flow through relay operating coil. If this
difference is equal to or grater than the pick up value the
relay will operate and open the circuit breaker and isolate
the faulty section.
mainly used in two winding transformers

a induction motar has 30-35% exciting current at no load but in transformer it is only 2-3% ofbrated current why any reason?

1 Answers   century,

---

on what factor insulation resistance depends

2 Answers   Uttam Sugar,

---

1. What is differential relay? How it operates? 2.How to calculate the Short Circuit Impedance in Transformer? 3.What is the alternate solution for testing of polarity by using polarity tester while its milli ammeter does not works? 4. While testing the 33KV Busbar by using Hipot kit, what should be the test voltage we have to apply? 5. What is the procedure/activities to be taken to inject the current more than 2000A by using 2000A Loading Transformer? 6. Explain how you can give the overload setting to any Motor Protection Relay for a HT motors with formula and example? 7. Why restricted earth fault protection is needed? Why can’t differential Protection is sufficient? 8. What should be the minimum and maximum ohmic value for earthing? 9. Why DC Currents are not used in transformer? 10. What is the Frequency while we step up the voltage from 220V to 11KV? Is it possible? Explain it?

0 Answers  

---

assume we are put both df/dt and vector surge relay in same bus the df/dt relay setting is +5 hz an -5HZ. we want operat the vector surge relay before the df/dt how i calculate the setting of the vector surge relay.

1 Answers  

---

plz send me Bhel, Mahagenco, sbi previous exam paper for electrical engineer on my email-id kambali_smita@yahoo.co.in

0 Answers   Bhel,

---

what is the principal of starting of a three phase induction motor.

2 Answers   Moser Baer,

---

What is dc current source?

0 Answers  

---

How to calculate earth flat size for 250 Kva DG and transformer?

8 Answers   Deepak Fertilisers,

---

last week we did the REF relay test by closing single pole (R phase) of CB and apply 380V at the primary of delta transformer. we get 33A at the primary of the R phase star end. but we get 380A at both R an B in delta side. how and why?

1 Answers   Siemens,

---

I want Primary side delta and Sec side Star connection transformer . but i have received Star - Star transformer ,shall i use the same transformer by giving the only 3 ph on Primary side without Neutral connection on the Starpoint.

5 Answers  

---

if voltage bt phase & nutral is 38v in a panel board . whats the root cause.

0 Answers  

---

WHY HUMMING SOUND OCCURED IN HT TRANSMMISSION LINES?

6 Answers  

---