Answer / tareq harb

There are 3 types of excitation systems:
AREP, PMG & Self excitation.

in self excitation the AVR (Automatic Voltage Regulator)
takes its power directly from the out put terminals of the
generator, the main disadvantage of this method is that
when the generator output volatage drops the feeding to AVR
will be insufficient. suppose SHORT CKT fault takes place
on generator terminals as a result the output voltage will
drop too much & AVR shuts down directly with out feeding
this short CKT, if running on island mode (load sharing
mode) the hole system will trip.

But in PMG excitation system, PMG will feed AVR with the
same power nevertheless out put volatge, in case of short
ckt PMG alternator can supply 3 times its rated current for
10 seconds giving enough time for generator breaker to trip
eliminating the short ckt with out affecting the system.

as we see the main advange of PMG ALTERNATORS is its
enhanced immunity against short ckts.

Self excited systems is preferable in single mode operation
as it is cheaper & shorter prime movers.

PMG is strongly recommended in island mode operation.

Answer / j.c.das

PMG or Permanent Magnet Generator are used in brushless
excitation system. It is advantageous from the maintenance
point of view. It doesn't employ carbon brushes as it does
not have a commutator and so no regular wear and tear as in
carbon brushes.

WHY R USE IN BRUSH IN THE MOTOR?

6 Answers   L&T,

---

1.main parts of generator? what is used A-check,B-check,C- check? 2.what is FM200 system in data centers? 3.difference between pac,ahu?

0 Answers   TATA,

---

Can anybody explain Why starters are not used for motor starting in industries?

9 Answers  

---

Which transformer is suitable for 220/11 kV, 60 MVA, distribution , Y-Y or D-Y or Y-D, give comparison for the same.

3 Answers  

---

Dear All, I am new in construction company , my boss ask a question at time of interview , If we have 60MW generation and Single Power Transformer step-up we have. if CMR 50/60MVA , ONAN, ONAF respectively , is it sufficient or not ? for that much power to transfer,

0 Answers  

---

How to calculate the cable size (XLPE)for suitable to 120KW load (if Motor or heaters etc)

4 Answers   SSC,

---

Can we put 3 layers of cable tray while installing tray

0 Answers   NTPC, Siemens,

---

What is the difference between earthing & neutral.

2 Answers  

---

what is neutral plane shift?

1 Answers  

---

For 132 KV line, PT or CVT which is prefered for measuring & protection? is there any IS or IEE standard available?

1 Answers  

---

what is the use of interposed & reverse voltage transformer

2 Answers   Anjani Steels,

---

an amazing situation was faced when an alive distribution panel with 415 volts and carrying almost 200Amps has become short and this metal cubical showing 220 volts against neutral and earth. to redress any confusion i checked the panel with help of single 200watts test lamp which also glowing with max.intensity b/w neutral & metal body of DB. amazing situation is that i hold the DB firmly more than once with necked foot means without insulated shoes but not received any electrical shock. whereas our all running gen sets neutral points also proper grounded and this short DB was completely earthed , this is beyond my understanding . any body explain how is it possible . our running gen set neutral also grounded firmly

1 Answers  

---