kurt jorgensen


{ City } ipswich
< Country > australia
* Profession * applicaton engineer
User No # 101223
Total Questions Posted # 0
Total Answers Posted # 96

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Answers / { kurt jorgensen }

Question { 4162 }

can alternators work at leading power factor?


Answer

Alternators can work on slight leading power factor. If the
leading power factor is too great the AVR will lose control
of the voltage and the voltage will rise above the normal
voltage. The further the PF is from unity the higher the
voltage.

Is This Answer Correct ?    0 Yes 0 No

Question { 4723 }

Hello sir
This is prakash from
bangalore i have a doubt why we have to
maintain DG power factor in the range
0.78 to 0.8
Perhaps i f it is increased means what
will happen in DG


Answer

DG's are usually rated at 0.8 PF lagging. There is no
issues with running the DG at another higher or lower
lagging PF. Usually the output kw of the engine is set at
80% of the kva rating. For example a 100 kva DG will have
an engine rated at 80 kw. This will al;low for a full load
current of about 140 amps at 0.8 PF. Increasing the PF
towards unity the maximum load current must be reduced
until it is about 110 amps otherwise the engine will be
overloaded. If the PF is reduced below 0.8 PF the maximum
current must not exceed 140 amps. This means the kw of the
load must be reduced. This is to stop the windings in the
alternator being burnt.

Going to a leading PF will cause voltage instability and
can cause damage to the alternator.

Is This Answer Correct ?    1 Yes 0 No


Question { 4538 }

What will happen if the generator turns in a wrong
direction?


Answer

A generator can operate in both directions. The main reason
for only operating in one direction is that the prime
movers are only designed to operate in one direction.
Often the design of the cooling fan will also work in both
directions. What will happen to the generator? The phase
rotation would be reversed.

Is This Answer Correct ?    0 Yes 1 No

Question { 5489 }

what is difference b/w CFL and Ordinary lamps? which one is
useful for power saving?


Answer

CFL is compact fluroscent lamp.
Like all fluroscent lamps they use less power for the same
light. 11 watt CFL is the same as 75 watt ordinary lamp.

Is This Answer Correct ?    0 Yes 0 No

Question { 3899 }

after syncnhronistion how generator speed controlled by grid


Answer

The generator is magnetically coupled to the grid
frequency. If the fuel to the generator is increased the
generator will try to increase speed but as it is
magnetically locked to the frequency it will take more load
instead. The reverse will happen if the fuel is decreased.
Under some circumstances the magnetic coupling can be
broken. If this happens the energy from the grid will try
to drive the generator back into synch. This can cause
extensive damage to the generator and/or switchgear.
Therefore protection should be used to stop this from
happening.

Is This Answer Correct ?    0 Yes 0 No

Question { 4148 }

DG drop how much freqency at 100% load?


Answer

If the governing is set to isochronous there will be very
little drop in frequency.
If the governing is droopp it is usually set to between 3
and 5% depending on application.

Is This Answer Correct ?    0 Yes 0 No

Question { 6198 }

In power generator sets, when they are coverted from 50hz
to 60hz, the kva rating after conversion increases. For
example, the manufacturer of a perkins 200kva @ 50Hz
generator set has mentioned it to become 220kva after
converstion to 60hz. What is the relation between the
frequency & the KVA rating. Any formula please.


Answer

The main reason for the increase in the kva is that the
diesel engine produces more HP at 1800 rpm than at 1500 rpm.
This allows a higher kw output. The alternator can also
handle the higher current and therefore the kva is
increased. Note that the rated power factor stays the same.
This is because the amount of cooling air is increased at
the higher speed.
The increase in the EMF per turn allows a higher voltage to
be generated but this is reduced by the AVR reducing the
excitation. This has no effect on the kva capacity of the
generator set.

Is This Answer Correct ?    0 Yes 0 No

Question { MahaDiscom, 36738 }

Why do we need ring main unit (RMU). what is its purpose and its advantages . what is the operating function of rmu


Answer

Usually a RMU is used to allow a feed of supply from 2
directions and tapping of to a transformer, etc.

Each of these supplies may have a number of RMU's in series
forming a ring. If a section of the feeder needs to be
isolated due to work or failure an RMU on each end of this
section can be opened without stopping any supply.

Is This Answer Correct ?    28 Yes 4 No

Question { 4305 }

In any plant or substation main incommer voltage RY - 415
V,YB - 400 V, BR - 387 V(in commer feed from transformer 11
Kv /0.415 KV) why found voltage differance in each phase?
plant have not self power plant it is depend on outsource
grid


Answer

First check the 11kv is correct. If the 11kv is different
on each phase the LT side will also be different.
If 11 kv is OK and the voltage is different on no load the
fault is in transformer as answer above.

Is This Answer Correct ?    1 Yes 0 No

Question { 2757 }

how you connect the induction motor first in star and then
delta in star-delta starter


Answer

This is done by taking a wire from each end of each winding
to the starter. When starting one end of each winding is
connected to a separate phase and the other ends are
connected together to form a star point.
When changing to delat the ends with the starpoint are
switched open and then switched to a phase each.
Having the correct phases on each end of the windings is
important otherwise the direction of rotation can be
reversed when changing to from star to delta.

Is This Answer Correct ?    1 Yes 0 No

Question { Dalkia, 4270 }

why trasformer rated in kva
why should have to maintain pf in our site 0.9


Answer

Only the kw is usable power. By having the power supply
power factor as close to unity as possible the amount of
current is reduced.

This means that transformers and wires for distribution can
carry more usable power without overloading.

Is This Answer Correct ?    1 Yes 0 No

Question { NTPC, 27023 }

What is the similarity and what is the difference between relays and PLC?


Answer

A relay is designed to act on one type of input signal
only. It may have adjustments for a range but can only
perform one function.
A PLC (programmable Logic Controller) can be made to
perform many differnt functions including the functions of
relays. this is done by selecting the type of inputs and
outputs required when buying and then programming to suit
the functions wanted.

Is This Answer Correct ?    15 Yes 0 No

Question { 2823 }

What will be the resultant out put voltage when two
different voltage rating batteries are vconnected in
parallel? pls. answer with example if available.


Answer

If two batteries are connected in parallel and have
different output voltages the one with the higher voltage
will try to drive the voltage backwards through the other
battery. This can cause damage to both batteries. For
example a 6 volt and a 12 volt battery. The 12 volt battery
would drive current through the 6 volt battery.

Is This Answer Correct ?    0 Yes 0 No

Question { NTPC, 7454 }

what is brushless generator.How does work it..??


Answer

Normally brushes were used with a commutator with
generators with a rotaring field or sliprings for
stationary field.
As the brushes always would require servicing generator
manufacturers found ways to eliminate them. To do this they
used 2 generators on the same shaft. A small one (exciter)
with a stationary field to produce a 3 phase supply on the
rotor. The output from this generator is rectified with the
rotating diodes and feed into the main rotor. This is a
rotating field generator.
The voltage is controlled by controlling the field of the
small exciter generator. A second benefit is that the field
current is reduced from anywhere between 25 to 100 amps to
only 2 to 10 amps. This makes the control of the field much
easier and cheaper.

Is This Answer Correct ?    1 Yes 0 No

Question { 3364 }

is it possible to flow a current between nutral and earth
in a circuit? although nutral and earth having same
potential diffrence?
i=0/r=0A
if any body now any solid reason because i am getting a
triping problem in rcbo due to nutral and earth shorting???


Answer

The reason you are getting tripping of the RCBO is the way
the RCBO works.
The RCBO senses the current in the phase and neutral. As
long as these are balanced it will not trip. It is designed
to trip if there is an inbalance. This is usually a current
flow between the phase and earth which is then not returned
by way of the neutral.
When the is a short between the earth and the neutral it
provides a parallel circuit. Some of the current will flow
through the earth and some through the neutral as they are
now connected together on both sides of the RCBO. The RCBO
senses an inbalance because not all of the phase current is
flowing back thriough the neutral and it therefore trips.

Is This Answer Correct ?    0 Yes 0 No

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