Why Generator & Alternator rated in kVA. Not in kW?
The power √3 VL IL Cos φ delivered by the alternator for the same value of current, depends upon p.f. (Power Factor=Cos φ) of the load. But the alternator conductors are calculated for a definite current and the insulation at magnetic system are designed for a definite voltage independent of p.f. (Cos φ) of the load. For this reason apparent power measured in kVA is regarded as the rated power of the alternator
if we check dc circuit through a tester its glow. why ?
if indeed
you do have one of the NEON type testers you will see two rods inside a glass
bulb. With AC, both will tend to glow. Actually they are taking turns glowing
at either 50 or 60 times per second, depending upon where in the world you
live. For DC, only one electrode will glow. It will indicate the NEGATIVE lead.
These units usually require somewhere around 55 to 60 volts to light up. Inside
the housing, there is a resistor to limit the amount of current the bulb can
draw.
What is inductance?
When
alternating current passes through a conductor it will induce timely changing
alternating magnetic field. According to lenz’s law this changing magnetic
field induces an emf which is opposing it’s own cause (i.e. current through
conductor). This opposition is called inductance. It is further segregated in
to two parts self inductance and mutual inductance.
What is the relation between power factor and power consumption?
As we all
know Total (Apparent) power = Real or Active power + Reactive power.
In a very
simple language, power factor basically means, out of the total apparent power
consumed by the load, how much useful or active or real power is present in it.
In fact power factor is indicator of this above mentioned fact.
So,
naturally power factor of unity (ideal case) indicates whole total power which
is consumed by load is Active power or Real power, which means there is no
reactive power consumed by load (case of Purely Resistive load).
As against
this zero power factor indicates that no power will be transferred between the
source and the load i.e whole power consumed by load will be just reactive
power (just to get magnetized), no Active or real power is transferred which is
actually used for doing useful work.
Consequences
of low power factor and its effect on total power consumed by load:-
So, consider
two loads, Load 1 and Load 2. Both have same power requirement for doing work
(i.e Active power requirement). Now load one have low power factor, so as
explained above out of total power which it draws from the source, Active power
will have lesser share in it. load 2 has high power factor so the total power which
it draws from source will contain more amount of Active power as compared to
load 1 having lower power factor.
So, as the
Active power requirement of both the loads is same, load 1 will have to draw
more Apparent power (total power) as compared to load 2 which has high power
factor, in order to have same amount of Active power as load 2.
Takeaway for
you from this Answer:
A load with
a low power factor draws more current than a load with a high power factor for
the same amount of useful power transferred.
Thus, a load
with low power factor will draw more apparent power as compared to a load with
high power factor for the same amount of useful power transferred.
The higher
current increase the energy lost in the distribution system, and require larger
wires and other equipment.
Because of
the above fact, Electrical utilities usually charges higher cost to industrial
or commercial customers, where there is a low power factor.
We all feel electrical shocks. Which is really responsible for the shock, voltage or current?
The ultimate
cause is the amount of electricity flow in the body, so it can be said to be
current.
However,
there are other factors, one of which is voltage, to consider:
1) Path of
flow: If the internal organs are in the path of current flow, much smaller
currents can cause a fatality.
Hence, if
the shock is applied between one arm and the other arm, such as when holding
Live wire in one hand and Neutral in the other, the current can pass through
the heart, causing death. The same source of electricity may perhaps not be
fatal if the points of the shock delivery are an arm and a leg, for example.
This is
probably also the reason that execution by electrocution is done by placing the
electrodes across the head. So that the current path is through the brain.
2)
Resistance of the body: This is the resistance offered by the human body to
electric flow. This can vary depending on moisture level. It can also vary with
voltage as mentioned in the next point.
3) Voltage:
Important to note that the resistance of the body changes according to voltage
applied! Hence, it is not just a simple linear increase of current with voltage
(in accordance with ohm's law).
The skin is
an insulator, and contributes greatly to the high resistance of the body (order
of Mega-ohms) for low voltages. However, at high voltages, dielectric breakdown
of skin occurs which drastically reduces resistance of body by almost 1000
times!
This is what
makes voltages above a certain level fatal, since it can cause current flow to
increase drastically.
4) Duration
of shock: In general, higher the duration of shock - greater the damage.
As an
interesting example, consider static electricity. We can easily build up static
potentials in excess of 10000 Volts, which is enough to break down air at short
distances! However, we don't see any deaths caused by handshakes. :)
This is
because, while the potential generated by static can be huge, the total amount
of source charge available is really small. So the duration of the current flow
is also too small to have any effect.
So to answer
the question, while it is the flow of electrons (current) that causes us
problems, there are other factors (including voltage) which can significantly
affect how much of this electron flow occurs.
A Step Up transformer _____________. how ?
Ans: Step Up
the level of Voltage & Step down the level of current
A Step up
transformer only step up the level of voltage and step down the level of
current.
Because the
input power is same.
So according
to P=VI→ I = P/V…. We can see that, when Voltage increases, current decreases.
So in Step
up transformer, input power is same, therefore, when voltage increases, then
current decreases.
If the frequency of 3-phase supply to the stator of 3-phase induction motor is increased, then synchronous speed is ________? Why ?
Ans:------
Increased
Explanation: As we know that; f = NSP/ 120
It is clear
that f ∝ NS i.e., frequency (f) is directly proportional to the
Synchronous speed (NS).
In more
clear words, when frequency increases, Speed also increases.
Why Battery rated in Ah (Ampere hour) and not in VA. ?
Battery
stores charge in the form of chemical energy and then converts it into
electrical energy to utilize for a specific time. The amount of available
charge is the capacity of a cell or battery which may be expressed in Ah
(Ampere-hour). Moreover, in a charged battery, the numbers of molecules are
limited to create a flow of electron in electric circuits, so, there must be a
limited number of electrons in a cell/battery which they motivate through a
circuit to fully discharge.
Now we have
the option to rate the battery capacity in Number of flowing electrons for a
specific time, but, it would be a headache, because there are a vast number of
electrons in it. So we have another
option (1C (Coulomb) = 6.25 x 1018 electrons, or 6,250,000,000,000,000,000 electrons.
In addition,
1A (Ampere) = 1 coulomb of electrons per second and,
1h = 3600
Seconds
Therefore;
1Ah = (1A) x
(3600s) = (C/s) x (3600s) = 3600 C.
∴ A (1 Ampere) = 1 Coulomb per second
= C/s
Why Generator & Alternator rated in kVA. Not in kW?
The power √3
VL IL Cos φ delivered by the alternator for the same value of current, depends
upon p.f. (Power Factor=Cos φ) of the load. But the alternator conductors are
calculated for a definite current and the insulation at magnetic system are
designed for a definite voltage independent of p.f. (Cos φ) of the load. For
this reason apparent power measured in kVA is regarded as the rated power of
the alternator.
Why Transformer Rating In kVA, Not in KW?
There are
two type of losses in a transformer;
1. Copper
Losses
2. Iron
Losses or Core Losses or Insulation
Losses
Copper
losses ( I²R)depends on Current which passing through transformer winding while
Iron Losses or Core Losses or Insulation
Losses depends on Voltage.
That’s why
the Transformer Rating may be expressed in kVA,Not in kW.
Why Motor rated in kW instead of kVA?
We know that
Transformer rating may be expressed in kVA as well as Generator and Alternator
rated in kVA Designer doesn’t know the actual consumer power factor while
manufacturing transformers and generators i.e. the P.F (Power factor) of
Transformer and Generator/Alternator depends on the nature of connected load
such as resistive load, capacitive load, and inductive load as Motors, etc. But
Motor has fixed Power factor, i.e. motor has defined power factor and the
rating has been mentioned in KW on Motor nameplate data table. That’s why we
are rated Motor in kW or HP (kilowatts/ Horsepower) instead of kVA.
In addition,
Motor is a device which converts Electrical power into Mechanical power. In
this case, the load is not electrical, but mechanical (Motor’s Output) and we
take into the account only active power which has to be converted into
mechanical load. Moreover, the motor power factor does not depend on the load
and it works on any P.F because of its design.
Why AC rated in Tons, Not in kW or kVA? A Guide about Airconditioner and Refrigeration
Why AC rated
in Tons, Not in kW?
AC
(Air-conditions and Refrigeration are always rated in Tons.
Air
conditioners are always rated in Tons capacityinstead of kW because Air
conditioners are designed on the basis of quantity of heat removal from room,
hall or specific area. Quantity of heat is termed in Tons means if an air
conditioner is able to remove 1000 kilocalories of heat or 4120 kilojoules or
12000 BTU of heat in an hour that AC rated as 1 Ton of AC because 1000
Kilocalories or 4120 kilojoules or 12000 BTU equal to one Ton of heat. Also,
this is the same case for freezer and refrigerator i.e. refrigeration system.
Good to
know:
BTU =
British thermal unit. A measurement of heat, specifically, the amount of heat
needed to raise the temperature of a pound of water by 1°F.
Definition
of Ton
A Ton of
refrigeration (RT) is approximately equivalent to 12,000 BTU/h or 3,516.8528 W
or 4.7142Hp.
A Ton of
refrigeration (RT) is a unit of power used to describe the heat-extraction
capacity of air conditioning and refrigeration equipments. It is defined as the
heat of fusion absorbed by melting 1 short ton of pure ice at 0 °C (32 °F) in
24 hours.
How many kW
and HP are there in 1 Ton?
1 Ton =
3.5168525 kW = 4.714Hp
Explanation
1 Ton =
12,000 BTU/h
1 Watt =
3.412141633 BTU/h
1 Ton =
12,000 / 3.412141633 = 3,516.8528 Watts = 3.5168528 kW.
1 Ton =
3,516.8528 Watts = 3.516 kW.
Also
1 Ton =
3,516.8528W / 746 = 4.7142798928 Hp →→→ (1 Hp = 746 Watts)
1 Ton =
4.714 Hp
How to
convert Ton to Kw and vice versa?
One
RT(Refrigeration Ton) = 3.5168528 kW…
1 RT =
3.5168528 kW
1 kW =
0.284345 RT(Refrigeration Ton)
1 kW =
0.28434517 RT
So,
The power P
in kW = Power P in RT (Refrigeration Ton) times 3.5168528….
P(kW) =
P(RT) × 3.5168528
Example
Convert 3
Ton AC into kW i.e. Convert 3 RT to kW.
Solution:
P(kW) = 3 RT
× 3.5168528
P(kW) =
10.55 kW
3 Ton AC =
10.55 kW
How much
Current in Ampere will a 2 Tons AC draw in Single Phase & Three Phase
System?
Suppose,
There are 230V and Power factor = Cosθ = 0.95 in Single Phase AC system…
1 Ton =
3,516.8528 Watts = 3.516 kW.
2 Ton = 2 x
3.516 kW = 7.032kW = 7032W
Power in a
Single Phase AC System
P = VxI Cosθ
and current…
I = P / (V x
Cosθ)….. Where Cosθ = Power factor
I = 7032W /
(230V x .95)
I = 32.18 A
Therefore, a
2 Ton AC (Air-condition in Single Phase AC system will take 31.18 Ampere
Current
And in Three
Phase System
Suppose,
There are 440V and Power factor = Cosθ = 0.85 in Three Phase AC system…
Power in a
Three Phase AC System
P =√3 x
VLxIL Cosθ and current….
I = P /(
√3xVxCosθ)
I = 7032W /
(1.732 x 440V x .85) Where Cosθ = Power factor and √3 = 1.732
I = 10.855 A
Therefore, a
2 Ton AC (Air-condition in Three Phase AC system will take 10.855 Ampere
Current
Good to
Know:This is just calculation based on Electrical formulas. In real, Air
conditioner current depends a lot on operating conditions such as ambient
temperature, refrigerant pressure, Energy Efficiency Ratio (EER) etc. for
instance, if EER is 6, then input power for 2 Tons Air conditioner is 24000BTU/
6 = 4000 watts..
If this is a
230 volt system, then air conditioner load current would be = 4000/(230x.95) =
18.5 A
For More
detail…Check the Air conditioner Name plate rating.
Another
similar rating is Coefficient of power (COP) which is the output power in watts
divided by input power, so with a COP = 1.8, for instance, input power for 2
Tons Air conditioner is 7032W / 1.8 =
3906 watts. Now you can find current by using the above method which is equal
to 18A approx.
How many 2
Ton A.C (Air conditioner) can I run on a 25 kVA Generator?
2 Ton = 2 x
3.516 kW = 7.032kW = 7032W
The
Efficiency of Utility Power Generator is 90% approximately.
Efficiency
of Generator = 25kVA x (90/100) = 22.5kVA
Now the
Number of 2 Ton AC (Air conditioners) which you can run on a 25 kVA Generator
smoothly..
22.5kVA /
7032W
= 3
So you can
run Three Air conditioners of 2 Tons each on a 25kVA Generator.
What is the
suitable rating of MCB for 2 Ton and 1 Ton AC (Air conditioner) and why?
As we have
calculated the load current for 2 Ton AC Air conditioner…
Calculated
Current for 2 Ton A.C = I = 32.18 A
Now 40A
Class “C” MCB (miniature circuit breaker) would be suitable for 2 Ton AC
(air-condition) because in starting time it takes more current of the full load
current
And 20 A
Class “C” MCB would be better for 1 Ton AC (air-condition)
Good to
Know:
Class “’C’
Type MCBs
Class “C”
Type MCBs are suitable for installations with high inrush of current at the
starting switching time. in other words, equipment and devices having inductive
loads such as air-conditioners, induction motors, fluorescent lamps,
transformers etc.
WHY POWER PLANT CAPACITY RATED IN MW AND NOT IN MVA ?
For the following reasons, a Power
plant capacity rating may be expressed in MW instead of MVA.
In a Generating station, the prime
mover (Turbine) generates only and onlyActive
Power. That’s why we rated a power plant capacity in MW instead of MVA. Its
mean no matter how large your generator is, but it depends on the capacity of
the engine (Prime mover/Turbine) I.e. a
50MW turbine connected to a 90MVA alternator in a power plant will generate
only 50MW at full load. In short, a power plant rating is specified in terms of
prime mover /Turbine (Turbine rating may be seen by nameplate rating which is
in MW or Horsepower (HP) not in MVA) and not by the alternator set coupled to
it.
Another thing is that, electric
power company charges their consumer for kVA while they generate kW (or MW) at
the power station (Power plant).They penalize their consumer for low Power
factor because they are not responsible for low power factor and kVA but you.
Moreover, in power plant, power factor is 1 therefore MW is equal to MVA …… (MW
= MVA x P.f).
Another interesting & funny
answer by one of our Facebook page fan…“Power House means, house of the Power,
and we know that the unit or power is Watt. That’s why we rated power plant
capacity in MW and not in MVA”
IMP POINTS ON POWER PLANT
Ø The
major heat loss in a steam power station occurs in Condenser, about 53%.
Ø The
thermal efficiency of a steam power station is about 28%.
Ø Cooling
towers are used where water is not available in sufficient quantity.
Ø The
running cost of medium power stations is about 15 paise per unit.
Ø In
a hydro-electric plant, spillways are used discharge surplus water on
the downstream side of dam.
Ø The
running cost of a hydro-electric plant is about 5 paise per unit.
Ø For
high head hydro-electric plants, the turbine used is pelton wheel.
Ø Francis
and Kaplan turbines are used for medium and
low heads.
Ø Surge
tank is provided for the protection of penstock.
Ø Of all the plants, minimum quantity of fuel is required in
nuclear power plant.
Ø The
running cost of a nuclear power plant is about 20 paise per unit.
Ø Diesel
power plants are used as Standby plants.
Ø India’s
first nuclear power plant was built at Tarapur.
Ø The
most simple and clean plant is hydro-electric plant.
Ø The
first nuclear power plant in the world was commissioned in ) U.S.S.R.
in 1954.
Ø Gas
turbine power plant is more efficient than steam power plant.
Ø Draft tube is used in reaction turbines.
Ø The
cost of fuel transportation is minimum in hydro-electric plant.
Ø The
cheapest plant in operation and maintenance is hydroe-lectric plant.
Ø Economisers are used to heat feed water.
(
GK MANIA-2
Q. सुभाष चंद्र बोस के
पिता का क्या
नाम था ?
Ans. जानकीनाथ
बोस
Q. वह अंग है,
जो पुन: उत्पन्न
होने के बाद
वृद्धि
भी कर सकता
है ?
Ans. यकृत
(liver)
Q. कागज का अविष्कार
कहाँ हुआ?
Ans. चीन में
Q. यूनेस्को
का मुख्यालय कहाँ
है?
Ans. पेरिस
में
Q. ग्रीनहाउस
प्रभाव किन गैसों
के कारण होता
है?
Ans. जल वाष्प, कार्बन डाइऑक्साइड,
मीथेन,
नाइट्रस ऑक्साइड, और ओजोन।
Q. अंतिम मुगल बादशाह
कौन था?
Ans. बहादुर
शाह जफर
Q. पर्यावरण
दिवस कब मनाया
जाता है?
Ans. 5 जून
Q. कौन सा बंदरगाह
विहीन देश है?
Ans. किर्गिज़स्तान
Q. भारत छोड़ो आन्दोलन कब
शुरू हुआ ?
Ans. 8 अगस्त
1942
Q. थाईलैंड
की मुद्रा क्या
है?
Ans. थाई बहत
Q. मानवीय शरीर में
सबसे
छोटी अस्थि कौन-सी
होती है?
Ans. स्टेपीज़
Q. इंटरपोल
का मुख्यालय कहाँ
पर है?
Ans. ल्यों,
फ्रांस
Q. 'Tee' शब्द
का सम्बन्ध किस
खेल से है?
Ans. गोल्फ
Q. भारत के मुख्य
न्यायाधीश कौन हैं?
Ans. न्यायमूर्ति
टी.एस. ठाकुर
Q. सीमांत गाँधी के नाम
किसे जाना जाता
है?
Ans. खान अब्दुल गफ्फार खान
Q. राष्ट्रीय
गीत की रचना
किस ने की
थी?
Ans. बंकिमचंद्र
चट्टोपाध्याय,
Q. कुंचिलाल
जल प्रपात कहाँ
स्थित है?
Ans. कर्नाटक
में
Q. दुनिया में सबसे
बड़ा गैर ध्रुवीय
रेगिस्तान?
Ans. सहारा
Q. सेशेल्स
द्वीप कहाँ पर
स्थित है?
Ans. माहे में
Q. बंदरगाह
विहीन देश कौन-सा है?
Ans. मध्य यूरोप में लिकटेंस्टीन,
जो स्विट्जरलैंड
और ऑस्ट्रिया से घिरा
हुआ है।
Q. वायु से होने
वाले परागण को
कहा जाता है?
Ans. वायुपरागित
(Anemophily) या वायु परागण
Q. हमारे आकाश में
सर्वाधिक चमकीला गृह
Ans. सिरियस
A
Subscribe to:
Posts (Atom)
Featured post
-
As we all know Total (Apparent) power = Real or Active power + Reactive power. In a very simple language, power factor ba...
