Why we can’t store AC in Batteries instead of DC?

We cannot store AC in batteries because AC changes their polarity upto 50 (When frequency = 50 Hz) or 60 (When frequency = 60 Hz) times in a second. Therefore the battery terminals keep changing Positive (+ve) becomes Negative (-Ve) and vice versa, but the battery cannot change their terminals with the same speed so that’s why we can’t store AC| in Batteries.

Also when we connect a battery with AC Supply, then It will charge during positive half cycle and discharge during negative half cycle because the Positive (+ve) half cycle cancel the negative (-Ve) half cycle, so the average voltage or current in a complete cycle is Zero. So there is no chance to store AC in the Batteries.

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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 Motorhas 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.

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Why alternator rated in kVA. Not in kW?

The power √3 V_L I_L 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.

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Why AC rated in Tons, Not in kW or kVA? A Guide about Airconditioner and Refrigeration

If you pick this article, You will be able understand; → Why AC rated in Tons, Not in kW?
→ Definition of Ton

→ How many kW and HP are there in 1 Ton?

→ How to convert Ton to Kw and vice versa?
→ How much Current in Ampere will a 2 Tons AC draw in Single Phase & Three Phase

System?
→ How many 2 Ton A.C (Air conditioner) can I run on a 25 kVA Generator?

→ What is the suitable rating of MCB for 2 Ton and 1 Ton AC (Air conditioner) and why?

and much more…

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 capacity instead 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 (R_T) is approximately equivalent to 12,000 BTU/h or 3,516.8528 W or 4.7142Hp.

A Ton of refrigeration (R_T) is a unit of power used to describe the heat-extraction capacity of air conditioning and refrigeration equipment. 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 R_T(Refrigeration Ton) = 3.5168528 kW…

1 R_T = 3.5168528 kW

1 kW = 0.284345 R_T(Refrigeration Ton)

1 kW = 0.28434517 R_T

So,

The power P in kW = Power P in R_T (Refrigeration Ton) times 3.5168528….

P_(kW) = P_(RT) × 3.5168528

Example

Convert 3 Ton AC into kW i.e. Convert 3 R_T to kW.

Solution:

P_(kW) = 3 R_T × 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

Andin 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 V_LxI_L 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.

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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”.   

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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 circuittofully 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 10¹⁸electrons, 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

But,

Why make up a new unit for battery capacity rating when an old one unit is doing just fine? L

Of course! To make your lives as technicians and students more difficult.    

As they do for electricity units… i.e. 1 Unit of Electricity = 1kWh = 1 board of Trade Unit…

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