Copper losses ( I²R)depends on Current which passing through transformer winding while Iron Losses or Core Losses or Insulation Losses depends on Voltage. So the Cu Losses depend on the rating current of the load so the load type will determine the powerfactor P.F ,Thats why the rating of Transformer in kVA,Not in kW.
What is the turns ratio of a transformer?
A transformer with a primary winding of 1000 turns and a secondary winding of 100 turns has a turns ratio of 1000:100 or 10:1. Therefore 100 volts applied to the primary will produce a secondary voltage of 10 volts.
What is the ratio of transformer?
Transformation ratio is the ratio of secondary voltage to the primary voltage and is equal to the ratio of the number of turns in the secondary winding to the number of turns in the primary winding, if leakage flux is neglected.
kW is the amount of power capable of doing work, while kVA is the “vectorial summation” of KVAR and KW. kW is kilowatts, while kVA is kilo Volts Amperes. kVA is equal to kW in DC circuits because the voltage and current are in phase. In AC circuit at unity power factor KVA=KW.
Direct current(DC) has no time varying field because current is constant as well as there is no relatively motion between coil and core(magnetic circuit) of the transformer. So there is no induced emf in secondary coil of the transformer. Transformer fails to transfer power from primary to secondary.
All neutral wires of the same earthed (grounded) electrical system should have the same electrical potential, because they are all connected through the system ground. Neutral conductors are usually insulated for the same voltage as the line conductors, with interesting exceptions.
The efficiency of a transformer depends on its design and is equal to the power output divided by the power input. It is necessary to use higher efficiency at the higher power levels because the amount of energy wasted is significant.
As seen, cupper loss of an alternator and transformer depend on current and iron loss on voltage. That is why rating of alternator and transformers is in KVA and not KW. Although losses of alternator and transformer depend upon its KVA or MVA rating but actual output varies with electrical power factor.
There are several ways to control the speed of an induction motor.
- Reduce the voltage applied to the motor.
- Control the current to the motor.
- Use a wound-rotor motor and control the resistance applied to the rotor windings.
- Control the frequency and voltage applied to the motor.
That's why we are rated Motor in kW or HP (kilowatts/ Horsepower) instead of kVA. in more clear words, Motor only consume active power and provide mechanical power in HP or kW at motor shaft. Moreover, the motor power factor does not depend on the load and it works on any P.F because of its design.
All Day Efficiency of a Transformer. Definition: All day efficiency means the power consumed by the transformer throughout the day. It is defined as the ratio of output power to the input power in kWh or wh of the transformer over 24 hours.
Eddy current loss= The ohmic losses in a metal body, due to the eddy currents flowing through it, induced by an alternating magnetic field. Hysteresis loss= The loss in form of heat when magnetisation of the material is made to alternate with respect to time.
A transformer is said to be on “no-load” when its secondary side winding is open circuited, in other words, nothing is attached and the transformer loading is zero. With the secondary circuit open, nothing connected, a back EMF along with the primary winding resistance acts to limit the flow of this primary current.
KVAR = Kilo Volt Ampere Reactive. It's a unit of reactive power. Actual Power consumed by loads is called Kilo Watt Power. All the Power given to the load is not utilized as useful power, some power is being wasted. The power which is not consumed is called Reactive power i.e KVAR.
iron loss which depend on the applied voltage, and the copper losses which are dependent on the current flowing through windings. As these power losses are independent of load power factor, so the temperature rise is governed by kVA and not kW. Assume a transformer with 3.5 kVA rating. 3.5 kVA is 3500 volt-amperes.
Active power does do work, so it is the real axis. The unit for all forms of power is the watt (symbol: W), but this unit is generally reserved for active power. Apparent power is conventionally expressed in volt-amperes (VA) since it is the product of rms voltage and rms current.
In order to reduce the eddy current loss, the resistance of the core should be increased. In other words, low reluctance should be retained. In devices like transformers, the core is made up of laminations of iron. ie,the core is made up of thin sheets of steel, each lamination being insulated from others.
That's why compare to copper loss, iron loss is very very less and it can be ignored during short circuit test. Iron losses in short circuit test are not absent they are just neglected. Because in the short circuit test the LV winding is short circuited which means high currrent and low voltage in the secondary side.
The reason behind core loss being constant is that hysteresis loss and eddy current loss both are dependent on the magnetic properties of the material used in the construction and design of the core of the transformer. So these losses are constant and do not depend on the value of load current.
An alternating current (AC) in one winding creates a time-varying magnetic flux in the core, which induces a voltage in the other windings. Transformers are used to convert between high and low voltages, to change impedance, and to provide electrical isolation between circuits.
Eddy current loss and hysteresis loss depend upon the magnetic properties of the material used for the construction of core. Hence these losses are also known as core losses or iron losses. Hysteresis loss in transformer: Hysteresis loss is due to reversal of magnetization in the transformer core.
A transformer consists of two electrically isolated coils and operates on Faraday's principal of “mutual induction”, in which an EMF is induced in the transformers secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding.
VA stands for (Volts X Amps) Kilo (Volt X Amps) or just (kVA) is the apparent rate, expressed in quantities of 1,000 VoltAmps, at which energy is being transferred. Kilo Watts (kW) is the real rate, expressed in quantities of 1,000 Watts, at which energy is being transferred. kW = kVA X (power factor).