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A (50/60 Hz) Transformer. Which one will give more Output? (When operates on 50 or 60 Hz frequency) A Transformer is designed to be operated on both 50 & 60 Hz frequency.  For the Same rating, which one will give more out put; when,   Operates on 50 Hz    Operates on 60 Hz Obviously!  It will give more out put when we operate a transformer (of same rating) on 50 Hz instead of 60 Hz. Because in previous posts, we proved that, in inductive circuit,  when frequency increases, the circuit power factor decreases . Consequently, the transformer out put decreases. Let’s consider the following example. Suppose, When Transformer operates on  50 Hz  Frequency Transformer = 100kVA, R=700 Ω , L=1.2 H, f= 50 Hz. X L  = 2πfL = 2 x 3.1415 x 50 x 1.2 = 377 Ω Impedance Z = √ (R 2 +X L 2 ) = √ (700 2 + 377 2 ) = 795 Ω Power factor Cos θ = R/Z = 700/795 = 0.88 Transformer Output (Real Power) kVA x Cos θ 100kVA...

Why Battery rated in Ah (Ampere hour) and not in VA. Why Battery rating 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 10 18  electrons , or 6,250,000,000,000,000,000 electrons. In addition,  1A (Ampere) = 1 coulomb of electrons per secon...

Why Motor rated in kW instead of kVA Why Motor rated in kW/Horsepower 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...

Explain the application of storage batteries. Storage batteries are used for various purposes, some of the applications are mentioned below: • For the operation of protective devices and for emergency lighting at generating stations and substations. • For starting, ignition and lighting of automobiles, aircrafts etc. • For lighting on steam and diesel railways trains. • As a supply power source in telephone exchange, laboratories and broad casting stations. • For emergency lighting at hospitals, banks, rural areas where electricity supplies are not possible.

What is slip in an induction motor? Slip can be defined as the difference between the flux speed (Ns) and the rotor speed (N). Speed of the rotor of an induction motor is always less than its synchronous speed. It is usually expressed as a percentage of synchronous speed (Ns) and represented by the symbol ‘S’.

Why back emf used for a dc motor? highlight its significance. The induced emf developed when the rotating conductors of the armature between the poles of magnet, in a DC motor, cut the magnetic flux, opposes the current flowing through the conductor, when the armature rotates, is called back emf. Its value depends upon the speed of rotation of the armature conductors. In starting, the value of back emf is zero.

What are the various kind of cables used for transmission? Cables, which are used for transmitting power, can be categorized in three forms: • Low-tension cables, which can transmit voltage upto 1000 volts. • High-tension cables can transmit voltage upto 23000 volts. • Super tension cables can transmit voltage 66 kV to 132 kV.

How can you relate power engineering with electrical engineering? Power engineering is a sub division of electrical engineering. It deals with generation, transmission and distribution of energy in electrical form. Design of all power equipments also comes under power engineering. Power engineers may work on the design and maintenance of the power grid i.e. called on grid systems and they might work on off grid systems that are not connected to the system.

Why AC systems are preferred over DC systems? Due to following reasons, AC systems are preferred over DC systems: a. It is easy to maintain and change the voltage of AC electricity for transmission and distribution. b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission c. From power stations, AC is produced so it is better to use AC then DC instead of converting it. d. When a large fault occurs in a network, it is easier to interrupt in an AC system, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt. Due to following reasons, AC systems are preferred over DC systems: a. It is easy to maintain and change the voltage of AC electricity for transmission and distribution. b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission c. From power stations, AC is produced so it is be...

State the difference between generator and alternator Generator and alternator are two devices, which converts mechanical energy into electrical energy. Both have the same principle of electromagnetic induction, the only difference is that their construction. Generator persists stationary magnetic field and rotating conductor which rolls on the armature with slip rings and brushes riding against each other, hence it converts the induced emf into dc current for external load whereas an alternator has a stationary armature and rotating magnetic field for high voltages but for low voltage output rotating armature and stationary magnetic field is used.

Why star delta starter is preferred with induction motor? Star delta starter is preferred with induction motor due to following reasons: • Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less losses. • Star delta starter circuit comes in circuit first during starting of motor, which reduces voltage 3 times, that is why current also reduces up to 3 times and hence less motor burning is caused. • In addition, starting torque is increased and it prevents the damage of motor winding.

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                                        MOVING IRON  • Moving-iron instruments are generally used to measure alternating voltages and currents.  • In moving-iron instruments the movable system consists of one or more pieces of soft iron, which are so pivoted as to be acted upon by the magnetic field produced by the current in coil. Components  • Moving element: a small piece of soft iron in the form of a vane or rod.  • Coil: to produce the magnetic field due to current flowing through it and also to magnetize the iron pieces.  • In repulsion type, a fixed vane or rod is also used and magnetized with the same polarity.  • Control torque is provided by spring or weight (gravity).  • Damping torque: the damping device consisting of an air chamber and a moving vane attached to the instrument spindle.  • Deflecting...