Electrical World

The two circuits are said to be coupled circuits if all or part of the electrical energy supplied to one circuit is transferred to the other circuit without having any electrical connection between them. Such coupled circuits are frequency used in the circuit analysis. The common examples of the coupled circuits are transformer, generator etc. 1. Magnetically Coupled Circuit       When the two circuits are placed very close to each other such that a magnetic flux produced by one circuit links with both the circuits, then the two circuits are said to be Magnetically Coupled Circuits. In this article, we will consider magnetically coupled circuits consisting coils or conductors. Such circuits are also called coupled inductors.        A wire of certain length, when twisted into coil becomes a basic inductor. If a current is made to pass through an inductor, an electromagnetic field is developed. A change in the magn...

An electrical machine is a device that convert the electrical energy into mechanical energy and vice versa. Transformer is also listed in electrical machine which change the voltage level of alternatering current without changing frequency. Take a look on this figure to understand the electrical machine. 1. Generator The Input is mechanical energy (from the prime mover), and the output is electrical energy.  An electrical generator is a device which converts the mechanical energy into electrical energy. The working principle of generator is that when a conductor rotate in magnetic field, an emf is induced in the conductor. A generator forces electrones to flow through an external circuit. There are two main parts of generator named as rotor and stator. In generator mechanical energy is applied to rotor. Rotor is connected to prime mover which is coupled to a turbine. The other source of mechanical energy are internal combustion engine, wind turbine, compressed air and hand c...

Hello Engineer's Q.[1] A transformer transforms (a) frequency (b) voltage (c) current (d) voltage and current Ans : D Q.[2] Which of the following is not a basic element of a transformer ? (a) core (b) primary winding (c) secondary winding (d) mutual flux. Ans : D Q.[3] In an ideal transformer, (a) windings have no resistance (b) core has no losses (c) core has infinite permeability (d) all of the above. Ans : D Q.[4] The main purpose of using core in a transformer is to (a) decrease iron losses (b) prevent eddy current loss (c) eliminate magnetic hysteresis (d) decrease reluctance of the common magnetic circuit. Ans :D Q.[5] Transformer cores are laminated in order to (a) simplify its construction (b) minimize eddy current loss (c) reduce cost (d) reduce hysteresis loss. Ans : B Q.[6] A transformer having 1000 primary turns is connected to a 250-V a.c. supply. For a secondary voltage of 400 V, the number of secondary turns should be (a) 1600 (b) 250 (c) 400 (d) 1250 A...

Q. What are the advantages of parallel operation of transformers? A. 1) To maximize electrical power system efficiency: Generally electrical power transformer gives the maximum efficiency at full load. If we run numbers of transformers in parallel, we can switch on only those transformers which will give the total demand by running nearer to its full load rating for that time. 2) To maximize electrical power system availability: If numbers of transformers run in parallel we can take shutdown any one of them for maintenance purpose. Other parallel transformers in system will serve the load without total interruption of power. 3) To maximize power system reliability. If any one of the transformers in a parallel system, is tripped due to fault other parallel transformers is the system will share the load hence power supply may not be interrupted. 4) To maximize electrical power system flexibility: Always there is a chance of increasing or decreasing future demand of power system. If i...

Q. What is the significance of vector grouping in Power Transformers? A. Every power transformer has a vector group listed by its manufacturer. Fundamentally it tells you the information about how the windings are connected (delta or wye) and the phase difference between the current and voltage. Example: DYN11 means Delta primary, Wye Secondary and the current is at 11 o clock referred to the voltage. Q. What is meant by regulation in a transformer? A. Voltage regulation in transformers is the difference between the no load voltage and the full load voltage. This is usually expressed in terms of percentage. Example: A Transformer delivers 100 volts at no load and the voltage drops to 95 volts at full load, The regulation capacity varies depending on the size and the application for which they are used. Q. Can a Single Phase Transformer be used on a Three Phase source? A. Any single phase transformer can be used on a three phase source by connecting the primary leads to any ...

Q. Why the transformer ratings are in kva? A. Since the power factor of transformer is dependent on load we only define VA rating and does not include power factor .In case of motors, power factor depend on construction and hence rating of motors is in KWatts and include power factor. Q. Is copper loss affected by change in power factor? A. Yes. Copper loss varies inversely with power factor.It depends on current in primary and secondary windings. It is known that current required is higher when power factor is lower Q. How do we minimize eddy current loss? A. By laminating the core we can minimize eddy current loss. Q. Does the transformer draw any current when its secondary is open? A. Yes. It draws No load primary current. Q. What is the difference between delta-delta, delta-star transformer? A. Delta-delta transformer is used at generating station or a receiving station for Change of Voltage (i,e) generally it is used where the Voltage is high & Current is l...

Q. What is a Transformer? A. A transformer is a static electrical apparatus designed to convert alternating current from one voltage to another .It transforms electrical energy from one circuit to another without any direct electrical connection, with the help of mutual induction between to windings. It can be designed to “step up” or “step down” voltages. Q. Explain the working principle of Transformer? A. Working principle of Transformer is based on Faraday’s Laws of Electromagnetic Induction. If an alternating current is applied to an electric coil, there will be an alternating flux surrounding that coil. Now if we bring another coil near the first one, there will be an alternating flux linkage with that second coil. As the flux is alternating, there will be obviously a rate of change of flux linkage with respect to time in the second coil. Therefore emf will be induced in it as per Faraday's laws electromagnetic induction. Q. How do you classify transformers based on ...

Q. What is meant by knee point voltage? A. Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a CT. It is the voltage at which a CT gets saturated.(CT-current transformer). Query:What is reverse power relay? Resolution:Reverse Power flow relay are used in generating stations's protection. A generating stations is supposed to fed power to the grid and in case generating units are off,there is no generation in the plant then plant may take power from grid. To stop the flow of power from grid to generator we use reverse power relay. Q:What is the difference between Isolator and Circuit Breaker? A:Isolator is a off load device which is used for isolating the downstream circuits from upstream circuits for the reason of any maintenance on downstream circuits. it is manually operated and does not contain any solenoid unlike circuit breaker. it should not be operated while it is having load. first the load on it must be...