ELECTRICAL EASY

There are two types of winding in a Conventional DC Motor, namely Filed Winding and Armature Winding. The purpose of Field Winding is to produce the working magnetic flux in the air gap and wound on the stator of the motor whereas armature winding is wound on the rotor. But in Permanent Magnet DC Motor or PMDC Motor, we do not use field winding rather permanent magnet is used to have the working flux in the air gap. The construction of rotor of PMDC is same as that of the Conventional DC Motor i.e. rotor of PMDC Motor consists of armature core, armature winding and commutator. Stationary Carbon Brushes are kept pressed on the commutator as in conventional DC motor. PMDC Motors are extensively used in automobiles for windshield wipers and washers, for blowers used in air conditioner and heaters, to raise and lower windows, in personnel computers disc drives etc. As millions of automobiles are manufactured per year, PMDC motors are also produced in millions. Maximum power rating...

The rating of AC Machines such as Transformer, Alternators etc. are determined by the heating and hence losses in them. These losses are made up of Ohmic (I 2 R loss ) and Core Loss and a small amount of friction & windage loss. The ohmic loss depends upon the current and the core loss depends upon the voltage, therefore the losses in an electrical AC machine are unaffected by the power factor of the load. In view of this, the rating of AC machinery is determined by volt-ampere of the load not by the load power alone. Therefore the Alternators or Synchronous Generators are rated in kVA or MVA. You may like to read  Losses in Electrical Machine - Core Loss and Eddy Current Loss It shall be noted here that the size of boiler or the fuel requirement is solely determined by the output power and not on the volt-ampere. For example, for 700 MW load at 0.85 power factor, the rating of Alternator or Synchronous Generator will be 823 MVA (700/0.85 = 823) while the fuel requir...

Open Circuit Test and Short Circuit Test are performed on a Synchronous Machine to find out the parameters of Synchronous Machine and hence to have an idea of their performance.  Open Circuit Test of Synchronous Machine is also called No Load, Saturation or Magnetizing Characteristics for the reason which will be clear after going through the post. For getting the Open Circuit Characteristics of Synchronous Machine, the alternator is first driven at its rated speed and the open terminal voltage i.e. voltage across the armature terminal is noted by varying the field current. Thus Open Circuit Characteristic or OCC is basically the plot between the armature terminal voltage E f versus field current I f while keeping the speed of rotor at rated value. It shall be noted that for OCC, the final value of E f shall be 125% of the rated voltage. Figure below shows the connection diagram for performing the Open Circuit Test of Alternator. As clear from the figure a...

The transformer which handles voltages and currents in the form of pulse are called Pulse Transformer. Pulse Transformer is mostly used in Power Electronic circuits as an Isolating Transformer to isolate source and load. It is also used in television, radar, digital computers etc. The main functions of the Pulse Transformer are as below: 1)       For changing the amplitude of voltage pulse 2)       For inverting the polarity of the pulse 3)       For coupling different stages of pulse amplifier 4)       As an Isolation Transformer It shall be noted here that the turn ratio of an Isolation Transformer is 1:1. The Pulse Transformer core is made of Ferrite. The input voltage to a Pulse Transformer is of discontinued type as shown in figure below. The most and basic requirement of such transformer is that it should reproduce input voltage at its primary to secondary as acc...

What is SATACOM? STATCOM or Static Synchronous Compensator is a power electronic device using force commutated devices like IGBT, GTO etc. to control the reactive power flow through a power network and thereby increasing the stability of power network. STATCOM is a shunt device i.e. it is connected in shunt with the line. A Static Synchronous Compensator (STATCOM) is also known as a Static Synchronous Condenser (STATCON). It is a member of the Flexible AC Transmission System (FACTS) family of devices. The terms Synchronous in STATCOM mean that it can either absorb or generate reactive power in synchronization with the demand to stabilize the voltage of the power network. Working Principle of STATCOM: To understand the working principle of STATCOM, we will first have a look at the reactive power transfer equation. Let us consider two sources V1 and V2 are connected through an impedance Z = Ra + jX as shown in figure below. In the above reactive power ...

Load Test of a Transformer is basically carried out for determining the maximum temperature rise of the Transformer. However is not viable to conduct this test by connecting the secondary of the Transformer to rated load. In case of small Transformer, rated load can be connected to the secondary of Transformer but for large Transformer, rated load capable of consuming rated power is not easily available and also this will lead to wastage of energy. Therefore the best and smart way to load a Transformer is to conduct Back to Back Test or Sumpner’s Test. It shall be noted here that, Back to Back Test or Sumpner’s test can also be conducted for calculating the efficiency of a Transformer but it is better to calculate the efficiency of Transformer using Open Circuit Test and Short Circuit Test of Transformer as this will give more accurate result. In this post we will focus on Back to Back Test or Sumpner’s Test of single phase Transformer. The Back to back Test on single phase tr...

Stray Load Loss: As we know that, when an electrical machine is loaded, load current flowing in the armature winding of the machine produces an mmf which distorts the space distribution of mmf produced or set up by the field winding in the air gap. This distortion of space distribution of mmf or flux density wave in the air gap of machine leads to increased loss in core as well as in armature conductors ( how in armature conductor? You will get the answer after reading the complete post) from it’s no load value. This increment in the core loss caused by the distortion of air gap flux plus the increment in ohmic loss i.e. I 2 R loss due to non uniform distribution of conductor current is called Stray Load Loss. Read Armature Reaction in an Electrical Machine for better understanding of distortion of flux density wave. In other words, we can say that Stray Load loss consists of two components: a) one originating in the iron part and other in the armature conductor. Again, i...