Contact Us


Powered by 123ContactForm | Report abuse

Popular posts from this blog

Why Armature Winding on Stator in Synchronous Machine?

Image
In Synchronous Machine, the armature winding is provided on Stator and field winding on Rotor which is contrary to other Electrical Machines. In fact there are certain issues due to which we provide armature winding on Stator. The benefits of this are as follows: More Economical: It is more economical to provide Armature winding on Stator and Field winding on rotor. Let us consider a three phase Star connected 750 MVA, 21 kV Synchronous Machine. Line Current = (750x10 3 )/(1.732x21) = 20,620 A If the armature winding is placed on the Rotor, we need three slip rings each capable of handling 20,620 A. Only not this, we need to provide slip rings with an insulation of (21/1.732 = 12.12 kV). The star point for grounding is also to be taken out through the fourth slip ring. Now, suppose the power requirement for the Field is 2 MW at 500 V. Then Excitation / Field Current = 2000/0.5 = 4000A In this case only two Slip Rings each capable of handling 4000 A is re...
Read more

Open Circuit and Short Circuit Characteristics of Synchronous Machine

Image
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...
Read more

Concept of Subtransient, Transient & Steady State

Image
The concept of Subtransient, Transient and Steady State arises in case of fault in an Alternator. Let us assume a sudden short circuit in three phase of alternator. The fault current will flow in all the three phases of alternator and its waveform will be as shown in figure below. When the alternator is short-circuited, the currents in all the three-phases rise rapidly to a high value of about 10 to 18 times of full load current, during the first quarter cycle. The flux crossing the air gap is large during a first couple of cycles. The reactance during these first two or three cycle is least and the short circuit current is high. This reactance is called subtransient reactance and is denoted by X". The first few cycles come under sub-transient state. After a first few cycles, the decrement in the r.m.s. value of short circuit current is less rapid than the decrements during the first few cycles. This state is called the Transient  State and the reactance in th...
Read more