Knowledge of short circuit current values is necessary for the following reasons. 1. Fault currents which are several times larger than the normal operating currents produce large electro-magnetic forces and torques which may adversely affect the stator end windings. The forces on the end windings depend on both the dc
Year: 2015
In the analysis of symmetrical three-phase short circuits the following assumptions are generally made. 1. Transformers are represented by their leakage reactances. The magnetizing current, and core fusses are neglected. Resistances, shunt admittances are not considered. Star-delta phase shifts are also neglected. 2. Transmission lines are represented by series reactances.
PER UNIT SYSTEM The per-unit system expressed the voltages, currents, powers, impedances, and other electrical quantities basis by the equation: Quantity per unit (pu) = Actual value/ Base value of quantity ADVANTAGES OF PER UNIT SYSTEM While performing calculations, referring quantities from one side of the transformer to the other
LOAD BUS A bus where there is only load connected and no generation exists is called a load bus. At this bus real and reactive load demand Pd and Qd are drawn from the supply. The demand is generally estimated or predicted as in load forecast or metered and measured from instruments.
Power flow studies are performed to determine voltages, active and reactive power etc. at various points in the network for different operating conditions subject to the constraints on generator capacities and specified net interchange between operating systems and several other restraints. Power flow or load flow solution is essential for
The magnetic rotor field is generated by a field winding F on the rotor which is fed with an adjustable direct current. In addition, the rotor has a short circuited damper winding D at the surface. This winding serves to dampen electrical and mechanical oscillations and to shield the field
Graph theory has many applications in several fields such as engineering, physical, social and biological sciences, linguistics etc. Any physical situation that involves discrete objects with interrelationships can be represented by a graph. In Electrical Engineering Graph Theory is used to predict the behavior of the network in analysis. However,
The dc generators and dc motors have the same general construction. In fact, when the machine is being assembled, the workmen usually do not know whether it is a dc generator or motor. Any dc generator can be run as a dc motor and vice-versa. All dc machines have five
A system is single or polyphase depending upon whether the sources feeding it are single or polyphase. A source is single or polyphase according to whether there are one or several driving voltages associated with it. For example, a three-phase source is a source containing three alternating driving voltages that
In the event of failure or non-availability of the primary protection some other means of ensuring that the fault is isolated must be provided. These secondary systems are referred to as ‘back-up protection’. Back-up protection may be considered as either being ‘local’ or ‘remote’. Local back-up protection is achieved by
