Electrical Engineering

Thevenin's theorem is only valid for linear and bilateral networks.Practically, linearity of any circuit is over a certain range.Hence it is only valid for certain range.

Power stations use step-up transformers to transmit power at a high voltage instead of a high current. This reduces the power lost in the transmission lines.

The container the transformer core and windings are placed inside is the tank.

The phase angle between voltage and current in a purely inductive circuit, under ideal circumstances where there is no resistance at all, is 90 degrees.

We need these interconnections because apart from delivery, the purpose of the transmission network is to pool power plants and load centers in order to minimize the total power generation capacity and fuel cost. Transmission interconnections enable taking advantage of diversity of loads , availability of sources and fuel price in order to supply electricity to the loads at minimum cost with a required reliability.

if channel width decreases , the drain current(Id) will also decrease .

but , Id will decrease up to a certain limit , when the jfet is in pinch off condition i.e. channel width is tends to zero (Vgs is very high) the Id will be constant then.

A tap changer is used to vary the turns ration between the windings of a transformer to make minor changes to the secondary voltage. An on-load tap changer enables the turns ratio to be altered without disconnecting the transformer. An off-load tap changer requires the transformer to be temporarily diconnected. On-load tap changers are installed on the high-voltage side of the transformer, where the current is lower.

its nothing but alternate occurence of pole/zero and zero/pole. ex: f(s)=s*(s+2)/(s+1). here we can easily sense that there is a occurence of zero(s=0),pole(s=-1),zero(s=-2).

It can be answered in two ways :

1. ratio of output & input voltages [Vout / Vin] i.e Drain voltage(Vds)/Source voltage(Vs).

2. multiplication of trans-conductance & drain resistance .

The series capacitors can be the cause of overcompensating on the power line and thus cause the following problems:-

a) Over voltages on the line when connected loads are smaller than the rated loads and this can damage the transformers and capacitors

b) Ferro-resonace phenomenon can cause very high volatges again can be damaging

c) The fault level of the poweer system will increase and if not considered in the design, the fault current could exceed thedesign limits.

Electromagnetic attraction relays have a fixed contact and a moving contact, attached normally to either a hinged plate, or the moving piston of a solenoid. The contacts are brought together by the magnetic attraction of an energized coil attached to one of the contact supports, or in the case of the solenoid, the coil which surrounds the moving piston. These relays can operate on either ac or dc inputs, and have virtually no time delay. This makes them ideal for instantaneous operations.

Electromagnetic induction relays operate on the principle of the induction motor - that is, magnetic flux applied to a rotor will develop torque in that rotor, and cause it to rotate. However, instead of spinning like a motor, the rotor in this type of relay has a mechanical stop or reset point, and a contact fixed to it that will eventually touch the stationary contact, when the input quantity meets or exceeds the predetermined setpoint. Relays of this type only operate with ac quantities, and, in many or most cases, can be adjusted to provide a time delay (which in reality simply moves the reset point farther away from the contact point, so that the rotor must rotate farther to pick up the contacts).

This is 3 Nos Two Winding Transformers put together to form of Three Phase transformer, HV is Star Connected & LV is Delta Connected in the LV phase is leading by 30 Degree with respect to HV phase

The ammeter does affect the flow of current in a circuit, however, the resistance of the ammeter is so small in comparison to the circuit that the effect is negligible. It is connected in series.

HOLDING CURRENT:

The minimum value of current that must be there to provide a path between anode and cathode to flow anode current and thus maintain a thyristor in the on state.0

LATCHING CURRENT:

The minimum anode current required to maintain a thyristor in on-state immediately after a thyristor has be triggered on.

IL>IHrate of flow of charge is known as current

Yes since the SCRs act as the real thyristors

Throttling.

True. Ohm's law states the voltage is resistance times current.

conclusion of dc power supply 9V

U0 stands for the nominal rms-value of the line potential measured with respect to earth.

Because full speed is unloaded. As you load the motor, speed decreases, and slip increases, with an accompanying increase in current.

100L : FRAME MEANS

100mm is the height of the Center of the Motor shaft from it's base.

If i'm wrong, please let me know

phani_raj@rediffmail.com

To move, an electric motor must have one magnetic field slightly ahead of another. the magnetic attraction causes a pull that makes the magnets get closer together. To keep it moving, you need to move the magnet further away so that it never reaches the other magnet.

Ok. So how do you keep moving it ahead? Well, you use an electro-magnet rather than a permanent magnet. You put multiple electro-magnets in a circle around the shaft of the motor. You put a permanent magnet on the outside of the shaft separated by an air gap. Then you switch on the power to the electromagnet it causes the shaft to rotate so that the electro and permanent magnets line up. To keep it going, you have to switch to the next electro-magnet on the shaft that is slightly off alignment with the permanent magnet. Every time one of the shaft's multiple electromagnets try to line up you switch over to the next one so that they are always pulling toward the fixed permanent magnets.

So, how do you do the switching? One way is to have the electromagnets connection wires stick out of one side of the shaft so that the set of electromagnets that are close to the magnet are connected. The contacts that aren't rotating are called brushes. The inner wires that connect different electro-magnets for different rotations of the shaft are called a commutator. The brushes are always in contact with the commutator and so they wear down after a while. One strike against brushes. There is another strike that has to do with when you put a big load on the motor. The magnetic field ends up rotating such that when you switch poles there is still current in the wires. Because the electromagnet is inductive a sudden change in current causes a huge voltage spike (think lim Ldi/dt with t -> 0). That voltage spike causes sparks that cause the commutator and brushes to wear even faster.

So, brushles -- get rid of the brushes. Put the permanent magnet on the shaft and put the electro-magnets in a circle around the shaft. Also - put some tiny magnetic sensors around the motor. To switch the right electro-magnet on you connect the wires to the power source using a semi-conductor switch. The switches are generally Metal Oxide Field Effect Transistors (MOSFETS) which have built in diodes for that over-voltage Ldi/dt thing.

Now you have a microprocessor or some specially designed electronics connected to the magnetic sensors (Hall effect devices) and to the semiconductor switches. When the magnetic sensor turns on because the motor is at an angle in which a certain electro-magnet should be turned on, the microprocessor or electronics switch on the appropriate semiconductor switch (MOSFET) connecting the correct electromagnet to the power source. So, no bruches. Just semiconductor switches, sensors, and a control circuit.

Hope this is helpful,

Al

I hope this makes sense and it really