Electrical Engineering

to reduce the flow of current & keeping the current through galvanometer within safe limits.

Insulator. Like wood.

sample question papers for diploma in e&tc

AC to DC convertor. Or build your own with four diodes,reostat, and filters.

This type of circuit is known as a rectifier and is usually done with diodes, which block portions of the + and - cycles at a given point in time, allowing the other part of the cycle to pass. Rectification can be either full or half wave.

No

Yes, if you are talking about the normal carbon composition types having colour codes. But there are some non-linear types too.

If you're using it in reference to electrical service it generally means non-business hours. Off-peak electric service for instance is electric service that is at a much lower rate, however the electric company shuts off the service for a certain period of time each day, usually during the highest demand.

In electrical circuits series and parallel are two basic ways of wiring components. The naming comes after the method of attaching components, i.e. one after the other, or next to each other. As a demonstration, consider a very simple circuit consisting of two light bulbs and one 9V battery. If a wire joins the battery to one bulb, to the next bulb, then back to the battery, in one continuous loop, the bulbs are said to be in series. If, on the other hand, each bulb is wired separately to the battery it is wired in a parallel circuit.

The main wire in a bulb is the filament - which gets hot enough to give out light without burning away - and there are two other wires to take electricity to and from that filament.

Theoretically, Ohm's law says V=I*R where V is the Voltage, I is the current and R is the resistance. Consider a purely resistive load. As the resistance 'R' is fixed, above equation implies I=V/R.

Next, consider the way power is calculated: Power = V*I. Substituting I from above, Power = V*(V/R) = (V*V)/R. Assuming that R is constant, this implies that as you increase the voltage, the power increases by square of it. So, if one increases the voltage by 10% (say, from 100 to 110), The power increases from (100*100)/R to (110*110)/R, in other words, from 10000/R to 12100/R - an increase of 21%.

In general:

Increase by 5% in Voltage implies increased power consumption by 10%

Increase by 10% in Voltage implies increased power consumption by 21%

Increase by 20% in Voltage implies increased power consumption by 44%

Increase by 30% in Voltage implies increased power consumption by 69%

HOWEVER, please note that Resistance is a function of Heat as well. As a resistive load (like Incandescent Bulb) heats up on passing current, R actually decreases so actual savings may be slightly lower than above theoretical values. MOREOVER, not all loads are purely resistive - e.g., fans, refrigerators etc are inductive. So, some experiments suggest that net voltage drop of 10% lead to a power saving of about 14-20%, drop by 20% lead to 18-28% saving...depensing on the load composition and also the usage.

Many electric distribution companies across the globe try to increase the Voltage by up to 25% in low loss areas while decreasing it by similar amounts from permissible levels in high loss areas! This way, at the cost of consumer, they cover their losses.

Pinball games use complex arrays of series and parallel circuits. So do electric stoves.
But let's look at a simple one ... a toaster.

The toaster has several heating elements ... maybe four individual heating wires, one on each side
of the bread slot, and two bread slots in the machine. They're all in parallel ... one end of each heater
goes to one prong of the electric plug, and the other end of each heater goes to the other end of the plug.

BUT ... in series with one group of heater ends is a very important circuit element: the Switch.
When the switch is in a high-resistance state ("OFF"), no current flows through any branch in the
parallel section, i.e. the heaters remain cold. When the switch is in the low-resistance state ("ON"),
current flows through all of the parallel branches, and the result is toast.

In manual star delta starter, the change over from star to delta does not happen automatically. The operator or user puts on the starter, and after few seconds he pushes a lever or handle to change over to Delta.

In automatic method, change over happens from star to delta using an automatic preset timer.

Don't know of any three phase low voltage motors. Perhaps it's a "stepper motor". Stepper motors are typically computer controlled, with the computer pulsing different pairs of wire to cause the motor to "step".

What does the question refer to? Induction motors? Transformers? For transformers, the no-load voltage is the voltage -- across the secondary or primary -- when there is no load attached to the secondary, that is, when there is no current in the secondary. No-load current really only makes sense when talking about a motor, because current is flowing in the device even when it's not under load. A rule of thumb is the no-load current is about a third to one half the full-load current.

A 1000 watt device operated continusouly for 1 hour would equal 1 Kwh.

The brightness of an incandescent light bulb depends on the voltage applied across its terminals. Connecting one, two, or five light bulbs of the same rating to a battery in parallel will provide the same brightness from each bulb.

If the load is single equipment, calculating the capacity of the generator or transformer is fairly straight forward. If the load is mix of various several different equipment it would be more complicated to arrive at transformer / Generator capacity. Complexity increases if you have to estimate some future unknown loads.

The rating of the generator or transformer should be such that it is loaded optimally, average being say 80 to 95 %. Since maximum efficiency of generator or transformer generally occur at these range. Also this ensures that it is not overloaded continuously and there is room for occasional short time full load too. You need to check the data sheet of the transformer or generator for more correct information.

One need to know the maximum load or peak load, average load and diversity factor and load factor. These values drive the decision on the rating of the transformer or Generator.

A megger test is used to look at the insulation properties of motor windings, electric wiring, high power antenna mounts, and other similar items. The voltages are a lot higher than they are with a normal Volt-ohm meter. You will turn the device off and connect it to a source of power. The circuit breaker being testing should be closed and then disconnect the line-side circuit. Connect the output terminals and turn on the test set. Get the desired current and make any necessary adjustments. Then, you will hit the 'start' button and get your readings.

An electric motor could run a generator to power itself, but this is a lossy system, so an outside power source would have to supply the power due to the losses. And if the motor was being used for anything else, the real power losted due to this other use would have to be made up as well. You don't get anything for free.

No. This is perpetual motion, which is impossible, the problem is that everything has losses, like friction, drag, etc., and no matter how clever you get, the best you can do is that you can ALMOST make it work. Don't waste time pursuing this beyond understanding why it does not work.

Air cooled

water cooled

oil cooled

Totally enclosed fan cooled

Refrigerant cooled

A BSEE degree from an accredited University or College is the starting point. From there you can pursue advanced degrees or obtain a Professional Engineers license by passing a test.

Shunt means parallel only..................