Electrical Engineering

You adjust the voltage and RPM on the second generator to be slightly higher than the first. How much higher depends on the system and generator design.

While monitoring a synchrometer, you pick a relative phase position (again, depending on design) and close the second generator to the first at the selected moment in phase/time.

You immediately monitor and adjust power and vars to make sure the second generator is not too over or under loaded.

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Paralleling generators

The following is for three phase manual paralleling of two generators. Today's control systems will sense and do this operation automatically but the general process is the same. There are a couple of factors that have to be met when paralleling generators. The process of paralleling generators is called synchronization. What this means is that both generators have to be in phase with each other and running at the same speed. The generator that is running is called the lead generator and the one that you are trying to parallel is called the lag generator. There are two types of instrumentation used in synchronising, one is a light bank and the other a bit more sophisticated is a synchroscope meter. The synchroscope indicates whether the lag generator is faster, slower or in phase with the bus. The lag generator is brought up to speed just under the RPM of the lead generator. The synchroscope will be revolving very slowly in a clockwise rotation at this point. When the hand on the synchroscope reaches the 11 o'clock position the switch is thrown to bring the generator on to the bus tying the two generators together.

The light system of paralleling generators has lamps hooked in series and connected between the hot lead of the lead generator and the hot lead of the lag generator. When one generator is running faster than the other one, the lights will blink off and on as the generators come in and out of phase with each other. Adjusting the throttle of the lag generator and bringing it closer to synchronise speed will cause the lights will start to pulsate slower and slower until they go off for a period of seconds and then on for a period of seconds. At this point the two generators are electrically paralleled. Count the time between on off on of the lights. At half the off time (zero voltage) throw the switch and the generators will lock together, the two generators will be running in parallel with each other. Manually to keep them paralleled requires a bit of work, as the faster generator will try and take the load and motor the other one. This is where a governor is a great asset. If the generators are tied together out of phase two things could happen. The least problematic would be the generators breaker will trip. The second and most dangerous is if the lag generator is just a little bit out of phase when the switch is thrown, then the generator will be jerked into phase lock as momentary heavy current flows between the two generators. The sudden loading of the generator has been known to break crankshafts of the engine driving it.

when machine is taking electrical supply and produces flux, torque etc inside and gives mechanical (rotational) output it is MOTOR

but when this motor is connected to some thing which results in drawing current and work to be done, that thing is LOAD

without any load motor has maximum speed and by increasing load speed decreases..

Anything connected to a supply which draws current is a 'load'. 'Heavy loads' draw a lot of current, whereas 'light loads' draw little current. So a motor represents a load to the electrical supply; this applies whether the motor is driving a 'mechanical load' or not. We use the term 'mechanical load' to describe whatever (fan, compressor, pump, etc.) is being driven by a motor.

A series circuit has the same amount of current at all points in the circuit.

It's not simply 'the same amount of current at all points''; it's the same current at all points.

No ~ the power supply is capable of supplying 5 Amps, but the device will only draw 1 Amp. Therefore the power supply can still safely supply another 4 Amps if required.

It's important to understand that the '5 A' referred to in the specification of your power supply is its capacity -the actual current drawn from the power supply is determined by the load you attach to it. So, if your load requires only 1 A, then that's how much current will be drawn from the power supply.

Magnets attract or repel (opposite poles attract: like poles repel), and electro-magnets can be turned on and off, or have their poles reversed, in an instant. So magnets are used instead of engines in a maglev train.

There are two kinds of Maglev systems:

1. EMS - ElectroMagnetic Suspension (Germany and China) - "pull" system. Magnets in the train are pulled forward by magnets in the track which are turned on just before the train arrives, and turned off as soon as the train is on top of them.
2. EDS - ElectroDynamic Suspension (Japan) - "pull, neutral, push" system. Superconducting magnets in the train are pulled forward by track magnets. When the train is over the track magnet the track switches to neutral, then to the opposite polarity. So the magnet behind the train then pushes it forward.

Yes. Power factor is a cosine related function. To understand this, you need to understand volt-amps versus watts...

Volt-Amps (VA) is volts times amps, which may seem to be the same as watts (W). This is true only for resistive loads, where the phase angle of volts is the same as that of amps. In that case VA is the same as W.

What happens with non-resistive or reactive loads, however, is that amps are not in phase with volts. In an inductive load, such as a motor, amps lags volts; while in a capacitive load, amps leads volts. In both of these cases, you cannot just multiply volts and amps to get watts, due to a phenomenon known as power factor; power factor being the ratio of apparent power to true power.

To visualize this, you need to draw the power circle. Since WikiAnswers does not presently support graphic images, please take a piece of paper and follow along with me...

Draw a circle. To make it easy to do the math, draw it centered at the origin, and pretend that it has radius of one. This way, the trigonometry is easy.

Consider that the radius of the circle is VA. (Do not confuse this with the trigonometry trick where we also consider the radius to be one.)

Now, pick a point on the circle. Twelve O'Clock is a purely resistive load, where volts and amps are in phase. Nine O'Clock is a purely inductive load, where amps lags volts by 90 degrees. Three O'Clock is a purely capacitive load, where amps leads volts by 90 degrees. In "normal" trigonometry, zero degrees is at 3:00 O'Clock, but, by convention, zero degrees when dealing with reactive power is accepted to be 12:00 O'Clock. Just keep the trigonometric identities straight in your mind.

In practice, with normal electric motors and all other things considered, we see a point on the circle at about 10:30 or 11:00 O'Clock. Let's pick 10:30, to make the math easy. So, draw a line from the origin to the upper left at an angle of 45 degrees with respect to the Y-Axis. Label this line VA.

Notice that VA is constant, no matter what the phase angle may be.

Now, draw two more lines; one from the point on the circle at 10:30 O'Clock straight down, perpendicular to and stopping at the X-Axis - label this line W, and one from that same point to the right, perpendicular and stopping at the Y-Axis - label this line VAR.

Label the angle of the first line with respect to the Y-Axis as phase angle. Positive meaning inductive, and negative meaning capacitive. Notice that, if you had a 45 degree capacitive load, intersecting at 1:30 O'Clock, the magnitude of the VAR line would be the same, though positive instead of negative, and the W line would still be the same.

Now, power factor is W / VA, the ratio of apparent versus true. In this case, since we picked 45 degrees as the phase angle - to make it easy - the ratio is 0.707, or the cosine of the phase angle.

A typical power meter will register less than the actual power. In the worst case of a purely inductive load, the power meter would register zero, though the VA is still what it always was. The power meter is "lying", due to the power factor - energy is still being transferred - and the equipment must be sized to handle it - that is why transformers and other things are often rated in VA instead of W. (Actually, KVA instead of KW.)

Now, if you are interested, and most power companies, engineers, and electricians are, then look at VAR. That is volts-amps reactive. There is a VAR power factor as well, simply the sine of the phase angle. In this case, again with 45 degrees, it is the same as the normal power factor, 0.707, however, we normally would call that -0.707, to differentiate between VAR (inductive) and VAR (capacitive).

Note that, if your phase angle is more than plus or minus 90 degrees, we are actually talking about a generator, instead of a load.

In practice, the phase angle is more like 20 to 30 degrees, so the power factor would be slightly higher, and the reactive power factor would be slightly lower. Power companies penalize large customers for poor power factors by measuring it and compensating their power meters or accounts to consider the perceived loss in energy or, more correctly, the increase in actual energy use. Also, poor power factor causes degradation of voltage on power lines, so power companies compensate with capacitor banks, shifting the phase angle back closer to zero