Electrical Engineering

The reason that current leads voltage in a capacitor is rooted in the way a capacitor works. Picture the capacitor. It's basically two conductive plates separated by a short distance and having a dielectric (insulator) between them. Now, let's specify that our cap (capacitor) is completely discharged and we'll hook it up to a DC voltage source through a switch. Flip the switch on and current will begin to flow, but it is important to look at what happens in just the first instant of time. Electrons will begin to accumulate on the negative plate and their presence there will drive electrons off the positive plate. The capacitor is building up a charge. It is developing a voltage across (or between, if you prefer) the plates. But electrons have to begin to pile onto the plate to actually create the difference of potential (voltage) between the plates. The moving electrons (and that's current) that are piling on the plate are already beginning to flow before the voltage is developed between the plates, so current is said to lead voltage in a capacitor.

In a capacitor, the current flowing in it depends on the voltage difference across it. On AC, this makes it charge if the voltage is increasing above zero, and discharge if the voltage is reducing towards zero.

Because a capacitor has almost no internal resistance, and most loads that it is connected to have only very small resistances in series with the capacitor, the charging and discharging currents depend pretty much on the rate at which the voltage is changing. At the zero crossing point of the sine-wave, when the voltage is actually zero, the rate of change of voltage is very high (the sine-wave is at its steepest), so the current is also very high. If the voltage is positive-going, the current is positive, and if the voltage is negative-going, the current is negative.

At the peak of the voltage waveform, the rate of change of voltage is zero or very low (the sine-wave is just about flat, and not really changing its voltage) so the current is zero, too.

Since the maximum positive current occurs when the voltage is passing through zero, going positive, and the maximum negative current happens when the voltage is passing through zero, going negative, the current peaks happen 90 degrees before the voltage peaks, so the current is said to lead the voltage. This is the same as saying the voltage lags the current by 90 degrees.

1 tr is equivalent to how many hp?

Vacuum circuit breaker is used in railway applications and as it is used in the applications where current chopping phenomenon is more

In a vacuum breaker the moving contact and fixed contact are sealed inside a vacuum chamber. Electrons cannot flow in a vacuum, therefore as soon as the moving contact seperates from the fixed contact the arc meets an infinite resistance and is immediately extinguished. Because of this, the gap between the fixed and moving contacts when the breaker is open need only be a tiny amount.

They are a safety feature in the case of an energy surge - without the fuse damage could be dome to the appliance, with the fuse if their is a surge of electricity it burns out the fuse so can't travel all the way to the appliance damaging it.

At resonance, the impedance of L and C completely cancel each other out, so you only have R left. If your circuit does not have any gain, then you should be able to determine the RMS current very easily by looking at the RMS voltage input divided by R.

Many lifts have the same functions. Thus, the four major load control functions found on a load lift are lift, lower, forward, and backward. Joystick Control Functions. 3-4. Joystick Control Functions (Button Pushed). 3-5. Service Brakes. 3-6 ... major contribution to safety if you, as the equipment users and operators: 1. ... Know that the machine can safety lift each load before attempting to lift. These are ...... Any problems discovered in the steps.

Phase lock loop is used in analog and digital communications to keep the phase of the output signal the same as the input signal.

As it's a safety factor, earthing is essential and mandatory. It's an electrical connection between the exposed metallic parts of an electrical

appliance or installation and the earth, regarded to have zero potential. Proper earthing provides an alternative and easy path for leakage or faulty current to flow. It ensures that any exposed conductive part of the appliance does not reach a

dangerous level of potential or voltage that endangers the user's life. A proper earthing system should have least electrical resistance, good corrosion resistance and ability of dissipating high faulty current.

It won't work. The slip rings work in conjunction with the brushes to connect a rotating part of the unit with the stationary part. We need to couple current into and out of the rotor, and without the slip rings for the brushes to ride on, we can't do that, and the motor won't work.

major component of power loss in a transformer is secondary resistance.when transformer is operated under no load,no current flows through the secondary.so under no load conditions transformer has just very small megnetic losses.

You have to know the power loading and phase angle (or power factor) between each pairh of the phases, otherwise you could be making serious errors.

Gain in a CE configuration of a BJT is collector resistance divided by emitter resistance, subject to the limit of hFe. The emitter bypass capacitor will have lower impedance at high frequency, so the gain will be higher at higher frequency, making this a high-pass amplifier.

The reactive power depends on the load and not the generator. Reactive power can be detected at the generator, and the load disconnected if there is too much being drawn.

A generators's voltage depends on the speed, and the power produced depends on the current in the field winding.

An alternator running on a bus bar, as in a grid system, runs synchronously with the grid it is connected to. In this case the power produced depends on the rate that steam is supplied to the turbine, and although the speed stays constant, any increase in power output is accompanied by an advance in the phase angle of the rotor.

To answer this question the voltage of the circuit must be stated. That is what the v in kva stands for.

No, not directly. The supply voltage has to rise or the resistance has to fall to get over-current. If there was a secondary control voltage that was part of a voltage control circuit for a higher voltage, it is conceivable that a voltage drop in control circuit could cause an over-voltage in the supply.

Motors are constant power devices, so this could be true for a motor. If you have a 1hp motor (loaded at 1hp), it will want to draw 1hp of power no matter the supply voltage. If the voltage dips, the motor will require more current to keep it spinning at it's normal speed.

A: An ammeter actually is a voltmeter measuring the voltage drop across a very small shunt resistance. They can measure AC or DC, make sure the meter is rated for the anticipated current, and always connect in series.

Any two legs of the 480V will give you 240 V Single phase.

I apologize for the wrong information here. A friendly member reminded me of the correct answer.

I stand corrected. Any two legs would be at 480 single phase. One leg to neutral will give you 277volts not 240 (408/1.73). You would need to install a step down transformer on the 277v line to achieve 240v.

emf in volts

To calculate X/R, you must know what X and R are, then simply divide. The transformer test report should provide this information, and if not, there are ANSII standard values that can be used as estimates.

The X value, or the % impedance are usually given explicitly in the test report (sometimes both, but not always). The R value may be given as load loss at the base MVA rating. To find % R, take the load loss (in watts or kilowatts), and divide by the base MVA.

The % impedance is = %R + j%X, so you may need to do some (vector) math to get %X if not explicitly given.

It will rotate faster.Since the fan is not designed for this, it will progressively ruin it.

Don't count on it. Your 18 watt device should be matched with the proper AC adapter. You cannot rely on the device to resist and limit a supply voltage more than 50% beyond its rated capacity. You wouldn't try to run a 110 volt electric shaver from a 220 volt receptacle, would you? If you try to purchase a fixed or universal (adjustable voltage) adapter you must also be concerned to match the polarity where the two meet. Some electronic devices are sensitive to mismatched polarity and will fail. Your best bet is to contact the manufacturer of the device to purchase a replacement ac adapter.

outside of improper polarity (assuming dc here, ac doesn't matter), if the VOLTAGE OUTPUT of the adaptor matches the INPUT VOLTAGE of the device it is powering, all is ok. as long as the current (milliampre rating) of the adaptor is equal to or exceeds the current rating of the device, all is ok. wattage is equal to voltage X amperes ... hence one cannot use the wattage rating of an ac adaptor to determine if it is is correct to use on a given device.

Perhaps. If the two devices accept the same range of voltages, the polarity is correct (although AC circuits do not care about polarity, reversed polarity is a serious safety hazard), and the power adapter to be used can provide at least the amount of current required by the device in question, then yes.

If the adapter is not rated to sufficient current, the device may or may not function -- the current will still be provided, but the supply voltage will drop. The power supply will generate additional heat.

A voltage mismatch may destroy the device.

Mismatched polarity for a device requiring DC power will not work and may damage the device. Mismatched polarity for a device requiring AC power will work, but may present a shock hazard, as many cases are connected to the neutral wire. Reversing the polarity will cause the case to be wired to 120V.

The term 9KA for an MCB might refer to a specific part that goes with a miniature circuit breaker. These parts can be found on most websites that offer electrical equipment.

Air cooling ,hydrogen gas cooling ,water cooling