Electrical Engineering

Stepped wave Inverter is simple but has lower order harmonics which cannot be eliminated by filters.These harmonics can be eliminated by the Space Vector PWM technique.

In the space vector PWM technique, there is 15% increment in maximum voltage compared to PWM, hence Space Vector enables efficient use of DC voltage.Space Vector Modulation provides excellent output performance, optimized efficiency and high reliability compared to similar Inverters with conventional PWM

The voltage drop across a good fuse is very nearly zero, under nominal current conditions.

The voltage is not exactly zero because you do want the fuse to have some resistance in order to develop enough voltage drop and dissipated power under fault conditions to blow.

Depends on the jurisdiction, but usually yes.

Resistors, capacitors, inductors, transformers, diodes, transistors, integrated circuits, power sources are the basic building blocks.

Generally, the plotting of open circuit characteristics curve of a dc shunt generator is used to determine the rate of change of no-load terminal voltage(same as induced emf (Eo)) with variation in field-current( I sub. f).We find from the plot that:-

a)Initially field current is zero.However due to residual magnetism at the field poles, a small amount of emf is induced.It would drive a small amount of field current according to the expression- I sub.f=Eo /R +Rsh.

b)After this ,a voltage build-up process,l be observed due to strengthening of field flux & consequently,the emf.

c)Finally, the magnetic poles tend to saturate.Hence, no significant flux-increment is observed w.r.t field current.Thus emf remains const. for higher values of field current.

A fixed capacitor has a fixed capacitance (within certain limits influenced by aging).

So it can fulfill any function that a (variable) capacitor fulfills, beside changing its capacitance easily (e. g. by turning a wheel).

It depends on the size of the cord and the volts it carries-

But to find how much VOLTAGE a wire consumes...

It could be found by V = I X R

Usually the resistance of electrical wires is not TOO important- its important when you try to force large amounts of current through a long piece of wire. So lets say a wire is very long and was connected to a battery that had 15 volts and the resistance of the thin wire is 0.2, V=15 x 0.2 = 3 volts. Three volts is not a big deal if you have a high voltage power supply, but if you are using say a 12 volt car battery the length of the wire would take one quarter of the available voltage-which is why a automotive batteries cable is thick -to reduce its resistance below 0.2Ohms.

This is still sort of an in-direct answer- but it might help.

Anode is positive, cathode is negative

a thyristor can be considered as two complementary transistors , one pnp- transistor, and other npn transistor

A PN junction diode is a non-linear component and it consists of two junctions namely P-junction & N-junction where the majority and minority charge carriers are present like electrons and holes. It is also known as a semiconductor diode or PN junction diode. This diode includes two terminals namely anode and cathode, where a p-type semiconductor is an anode (positive voltage) and N-type semiconductors are cathode (negative voltage). The flow of current in the diode is in one direction only because it opposes in another direction with high resistance.

Fluxvalve Theory

10. The fluxvalve , consists of a sensitive pendulous element which is free to swing within limits (usually ± 25°) but fixed to the aircraft in azimuth. The element is suspended by a Hooke's Joint with the whole assembly being hermetically sealed in a case partially filled with oil to dampen oscillations. A deviation compensator is usually mounted on top of the unit.

73 Radio Magnetic Compass

11. The pendulous detector element resembles a three spoke wheel with the spokes 120° apart and slotted through the rim. The rim forms a collector horn for each spoke. The horns and spokes are made up of a series of metal laminations having a high magnetic permeability. Each spoke has a vertical cross-section similar to that shown in Fig 12-2. The spoke consists of two superimposed legs which are separated by plastic material and opened out to enclose the central hub cone. This cone has an exciter coil wound round it on a vertical axis, and each spoke has a pick-off coil wound round both legs on a horizontal axis. The exciter coil is fed with 400 Hz single phase AC. The output of the secondary or pick-off coil is an 800 Hz single phase AC current, the amplitude and phase representing the relationship of magnetic North to the aircraft longitudinal axis (magnetic heading).

Fig 12-2: Vertical Cross-section of Spoke

12. In order to appreciate the operation of the fluxvalve it is necessary to consider an individual spoke. The function of a spoke will be developed in a series of diagrams (Figs 12-3 to 12-10).

13. If a single coil is placed in a magnetic field, the magnetic flux passing through the coil is maximum when the axis of the coil is in line with the direction of the field, zero when the coil lies at right angles to the field, and maximum but of opposite sense relative to the coil when turned 180° from its original position. For a coil placed at an angle θ to a field of strength H (Fig 12-3) the field can be resolved into two components, one along the coil equal to H cos θ and the other at right angles to the coil equal to H sin θ. The H cos θ component is parallel to the coil and is the effective flux producing element. Therefore, the total flux passing through the coil is proportional to the cosine of the angle between the direction of the coil axis and the direction of the field. The coil output curve is shown at Fig 12-4. If the coil is in the horizontal plane with its axis parallel with the aircraft longitudinal axis, its output is affected by the horizontal component of the Earth's magnetic field and the flux passing through the coil is proportional to the magnetic heading of the aircraft.

Fig 12-3: Magnetic Flux Components

Fig 12-4: Variation of Flux with Theta

14. Unfortunately, the simple concept just described cannot be used without modification as a heading reference system for two important reasons. Firstly, the voltage induced into a coil depends

FIS Book 4: Instruments 74

on the rate of change of flux. Therefore, once established on a heading, there would be no change of flux and, consequently, no induced voltage. Secondly, the output of the simple detection device would be subject to heading ambiguity, i.e. there are always two headings which cause the same induced output voltage. Therefore, the problem that must be solved is how to produce an output waveform which is proportional in some way (frequency, phase or amplitude) to the components of the Earth's field and linked with the coil. This is achieved in the fluxvalve by introducing an alternating magnetic field in addition to the static field caused by the horizontal component of the Earth's magnetic field.

15. Fig 12-5 shows the relationship between flux density (B) and magnetizing force (H) known as the hysteresis loop for the permalloy commonly used in the legs of the flux valve spokes. Permalloy has a very high magnetic permeability (μ = B/H) and a corresponding low hysteresis loss. In the following discussion the hysteresis loop is represented by a single line curve.

Fig 12-5: Hysteresis Curve for Permalloy

Fig 12-6: Simple Fluxvalve

Fig 12-7: The Effect of Excitation Current in the Top Leg Only

16. One spoke of the three-spoke fluxvalve is shown diagrammatically in Fig 12-6. It consists of a pair of soft iron (usually permalloy) cones each wound with a primary coil. The winding on one core is the reverse of that on the other. The AC supply is just sufficient, at peak power, to saturate magnetically each of the parallel soft iron cores. A secondary coil, wound round the two primaries, is linked with the circuit, and any change of flux through it induces a voltage and current flows.

17. Fig 12-7 shows the 400 Hz alternating flux induced in the top leg by the excitation current considering only the top leg of the spoke and the effect of the excitation.

75 Radio Magnetic Compass

18. Now considering the bottom leg only; the flux induced in this leg by the excitation current will at any instant be in the opposite direction to that induced in the top leg, i.e. the flux in the bottom leg is 180° out of phase with the flux in the top leg as shown in Fig 12-8.

19. Since the top and bottom legs are identical, the amplitudes of the flux of the two legs are equal but 180° out of phase with each other relative to the pick-off coil, which is wound round both legs. Therefore, the resultant flux cutting the pick-off coil, which is the algebraic sum of the flux in the top and bottom legs is zero as shown in Fig 12-9.

Fig 12-9: The Effect of the Excitation Current in Both Legs

Fig 12-8: The Effect of the Excitation Current in the Bottom Leg Only

20. If the horizontal component of the Earth's magnetic field (H) is now added in line with the spoke, it will induce a steady flux in both legs of the spoke which will be added to the flux due to the excitation current. The effect, as shown in Fig 12-10, will be to bias the datum for the magnetizing force, due to the excitation current, on the B-H curve by an amount equal to H. The strength of the excitation current is so arranged that the effect of the introduction of the Earth's magnetic field component is to bring the flux density curves in Fig 12-10 onto the saturation part of the hysteresis curve. The resultant flux cutting the pick-off coil, which is the algebraic sum of the fluxes in the top and bottom legs, will no longer be

Fig 12-10: The Combine Effects of the Excitation Current and the Component of the Earth's Field

zero but will have a resultant proportional in amplitude to heading. The emf induced in the pick-off coil

FIS Book 4: Instruments 76

is proportional to the rate of change of flux cutting the coil and therefore will have a waveform approximating to a sine wave at 800 Hz, i.e. twice the frequency of the excitation current as shown in Fig 12-10. It has been found by experiment that the amplitude of the emf is proportional to H. Therefore, the emf in the pick-off coil is a measure of H, i.e. the horizontal component of the Earth's magnetic field in line with the spoke. This should be apparent from Fig 12-10 in that, if a greater H is detected, the excitation current is biased further from the mid-point of the hysteresis curve, and the imbalance between the upper and lower leg fluxes will increase. Therefore, a greater resultant flux exists which will induce an emf of greater amplitude in the pick-off coil. A plot of the amplitude of the pick-off coil output voltage would show that it varies as the cosine of the magnetic heading.

21. Limitations of the Simple

Single Spoke Detector. It should be apparent that there are two magnetic headings corresponding to zero flux (90° and 270°) and two headings corresponding to a maximum flux. The two maximum values give the same reading on an AC voltmeter since the instrument cannot take into account the direction of the voltage. For any other value of flux (other than zero), there will be four headings corresponding to a single voltmeter reading. This ambiguity is overcome by using a fluxvalve having three spokes (each spoke similar to the single spoked device previously discussed) with 120° separation as shown in Fig 12-11. Regardless of the heading, at least two of the spokes will have a voltage induced and their vector sum points to magnetic North (Fig 12-12). The simple one-spoke detector suffers from another limitation in that the value of H changes with magnetic latitude. This produces a change in the static flux linking the spoke, even though the heading may remain unchanged. This limitation is

Fig 12-11: Detector Unit and Transmission System -

schematic

Fig 12-12: Operation of the Three-spoke Fluxvalve

Fig 12-13: Eliminating Latitude Ambiguity

77 Radio Magnetic Compass

overcome in the three-spoke fluxvalve because the flux associated with each spoke will change in proportion to the change in H. The resultant field across the receiver stator is still aligned with H (Fig 12-13).

22. In the three-spoke fluxvalve a single primary coil excites all six cores. If a single arm of the fluxvalve is considered, it will be apparent that the top and the bottom of the exciter coil have opposite polarity. The flux induced in the upper core of the spoke is equal and opposite to that induced in the lower core and this is exactly the effect produced by the primary windings in the simple fluxvalve. The three arms of the fluxvalve are wound with secondary or pick-off coils which are star connected. The exciter coil is fed with 400 Hz single-phase current so that each of the three pick-off coils has an emf at 800 Hz induced in it whose amplitude is proportional to the magnetic heading of the aircraft. Each core of the fluxvalve is fitted with a flux collector horn to concentrate the Earth's lines of force through the core. This increases the static flux and therefore the induced voltage.

A: this chip is defined as a timer but it can be used for other reasons and applications.

The power dissipated across a resistor, or any device for that matter, is watts, or voltage times current. If you don't know one of voltage or current, you can calculate it from Ohm's law: voltage equals resistance times current.

So; if you know voltage and current, power is voltage times current; if you know voltage and resistance, watts is voltage squared divided by resistance; and if you know current and resistance, watts is current squared times resistance.

A: To begin with the leads polarity of the meter must be ascertain. Assuming the red is positive voltage then that lead will have a positive potential to check a diode connect the red lead to the anode and the black to the cathode and it should read some Resistance

when a LED is subjected to a high voltage it will heat up and burn the internal junction, which will leave the LED open circuit.

Motor size depends upon number of factore.

1- flow of pupm

2- required head

3- efficiency of pupm used

4- efficiency of electric motor used

The formula is

H.P required= Q.H\ 3960. Pump efficiency. Motor efficiency

where Q= GPM

H= Ft

Efficiency= In fraction( 70 % = 0.7)

Engr. Usman Khalid

+923336901945

usman.engr87@gmail.com

series

I'm not sure where you are getting your information. Capacitors come in a large range - nano farad to several farad. The higher the farads, the bigger (in general) the capacitor will be. For example, amazon has a 1 F, 20 volt cap for ~76.00. I would consider this to be "generally available in the market". If you want a 1 farad cap for 120 volts, it's going to be substantially bigger than this one (20 volt is ~5 lbs.).

The world biggest distribution substation is in DELHI TRANS CO .

Resistor tolerance is how accurate the resistor value is. You may have a 10% tolerance, 820 ohm resistor, which means the actual value of resistance is 820 ohms +/- 82 ohms.

If you design a circuit that has very stringent requirements for resistor values, you may need to purchase a resistor that has a smaller tolerance (like 5, 2, 1, .5%). The smaller the tolerance, the more expensive it will be (generally).

A hybrid grid mini-system