Electrical Engineering

You cannot 'reverse' the polarity of a transformer -it is either wound with 'additive polarity' or 'subtractive polarity', and there's not much you can do about it!

For a single transformer, its polarity doesn't really matter. But if you are going to parallel two transformers, then you must know the polarity of each transformer in order to avoid harmful circulating currents in their secondary windings.

A '33-kV transformer' is a three-phase primary-distribution transformer, used in the UK's electricity system to step down the 33-kV primary-distribution voltage to the 11-kV secondary-distribution voltage -the lowest voltage used in the high-voltage distribution system. These transformers are categorised as 'power transformers', and are located in what are termed 'primary substations'.

Because the line conductors are uninsulated, and must be kept at a safe distance above ground level.

the back emf increases so that high currents doesn't pass through the field windings

It's an archaic expression, which is not usually used these days. But 'voltage' was considered to equate to 'pressure' in, say, a hydraulic system. So the term pressure (as well as 'tension') has, in the past, been used in place of 'voltage' or 'potential difference', as in 'pressure coil' or 'high-tension transmission'. In North America, a 'voltage coil' is frequently termed a 'potential coil'.

All types of generators induce EMF in sinusoidal wave form. (A.C.) In a D.C. generator the function of a commutator is to convert A.C. EMF into D.C.

The commutator rectifies the output that is the alternating current so as to produce unidirectional alternating current (pulsating DC). This reverses the negative polarity current to a positive one so as the output is a pulsating DC.

Lock out Relay is the Master Trip relay( It is a latch relay once operated we have to reset it by manual) Which is used for Generator protection,Transformer protection,Turbine protection (Fixed in indoor Panel, Standard manufacturer only making those relays) if it operated because of any fault in above the after clearing all the fault we have to reset it by hand(normally available 110Volts or 220Volts DC).

pg clamp is known for parallel groove clamp,especially used in transmission line to hold transmission conductors in parallel.

Capacitors are used to improve an inductive load's power factor towards unity. The power factor before and after adding the capacitor bank depends entirely on the inductive/capacitive values involved.

Since internal resistance of the ameter will increases the resistance of the circuit. Thus decreasing the current giving an errorenous reading.

An overload trip is due to too much load on a circuit (for example, my wife running a hair dryer and portable heater on the same outlet). An over current trip is the same thing, but it can also refer to an actual fault condition where conductors have come in contact with eachother/shorted.

In dc shunt motor,base speed is 500 rpm and its field current is 17A, top speed is 1200 rpm and field current is 5.6 A.But 600 rpm it has reduced by 10A It is normal? How

A rotating d.c. motor generates a back-emf which opposes the supply voltage and reduces the current drawn by the motor. When the motor is stationary, it cannot generate this back emf and, so, the only opposition to current is the resistance of its windings which is relatively low. So, on startup, the current is large; as the machine starts to run, the resulting back emf, acts to reduce the current.

The relation between resistance R, Current I and voltage V is:

R= V/I

Therefore: 60 = 12 / I <=> I = 12 / 60 = 0.2 amp

Where are you typing it? In a MS Word document go to "Insert" on the menu bar, click on "symbol" and scroll down until you see the micro symbol and click on it. In MS 2003 it's about 8 lines down in that menu.

When the load current exceeds the SCR current rating, SCRs are connected in parallel to share the load current. Further the holding currents of the devices should not be so much different that at reduced load current one of the device gets turned-off because of fall of current through it blow its holding current value.

A 'leading' power factor indicates that the load current is leading the supply voltage. Since power factor is the cosine of the angle by which the load current either leads or lags the supply voltage (i.e. the load's phase angle), a cosine of 0 corresponds to a phase angle of 90 degrees.

So, a power factor of 0 (leading) indicates that the load current is leading the supply voltage by 90 degrees, which means that the load must be purely capacitive.

No. A constant DC current of sufficient magnitude

induces smoke in a transformer.

the process of reversing the current through individual armature coils, and then conducting the direct current to the external circuit during the brief interval of time each commutator segment is passing under a brush

Resistivity of Copper = 1.68x10^-8 radius of wire = 1.7x10^-3m/2 = 8.5x10^-4 A =pi*(8.5x10^-4)^2 = 2.310^-6m^2 Plugging in the numbers: R = 2.6x10^-2 = .026 Ohms

On a multimeter, a high resistance would indicate a high Ohmic value and a low resistance would indicate a low Ohmic value. Specific values would be relative to device you are measuring.

A transformer has two coils coupled via the magnetic field, and when it has no load all you see is the inductance of the primary coil, which has to be fairly high to create the necessary amount of magnetic flux.

When the transformer supplies a resistive load, the input looks much more resistive.

It depends totally on the voltage used.

In a single-phase circuit like a house fed from 4-wire three phase in the street, the current flows in the live and neutral wires. The neutral currents from a street of houses are expected to cancel each other so that the overall current in the neutral leaving the transformer is small.

The current through each resistor is equal to the voltage across it divided by its resistance for series and parallel circuits.