eeefacts

CIRCUIT BREAKER Electrical circuit breaker is a switching device which can be operated automatically or manually for protecting and controlling of electrical power. A circuit breaker can make or break a circuit either manually or automatically under all condition as in no-load, full-load and short-circuit conditions. It is often desirable and necessary to switch on or off the various circuits in power system. In earlier days, this function used to be performed by a switch and a fuse placed in series with the circuit. However, it presents two disadvantages.  Firstly, when a fuse blows out, it takes quite time to replace it and restore supply to the consumer.  Secondly, a fuse cannot successfully interrupt heavy fault currents that result from faults on high-voltage and large capacity circuits. Due to these disadvantages, the use of switches and fuses is limited to low-voltage and small capacity circuits. This necessitates for a more dependable means of c...

S ubstation A Substations generally have switching, protection transformer and control equipments. A substation performs no. of function in electrical systems. Substations transform voltage from high to low level, or the reverse, frequency conversion, PF improvement or perform any of several other important functions.  Between the generating station and consumer, electric power may flow through several substations at different voltage levels. In a large substation, Circuit Breaker are used to interrupt any short circuits or overload currents that may occur on the network. A substation may include transformer to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages. Substations may be owned and operated by an electrical utility, or may be owned by a large industrial or commercial customer. Substations may be on the surface in fenced enclosures, underground...

Current Transformer (C.T) Current Transformer is a instrument transformer used to reduce the current of power system to a lower level to make it feasible to be measured by small rating Ammeter. A CT is basically a step up voltage type transformer . Primary of C.T. is having very few turns. Sometimes single bar primary is also used. Primary is connected in series with the power circuit. The secondary is having large no. of turns. Secondary is connected directly to an ammeter. As the ammeter is having very small resistance. Hence, the secondary of current transformer operates almost in short circuited condition. As the power remains same on both sides, when the voltage on secondary side increases, cause the secondary side current to decrease. One terminal of secondary is earthed to avoid the large voltage on secondary with respect to earth. Which in turns reduce the chances of insulation breakdown and also protect the person working nearby it against the high vol...

Instrument Transformer    The  Instrument transformers are use to step down the AC System voltage and current. The voltage and current level of power system is very high. It is very difficult and costly to design the measuring instruments for measurement of such high level voltage and current. Generally measuring system are designed for 5 A and 110 V. The measurement of such very large voltage and current, can be made possible by using the Instrument transformers with small rating measuring instruments. Therefore these instrument transformers are very popular in modern power system. 1. Current Transformer  Current Transformer is used to step down the current of power system to a lower level to make it to be measured by small rating Ammeter. 2. Potential Transformer Potential transformer used to step down the voltage of power system to a lower level to make it to be measured by small rating voltmeter i.e. 110 – 120 V voltmete...

Why Transformers Can’t step Up Or Step Down A DC Voltage or Current? It is because transformer works on the principle of electromagnetic induction i.e. it will work only with currents that produce varying magnetic field that will cut the conductors and induce EMF. The flux produced in the transformer will not change in its magnitude but rather remain the same and as a result EMF will not be induced in the secondary coil except at the moment of switching on, So the transformer may start to smock and burn because; In case of DC supply,  Frequency is zero . When you apply voltage across a pure inductive circuit, then according to                               X L = 2 π f L If we put frequency = 0, then the overall X L  (inductive reactance) would be zero as well. Now come to the current, I = V / R (and in case of inductive circuit, I = V / Xl )   ….  Basic...

An underground cable essentially consists of conductors covered with suitable insulation and surrounded by a protecting cover.   There are several types of cables are available, the type of cable to be used will depend upon the working voltage and service requirements. Some important points about cable The cable must have proper thickness of insulation in order to give high degree of safety and reliability at the voltage for which it is designed. The conductor size should be such that the cable carries the desired load current without overheating.     The conductor used in cables should be tinned stranded copper or aluminium of high conductivity to become flexible and carry more current. The cable must be provided with suitable mechanical protection so that it may withstand the rough use in laying it.    The materials used in the manufacture of cables should be such that there is complete chemical and physical stability throughout   Constru...

Insulation Resistance of cable The load current flows through the core of the cable whereas leakage current i.e., the current which is not useful flows from the conductor to the sheath through the dielectric material. The flow of leakage current is shown by dotted lines.   The resistance of any material is given by Where   ρ is the specific resistance of the material   l the length of the current path   A is the cross section Here dR represents the differential leakage resistance for unit length of the cable.   we first write an expression for the insulation resistance of an annular cylinder with radii x and (x + dx) as measured from the centre of the core. Where, the length of the cable is L unit the leakage resistance

A transmission line has three constants Resistance, inductance and Capacitor, distributed uniformly along the whole length of the line. The resistance and inductance form the series impedance. The capacitance existing between conductors for 1-phase line or from a conductor to neutral for a 3-phase line forms a shunt path throughout the length of the line.  Therefore, capacitance effects introduce complications in transmission line calculations.   So we classified the transmission lines based on the capacitance of line Depending upon the manner in which capacitance is taken into account, the overhead transmission lines are classified as : (i)  Short transmission lines . Due to smaller length and lower voltage, the capacitance effects are small and hence can be neglected, the length of an overhead transmission line is up to about 50 km and the line voltage is comparatively low it is usually considered as a short transmissi...

The most commonly used transistor configuration is the  NPN Transistor . In this, we used common emitter configuration of NPN Transistors. The transistor has three regions, namely ; emitter, base and collector. The base is much thinner than the emitter while collector is wider than both as shown. However, for the  sake of convenience, it is customary to show emitter and collector to be of equal size. The emitter is heavily doped so that it can inject a large number of charge carriers (electrons or holes) into the base.  The base is lightly doped and very thin ; it passes most of the emitter injected charge carriers to the collector. The collector is moderately doped The resistance of emitter diode (forward biased) is very small as compared to collector  diode (reverse biased).  Therefore, forward bias applied to the emitter diode is generally very small  whereas reverse bias on the collector diode is much higher.    ...

Stability of system In linear time invariant system we have: 1.     If input is zero output also zero. 2.     It should be independent of any non linear operator like square , cube ,root, sine, log etc. on either input side or output side. 3.     Differential operator is linear operator .   There should not be any time scaling i.e. coefficient should be   independent of time. Stability of LTI system may be defined as :   When system is subjected to bounded input output must be bounded. That is it must follow the BIBO (bounded input and bounded output) criterion. The stability of system is depends upon roots of characteristics equation i.e.                     1+G(s) *H(s) = 0 A.     Addition of pole always results in stability. B.     Addition of zero results in stability. ...

Control systems types Linear & Non-Linear System. A system is said to be linear if it follows the  superposition principle and homogeneity whereas a  Non-Linear System   does not follow at least one of these rules. Mathematically, it can be written as: Additivity   If the input signals are time varying   x1(t) and x2(t) then   corresponds to output signals y1(t) and y2(t), then  x1(t) + x2(t) = y1(t) + y2(t)  ( additivity ) Homogeneity   If the input signals x1(t) corresponds to output signal y1(t) , and “a” be any scalar then their product will be a.x1(t)=a.y1(t)  ( Homogeneity ) Digital or Discrete System In these types of control systems, we have a discrete signal (or signal may be in the form of pulse) as the input to the system. We can convert various input signal like sinusoidal type signal into square type signal etc into a discrete form using the electronic switch. Sin...

Transfer Function The transfer function of a linear , time-invariant , differential equation system is defined as the ratio of the Laplace transform of the output (response function) to the Laplace transform of the input (driving function) under the assumption that all initial conditions are zero. Above fig. shows the Block Diagram of Closed Loop Control System, where all variables are in laplace form i.e. E(s)  = Error Signal G(s) =  Forward Path Transfer Function. Y(s) =  Output Signal X(s) =  Reference Input Signal               H(s) =  Feedback Transfer Function. B(s) =  Feedback Signal. Transfer function of system is   From the block diagram,         Y(s) = G(s).E(s) ........1 B(s) = H(s).Y(s) ........2 E(s) = X(s) + B(s) .......3     (For positive feedback) ...