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Capicitor Application Issues

Capacitors must be built to tolerate voltages and currents in excess of their ratings according to standards. The applicable standard for power capacitors is IEEE Std 18-2002, IEEE Standard for Shunt Power Capacitors.

Heat as one of most common cause of motor failure

This slide speaks about that how motor operation fails due to heat. how heat affect motors?

Monday, 12 May 2014

An example of calculating the technical losses of T




Earthing Transformer




Electric Shock Current, Where Does it Go?




Explain the working principal of the circuit breaker?

Circuit Breaker is one which makes or breaks the circuit. It has two contacts namely fixed contact & moving contact. Under normal condition the moving contact comes in contact with fixed contact thereby forming the closed contact for the flow of current. During abnormal & faulty conditions (when current exceeds the rated value) an arc is produced between the fixed & moving contacts & thereby it forms the open ckt. Arc is extinguished by the Arc Quenching media like air, oil, vacuum etc.

What happens if i connect a capacitor to a generator load?

Connecting a capacitor across a generator always improves power factor, but it will help depends up on the engine capacity of the alternator, otherwise the alternator will be over loaded due to the extra watts consumed due to the improvement on pf. Secondly, don't connect a capacitor across an  alternator while it is picking up or without any other load.

what is power factor? Whether it should be high or low? why?

Power factor should be high in order to get smooth operation of the system. Low power factor means losses will be more. it is the ratio of true power to apparent power. it has to be ideally 1. if it is too low then cable over heating &equipment overloading will occur. if it is greater than 1 then load will act as capacitor and starts feeding the source and will cause tripping.(if pf is poor ex:0.17 to meet actual power load has to draw more current(V constant),result in more losses if pf is good ex: 0.95 to meet actual power load has to draw less current(V constant),result in less losses).

There are a Transformer and an induction machine. Those two have the same supply. For which device the load current will be maximum? And why?

The motor has max load current compare to that of transformer bcoz the motor consumes real power.. and the transformer is only producing the working flux and its not consuming.. hence the load current in the transformer is because of core loss so it is minimum.

what is meant by insulation voltage in cables?explain it?

It is the property of a cable by virtue of it can withstand the applied voltage without rupturing it is known as insulation level of the cable.

what is boucholz relay and the significance of it into the transformer?

Boucholz relay is a device which is used for the protection of transformer from its internal faults; it is a gas based relay. whenever any internal fault occurs in a transformer, the boucholz relay at once gives a horn for some time, if the transformer is isolated from the circuit then it stop its sound itself otherwise it trips the circuit by its own tripping mechanism.

What is the difference between Isolator and Circuit Breaker?

Isolator is a off load device which is used for isolating the down stream circuits from upstream circuits for the reason of any maintenance on down stream circuits. It is manually operated and does not contain any solenoid unlike circuit breaker. it should not be operated while it is having load. first the load on it must be made zero and then it can safely operated. Its specification only rated current is given. But circuit breaker is on load automatic device used for breaking the circuit in case of abnormal conditions like short-circuit, overload etc., it is having three specification 1 is rated current and 2 is short circuit breaking capacity and 3is instantaneous tripping current.

What are the transformer losses?

TRANSFORMER LOSSES - Transformer losses have two sources-copper loss and magnetic loss. Copper losses are caused by the resistance of the wire (I2R). Magnetic losses are caused by eddy currents and hysteresis in the core. Copper loss is a constant after the coil has been wound and therefore a measureable loss. Hysteresis loss is constant for a particular voltage and current.Eddy-current loss, however, is different for each frequency passed through the transformer

Define IDMT relay?

It is an inverse definite minimum time relay. In IDMT relay its operating is inversely proportional and also a characteristic of minimum time after which this relay operates. It is inverse in the sense ,the tripping time will decrease as the magnitude of fault current increase

Where should the lighting arrestor be placed in distribution lines?

Near distribution transformers and out going feeders of 11kv and incoming feeder of 33kv and near power transformers in sub-stations.

What is the difference between MCB & MCCB,Where it can be used?

MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small current rating circuit. MCCB moulded case circuit breaker and is thermal operated for over load current and magnetic operation for instant trip in short circuit condition. under voltage and under frequency may be in built. Normally it is used where normal current is more than 100A.

Why we do 2 types of earthing on transformer ie: body earthing & neutral earthing, what is function.

The two types of earthing are Familiar as Equipment earthing and System earthing. In Equipment earthing: body (non conducting part) of the equipment should be earthed to safeguard the human beings. System Earthing: In this neutral of the supply source (Transformer or Generator) should be grounded. With this, in case of unbalanced loading neutral will not be shifted .so that unbalanced voltages will not arise. We can protect the equipment also. With size of the equipment ( transformer or alternator)and selection of relying system  earthing will be further classified into directly earthed, Impedance earthing,resistive (NGRs) earthing

Why ELCB can't work if N input of ELCB do not connect to ground?

ELCB is used to detect earth leakage fault. Once the phase and neutral are connected in an ELCB, the current will flow through phase and that much current will have to return neutral so resultant current is zero. Once there is aground fault in the load side, current from phase will directly pass through earth and it will not return through neutral through ELCB. That means once side current is going and not returning and hence because of this difference in current ELCB will trip and it will safe guard the other circuits from faulty loads. If the neutral is not grounded, fault current will definitely high and that full fault current will come back through ELCB, and there will be no difference in current.

Why series motor cannot be started on no-load?

Series motor cannot be started without load because of high startingtorque. Series motor are used in Trains, Crane etc

Why in a three pin plug the earth pin is thicker and longer than the other pins?

It depends upon R=rho l/a where area(a) is inversely proportional to resistance (R), so if (a) increases, R decreases & if R is less the leakage current will take low resistance path so the earth pin should be thicker. It is longer  because the First to make the connection and last to disconnect should be earth Pin. This assures Safety for the person who uses the electrical instrument.

Why Delta Star Transformers are used for Lighting Loads?

For lighting loads, neutral conductor is must and hence the secondary must be star winding. And this lighting load is always unbalanced in all three phases. To minimize the current unbalance in the primary we use delta winding in the primary. So delta / star transformer is used for lighting loads.

What are the advantages of star-delta starter with induction motor?

The main advantage of using the star delta starter is reduction of current during the starting of the motor. Starting current is reduced to 3-4 times Of current of Direct online starting.(2). Hence the starting current is reduced; the voltage drops during the starting of motor in systems are reduced.

Why is the starting current high in a DC motor?

In DC motors, Voltage equation is V=Eb-IaRa (V = Terminal voltage,Eb= Back emf in Motor,Ia = Armature current,Ra = Armature resistance).At starting,Eb is zero. Therefore, V=IaRa, Ia = V/Ra , where Ra is very less like 0.01ohm.i.e,Ia will become enormously increased

What is meant by regenerative braking?

When the supply is cut off for a running motor, it still continue runningdue to inertia. In order to stop it quickly we place a load (resistor) across thearmature winding and the motor should have maintained continuous field supply.so that back e.m.f voltage is made to apply across the resistor and due to loadthe motor stops quickly. This type of breaking is called as "RegenerativeBreaking

Power System (The Electric Power Engineering)





Power Electronics Design A Practitioners Guide





power electronics




Newnes Electrical Power Engineers Handbook