significance of it in to the transformer?
Answer: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 other wise it trips the circuit by its own tripping mechanism.
Electrical interview question:What is SF6 Circuit Breaker?
Answer:SF6 is Sulpher hexa Flouride gas.. if this gas is used as arc quenching medium in a Circuitbreaker means SF6 CB.
Electrical interview question:what is ferrantic effect?
Answer:Output voltage is greater than the input voltage or receiving end voltage is greater than the sending end voltage.
Electricalinterview question: what is meant by insulation voltage in cables? explain it?
Answer: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.
Electrical interview question: Why we do 2 types of earthing on transformer (ie
body earthing & neutral earthing * what is function. i am going to install a 5oo kva transformer & 380 kva DG set what should the earthing value?
Answer:The two types of earthing are Familiar as Equipment earthing and system earthing. In Equipment earthing: body ( non conducting part)of the equipment shouldd be earthed to safegaurd 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.
Electrical interview question:What is the difference between MCB & MCCB* Where it can be used?
Answer: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 inbuilt. Normally it is used where normal current is more than 100A.
Electrical interview question:Where should the lighting arrestor be placed in distribution lines?
Answer:Near distribution transformers and out going feeders of 11kv and incomming feeder of 33kv and near power transformers in sub-stations.
Electrical interview question
efine IDMT relay?
Answer: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.
Electrical interview question:What are the transformer losses?
Answer: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 measurable loss. Hysteresis loss is constant for a particular voltage and current. Eddy-current loss* however* is different for each frequency passed through the transformer.
Electrical interview question:What is meant by regenerative braking?
Answer:When the supply is cutt off for a running motor* it still continue running due to inertia. In order to stop it quickly we place a load(resitor) across the armature 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 load the motor stops quickly.This type of breaking is called as "Regenerative Breaking".
Electrical interview question:Why is the starting current high in a DC motor?
Answer:In DC motors* Voltage equation is V=Eb-IaRa (V = Terminal voltage*Eb = Back emf in Motor*Ia = Armature current*Ra = Aramture 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.
Electrical interview question:What are the advantages of star-delta starter with induction motor?
Answer
1). 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.
Electrical interview question:Why Delta Star Transformers are used for Lighting Loads?
Answer: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.
Electrical interview question:Why in a three pin plug the earth pin is thicker and longer than the other pins?
Answer: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 The First to make the connection and Last to disconnnect should be earth Pin. This assures Safety for the person who uses the electrical instrument.
Electrical interview question:Why series motor cannot be started on no-load?
Answer:Series motor cannot be started without load because of high starting torque. Series motor are used in Trains* Crane etc.
Electrical interview question:Why ELCB can't work if N input of ELCB do not connect to ground?
Answer: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 a ground 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 wil 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.