[Set2]AE KSEB Interview Questions|Basic Electrical Engineering Interview Questions

Electrical Interview Questions : These questions are useful for Assistant Engineer Electrical KSEB, Sub Enginner Electrical and other electrical Exams.

Contents

Electrical Interview Questions

What is Boucholz relay and the 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 otherwise it trips the circuit by its own
tripping mechanism.

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What is SF6 Circuit Breaker?

Answer : SF6 is Sulphur hexa Fluoride gas. If this gas is used as arc quenching medium in a Circuit
breaker means SF6 CB

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What is ferrantic effect?

Answer: Output voltage is greater than the input voltage or receiving end voltage is
greater than the sending end voltage.

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.

Why we do 2 types of earthing on transformer?

Why we do 2 types of earthing on transformer?(i.e. 🙂 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 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.

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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 shortcircuit condition. Under voltage and under frequency may be inbuilt. Normally it is used where normal current is more than 100A

What is use of lockout relay in ht voltage?

Answer: A lock-out relay is generally placed in line before or after the e-stop switch so the
power can be shut off at one central location. This relay is powered by the same electrical
source as the control power and is operated by a key lock switch. The relay itself may
have up to 24 contact points within the unit itself. This allows the control power for
multiple machines to be locked out by the turn of a single key switch.

What is the difference between earth resistance and earth electrode resistance?

Answer: Only one of the terminals is evident in the earth resistance. In order to find the
second terminal we should recourse to its definition: Earth Resistance is the resistance
existing between the electrically accessible part of a buried electrode and another point of
the earth, which is far away. The resistance of the electrode has the following
components

( A) The resistance of the metal and that of the connection to it. (B) The
contact resistance of the surrounding earth to the electrode.

Which power plant has high load factor?

All base load power plants have a high load factor. If we use high efficiency power plants to
supply the base load, we can reduce the cost of generation. Hydro power plants have a higher
efficiency than thermal & nuclear power plants.

Why an ac solenoid valve attract the plunger even though we interchanges the terminal?
Will the poles changes?

Answer: Yes because the poles changes for every half-cycle of ac voltage so the polarity of AC
voltage is continuously changing for every half cycle. So, interchanging of terminals in ac system
does not show any difference. That’s why the ac solenoid attract the plunger even though it’s
terminals are interchanged.

Define 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.

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 is loss is constant for a particular voltage and current.
Eddy-current loss, however, is different for each frequency passed through the transformer

What is meant by regenerative braking?

Answer: When the supply is cut off for a running motor, it still continue running due to inertia. In
order to stop it quickly we place a load (resistor) across the armature winding and the motor
should have maintained continuous field supply. So that back emf 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”.

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 = 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 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.

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.

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 First to make the connection and last to
disconnect should be earth Pin. This assures Safety for the person who uses the electrical
instrument.