In this article, I am going to list all the most frequently asked electrical interview questions with their answers. This article will be equally helpful for all electrical engineering professionals, from students to working professionals. These questions are taken from various real-time electrical engineering interviews and are frequently asked in various industries. Also, the knowledge of these questions will also help you in your electrical practices. So, I suggest reading and bookmarking this article, if you want to excel in your electrical engineering career. If you are a fresher electrical engineer, then you must prepare all these questions to create your electrical engineering interviews.
Q. 1 – What is Electrical Engineering?
Ans. – Electrical Engineering is a branch of engineering that deals with the study, design, and applications of electricity, electromagnetism, and electronics.
Q. 2 – What is electricity?
Ans. – Electricity is a form of energy that is obtained from other forms of energy, such as heat, light, etc.
Q.3 – What are the types of electricity?
Ans. – There are two types:
- Static Electricity
- Current Electricity
Q. 4 – What is static electricity?
Ans. – Static electricity means electricity at rest i.e., electricity due to static charge is called static electricity.
Q. 5 – What is current electricity?
Ans. – Current electricity means electricity in motion which is due to the flow of electrons in a conductor.
Q. 6 – What are the types of electric current?
Ans. – There are two types of electric current:
- Direct Current (DC)
- Alternating Current (AC)
Q. 7 – What are the different methods of producing electricity? Give examples.
Ans. – The methods of producing electricity are:
- Through friction: static electricity is produced.
- Through chemical action: as in cells and batteries.
- Through mechanical work: generators produce electricity by this method.
- Through heat: thermal electricity.
- Through lighting effect: as produced in photo voltaic cells.
Q. 8 – Explain the difference between direct and alternating current.
Ans. – Direct current (DC) is the flow of electric charge in only one direction. While the alternating current (AC) is the flow of electric charge that periodically reverses its direction and continuously changes the magnitude
Q. 9 – Where is D.C. used?
Ans. – Common examples where DC is used are:
- Battery charging
- Electroplating
- Electrolysis
- Relays
- Traction motors
- Cinema projector
- Remote controls
- Watches and clocks, etc.
Q. 10 – Where is A.C. used?
Ans. – Common applications where AC is used:
- Household appliances
- Fan and coolers
- Refrigerators
- Air conditioners
- Induction motors
- V. Set etc.
Q. 11 – What is active, reactive, apparent, and complex power?
Ans. – Active, reactive, apparent, and complex powers are defined below:
- Active Power: It is the actual power that is delivered to the load such as heaters, motors, and other electrical loads, and is consumed in the circuit in the form of heat, light, or mechanical work. It is usually denoted by the symbol P and is measured in watts (W).
- Reactive Power: The AC power that continuously flows back and forth between source and load is called reactive power. It is usually denoted by Q and is measured in VAR (Voltage-Ampere Reactive).
- Apparent Power: It is the product of voltage and current without considering the phase difference between them. It is a combination of active power and reactive power. It is basically the total power delivered to the load. It is denoted by the symbol S and is measured in Volt-Ampere (VA).
- Complex Power: It is the product of voltage and current considering the phase difference between them. It is obtained by taking the phasor sum or vector sum of the active power and reactive power. It is denoted by S* and is measured in VA.
Q. 12 – What is a leading and lagging power factor and how can you improve it? State the methods of power factor correction.
Ans. – The cosine of the angle between voltage and current is called the power factor. If the current leads the voltage, it causes a leading power factor. If the current lags voltage, then it is called a lagging power factor. Most loads are inductive and have a lagging power factor.
The following methods are used to improve the PF (to compensate for the effect of the lagging power factor):
- Static Capacitor – The capacitor can provide a leading current that compensates for the lagging component of the current and improves the power factor.
- Synchronous Condenser – It is basically an over-excited synchronous motor running at no load and has a leading power factor.
- Phase Advancer – A phase advancer is an AC exciter that is connected to the main shaft of the motor and operated by the rotor circuit of the motor to improve the power factor. Phase advancer is widely used to improve the power factor of induction motors in industries.
Q. 13 – Why do we improve the power factor?
Ans. – The reasons for improving the power factors are listed below:
- To reduce line losses: Line losses (I2R) depend on current. The low-power factor draws a large amount of current as compared to the high-power factor. Hence, the power factor improvement reduced the line losses by reducing the line current.
- To reduce the kVA rating and size of electrical equipment: The power factor is inversely proportional to kVA. Hence, the low power factor of the equipment has a high kVA rating and hence is larger in size. So, a high power factor is desired.
- To reduce conductor size and cost: Low power factor causes high current to flow through the transmission lines. Therefore, large conductors are required to transmit the high amount of current due to low power factor which adds the extra cost of conductor material. Hence, if the power factor of the system is improved, it will reduce the conductor size and hence the cost.
- To improve the voltage regulation and reduce voltage drop: The large current due to low PF results in a high voltage drop that requires more regulation than usual. Hence, the power factor is to be improved to reduce the need for voltage regulation.
- Lower efficiency: The line losses due to the high current flow and voltage drop reduce the efficiency of the system. The efficiency is maximum at the unity power factor. Therefore, power factor improvement is also required to increase the overall efficiency of the system.
Q. 14 – What a unilateral and bilateral circuits?
Ans. – A unilateral is an electric circuit whose properties change with the change in the direction of current flow or the voltage polarity. Whereas, the properties of a bilateral circuit do not change with the change in the direction of current or the voltage polarity.
Q. 15 – What is a linear and non-linear circuit?
Ans. – In a linear circuit, the relation between the current and voltage is linear, i.e., they are directly proportional to each other and have a straight-line curve passing through the origin. The circuit parameters like frequency, resistance, inductance, capacitance, etc. remain constant with changing current and voltage.
On the other hand, in a non-linear circuit, the current and voltage do not have a linear relationship or do not have a straight line passing through the origin of the curve. The electrical parameters of such an electric circuit change with any change in voltage and current.
Q. 16 – What could be the methods for the current to double in a linear circuit?
Ans. – There are two methods for increasing the current in a linear circuit:
- Reduce the total resistance of the circuit to half.
- Double the supply voltage in the circuit.
Q. 17 – Why is the Battery rating in Ah (Ampere hours) and not in VA or Watts?
Ans. – A battery converts chemical energy into electrical energy which is basically the charge stored inside the chemicals. Hence, a battery can supply a current for a specified time, thus Ampere-hour (Ah) is used as the unit for its rating. Also, the batteries supply direct current that has no phase or frequency associated with it. Thus, there is no concept of power factor and reactive power. Hence, there is no need to express it in VA or Watt.
Q. 18 – What are primary and secondary cells?
Ans. – The primary cell is a type of non-rechargeable cell that cannot be recharged once it is used. They can never be used after they get fully discharged and have to be disposed of. Primary cells are mainly used in toys, handheld devices, remote controls, electronic gadgets, etc.
A secondary cell is a type of rechargeable cell that can be recharged several times depending on its life cycle and can be used over and over again. However, they are relatively expensive compared to the primary cells. Secondary cells are widely used in cell phones, smartphones, laptops, electric trimers, vehicles, etc.
Q. 19 – What are the limitations of Ohm’s law?
Ans. – Ohm law cannot be applied to a unilateral circuit or a non-linear circuit. The fundamental condition for Ohm’s law is that the resistance of the circuit must be constant. Since, the resistance of a non-linear or unilateral circuit changes with any change in voltage and current. Hence, it cannot be applied to such a circuit. Also, to apply Ohm’s law, the temperature must remain constant.
Q. 20 – Does current lead or lag the voltage in an inductive and capacitive circuit?
Ans. – The current lags the voltage in an inductive circuit, while the current leads the voltage in a capacitive circuit.
Q. 21 – Define the term Capacitance and Inductance
Ans. –
- Capacitance: It is the ability of a circuit component to store electric charge between two metal plates when there is a potential difference between them. It is denoted by C and is measured in Farads (F).
- Inductance: It is the ability of a conductor to oppose any change in the current through it. It is denoted by L and is measured in Henry (H).
Q. 22 – Why do the capacitors work on AC only?
Ans. – Capacitor offers infinite resistance to dc current i.e., it blocks the dc current. It allows only the AC current to pass through.
Q. 23 – What is the maximum power transfer theorem?
Ans. – It states the condition for maximum power transfer from source to load. MPT states that in a linear, bilateral network, the maximum amount of power will be transferred from the source to the load when the load resistance equals the internal resistance of the source.
Q. 24 – Explain Thevenin’s Theorem in a single sentence.
Ans. – Thevenin’s theorem states that any linear bilateral complex circuit can be reduced into a simple two-terminal electric circuit with one voltage source and a resistance connected in series with it.
Q. 25 – Explain Norton’s Theorem in a single sentence.
Ans. – Norton’s theorem states that any linear bilateral complex circuit can be transformed into an equivalent simple circuit having a single current source with a parallel resistance.
Q. 26 – Explain the superposition theorem.
Ans. – The current through or voltage across any circuit component is equal to the algebraic sum of the currents or voltages produced independently by each source acting alone. In other words, this theorem allows us to solve a complex electric circuit having multiple sources using only one source at a time.
Q. 27 – What do the different colors of wires indicate? Or mention what the different colors on wires indicate.
Ans. – In an electrical wiring system, the different colors of wires are used for phase indication. Different colors represent different phases, the neutral and earth wire. The color code may differ around the world as per the standard used. The common color coding of wires is explained here.
- Black Wire: The black wire is used for power supply in all circuits. Any circuit wire with this color is considered a hot or live wire. Black is never used for a neutral or ground wire.
- Red Wire: The red color wire is a secondary live wire in a 220-volt electric circuit and it is used in some types of interconnections. In an electric circuit, we can join the red wire to another red wire or to a black wire.
- Blue and Yellow Wire: These two-color wires are used to carry power, but they are not used for wiring the outlets for common plug-in electrical devices. Instead, they are used for the live wire pulled through the conduct. We can see the yellow wire in the fan, structure lights, and switched outlets.
- White and Gray: These color wires are used as neutral wires. They carry the current to the ground or back to the source. We can connect white and gray only to other white and gray wires.
- Green: It is connected to the ground terminal in an electric box and runs from the electric box to the earthing bus bar within an electric panel.
Q. 28 – Explain the working principle of the circuit breaker.
Ans. – A circuit breaker is a switch used to make or break the circuit. It has two contacts namely, a fixed contact and a moving contact. Under normal operating conditions, the moving contact remains in contact with the fixed contact and thus forms a closed contact for the flow of electric current.
During abnormal or faulty conditions i.e., when the current exceeds the rated value, a gap is created between the fixed and moving contacts and thereby it forms the open circuit. While separating the fixed and moving contacts, an arc is produced that is extinguished by the arc-quenching media such as air, oil, vacuum, etc.
Q. 29 – What is a vacuum circuit breaker?
Ans. – A circuit breaker is a device that breaks the circuit by opening the contact terminals. During the opening, an arc is produced between the terminals that can be quenched using different types of mediums. In a vacuum circuit breaker or VCB, the medium for arc quenching is a vacuum. The vacuum has an excellent arc quenching ability as compared to air. Hence, VCBs are used in high-voltage circuits.
Q. 30 – What is the difference between MCB and MCCB?
Ans. – MCB stands for ‘Miniature Circuit Breaker’ and it is mainly used for current ratings lower than 100 amperes with interrupting ratings of less than 18 kA. Its tripping characteristics cannot be adjusted and it is mainly used for domestic purposes.
MCCB stands for ‘Molded Case Circuit Breaker’. It has a relatively high current rating of around 2500 amperes with an interrupting rating between 10 kA and 200 kA. Also, its tripping characteristics can be adjusted as per requirements. It is mainly used in industries in motor control circuits.
Q. 31 – What is the difference between a single-pole and a double-pole circuit breaker?
Ans. –
- Single-pole circuit breakers are used to break/make only a single-phase, i.e. only one live wire.
- Double-pole circuit breakers are used to make/break both phase and neutral wires.
Q. 32 – What is the difference between a fuse and a circuit breaker?
Ans. –
- The fuse is made of a metal wire called a fuse element that melts when the current through it exceeds a specified limit. It is used to provide overload and overcurrent protection to the circuit. It is a single-use device that needs to be replaced once melted.
- The circuit breaker is an electromechanical or electronic switch that opens the circuit during overcurrent, overvoltage short-circuits, or any other fault condition. It can work automatically using motors as well as manually using handles. It can be used over and over again just by resetting it.
Q. 33 – What is the difference between a circuit breaker and an Isolator?
Ans. –
- A Circuit Breaker is a protective electromechanical or electronic device that is used to control the flow of current or protect the circuit from fault conditions. It automatically breaks the circuit in case of fault conditions such as overcurrent, short-circuit, etc. It can be also used to break the circuit. It can be operated in both ON and OFF supply conditions.
- An isolator is a mechanical switch used to isolate or off the power supply in electric power lines. It is an off-load device i.e., it can be operated only when the power supply is off.
Q. 34 – Why Motor rated in kW instead of kVA?
Ans. – An electric motor has a definite power factor. Hence, its rating is specified in kW or HP (horsepower). In other words, an electric motor consumes active power only and delivers mechanical power output which is measured in HP or kW and that is why motor rating is given in Watts, kW, or HP. All the load devices are always rated in Watts or kW.
Q. 35 – What is the definition of generator and motor?
Ans. – An electric motor is an electromechanical energy conversion device that converts electrical energy into mechanical energy.
An electric generator is an electromechanical energy conversion device that converts mechanical energy to electrical energy.
Q. 36 – What is a motor starter?
Ans. – A Motor Starter is a circuit that connects the motor to the power supply and controls and reduces the starting current which can damage the windings of the motor. It provides soft starting or stopping of the motor and also provides protection against overload, overcurrent, overvoltage, etc.
Q. 37 – What are the different methods for starting an induction motor?
Ans. – The following are some common methods widely used for starting an induction motor:
- DOL (Direct Online Starter)
- Star-Delta Starter
- Autotransformer Starter
- Resistance Starter
- Series Reactor Starter
Q. 38 – What is the difference between a generator and an alternator?
Ans. – The alternator and generator both operate on the principle of Faraday’s law of electromagnetic induction.
An alternator is an electromechanical machine that converts mechanical energy into alternating current electricity. It always generates an alternating current supply.
A generator is an electromechanical device that converts mechanical energy to either AC or DC electricity. Hence, an alternator is also a generator.
Q. 39 – What are the advantages of a star-delta starter with an induction motor?
Ans. – The chief advantages of star-delta starter are:
- It decreases the starting current drawn by the induction motor as it is 6 to 7 times more than the full-load current which can damage the windings of the motor.
- It eliminates the voltage drop problem, as the large amount of starting current results in a high voltage drop along the power line which may damage other electrical appliances connected to the line.
- It has a simple operation.
- The cost of this starter is comparatively very low.
- This starter has a good torque-current performance.
Q. 40 – Why is the starting current high in the DC motor?
Ans. – At the starting condition, the DC motor has no back emf. Thus, when the DC motor is started, the armature current is controlled by the armature circuit resistance only. However, the resistance of the armature circuit of a DC motor is very low and when the full supply voltage is applied to the motor at the standstill condition, the armature current becomes significantly high which can damage the windings of the motor.
Q. 41 – What is the slip of an induction motor?
Ans. – The difference between the synchronous speed (Ns) and the rotor speed (Nr) of an induction motor is called slip. It is denoted by S. In actual practice, the slip is given in percentage. The slip in an induction motor occurs because the rotor speed of the induction motor is always less than its synchronous speed.
Q. 42 – Why can’t a series motor be started on no-load?
Ans. – The flux produced by the field winding in a DC series motor is directly proportional to the load current. Hence, at no-load or light load, the load current is very small, and hence the flux that causes the speed to be infinity i.e., very high, as the speed is inversely proportional to the flux. Therefore, a DC series motor should never be started on no-load.
Q. 43 – Explain the principle of induction motor.
Ans. – In an induction motor, we give AC supply to its stator windings, a rotating magnetic field is produced in the stator due to the flow of current in the windings. The rotor winding is so arranged that each coil acts as a short circuit.
The magnetic flux of the stator cuts the short-circuited rotor winding. Due to short-circuited winding, the current will start flowing through the rotor winding according to Faraday’s law of electromagnetic induction. The currents flowing through the rotor winding, produce another magnetic flux in the motor.
Now, there are two magnetic fluxes inside the motor, one is due to stator currents, and another is due to rotor currents. The rotor flux lags behind the stator flux as per inductor property. Due to this magnetic action, the rotor will experience a torque that will make it rotate in the direction of the stator’s rotating magnetic field. This is how an induction motor works.
Q. 44 – What is the difference between a four-point starter and a three-point starter?
Ans. – The starter which consists of three terminals is known as a three-point starter. It has three terminals namely, armature, field, and line. It has a no-voltage coil (NVC) connected in series with the field winding.
Whereas, the starter that consists of four terminals is called a four-point starter. It has four terminals namely, armature, field, line, and an additional terminal. This additional terminal is used to connect the no-voltage coil (NVC) in parallel with the shunt field winding.
Q. 45 – What is meant by regenerative braking?
Ans. – Regenerative braking occurs when the speed of an electric motor exceeds the synchronous speed. This is called regenerative braking because, in this braking mode, the motor operates as a generator and supplies power back to the supply line. The main condition for regenerative braking to take place is that the rotor has to rotate at a speed greater than the synchronous speed.
The main disadvantage of regenerative braking is that the motor has to run at a super-synchronous speed which may mechanically damage the motor. However, regenerative braking can also be achieved at sub-synchronous speed if a source of variable frequency is available.
Q. 46 – What is plugging breaking?
Ans. – In this type of electric braking method, the terminals of the power supply are reversed, consequently, the generator torque also reverses and resists the forward rotation of the motor, and hence the speed of the motor decreases. During plugging braking, an external resistance is also inserted into the circuit to limit the current. The major disadvantage of this method is the high power wastage.
Q. 47 – What is dynamic breaking?
Ans. – In this electrical braking method, the motor in the running condition is disconnected from the source and connected across a resistance. When the motor is disconnected from the power supply, the rotor keeps rotating due to inertia and it operates as a self-excited generator.
When the motor operates as a generator, the flow of current and direction of torque reverse. During the braking, the sectional resistances are cut out one by one from the circuit to maintain the steady torque. This is also known as rheostat braking.
Q. 48 – What is meant by armature reaction?
Ans. – In an electric motor or generator, the effect of armature flux on the main field flux is known as armature reaction. It has the following two adverse effects on a machine:
- It distorts the main flux.
- It decreases the magnitude of the main flux.
Q. 49 – Which motor has high starting torque and starting current: DC motor Induction Motor or Synchronous Motor?
Ans. – The DC series motor has the highest starting torque out of the given three motors and for this reason, they are widely used in electrical machines that require high-starting torque, such as cranes, hoists, lifts, trains, etc.
Q. 50 – What is a universal motor?
Ans. – A universal motor is one that can operate on both a DC power supply and a single-phase AC supply.
When a universal motor is supplied from a DC power supply, it operates as a DC series motor.
When it is supplied from an AC supply, it generates a unidirectional torque. Because its armature winding and field winding are connected in series and are in the same phase. Therefore, When the polarity of AC supply changes periodically, the direction of the current in the armature and the field winding reverses at the same time, and results in a unidirectional torque production.
Q. 51 – What are some of the most common causes of transformer humming?
Ans. – The following are some major causes of transformer humming:
- Electric humming noise around electrical transformers is caused by the stray magnetic fields that cause the enclosure and other accessories of the transformer to vibrate.
- Magnetostriction is another cause of vibration, in which the core iron slightly changes its shape when exposed to magnetic fields. Transformer humming noise is produced by the core.
Q. 52 – What is the voltage regulation of the transformer and why is it important?
Ans. – The voltage regulation of a transformer is defined as the change in the secondary voltage from no-load to full-load condition.
Ideally, the secondary voltage of a transformer must remain the same at all load conditions, which is the zero-voltage regulation condition. But practically, the secondary voltage of the transformer changes with the power factor of the load.
The voltage regulation is important because it provides the value of the efficiency of the transformer. It is best practice to select a transformer with low voltage regulation.
Q. 53 – There is a transformer and an induction motor. The two have the same supply. For which device the load current will be maximum and why?
Ans. – For the same rating and same load conditions, the losses occurring in both devices will be different due to their construction and working.
The transformer has no moving parts therefore it will take a smaller magnetizing current in the same load condition. Whereas, An induction motor has an air gap between its primary (stator) and secondary (rotor) windings which will require a higher magnetizing current due to its higher leakage reactance than the transformer.
The induction motor has moving parts and will have to overcome the windage losses that occur due to the rotation of the rotor. For this reason, an induction motor will take more load current as compared to the transformer.
Q. 54 – How many types of cooling systems are there in transformers?
Ans. – The types of transformer cooling systems are:
- ONAN (Oil Natural and Air Natural)
- ONAF (Oil Natural and Air Forced)
- OFAF (Oil Forced and Air Forced)
- ODWF (Oil Direct and Water Forced)
- OFAN (Oil Forced and Air Forced)
Q. 55 – What is an ideal transformer?
Ans. – An ideal transformer is an imaginary or theoretical model of a practical transformer in which no losses occur at all.
In other words, an ideal transformer is one that has input power equal to the output power i.e., they have 100% efficiency.
Q. 56 – What output power you will get from an ideal transformer and why?
Ans. – An ideal transformer does not have any kind of losses like hysteresis loss, eddy current loss, etc. Thus, the output power from an ideal transformer is exactly equal to the input power. This is because an ideal transformer has 100% efficiency.
Q. 57 – What are transformer efficiency and all-day efficiency? What is the condition for maximum efficiency?
Ans. –
Transformer Efficiency:
The efficiency of a transformer is defined as the output power divided by the input power. Some part of the input power is wasted in internal power losses of the transformer.
$$\text{Efficiency }(η) = \frac{\text{Output Power}}{\text{Input Power}}$$
All-Day Efficiency:
For a transformer, the ratio of energy delivered in kilowatt hour (kWh) to the energy input in kWh for 24 hours is called all-day efficiency.
$$η_{all-day} = \frac{\text{Output in kWh}}{\text{Input in kWh}}$$
Condition for Maximum Efficiency:
In a transformer, when the copper loss becomes equal to the iron loss, then the transformer gives maximum efficiency. Hence, the condition for maximum efficiency of a transformer is,
$$\text{Cu Loss }(W_\text{cu}) = \text{Iron Loss }(W_\text{i})$$
Q. 58 – Why the current transformer’s secondary winding should not be opened when there is a current flowing in its primary?
Ans. – The current transformer is a type of step-up transformer that increases the voltage and decreases the current on the secondary side. For the open secondary condition, the primary current becomes the magnetizing current that produces an infinitely high secondary voltage which can damage the insulation as well as cause danger to the operating personnel.
Q. 59 – Why are transformers rated in kVA?
Ans. –
kVA = kV (kilo-Volt) × A (Ampere)
kW= kV (kilo-Volt) × A (Ampere) × Power Factor
The Power factor only depends upon the nature of the load i.e.,
- Inductive load – lagging power factor
- Capacitive load – leading power factor
- Resistive load – unity power factor
A transformer does not work as a load in the circuit, but it is a device used to transform the voltage and current and does not consume power. Hence, if you think that a transformer is a load device then you are wrong. A transformer does not consume any power, it only transfers power with increasing and decreasing voltage and current that is the first reason why a transformer is always rated in kVA.
Another reason is, that when the transformer is designed, the manufacturer does not know which type of load will be connected to it. Since the power factor depends upon the type of load. If an inductive load is connected then the current will be lag that flows through the secondary winding of the transformer as well as the primary winding of the transformer.
We also know that pure inductive and pure capacitive loads do not practically exist. Every load has a finite resistance even if it is inductive or capacitive. For example, an electric motor is connected to the transformer which is a combination of inductive and resistive load. The motor draws both reactive power (kVAr) and active power (kW). Thus, the power supplied by the transformer is the phasor sum of reactive power (kVAr) and active power (kW) which is kVA.
There is another reason behind the rating of a transformer in kVA that is the copper loss (I2R) occurs due to the flow of the current in the transformer windings and the iron or core loss occurs due to the voltage across windings. These losses do not depend on the power factor of the load. Hence, it is also the reason why a transformer rating is in kVA and not in kW.
Overall, when manufacturers design a transformer, they have no idea what kind of load will be connected to the transformer. The load could be resistive (R), inductive (L), capacitive (C), or mixed load (R, L, and C). Thus, there would be different power factors at the secondary (load) side of the transformer. The output of real power may vary depending on the power factor. Hence, the manufacturer denotes it as “the given transformer can provide x amounts of amperes at y amount of voltage”. That is why, they use VA i.e., voltage × Amperes, instead of W to rate a Transformer.
Q. 60 – What will happen if DC supply is given to the primary of a transformer?
Ans. – A transformer has high inductance and low resistance. In the case of DC supply, there is no inductance, only resistance will be effective in the electrical circuit of the transformer. Thus, a very high electrical current will flow through the primary winding of the transformer. This can cause burnout of coil and insulation.