What are the 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.

IDMT relay ?

 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 increases.

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

 Yes because the poles change for every half-cycle of ac voltage so the polarity of AC voltage is continuously changing for every half cycle. So, the interchanging of terminals in the ac system does not show any difference. That's why the ac solenoid attracts the plunger even though its terminals are interchanged.

Which power plant has high load factor?

 All baseload 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. Hydropower plants have a higher efficiency than thermal & nuclear power plants.

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

  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.

What is use of lockout relay in ht voltage?

 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 MCB & MCCB, Where it can be used?

 MCB is a miniature circuit breaker that is thermal operated and uses for short circuit protection in a small current rating circuit. MCCB molded case circuit breaker and is thermal operated for overload 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

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 the insulation level of the cable.

What is ferrantic effect?

 The output voltage is greater than the input voltage or receiving end voltage is greater than the sending end voltage

What is SF6 Circuit Breaker?

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

What is Buchholz relay and the significance of it in to the transformer?

 Buchholz relay is a device which is used for the protection of the 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 stops its sound itself otherwise it trips the circuit by its own tripping mechanism.

What is the difference between Isolator and Circuit Breaker?

  The isolator is an offload device that is used for isolating the downstream circuits from upstream circuits for the reason of any maintenance on downstream circuits. It is manually operated and does not contain any solenoid, unlike a circuit breaker. It should not be operated while it is having a load. First, the load on it must be made zero, and then it can safely operate. 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 a short circuit, overload, etc., it is having three specifications 1 is rated current and 2 is short circuit breaking capacity and 3 is instantaneous tripping current.

What is power factor? Whether it should be high or low? Why?

 The power factor should be high in order to get a smooth operation of the system. A 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 overheating &equipment overloading will occur. If it is greater than 1 then the load will act as a 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)

What is CT and PT ?

The term C.T means the current transformer, and the term P.T means potential transformer. In-circuit where measurements of high voltage and high current are involved, they are used there. Electrical Interview Page | 2 Particularly when a measuring device like a voltmeter or ammeter is not able to measure such a high value of quantity because of the large value of torque due to such high value it can damage the measuring device.so, CT and PT are introduced in the circuits. They work on the same principle of a transformer, which is based on the linkage of electromagnetic flux produced by primary with secondary. They work on the ratio to which they are designed. E.g. if CT is of ratio 5000\5A and it has to measure the secondary current of 8000A.then ANS=8000*5\5000=8Aand this result will be given to ammeter .and after measuring 8A we can calculate the primary current. The same is the operation of PT but measuring voltage.

What is stepper motor? What is its uses?

  Stepper motor is the electrical machine which acts upon input pulse applied to it.it is one type of synchronous motor which runs in steps in either direction instead of running incomplete cycle.so, in automation parts it is used.

What is the function of anti-pumping in circuit breaker?

 when the breaker is close at one time by close push button, the anti-pumping contactor prevent reclose the breaker by close push button after if it already close.

Explain the working principal of the circuit breaker?

 Circuit Breaker is one that makes or breaks the circuit. It has two contacts namely fixed contact & moving contact. Under normal conditions, 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 forms the open circuit, Arc is extinguished by the Arc Quenching media like air, oil, vacuum, etc.

Why the capacitors works on ac only?

 Generally, the capacitor gives infinite resistance to dc components (i.e., block the DC components). It allows the ac components to pass through.

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 upon the engine capacity of the alternator, otherwise, the alternator will be overloaded 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 ammeter ?

 ammeter (from Ampere Meter) is a measuring instrument used to measure the current in a circuit. Electric currents are measured in amperes (A), hence the name. Instruments used to measure smaller currents, in the milliampere or microampere range, are designated as milliammeters or microammeters. Early ammeters were laboratory instruments that relied on the Earth's magnetic field for operation. improved instruments were designed which could be mounted in any position and allowed accurate measurements in electric power systems. It is generally represented by the letter 'A' in a circuit.

Types of Ammeter