Explore topic-wise InterviewSolutions in Current Affairs.

a. OR gate. 

b. AND gate. 

c. NAND gate. 

d. NOR gate. 

e. Inverter gate. 

f. Exclusive OR gate. 

g. Equivalent gate.

Insulated wire: A conductor or multi-stranded conductor which has a insulating material on it is called a insulated wire. 

Pre-job briefing: Unit no, DR/WP/, USI/system/load, Job description, Eqpt history, 

Scope of Job, Any special tool or equipment required, Safety/Alarm, Procedures, expectation for the job, tech specifications requirements, communication, FME requirements, environmental concepts, any abnormal conditions. 

 Post job briefing: Details of work done, difficulties faced, deficiency found, parts replaced, experience to be communicated, review modification, review procedure, any suggestions, drawing updating, updating of history card, completion of checklist, any testing/logic checks required, clearance for surrendering permit.

Activities of station by which performance is judged by public.

a. Capacity factor. 

b. Availability factor. 

c. Radiation release (gas and liquid effluents). 

d. Thermal release. 

e. Man-rem. 

f. Development programs. 

g. Public awareness. 

h. Usefulness of the plant product to the public. 

i. Employment and other facilities provided to the local public. 

j. The Basic amenities provided to the employees. 

k. The standard of living of the employees. 

l. The profit earned by the Plant. 

m. The quality and cleanliness in and around the Plant. 

Cable: One or more insulated conductor enclosed in a protective mechanical sheathing of either GI wire or GI strip or aluminium to protect the insulation from mechanical damage. 

Advantages of Planned Maintenance.

1. As the name reflects maintenance jobs planned properly ie. manpower, tools, tackles, required for maintenance is well planned and readily available or reserved for planned job 

2. Procedures for doing the job in well known before doing the job and job can be performed as per procedure/checklist. 

3. It saves the time and unplanned outages of equipment. 

4. Common facilities/tools/tackles/ in the section in the section can be made available at the right time as job and requirements for that are already well planned. 

5. Overtime to employees can be limited. 

6. Job can be done systematically, accurately as a quality job can be expected.

Disadvantages of Unplanned maintenance. 

1. Unplanned job won’t have any expectations when to start when to stop. 

2. Manpower/tools tackles were available/not available at the right time is not ensured. 

3. Job may have to do in hurry which can lead to mistaken or job can be done leisurely (no sufficient work front for the available manpower.) so wastage of man-machine tools etc. 

4. In NPP we cannot accept unplanned jobs, as all works are safety-related/important. 

Effective, open communication is essential for safe and efficient performance of plant maintenance. Expressing concerns describing assignments, discussing problems, are few aspects of maintenance of communication. Clear and unambiguous communication is an integral part of procedure compliance and safe work practice. The following additional communication practices will be followed.

a. Repeat back is used to ensure accurate communication, especially when portable radios, headsets, or telephones are being used. 

b. Upon completion of a task, technicians shall report job completions to their supervisors and seek additional assignments. 

c. To conform to the principle of solving problems at the lowest possible level, potential grievance issues are to be discussed with the first line supervisor. 

d. Plant approved terminology, equipment identification and abbreviations are to be used at all times. 

e. 2-way communication is required at times! 

f. Listen

g. Understand

h. Then reply or repeat message.

Foreign material is defined as material that is not part of a system or component as designed. This includes dirt, debris, broken or missing parts, slag, tools rags, liquids/chemicals, lapping compounds, grinding particles and any other item that would affect the intended operation of a system or component 

All personnel shall assume responsibility for preventing the introduction of foreign material into systems. This will minimize damage or harmful effects. Such as corrosion, fuel damage, component malfunction, or failure, changes in chemistry. Reduced heat transfer, increased radiation levels, changes in system flow characteristic and improper contact operation. 

Specific actions include the following:

Work packages will be planned using field walk downs to determine specific FME recommendations 

If temporary dams are installed which will not be readily visible upon system closure, verification of removal shall be included in the checklist.  

Due to the presence of N₁₆ & O₁₇, which are high gamma emitter, their field is around 7 mev. 

By cementing. 

Station type, heavy duty, gap less zinc oxide. 

The parts of a cable gland are.

a. Check nut. 

b. Nipple. 

c. Metal washer. 

d. Neoprene rubber. 

e. Metal washer. 

f. Compression nut

35% of conductivity will be reduced due a small impurity in the conductor.

The advantages of PVC insulated cable are.

a. Plumbing is not required. Joints can be made easily. 

b. As PVC is light the injury caused to it while laying is less. 

c. It is corrosion resistant. 

d. It has high fire retarding property. 

e. It does not break down even if moisture enters. 

When three conductors are clamped together the fluxes around the conductors are get cancelled 

Impregnated paper.

Unprotected insulated wire: Unprotected insulated wire is which the insulation of the wire is not covered by a protective sheathing to prevent it from mechanical damage. 

Cap = galvanised cast iron 

Pin = forged steel pin 

Insulator = porcelain.  

The maximum electrical potential gradient that a material can withstand without rupture usually specified in volts/millimetre of thickness. This also has known as electric strength. 

Argon-41, Tritium, fission products, noble gases & Iodine particulates. 

Conductor: A material of low resistance used to transmit electrical energy. Examle wires, cables, bus bars etc. 

Saline atmosphere will deposit on the insulators causing its flashover. The building kept under positive pressure compared with outside thus preventing the (saline) air entering from outside to inside the building.  

DC shunt motor: shunt motor speed varies slightly from no load to full load. 

DC series motor: series motor speed varies greatly as load changes. 

DC compound motor: the compound motor contains both a shunt field and a series field and therefore has characteristics between the shunt and the series motors. This motor has the good starting torque characteristics provided by the series field, while the shunt field provides for a relatively constant speed. 

The high voltage that will appear across the contact just after the quenching of the arc is called restriking voltage.

Self-excited generator: In a self-excited generator the field winding is excited by an external DC source like a battery etc.

Separately excited generator: In a separately excited generator the field poles have some residual magnetism. When the armature is rotated a small emf is induced in it. This is fed to the field winding and if the current direction is such that it adds the residual magnetic flux to the field winding and the field strength is increased. The more emf in the armature, which is again fed to the field winding and goes on till the generator builds up voltage. 

Speed of a DC motor is inversely proportional to the field flux.

In star connection line current is equal to the phase current and line voltage is √3 times that of phase voltage. 

In delta connection line voltage is equal to the phase voltage and line current is √3 times that of phase current. 

The number of cycles per second is called the frequency. 

ABCB – Air blast circuit breaker. 

ACB – Air circuit breaker. 

Bus coupler CT's- live tank design 2000-1000A/1A 

All other CT's- dead tank design 800-600-400A/1A - lines and GT. 125A/1A – SUT 

This assembly is provided to have uniform voltage gradient. 

Instantaneous overcurrent protection 

Bus bar differential protection 

Local breaker back up protection 

Due to lightning and switching surges, high voltages are induced in the lines. If equipment. Connected is subjected to this high voltage the insulation will fail. In order to avoid the failure of insulation, the LA is used. When the la is subjected to high voltage it will conduct and discharge the current to the earth. 

(It will divert the overvoltages to earth and protect the substation) 

Carrier communication signals are sent through the lines. These are high frequency signals. This signal should be prevented from entering the switchyard. The wave trap is LC ckt, which is tuned for 50 Hz. Since it is connected in series with the line it will effectively block the carrier signal entering into the switchyard.

The salt contamination in the switchyard is avoided by providing indoor switchyard in MAPS. Because the plant is just 300 metres away from the seashore and the atmosphere is saline. This salt will get deposited on the insulators and on the conductors used in the switchyard. Due to this deposition insulators may fail to unnecessary trip the system and conductor used must be copper for better performance instead of low cost aluminum. So to avoid unnecessary trip and to have low cost of installation and spare parts of aluminium indoor switchyard is used.

Used as coupling capacitors for PLCC. 

Directional earth fault protection 

Directional overcurrent protection 

Local breaker back up protection 

Pole discrepancy 

Main protection (distance protection) 

An electric motor converts electrical energy in to mechanical energy. 

When a conductor cuts the magnetic lines of forces, an Electro motive force (emf) is generated. 

The magnitude of the generated voltage is directly proportional to the rate of change at which a conductor cuts the magnetic lines of force. 

Primary cell: The electrolyte in primary cell is chemically irreversible. That is once the cell is discharged it cannot be recharged. It should be replaced with a new cell. The cells can supply only low currents and have low efficiency. They supply intermittent current. Their internal resistance is more. These cells are comparatively cheap. 

Secondary cell: These cells are chemically reversible. They can be discharged and charged. They can supply large currents because their internal resistance is less. These have high efficiency compare to primary cells. These can supply constant current. These are comparatively costly.  

Physical properties 

1. Colourless 

2. Odourless 

3. Non-toxic. Pure SF6 gas is not harmful to health. 

4. Non-inflammable.

5. Density- more gas density, 5 times that of air at 20°C and at atmospheric pressure. The gas starts liquefying at certain low temperature. The temperature of liquefaction depends on pressure. At 15 kg f / cm² the gas starts liquefying at 10°C. Hence this gas is not suitable for high pressures >15 kg f / cm² 

6. The heat transferability of SF6 gas is 2 to 2.5 times that of air at same pressure. Hence for equal conductor size, the current carrying capacity is relatively more.

Chemical properties.

1. Stable up to 500°C. 

2. Inert gas due to the chemical inertness. The life of the metallic parts, contacts is longer in SF6 gas. The components do not get oxidised or deteriorated. Hence the maintenance requirement is reduced. However, moisture is very harmful to the properties of the gas. In the presence of the moisture, hydrogen fluoride is formed during arcing which can attract the metallic and insulating parts in the circuit breaker.

3. Electronegative gas – Ability of an atom to attract means carrying a negative electric charge.

These advantages offer increased safety, reduction in size, weight, noiseless operation, easy installation, handling and maintenance. 

Freewheeling diode is used to protect the semiconductor components used in the charger from the back emf, which is induced in the inductive coils of relays when the supply to the relays is cut off. The magnetic field in the relays collapses and induces high voltage in reverse direction. This emf is shunted by the freewheeling diode, which is connected in reverse bios with the output. 

DC filter is used to smoothen the output, which has ripple. Ripple frequency is same as system frequency for half wave rectifier and 2 times of system frequency for full wave rectifier. The filter, which is a capacitor, will oppose any change in voltage. Thus the ripple will not be allowed to come to zero. 

220 kV, SF6 breaker, single pole, puffer type. 

Pole column filled with SF6 

Pneumatic drive system with compressed air circuit 

Control cubicle unit 

This used for drive for opening and closing of the contacts. 

(Arc quenching is taken care by SF6 gas) 

To discharge the trapped electrical charges to ground to give complete isolation. 

(To discharge the residual potential)

Electric generators are called a dynamo that converts mechanical energy into electrical energy. A dynamo consists of two basic parts- the stationary part and the rotating part.

It is an instrument to measure the current flowing in a circuit. It is always connected in series with the load.  

7 kg/cm² - normal pressure 

5.2 bar - alarm 

5.0 bar - closing/tripping operation blocked.

The indications of a fully charged cell are.

a. The colour of the + ve plates will be dark brown. This can be seen only if the battery has transparent cover. 

b. Voltage per cell will be a 2.15 volts. 

c. Gassing in the will electrolyte will indicate. But the current is splitting up water to H₂ and O₂. Because the positive and negative plates are fully converted to their original constituents.