1. Natural oil cooling method have some limitations due to which it is adopted for transformers up to a rating of ____________
a) 3000 kVA
b) 1000 kVA
c) 500 kVA
d) 250 kVA
Explanation: For the transformers n higher kVA ratings can be used with this cooling method. While transformers having capacity beyond 5 MVA, due to some improper limitations forced cooling is used. Natural cooling is based on the important phenomenon seen in fluids that when oil is heated up, moves in upward direction.
2. What is the function of spacers?
a) To insulate the coils from each other
b) To provide free passage to the cooling oil
c) To insulate coils and provide free passage
d) Cannot be determined
Explanation: The winding layers of transformer are separated by spacers. One or more spacers are provided here, along with at least one integrated electrical discharge barrier extending off the central body of the spacer in the vicinity of the area where the spacer is in contact with a winding.
3. Which of the following is the most important quality required for chemical in breather, so that it can be used perfectly in an electrical transformer?
a) Ionizing air
b) Absorbing moisture
c) Cleansing the transformer oil
d) Cooling the transformer oil
Explanation: Most of the power generation plants use silica gel breathers fitted to the conservator of oil filled transformers. The purpose of silica gel breathers is to absorb the moisture in the air sucked in by the transformer during the breathing process
4. Which chemical is used in breather?
a) Asbestos fibre
b) Silica sand
c) Sodium chloride
d) Silica gel
Explanation: In order to absorb moisture from air while breathing process, breather chemical is used. So, breather chemical should possess the required ability of absorbing moisture. In all chemicals available as on today, silica gel is most perfect and best material that can be used for such process.
5. A transformer oil used in an electrical transformer must be free from ________
a) Gases
b) Odour
c) Sludge
d) Moisture
Explanation:Transformer oil serves the purpose of cooling and it also acts as an insulator between primary and secondary winding, thus it must be free from moisture else it will conduct electric current through it, leading to failure of a transformer.
6. On which of the following transformer, Buchholz’s relay can be fixed on?
a) Auto-transformers
b) Air-cooled transformers
c) Welding transformers
d) Oil cooled transformers
Explanation: Buchholz relay is used in transformers for protection against all kinds of faults. Buchholz relay is a famous and mostly used gas-actuated relay, which is installed to serve its best in oil-immersed transformers. It gives an alarm, via its electrical circuitry, if any fault occurs in the transformer.
7. Gas is liberated due to temperature limit and due to dissociation of transformer oil after ___________
a) 50°C
b) 80°C
c) 100°C
d) 150°C
Explanation: Gas is usually not liberated due to dissociation of transformer oil. But when the oil temperature exceeds 1500, it dissociates and liberates. It is found that hydrogen H2 and methane CH4 are produced in large quantity if internal temperature of transformer rises up to 150oC to 300oC due to abnormal thermal stresses.
8. Buchholz’s relay will give warning and protection against ___________
a) Electrical fault inside the transformer itself
b) Electrical fault outside the transformer in outgoing feeder
c) For both outside and inside faults
d) Cannot be determined
Explanation: Buchholz relay is used in transformers for protection against all kinds of faults which are tend to happen inside a transformer. It is most famous gas-actuated relay which is installed in an oil-immersed transformer
9. Which of the following listed component will see and perform according to changes in volume of transformer cooling oil due to variation of atmospheric temperature during day and night?
a) Conservator
b) Breather
c) Bushings
d) Buchholz relay
Explanation: Conservator is an additional tank provided with transformer which stores oil when it gets expanded due to temperature rise. It also serves another important purpose that is, as a reservoir of transformer oil. Thus, at all temperature variations of day and night transformer can work without any problem
10. What should be ideal volatility and ideal viscosity of the transformer oil?
a) Low, low
b) High, high
c) Low, high
d) High, low
Explanation: Transformer oil has a low viscosity, high flash point, high dielectric strength, high resistivity. It has a low pour point and low volatility with good gas absorbing properties, while It resists oxidation, sludging and emulsification with water.