Transformers Multiple Choice Questions & Answers (MCQs) on “Transformer Installations”.
1. Transformers are generally designed for ___________
a) on-site problem solving
b) one-time use
c) off-site problem solving
d) short-time use
Answer: a
Clarification: Every transformer is designed for use of it for multiple years, thus transformers are designed to handle the problems on site itself, because it not only saves time but also makes repairing work easy.
2. When all additional clamping is removed from a transformer?
a) When transformer is made start
b) After start of transformer function
c) Instant before start of transformer function
d) At the time of installations
Answer: d
Clarification: When the tank is correctly positioned on the plinth it must then be carefully examined for any signs of damage or any other indication that it might have been mishandled during transport. Any special provisions by way of protection applied during transport must be removed. If additional clamping has been applied to the core and windings for transport, this must be released or removed according to the instruction manual.
3. While transformer is transported, its valves are _______________
a) kept open
b) closed with blanking plates
c) can be kept open or can be closed according to type
d) valves are absent
Answer: b
Clarification: Removal of blanking plates giving access to the tank. Such opening of the tank must be kept to a minimum time, to reduce the possibility of moisture entering the tank; to assist in this, manufacturers of large high-voltage transformers provide equipment to blow dry air into the tank and thus maintain a positive internal pressure.
4. If any transformer is not in operation for some months, still it is advisable to keep it filled with _______________
a) nitrogen
b) oil
c) normal air
d) hydrogen helium mixture
Answer: b
Clarification: Even if the transformer is not required for service for some months, it is desirable that it should be filled with oil as soon as possible and certainly within three months of the original date of draining the oil in the factory. If it is being kept in storage for a period longer than three months at some location other than its final position, it should similarly be filled with oil.
5. When oil filling procedure has to be started?
a) After fitting of all bushings
b) After replacing access covers
c) After erection of conservator and Buchholz pipework
d) After fitting bushings, replacing covers, erecting pipework
Answer: d
Clarification: When all bushings have been fitted, access covers replaced, and conservator and Buchholz pipework erected, any cooler bank erected and associated pipework installed or tank-mounted radiators fitted, preparations can begin for filling with oil.
6. Materials used in construction of transformer are stressed ______________
a) electrically
b) mechanically
c) both electrically and mechanically
d) magnetically
Answer: c
Clarification: The materials used in their construction are highly stressed both electrically and mechanically, and to achieve satisfactory operation extensive precautions are taken in manufacture, particularly in respect of insulation quality.
7. After site erection vacuum is made with pressure range of ___________
a) 1 mbar
b) 3 mbar
c) 7 mbar
d) 15 mbar
Answer: c
Clarification: After completion of site erection, a vacuum pump is applied to the tank and the air exhausted until a vacuum equivalent to between 5 and 10 mbar can be maintained. If this work is carried out by the transformer manufacturer, or his appointed subcontractor, there will be no doubt as to the ability of the tank to withstand the applied vacuum.
8. For 400 kV transformer, moisture content required is _______________
a) below 0.1%
b) below 0.5%
c) above 0.5%
d) below 1%
Answer: b
Clarification: When a new 400 kV transformer is processed in the factory, the aim is to obtain a moisture content in the cellulose insulation of less than 0.5%. When an oiled cellulose insulation is exposed to atmosphere, the rate of absorption of moisture depends on the relative humidity of the atmosphere.
9. Which readings should be taken while drying out process of transformer?
a) Insulation reading between HV and LV
b) Temperature
c) Time
d) Insulation, temperature, time all readings
Answer: d
Clarification: During the drying-out process the following readings should be taken at frequent regular intervals: Insulation resistance between high-voltage and low-voltage windings and between each winding and earth, temperature and time.
10. Short circuit method is used for _____________
a) drying out the transformer and oil simultaneously in the transformer tank
b) drying the transformer only, out of its tank.
c) for any type of drying
d) never used
Answer: c
Clarification: Short-circuit method is also used for: Drying out the transformer and oil simultaneously in the transformer tank, drying the transformer only, out of its tank. During the process, the low-voltage winding is short-circuited, a low single-phase or three-phase voltage being applied to the high-voltage windings.