This set of Transformers Multiple Choice Questions & Answers (MCQs) focuses on “Transformer Maintenance”.
1. In how many types transformers can be used with relay protection system?
Explanation: The relay is available in two forms: (a) for use with line current transformers with ratios matched to the load current to give zero differential current under healthy conditions; (b) with tapped interposing transformers for use with standard line current transformers of any ratio.
2. Ingress of air into the oil tank can be avoided by using ___________
b) plastic coatings
c) metal coatings
Explanation: Relay are used to protect the transformer circuitry in core-bolt insulation failure, short-circuited core laminations, bad electrical contacts, local overheating, loss of oil due to leakage, ingress of air into the oil system.
3. When tripping of the transformer from the main circuit is required?
a) Local overheating
b) Short-circuited core laminations
c) Core-bolt insulation failure
d) Puncture of bushings
Explanations: For all other options removing transformer from the circuit is not necessary as alarms and consequent actions help to remove that fault. While in following four cases transformer must be removed from the main circuitry: (a) short-circuit between phases, (b) winding earth fault, (c) winding short-circuit, (d) puncture of bushings.
4. Transformers used generally don’t belong to type “construct and forget.”
Explanation: Transformers generally have no moving parts and there is nothing to wear out, so that there is little to be maintained. Indeed, many small transformers, particularly those installed in distribution networks, once commissioned remain in service for many years with minimal attention. These are examples of the ‘fit and forget’ methodology.
5. Which of the following is the reason relating to the maintenance while operation?
a) To obtain the maximum practicable operating efficiency
b) To obtain optimum life
c) To minimise the risk of premature and unexpected failure
d) Maximum efficiency, life, minimum temperature
Explanation: The objects in maintaining any item of plant are: To obtain the maximum practicable operating efficiency, to obtain optimum life, to minimise the risk of premature and unexpected failure.
6. Stored oil should be checked continuously for _________________
a) impurities in the oil
b) oil levels
c) oil moisture content
d) oil reactions
Explanation: Bulk oil storage tanks will be fitted with a breather usually of the silica gel type. It is important that the desiccant in this should be frequently checked and maintained in a dry state. Oil stored in drums will also breathe via the bungs on the covers.
7. Dissolved gas contents are need to be observed because _____________________
a) dissolved oxygen
b) dissolved gases from outside air
c) dissolved gases from arcs occurring in the transformer
d) all dissolved gases
Explanation: The generation of gas in oil-filled equipment by disruptive discharges (sparks and arcs) and severe overheating results from the chemical reactions which occur as a result of such faults. The resultant effect of the high thermal and disruptive discharge conditions are due to the severity of the fault and the presence of other materials such as solid insulation.
8. How many places of arcing can possible?
a) 4 places
b) 5 places
c) 8 places
d) 2 places
Explanation: Arcing of winding clamping-pressure adjusting screws, arcing of a connection to a winding stress shield, burning of core plates at their edges consistent with severe circulating currents, indication of overheating of core frames and adjacent core frame insulation.
9. What is the advantage of gas-monitor?
a) Time delay
b) Alarms at presence of a particular gas
c) Less efficiency
d) Requires high power
Explanation: The disadvantage of this device is that it simply alarms at the presence of a particular gas. As should be evident from the above, it is not so much the presence of gas, or gases, which are indicative of a fault so much as a sudden change in the status quo.
10. For high reliability of transformer action, how many fundamental checks should be done?
d) Can’t tell
Explanation: User must regularly monitor three fundamental cases for good efficiency: breather systems must be adequately maintained so that water content is kept at the lowest practicable level, the transformer must be adequately cooled at all times, any overloading maintained within permitted limits and action taken on any indications of possible overheating, the transformer must not be subjected to excessive over voltages.
Sanfoundry Global Education & Learning Series – Transformers.
To practice all areas of Transformers, here is complete set of 1000+ Multiple Choice Questions and Answers.