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Useful Electrical Questions and Answers Part – 4

Insulation Resistance Measurement

1)    What value AC meters show, is it the RMS or peak voltage?

2)    Why in the transmission tower construction Middle arm is longer than the upper and lower Arm.

3)    What is the difference between Surge Arrester & Lightning Arrestor

4)    How Corona Discharge Effect Occur in Transmission Line?

5)    Methods to reduce Corona Discharge Effect:

6)    How to test insulators?

7)    How to identify the starting and ending leads of winding in a motor which is having 6 leads in the      terminal box

8)    How to measure Transformer Impedance?

9)    Why Bus Couplers are normally 4-Pole. Or When Neutral Isolation is required?

10) Why Three No’s of Current transformer in 3 phase Star point is grounded.

11) What is tertiary winding of Transformer?

12) Why do transformers hum?

13) How can we reduce airborne noise?

14) What is polarity, when associated with a transformer?

15) What is exciting current?

16) Can a three phase transformer be loaded as a single phase transformer?

17) What are taps and when are they used?

18) What is the difference between “Insulating,” “Isolating,”and“Shielded Winding” transformers?

19) Can transformers be operated at voltages other than nameplate voltages?

20) Can a Single Phase Transformer be used on a Three Phase source?

21) Can Transformers develop Three Phase power from a Single Phase source?

22) Can Single Phase Transformers be used for Three Phase applications?

23) Difference between Restricted Earth Fault & Unrestricted Earth Fault protections?

24) Can transformers be operated at voltages other than nameplate voltages?

25) How many types of cooling system it transformers?

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

27) There are a Transformer and an induction machine. Those two have the same supply. For which device the load current will be maximum?

28) Where the lighting arrestor should be placed in distribution lines?

29) Why Delta Star Transformers are used for Lighting Loads?

30) NGR grounded system vs. solidly grounded system

31) Why Do not We Break Neutral in AC Circuits?

32) What is Minimum Value of Insulation Resistance / Polarization Index?

Minimum Insulation Resistance TEST SPECIMEN
R1 min = kV+1 R1 min = 100 For most windings made before about 1970, all field windings, and others not described below For most dc armature and ac windings built after about 1970 (form wound coils)
R1 min = 5 For most machines with random -wound stator coils and form-wound coils rated below 1kV

33) What is service factor?

34) Calculate the size the CT on the neutral point of the secondary side of 11/0.415 kV Transformer

35) When should we use Molded Case Circuit Breakers and Mini Circuit Breakers?

Useful Electrical Questions and Answers Part – 3

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