Question

Q1. The major cause of voltage sag is
A. Malfunction of primary component
B. Equipment Failure
C. Starting of large Induction Machine
D All the above
Q2. What should be the value of sag for proper operation of overhead transmission line?
A. High
B. Low
C Neither too low nor too high
D. Anything
Q3. The harmonic current distortion in adjustable speed drive is __________.
A. Constant
B. Not Constant
C High
D. Low
Q4. Reducing the number of short-circuit faults in a system, reduces
A. Sag
B. Interruptions
C Sag & Interruptions
D. None of the above
Q5. During normal operation, the UPS takes its power from the supply, rectifies the ac voltage to dc and inverts it again to ac with the
A. Same frequency and rms value
B. Different frequency and rms value
C Same frequency and different rms value
D. Different frequency and same rms value

Answer 1

1. answer option D all the above

The main cause of voltage sag is

Malfunction of primary component : Due to insufficiently tightenend box screws on power conductors. it leads to increase the system impedance and exaggegerates the cuffct f current increases

Equipment failure: Fault will be quickly removed by fuse or circuit breaker they will drag the voltage down until the protective device operates which can take anywhere from few cycles to few seconds

Starting of large induction machine: Due to starting large induction machine it draws about 150 to 500% of their operating current

These are the main reasons for voltage sag  

2. answer option C Neither too low nor too high

if the sag is too high more conductor material is required and resulting more weight on the supports.

if the sag is too low there is more tension in the conductor and it is liable to break if any additional stress due to vibrations and change in temperature occurs

So the value will neither too low nor high

3. Answer option B Not constant

Total Harmonic Dstortion decreases as the current increases

As the load increases amount of  Total Harmonic Dstortion decreases relative to the fundamental component but Total Harmonic Dstortion increases relative to the maximum demand of the load

4. Answer option C Sag and interruptions

When a fault is on the transmission system all loads are exposed to voltage sag during the fault as soon as fault is cleared all loads except the one connected to the faulted circuit will have their voltage go back to the normal. at the same time during the reclosing intervals the loads connected to the fault line will experience a voltage interruptions As the numner f faults reduces it reduces sag and interruption s

5.Answer option A same frequency and rms value

During normal operation same voltage and frequency will appears in the output also provided there is no drop in the mains may be small allowable drop of 1Hz and .5% of voltage otherwise almost same