DC Motor Malfunction problem and experience gained in solving the case explained in detail.

1. TROUBLESHOOTING-1:
DC MOTOR SPEED
FLUCTUATION
By: D K Singhal, deveshksinghal@gmail.com

2. Experience
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 Many of you have heard the stories of space
writing pen and empty soap box problem.
 This is the first presentation of the series. The
objective of this series is to present different
problems faced in the mills and how these were
solved, thus sharing the experience for the benefit
of all.

3. DC Motor Speed Fluctuation
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 This is a real case of a paper mill.
 The mill was having a paper machine driven by a
big 110kW DC motor through a DC drive.
 Power supply was from one of the three 380kVA
DG sets.
 Other DG sets was supplying power for pulping,
pulp preparation, ETP, Office lighting etc.
 The plant was running smooth.

4. Problem Appears
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 One day, electrician observed hunting in DC motor
current. The current, while otherwise 220-230A,
fluctuated between 160-280A. (FLC: 270A)
 Initially, output voltage was OK, but after some time
voltage fluctuation started.
 DC Motor: Speed α voltage
 After some time, paper machine operator observed
paper becoming too tight and slack periodically.

5. Paper Machine Photograph
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6. Problem
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 Machine was stopped, DC motor was shut and
restarted again (like you do when ‘Windows’ hangs
your laptop).
 The problem vanished for some time, but restarted
after 30-40 minutes. Again.

7. Call the Supplier
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 As an immediate action, the AC drive supplier was
contacted and he suggested to adjust P4, P7, P11
pots one by one in clockwise or anticlockwise
direction.
 We did, and the problem solved by P4 itself.
 Next day, we called him just to say ‘Thanks’.
 He further suggested to try P4 in case of future
problems; if problem persists then P7, and finally
P11 in future.

8. Drive
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9. Problem Returns
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 Within a few weeks, the problem became quite
common.
 Amperage hunting, paper tension fluctuation,
adjustment of P4, P7 and/or P11, otherwise restart
the paper machine started looking normal.
 But the real problem was not the problem itself.

10. Real Problem
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11. Real Problem
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 Real problem was “Why?”
 Why this problem was appearing again and again?
 Why this problem appeared mainly
in the evening or early at night.

12. Could ‘Astrology’ be behind this?
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13. Poor Stars
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 When you are stuck with a frequent or a difficult
problem, not only the poor stars are showing their
full power, but many of your co-workers and
subordinates distract you from the root cause of the
problem. Of course, unknowingly.

14. Oh Yes!. Poor Stars
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 In fact, the mill was really in trouble financially
(poor stars!) , and was forced to buy diesel (HSD)
from a local petrol pump.
 Normally, the mill received diesel in the evening,
and after the diesel was poured in service tanks,
the problem started after half an hour or so.

15. Fuel Filters Choking
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 On further investigation, the DG operators also
indicated that the fuel filters were more choked
compared to earlier times, probably due to HSD
procured locally.
 They did not inform about the observation as per
the DG set supplier guidelines, the fuel filters need
to be replaced every 300 hours.

16. Adulteration in HSD
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 There could be several issues. Either the supplier
was giving the mill HSD of poor quality, or there
was possibility of adulteration by the tractor trolley
driver who supplied the same from petrol pump to
the mill.
 Immediately, it was decided that the mill will use
HSD procured directly from the depot, and the
problem never appeared again.

17. Lesson Learnt
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 Some electrical problems might arise from non-
electrical sources. Look all the possible causes which
may trigger the problem.
 Unfortunately, the mill had no good instruments like
CRO, power analyzer etc., otherwise this problem
might have been identified much earlier.

18. Thank You.
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19. About D K Singhal
 Born in 1968, D K Singhal is B.E., M.E. (Pulp & Paper, 1993) from Dept. of Paper
Technology, University of Roorkee (now IIT, Roorkee). He was certified as Certified
Energy Auditor in 2004 with Bureau of Energy Efficiency. He is also a Chartered
Engineer.
 With nearly 8 dozen publications, he has emphasized on development of low cost
technologies and management practices for quality and profitability improvement.
With publications on energymanagertraining.com, slideshare.net and
paperonweb.com, he has been constantly contributing to IPPTA(Indian Pulp & Paper
Technical Association). He is also serving IPPTA as a member of Editorial Board.
 An initiative by D K Singhal, a cyber campaign initiated against unjustified
targeting of paper industry by “Idea” mobile, in their “Sirjee” advertisement
campaign, after which this advertisement was taken off air.
 He also moderates a group, “PaperTechnology” (earlier with Yahoo, now at
Facebook) with more than 1800 members from India and abroad to discuss
problems related to pulp & paper making for more than 6 years.
He can be contacted at deveshksinghal@gmail.com
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