TROUBLESHOOTING-1:

DC MOTOR SPEED

FLUCTUATION

By: D K Singhal, deveshksinghal@gmail.com

Experience 2

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.

DC Motor Speed Fluctuation 3

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.

Problem Appears 4

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.

Paper Machine Photograph 5

Problem 6

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.

Call the Supplier 7

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.

Drive 8

Problem Returns 9

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.

Real Problem 10

Real Problem 11

Real problem was “Why?”

Why this problem was appearing again and again?

Why this problem appeared mainly

in the evening or early at night.

Could ‘Astrology’ be behind this? 12

Poor Stars 13

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.

Oh Yes!. Poor Stars 14

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.

Fuel Filters Choking 15

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.

Adulteration in HSD 16

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.

Lesson Learnt 17

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.

Thank You.

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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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