ISO 9001:2015 OHSAS 18001:2007 Certified Company
Case Study - Are you sure your Generators/Motors are safe?
www.systemprotection.in
+91-265-2225137
Background
It was just another day and anoth-
We immediately dispatched 2 of
er morning of January 2019, on w
our engineers along with the test
hich we received a call from a new
sets required, by the first flight
Customer in Metal Sector, from
available and were soon on the
Chhattisgarh. And urgently, they
job. In less than a day, we were
wanted us to test and commission
up and working.
an old 10 MW, 11 kV Generator along with its relaying, schemes
Findings‐ at Site
and complete testing. ‐ The initial forensics were found On enquiring about such urgency, we learnt that their original Generator rated 12 MW, 11kV got burnt (stator) and was sent for repairing, this 10 MW was taken on rental basis and a temporary solution. As we all know that in our industry, Generator failure is nothing less than an air‐crash and this criticality warranted extensive
from the fault records of the Relay. We learnt that the Relay (and GCB eventually) was tripped on NPS protection, which is normally a time delayed protection. It was a surprise, because normally when such fault occurs (stator failure), other protections take care, NPS is something like last line of defense.
and methodical analysis like an air‐crash investigation.
‐ So, such a surprising observation just at the start of the
Hearing this, the day went into a
job prompted us to be extra
tizzy and we immediately started
vigilant. This protection system.
preparing a checklist (we’ll see it later in a diagram) to find out the Root Cause. And unless we find the Root Cause and solve it, this rented Generator was in danger and the upcoming repaired Generator too!
www.systemprotection.in
+91-265-2225137
‐ And then came the moment of
‐ Following actual images clearly
reckoning, and you know from
show the fault. So, 90 % Stator
where? NCT wiring was the
Earth Fault Protection (51S) did
culprit for the Generator burn‐out!
not operate due to non‐wiring of
Least expected fault for a
NCT secondary S2 to Relay.
Protection Engineer so to speak (It
Generator kept running on this
was found while carrying out
serious a fault which finally led
Stator Earth Fault scheme
to heating and eventually, NPS
checking).
operation operated on time delay. But by the time NPS operated, the damage was already done.
www.systemprotection.in
+91-265-2225137
‐ NCT, which is used for Stator
‐ Reverse Power and Forward
E/F Protection, was wired up to
Power Protections were set but
TB in CRP correctly. But from TB
with wrong logic. Logic was so
to Relay, wire S2 was missing/not
wrongly set that neither Alarm
connected on Relay. So even in
could be generated nor Tripping!
case of Stator E/F, Relay wouldn’t
With the set logic, these
have sensed nor operated nor
protections were rendered
tripped the relevant breakers. This
useless. Corrected by changing
fault was simply corrected by
the logic.
connecting a 2.5 sq. mm wire. ‐ Similarly, this wrong logic error ‐ Differential Protection setting
was observed in Under Voltage,
was found high, besides, the
Under Frequency and Over
reference for the settings was not
Frequency Protections. All these
available, we recommended to
were set alright, but the set logic
furnish us the OEM data,
didn’t let these protections
compiled during commissioning
generate any Alarm or Tripping
and to carry out the fresh Studies
signals, imagine! Corrected by
on Relay Co‐ ordination, Power
changing the logic.
System and Load Flow. ‐ LBB Protection tripping was ‐ Suppose both the above
assigned to Output No. 3, but as
protections, Stator E/F and
per the OEM Manual of the
Differential, are alright and
Generator Protection Relay, this
operate and generate alarm and
Output No. 3 must be used for
trip signals faithfully. And as we
other designated functions and
all know, both these are Class A
not this. Corrected by changing
protection and must cut the very
the logic and wiring.
source of the fault. Here in this case, it’s AVR. And you know what we found? AVR could not be tripped because inter‐panel wiring was not done. Corrected and now stands rectified.
www.systemprotection.in
+91-265-2225137
� Following Diagram will help us understand this critical event better.
www.systemprotection.in
+91-265-2225137
Conclusion – How our insightful actions helped the Industry
‐ Not only our team verified that
‐ And at last, we w're happy to
the newly installed Generator of
"wow" the customer, who learnt
10 MW has all the protections
at last, the difference between
available, they verified that it
symptom‐solving‐agents and
operates, and operates correctly.
roper Doctors.
And generate a correct tripping sequence too. No burning of Generator fro now onwards,
‐ The above are in fact the major
the way a safe and reliable
problems found and corrected.
protection system should be.
Though, during our very busy 3‐ days (and nights too) at site, we also observed many minor
‐ By doing so, we also ensured
abnormalities and corrected as
complete protection of 12 MW
many as possible. Well, to know
Generator which will be put in
more, call/write to us, we’ll be
place after due repairs. Settings
happy to save your assets too!
need to be verified/corrected with rewinding data but more or less, the machine will be protected.
- And if you’re looking for a dedicated agency who understands the direct link
‐ Generator is an expensive asset
between your assets and your
itself, and the loss of production
revenue, we’ll be happy to assist
in a continuously running plant
you, anytime, anywhere.
due to failure of a Generator can run in to crores. All our efforts are viewing the problems from customers’ point and resolving them in totality. Testing, as such, is an isolated job, but when it is
Regards System Protection
done in a way which affects the end‐results (production/revenue), th And that’s what we delivered.
www.systemprotection.in
+91-265-2225137
CONTACT INFORMATION 301/2/306, Silverline Complex,Opposite BBC Tower,Sayajigunj,Vadodara - 390 005, Gujarat, India. bdm@systemprotection.in
www.systemprotection.in
+91-265-2225137