1. MEDIUM VOLTAGE VARIABLE FREQUENCYDRIVE –FAULT FINDING
AND RECTIFICATION REPORT
LOCATION : RO PLANT KHORFAKKAN
EQUIPMENT DETALIS : POWER FLEX 7000 B FRAME – ALLEN BRADELY
DRIVE DETAILS :MEDIUM VOLTAGE,AIR COOLED VARIABLE
FREQUENCY AC DRIVE
MOTOR DETAILS :6600 VOLT,2000 HP,10-50 Hz SPEED RANGE
TAG NO :P-040-001
THE TEAM MEMBERS
Team Leader : Mr.Rajendrakumar.A.P, EMD Supervisor
Assistance : Mr. Mathews, Plant operator.
Supporting Team : Mr. Poly, Shift Supervisor
: Mr. Jobin, Plant Operator
Report Prepared By:
Mr.Rajendrakumar.A.P
Electrical Supervisor
RO plant Khorfakkan

2. FAULT REPORT
The operation In Charge reported on 15.04.2015 at 03:45 hrs that plant tripped on VFD fault. There
was no abnormality or any serious issues like burn smell etc, so it was decided to take up the issue
during general shift at 07:00 hrs in the morning.
On visual inspection the following faults observed in the VFD Display unit and noted to the
maintenance register.
1. 2U1C Fbk F0 Loss
2. 2U4A Fbk F0 Loss Time: 03:41:37 hrs
FAULT SHOWN IN THE DISPLAY 1
As a preliminary step
- Fault Acknowledged
- Given Reset, Found the fault is persisting.(NOTE : No more attempts should be made to
RESET the fault)
FAULT FINIDNG: THE ORIGIN OF FAULT AND LOCATION
- Referred to the original manual and the list of faults and possible reasons

3. - It is found clear from the trouble shooting that the fault is Major.
- Obtained work permit from the operation In Charge.
- Isolated 6.6 kv
- Opened the VFD panel isolator
- Obtained the KEY (mechanical Interlock) from the isolator panel to open the MV voltage
panels.
- Discharged the 6.6 KV with the help of Earth rod..Enough time given to ensure proper
discharge of any static charge to ensure the safety of working personnel.
- Visual inspection made to ensure the physical status of all components and any possible
damages.
- Located the rectifier bridge and associated circuits ( with control supply ON)
- Checked the cable tags to find out the fiber optic cable responsible for the fault and
inspected for any physical damage and found to be in good condition.
- Further inspection revealed that SGCT (Symmetrical Gate Fired Thyristors) firing cards of
the respective ( 2U1C, 2U4A) rectifier bridge not getting the power supply. Identified the
terminals and verified the DC 20 Volt is not available.
- Followed the drawing to see the source of power supply. The power supply was from
IGDPSM(Integrated gate driver power supply module).Found that, two out of six voltage
outputs are not working.
- The failure of the power supply module seemed to be secondary. The root cause can be the
card which uses the power supply.
- Checked the healthiness of the SGCT firing cards. Found that the respective cards are faulty.
- 2 Nos SGCT firing cards and 1 no of IGDPS Module found faulty. Referred to the manual
for replacement procedure. It was advised to change all the (one arm of rectifier bridge is
consists of three series thyristors) the thyristor cards at a time.ie,2 sets of integrated thyristor
firing cards, consisiting of three cards each.
- Checked the healthiness of all thyristors in the rectifier bridge and found healthy.
CONCLUSION
- Replacement of faulty cards
- SGCT Firing Card : 2 sets of 3 cards each
 : Card No:80173-109-01
 : Make: Mitsubishi Electric Company.
- IGDPSM :1 No
 : Card No:80026-044-06
 : Make: Rockwell
The requirements and the contact person details mailed to Mr.Ajay Alias, Station Manager.
PROCUREMENT OF SPARES
- Conformed the non-availability of cards at RO khorfakkan Stores on 15.04.2015 itself.

4. - Upon enquiry throughout the day, it is learned that procuring new cards will take one month
to three months or more.
- On 16.04.2015 as per information from station manager, checked the availability of cards at
any other plants with the help of stores In charge and found that Layyah Plant is having
spare cards .Information passed to Station Manager.
- Finally at 20.00 Hrs all arrangements were organized Mr.Faizal Sarkal to collect the spare
cards from layyah.
- Along with Station manager, I went to collect the cards from layyah power plant. After
verifying the cards, gate pass prepared and took the cards to RO Khorfakkan and reached the
plant early morning 03:00 hrs on 17.04.2015.Kept the Cards at a safe place.
IGDPSM SGCT FRING CARD
FAULT RECTIFICATION WORK – 17-04-2015 AT 08:00 Hrs
- Started organising the work at 8.00 hrs in the morning. List given to supporting team for
additional tools and equipment’s to be arranged. Air Blower, Vacuum Cleaner, Electrical
Contact Cleaner, Brushes.
- Control power supply switched OFF.
- Ensured the IGDPS module is not having any power supply.
- Noted down all the connection details to the IGDPS Module in the register.
- Removed the tying clips to the connecting cables
- Disconnected from respective terminals
- Unscrewed the 4 no’s fixing bolts
- Unpacked the new IGDPS module pack.
- ALL CARDS TO BE HANDLED CAREFULLY.THE INTERNAL PORTION SHOULD NOT BE
TOUCHED.ANY STATIC CHARGE CAN DESTROY THE CARD COMPONENTS.BODY STATIC
CHARGE SHOULD BE DISCHARGED BEFORE TOUCHING THE CARD AND HOLD THE CARDS BY
ITS SIDES SUCH A WAY THAT IINSIDE PORTION IS EXCLUDED.THE USE OF GROUNDED
WRIST STRAP IS MOST RECOMENDED
- Screwed the new card to the position.

5. Work underprogress
FaultySGCT Cards removed FaultyIGDPSmodule
- Noted down connection details to the 6 SGCT firing cards. The optical fibre cables
connected to the boards should be carefully handled; its bending radius should not be less
than 50 mm.

6. - Before going ahead with fixing the new SGCT firing cards, clean the panel with air blower
and vacuum cleaner. Use of these two equipment’s should be made carefully. Also clean
the heat sinks of the removed cards properly.
- Unpack the cards carefully and keep the Electrical joint compound safely. See the
instruction manual included. Follow the procedure as per the instruction manual for
removal and fixing the cards.
-

8. - Check healthiness of all thyristors of the new cards.
- Re-connect the input power connection to the IGDPS module.
- Take care not to connect the output power cables to Double ensure the proper tightness of
the clamp by checking the indicating washer turning resistance.
- Upon completion of fixing the thyristors, Re connect all optical fibre cables and power
cables as per noted down earlier to the IGDPS module.
- Ensure the panel is ready by all means, no tools or clothes should not be their inside the
panel.
- Switch On the Control power Supply
- Check the output voltages of the IGDPS module.
- After ensuring the correct output voltage reconnect the cables to the output terminals as
per noted down in the register.
- Checked the LED s indications in the SGCT cards, found correct.
- RESET fault in the display/controller Unit. Fault got RESET.
- Cleaned the rest of the panels and all filters.
- Closed all the panels, following the mechanical interlocks.
- Closed the VFD isolator
- Charged the 6.6 KV breaker
- Found the VFD Ready Indication.
- Given clearance to start the plant at 16.00 Hrs.
- During the starting of the motor one person was kept at the motor end to observe
abnormality if any. One person was at 6.6 KV breaker and two persons at VFD. At 17:00 Hrs
VFD started and found Start up and all parameters normal.

9. - Kept the VFD under observation for 8 hours.
- Found all parameters normal for rest of the operation and successfully concluded.
Special Thanks for Moral Support over phone
: Mr.Ajay Alias, Stn.Manager RO Khorfakkan
Special Thanks to all my TEAM Members.
-THANKS-

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