CASE-1:FAULT ANALYSIS ON SWITCHED MODE POWER SUPPLY.

Fault : National Network Operating Centre (NNOC) Panel officer

called me and told one of site was Out Of Service for 40 minutes, before 30 minutes at 14:30 hrs, now site is radiating normal and no alarm appeared in Craft shell Network Management System or Clarity Network Management System.

I started towards site and at half way NNOC Panel officer called me and told site was once again Out Of Service for 37 minutes, before 10 minutes, at 16:27 hrs, now site is radiating normal and no alarm appeared in Craft shell Network Management System or Clarity Network Management System.

Fault analysis :I reached the site at 18:00 hrs, checked the Lucent Modcell 4.0 CDMA system, Nortel transport system, Optical Fiber system, SMPS, Battery, Precision Air Conditioner and Diesel Generator found all are working normal and load was on State electricity Board supply.

While I was carrying out checks the State electricity Board supply was interrupted, before Diesel Generator fed power, the site was isolated. I was in front of SMPS and noticed 30 sec (approximately) there was no indication on Main Control Unit of SMPS Controller. Now I am sure the Fault area was either SMPS or Battery Bank.

I requested from Maintenance Engineer Mr K. Sampath and NNOC for checking of the SMPS and Battery. I was permitted to carry out my checks at the Maintenance window at 00:00 hrs to 06:00 hrs.

At 00:00 hrs the Site was put down by removing the power to Lucent Modcell 4.0 CDMA system, Nortel transport system.

I removed the Alternating Current to SMPS. The SMPS did not provide any out put.

I Checked the MCU, which is responsible for giving power to Low Voltage Disconnect Contractor at the given terminals 50.2 V DC was available.

I checked the voltage at the input and output end of DC Contractor’s and found no out put at out put end but DC contractor’s Coil is being fed 50.2 V DC by MCU.

I removed the DC Contractor from SMPS and Dismantled. I checked the resistance of coil found infinity.

I replaced the DC Contractor Coil with New coil and fitted on SMPS.

Checked the SMPS as per procedure and its functions are normal.

Conclusion :The site was Out of Service Thrice Due to the Failure of

SMPS DC Contractor’s Coil was open.

The Single line power supply diagram of Base Transreceiver Station

415 V 3Φ50 HZ SEB Incomer

DG Auto Mains Failure

Change OverSwitch

Lighting Circuits

Alternating Current Distribution Box

PAC SMPS

DC 48 V OUTPUT

Fire AlarmSystem

Security AutomationSystem

Nortel TN-1C

Modcell4.0

48V DC to 12 V DC-DC Converter

Battery Bank48 V 280 AH

CASE-2:FAULT ANALYSIS ON SWITCHED MODE POWER SUPPLY.

Fault : National Network Operating Centre (NNOC) Panel officer

called me and told one of site was Out Of Service for 40 minutes, before 30 minutes at 10:30 hrs, now site is radiating normal and no alarm appeared in Craft shell Network Management System or Clarity Network Management System.

I started towards site and at half way NNOC Panel officer called me and told site was once again Out Of Service for 37 minutes, before 10 minutes, at 11:57 hrs, now site is radiating normal and no alarm appeared in Craft shell Network Management System or Clarity Network Management System.

Fault analysis :I reached the site at 17:00 hrs, checked the Lucent Modcell

4.0 CDMA system, Nortel transport system, Optical Fiber system, SMPS, Battery, Precision Air Conditioner and Diesel Generator found all are working normal and load was on State electricity Board supply.

While I was carrying out checks the State electricity Board supply was interrupted, before Diesel Generator fed power, the site was isolated. I was in front of SMPS and noticed 30 sec (approximately) there was no indication on Main Control Unit of SMPS Controller. Now I am sure the Fault area was either SMPS or Battery Bank.

I requested Maintenance Engineer Mr K Sampath and NNOC for checking of the SMPS and Battery but they permitted to carry out my checks at the Maintenance window at 00:00 hrs to 06:00 hrs.

At 00:00 hrs the Site was put down by removing the power to Lucent Modcell 4.0 CDMA system, Nortel transport system.

I removed the Alternating Current to SMPS. The SMPS did not provide any out put.

I Checked the MCU, which is responsible for giving power to Battery Contractor terminals 50.2 V DC was available.

I checked the voltage at the input and output end of DC Contractor’s and found no out put at out put end and also no input power to DC contractor’s Coil and MCU is Blank.

During Load transfer from SMPS to Battery, Battery Bank Voltage Dropped to 2.4 V.

I checked the Individual Cell voltage and found one cell voltage was 0.8 V, when the load was applied to Battery Bank this cell did not provide any current hence the Bank Voltage dropped to 2.4 V.

I replaced the Battery cell with a new cell.

Checked the SMPS as per procedure and its functions are normal.

Conclusion :The site was Out of Service twice Due to the Failure of One

Weak Battery cell.