Facilities Management -Operations and MaintenanceFM/O&M/QA/RCA/XXX Root Cause Analysis Report 29.07.15

Subject: TRIP ON LV PANEL MDB-N DUE TO SMALL SIZE ACB FRAME (800-2000A)

Brief Description:

Operation reported a trip on fire pump during weekly test run this morning @ 3:20am 28/7/15. Upon start, there was a trip affecting the power supply on LV panel (MDB-N). LV panel (MDB-N) is located at the east staff car park utility building. Checks found 2500A Eaton ACB (incomer) was tripped and 2500A ACB for fire pump was also tripped, in which both ACB are located on same LV panel (MDB-N).

Analysis:

Subject Description / Details Remarks Background of LV panel

There at 3nos of ACB (Eaton make) on the LV panel, 2500 ACB (incomer) 3P, Fire pump ACB 2000A 3P and DG ACB 2500 4P. LV panel (MDB-N) is located at the east staff car park utility building. Contractor whom has installed the ACB is unknown.

Findings/Analysis Tripping of the Fire pump upon start was reported during the weekly test run carried out on 28-07-2015 at 03:20 hrs. The pump is powered thru’ LV supply from MDB-N located at east staff car park.

The tripping occurred when the motor was running on star. Found that Main Incomer ACB (Instantaneous trip) also tripped on the same fault as Fire Pump ACB (Instantaneous fault). The settings of the Main Incomer ACB and the Fire Pump ACB are same (Lds-1, ldt-2s, sds-2, sdt-0.1, Inst-2). On further checks on the Fire Pump ACB, it is found that the frame size of the chasis was smaller, with CAT#

EN203HADNSNNNWC having small contact thickness (for max. rating upto 2000A). Whereas the Fire Pump Incomer ACB is 2500A and suitable frame size for the chasis is CAT# EN324HADNSNNNWC rated (2500-3200A), having contacts more than twice in thickness.

We have observed carbon residue around the ACB and when racked out, and flashed melted copper due to the arc was found around the frame blade.

The R Y B phase jaws are observed to be melted due to the arc, which needs to be completely replaced.

Lapses/Accountability/ Ownership

PPM on the same LV panel was carried out on the 22/7/15, there was no abnormality noted generally on the panel, however the difference in size between the ACB module and frame was not noticed.

ACB was having partial and weak contact with one half of the jaw on all 3phases. The fire pump ACB frame size was of a small rating. The high starting current of the motor along with the weak contact caused single phasing which in turn resulted in enormous

high current / arc causing trip and damage to Fire Pump ACB and tripping of both ACBs (Main Incomer and Fire Pump ACB) on instantaneous fault.

The installation contractor has installed a wrong ACB frame on the LV panel.

Recommendations Communicate with the installation contractor for rechecks, and review on the installation requirement. During annual PPM, checks on the entire ACB frame shall be included for compatibility to avoid unexpected or repeated failure. OEM has recommended replacement of the existing 2500A ACB with 2000A, since the bus bar has been designed for same

2000A requirement as per the load.

Annexure - 1

QNCC FIRE PUMP MOTOR AND ACB PHOTOS

Fire pump panel.

Isolator star/delta contactor

Motor nameplate details

Fire pump vertically mounted

The melted flash copper residue

2500A incomer ACB frame CAT# EN324HADNSNNNWC 2000A FP CAT# EN203HADNSNNNWC Carbon deposit around frame body.

Affected jaws melted, due to the flash on the weak contact.

Fire pump 2000A ACB frame Cat#

ma

Main incomer 2500A ACB frame Cat#