Analysis Report on the Burning of the combiner Box

1     Problem Description

In the morning of July 28, 2019, the PEEC2 NINH PHUOC 58MW project found that the 1QA7 circuit breaker of the STS-2 in the 6.2 project tripped. It was found that the output AC cable of the 2-22 AC combiner box (SN: 2102404731KDJC000385) was burnt (as below picture).

2     Problem Analysis

The fault symptoms are as follows:

1. 1. 1. 1. The output power cables Phase A and Phase C of the AC combiner box are burnt.

         2. Thescrewsof the corresponding copper bars are securely installed.

1. 1. 1. 1. The burnt external cable fastening screws are burnt due to high temperature and are severely oxidized.

         2. The AC circuit breaker in the AC combiner box is not damaged, and the AC circuit breaker is normal.
            

Based on the physical principle:

The direct cause of the burning of cables and terminals is that the contact resistance is large. If there is a current passing through, the heat is generated for a long time. As a result, the cable and terminal are burnt.

Based on the preceding symptoms, the analysis conclusion is as follows:

The contact resistance of cables and terminals is high because the cables and copper bars are notreliably connected. (The screws in the combiner box are reliably connected.)

3     Improvement suggestions

We propose the following:

O M personnel check the installation and cable connections of all AC combiner boxes, ensure that the cables are securely connected, and Perform routine inspection during subsequent O&M.