Harmonic filter explosion from overheated bolt

What happened?

An explosion occurred in the harmonic filter, also known as an LC filter, of inverter 4 at the plant.

Damage was mostly concentrated in the front area of the filter cabinet.

No signs of electrical arcing were found on the upper alternating current (AC) busbars or on the back of the filter.

Further inspection of the capacitor filter identified a more heavily damaged section beneath one of the AC contactors.

A contactor input busbar had a hot spot at the connection bolt. Melted aluminium had fallen into the area below.

The busbar connection bolt was out of its normal position and showed signs of overheating.

Filter contactor within the inverter harmonic filter cabinet.

Why did it happen?

A possible hot spot was located at one of the filter contactor screws during visual inspection.

One of the contactor input busbars had a hot spot at the connection bolt.

The busbar connection bolt was found out of its normal position and showed signs of overheating.

Melted aluminium from the affected connection had fallen into the busbar area below.

Close-up of the overheated and damaged busbar connection bolt.

What did they learn?

The service team should proactively inspect the remaining inverters on site to identify any hot spots in the capacitor filter connections.

A fuse has been introduced to protect the contactor against a short circuit and help prevent damage to the capacitor filter assembly during an arc event.

Three microswitches should monitor the signals sent to the inverter main control printed circuit board (PCB).

A retrofit plan should be arranged and completed when the scope is confirmed and the material is available.

For projects entering commissioning, the bolts should be proactively checked and the results recorded.

Damaged busbar connection beneath the alternating current contactor.

Ask yourself or your crew

How can a similar hot spot develop in electrical connections at our site?

What inspection methods do we use to identify loose connections or hot spots before equipment is energised?

How do we know that inspection and maintenance controls for inverter filter connections are working?

What protective devices are installed to limit damage if an electrical arc or short circuit occurs?

What improvements should we make to commissioning checks, retrofit plans or maintenance records?

What happened?

An explosion occurred in the harmonic filter, also known as an LC filter, of inverter 4 at the plant.
Damage was mostly concentrated in the front area of the filter cabinet.
No signs of electrical arcing were found on the upper alternating current (AC) busbars or on the back of the filter.
Further inspection of the capacitor filter identified a more heavily damaged section beneath one of the AC contactors.
A contactor input busbar had a hot spot at the connection bolt. Melted aluminium had fallen into the area below.
The busbar connection bolt was out of its normal position and showed signs of overheating.
Why did it happen?

A possible hot spot was located at one of the filter contactor screws during visual inspection.
One of the contactor input busbars had a hot spot at the connection bolt.
The busbar connection bolt was found out of its normal position and showed signs of overheating.
Melted aluminium from the affected connection had fallen into the busbar area below.
What did they learn?

The service team should proactively inspect the remaining inverters on site to identify any hot spots in the capacitor filter connections.
A fuse has been introduced to protect the contactor against a short circuit and help prevent damage to the capacitor filter assembly during an arc event.
Three microswitches should monitor the signals sent to the inverter main control printed circuit board (PCB).
A retrofit plan should be arranged and completed when the scope is confirmed and the material is available.
For projects entering commissioning, the bolts should be proactively checked and the results recorded.
Ask yourself or your crew

How can a similar hot spot develop in electrical connections at our site?
What inspection methods do we use to identify loose connections or hot spots before equipment is energised?
How do we know that inspection and maintenance controls for inverter filter connections are working?
What protective devices are installed to limit damage if an electrical arc or short circuit occurs?
What improvements should we make to commissioning checks, retrofit plans or maintenance records?