Machine Shop · Case Study

ABB Hydraulic Mechanism Refurbishment

ABB AHMA hydraulic operating mechanisms tend to develop seal leaks over time. A leaking mechanism leaves the pump motor running continuously and can drive the breaker into a lockout condition. We've refurbished this type of mechanism many times, and have found the problem is reliably corrected by a complete replacement of all seals, a new hydraulic fluid filter and fluid change, backed by a full teardown, inspection, and a 24-hour pressure test.

01, The Problem

Why the mechanism
won't hold pressure.

As the hydraulic seals degrade, the mechanism can no longer hold pressure. The pump motor runs continuously trying to keep up, and the breaker can end up in a lockout condition. We've found the issue is generally solved by replacing every seal in the mechanism, not just the one that is visibly leaking.

Hitachi Energy's HMB replaced the AHMA, and it shares the same hydraulic architecture. The HMBs that come through our shop leak down the same way the AHMAs do. We rebuild both.

Symptom
Seals leak down

Hydraulic seals degrade over time and can no longer hold pressure.

Result
Motor runs constantly

The pump motor operates continuously trying to maintain hydraulic pressure.

Risk
Potential lockout

Left unaddressed, a leaking mechanism can drive the breaker into a lockout condition.

Teardown under
60 tons.

An example 550 kV mechanism is removed by the utility or service provider, crated, and shipped to our shop. Older vintage units hold a heavy disc spring under compression, it has to be secured with a 60-ton press before the mechanism can come apart. We designed and built a custom jig that holds the disc spring compressed so the mechanism can be removed safely, then completely disassembled and inspected for wear.

An example 550 kV mechanism, crated and received at our shop after removal in the field.
Fig. 01An example 550 kV mechanism, crated and received at our shop after removal in the field.
The disc spring held compressed in our custom-built jig under a 60-ton press, required before the mechanism can be removed.
Fig. 02The disc spring held compressed in our custom-built jig under a 60-ton press, required before the mechanism can be removed.
With the disc spring secured, the mechanism is removed, completely disassembled, and every part is inspected for wear.
Fig. 03With the disc spring secured, the mechanism is removed, completely disassembled, and every part is inspected for wear.

A cracked manifold,
re-made in-house.

The hydraulic manifold is removed and inspected. On this mechanism we found a crack in the manifold bore, so we machined a new manifold in our own shop rather than wait on an OEM replacement.

The hydraulic manifold removed from the mechanism for inspection.
Fig. 04The hydraulic manifold removed from the mechanism for inspection.
A crack was discovered in the manifold bore (circled). A new manifold was fabricated by Southern Switch & Contacts.
Fig. 05A crack was discovered in the manifold bore (circled). A new manifold was fabricated by Southern Switch & Contacts.

Resealed, tested,
and proven.

Once inspection is complete, every seal is replaced with new ones, a new hydraulic fluid filter is installed, and the unit is reassembled and recharged with new hydraulic fluid. The motor is tested to confirm proper operation, and the hydraulics are held under pressure for 24 hours to verify all seals are tight before the mechanism ships back.

The resealed mechanism reassembled and on test, hydraulics held pressurized for 24 hours to confirm every seal is tight.
Fig. 06The resealed mechanism reassembled and on test, hydraulics held pressurized for 24 hours to confirm every seal is tight.

Common questions

Can an ABB AHMA or Hitachi HMB mechanism be rebuilt instead of replaced?

Yes. Southern Switch & Contacts rebuilds both the ABB AHMA and the Hitachi Energy HMB, which shares the same hydraulic architecture and leaks down the same way. A complete teardown, full seal replacement, a new fluid filter and fluid change, and a 24-hour pressure test return the mechanism to service, and a cracked manifold is machined in-house rather than sourced from the OEM.

Have a leaking ABB mechanism?

Send us your hydraulic mechanism, we'll reseal, repair, and pressure-test it, and fabricate any cracked or discontinued parts in our shop.

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