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Dynamic motor test is improving equipment reliability for EDF energy

Opened in 1983, Hartlepool power station in County Durham is one of seven UK nuclear power stations built using two Advanced Gas Cooled Reactors (AGR). Owned and run today by EDF Energy, the 1,185MW plant is scheduled to continue operating until 2024.

Hartlepool currently provides around 2% of the UK’s peak power demand, so its safe, reliable ongoing operation is critical not just to the bottom line of its owner, but also to the stability of the country’s energy supply. The plant’s staff are always looking for ways to improve its operations, with a focus on three key performance indicators around safety, output and maintaining availability until the end of its planned operating life.

One recent innovation in that continuous improvement effort has been the introduction of a new approach that allows EDF to assess the operating condition of essential, but inaccessible equipment. That approach relies on dynamic motor analysis technology from SKF. The company initially developed its new condition monitoring technique to improve the reliability of a specific piece of equipment in the plant’s refuelling system. A single fuelling machine is used to refuel and exchange control rods on both reactors as well as transfer the items between various maintenance facilities.

In the AGR, fuel assemblies, comprising fuel and a carrier plug unit, are transported by the fuelling machine and raised/lowered at the reactor. Spent fuel assemblies are removed from the reactor by the same machine and transported through a series of cooling and disassembly operations.

A key part of the fuelling machine operation is a special plug that seals the reactor when the spent fuel is removed, protecting operators and the environment from radiation, that plug is moved by a 4m long lead screw assembly. When the lead screw eventually wears out, replacement is a costly and time consuming operation, requiring two six-person maintenance teams working on a 24-hour rotation for 14 days.

Regular maintenance and lubrication extends the life of the lead screw, but since even that requires eight hours of effort with the machine shut down, the power station’s engineers wanted a way to optimise maintenance intervals, balancing overall availability with service life. Conventional condition monitoring equipment could not be installed on the lead screw, due to its inaccessible position behind the plant’s radiation shielding.

The drive motor that operates the lead screw is accessible during machine operation, however, so the team looked for a way to use the performance and behaviour of the motor to infer information about the condition of the mechanism. Their answer came from the SKF Dynamic Motor Analyzer EXP4000. The EXP4000 is normally used to assess the condition of electric motors by analysing the motor and current while in operation, but the system can also estimate the torque delivered by a motor from voltage, current and speed data.

For their application, the Hartlepool team permanently installed an SKF Dynamic Motor Link EP1000 within the motor control cabinet. This module allows for the quick and safe connection of the EP4000 to measure the voltage and current signals via a low voltage plug mounted on the control panel door.

The team established a baseline torque profile by measuring the performance of a recently overhauled lead screw while the machine was in operation. Those measurements are repeated periodically and compared with the baseline figures to identify any significant increase in torque that might indicate a need to lubricate the screw. With that early warning, the plant’s operations team can schedule the appropriate maintenance at a time that fits in with the overall fuelling programme.

“Since the installation of the SKF equipment, the condition based maintenance approach has helped us operate the fuelling machine with considerably improved reliability,” says Grant Milwain, fuel route system engineer at EDF Hartlepool. “That means less downtime and unplanned maintenance and ensures we achieve our planned refuelling schedules.”

The success of the project has encouraged Hartlepool’s sister station, Heysham 1 in Lancashire, to adopt the same approach on its own fuelling machine. At Hartlepool, meanwhile, engineers are extending dynamic motor condition monitoring using the SKF EP4000 to a variety of other equipment, including boiler feed and cooling water pumps.

SKF (UK) Ltd