O&M – Balance of Plant: Jasper Generating Station

Heat-trace system reliability improvements

Jasper Generating Station
South Carolina Electric and Gas Co

910-MW, gas-fired, 3 × 1 combined cycle located in Hardeeville, SC
Plant manager: Steve Palmer
Key project participants: Tim Glover, operations superintendent; Rusty Mezel, maintenance superintendent; Noah Littleton, engineer Kevin Croft, E&I supervisor

Challenge.

In the midst of severe winter weather, the generating plant was forced off line as a result of a frozen instrument sensing line. A pressure transmitter impulse line, indicating the steam-turbine condenser vacuum, froze. This resulted from the failure of a HAND-OFF-AUTO switch on the heat-trace panel not “making up” in the AUTO position after the late fall preventive maintenance checks.There were no alarms presented locally or remotely for the fault condition. Investigating the problem, it was found that the alarm circuit is only energized if the switch contacts are made in the HAND or AUTO position. Restart of the units was further complicated by two other frozen components off of the same heat-trace circuit.

Solution.

The faulty switch was replaced. All heat-trace panels were electrically reconfigured so that the local and remote alarm circuits are energized regardless of the position of the HAND-OFF-AUTO switch—as long as the panel “master disconnect” is closed-in.

The remote alarm function was enhanced by adding both the “alarm state” and the “power state” of each of the four heat-trace panels to the closed-cooling-water graphic that CROs normally display on the Ovation® HMI.Further, a digital, LCD multi-meter was installed in each panel door, allowing the auxiliary operators to read the voltage, the current being drawn, and the power used in real time when making their rounds (Fig 99). The metering also serves as a tool for troubleshooting by E&I technicians.There was a slight variation among the local heat-trace panel thermostats when operating. To address this, the local thermostats that energize the heaters when in AUTO have been replaced by outputs from the DCS, allowing the heaters to energize in harmony.

Results.

The plant has suffered no further instrumentation upsets as a result of freezing weather. Operators have enhanced confidence in the efficacy of the heat-trace system as they are able to now see that it is working.