Gas Turbine Spark Plugs and Flame Detectors

Spark plugs
Combustion is initiated by means of the discharge from two high-voltages, non-retractable spark plugs bolted to flanges on the combustion chambers and mounted in a primary zone cup in adjacent combustors (N° 11 and 12).

These spark plugs receive their energy from ignition transformers. At the time of firing, a spark at one or both of these plugs ignites the gases in the primary zone of the chamber; the remaining chambers are ignited by crossfire through the tubes that interconnect the reaction Zones of the remaining chambers.

Spark Plug

Flame detectors
During the starting sequence, it is essential that an indication of the presence or absence of flame be transmitted to the control system. For this reason, a flame monitoring system is used consisting of eight sensors, each pair installed on four combustion chambers (n° 4 and 5, 10 and 11 primary and secondary zone) and an electronic amplifier which is mounted in the turbine control panel.

The ultraviolet flame sensor consists of a flame sensor containing a gas filled detector. The gas within this flame sensor detector is sensitive to the presence of ultraviolet radiation which is emitted by a hydrocarbon flame. A d.c. voltage, supplied by the amplifier, is impressed across the detector terminals. If flame is present, the ionization of the gas in the detector allows conduction in the circuit which activates the electronics to give an output defining flame. Conversely, the absence of flame will generate an opposite output defining "no flame". After the establishment of flame, if voltage is reestablished to the sensors defining the loss (or lack) of flame a signal is sent to a relay panel in the turbine electronic control circuitry where

auxiliary relays in the turbine firing trip circuit, starting means circuit, etc... Shut down the turbine. The FAILURE TO FIRE or LOSS OF FLAME is also indicated on the annunciator. If a loss of flame is sensed by only one flame detector sensor, the control circuitry will cause an annunciation only of this condition. Flame detectors are water cooled.

For more information about the flame detectors, see "Gas turbine subcontractor’s literature chapter" for G.T. control and protection system).