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General Information
TGA-0702-1 Turbine Generator Alarm System

The TGA-0702-1 Alarm System (Hereafter referred to as simply Alarm System) is based on the General Electric FANUC 90-30 series Programmable Logic Controller (PLC).  The PLC monitors all field inputs and initiates an alarm if any Turbine Generator parameter is out of range.

All program memory is stored in a non-volatile EEPROM (Electrically Erasable Programmable Read Only Memory). Whenever the system is rebooted (power is cycled off/on) the program will be reinitialized from the EEPROM.  While the system is in operation the program resides in RAM (Random Access Memory).  The PLC includes the following components:

1. A five slot back plane
2. A power supply which supplies the backplane with power, and also provides 24 VDC to operate the field inputs and the alarm window LED’s
3. An optically isolated 32 point digital input  module which monitors all the field inputs
4. A 32 point digital output module which illuminates the alarm windows, and also triggers a interface relay upon any alarm condition to sound the horn at the engineers alarm console.
   

The PLC input and output modules have individual LED’s to display the status of each input or output function.

The Alarm System utilizes a 27 segmented window LED-illuminated alarm panel to show the status of the various alarms.    (Three spare inputs are preprogrammed to alarm windows W11, W13, and W14, and are available for future use).
Two panel mounted pushbuttons are the only controls needed to operate the Alarm System.  The TEST pushbutton will light every annunciator window.  The ACKNOWLEDGE pushbutton will change the alarm indicator status from blinking to steady and unlatch any existing alarm, allowing it to clear itself automatically once the fault has cleared.

The Alarm System utilizes a "first-out" monitoring system which indicates the first alarm to occur, should multiple alarms exist before the ACKNOWLEDGE pushbutton is pressed. Whenever more than one alarm indicator is flashing, the first alarm to occur will flash at a faster rate than all others.  Another valuable feature is that each wiring connection to every Turbine Generator device is fully isolated and protected against inadvertent short circuits and ground faults.  Finally, all indicators are LEDs (Light Emitting Diodes), which have a virtually unlimited life span, and are immune to shock and vibration, which can shorten the life of common incandescent bulbs.

All alarm inputs include time delays to eliminate nuisance alarms, allow for the rolling of the ship, etc.  The length of each delay can be changed by changing the value in the PLC program.  The default time delay is set at 0.1 seconds.  Typically only level inputs will have increased time delays to prevent nuisance alarms from the rolling motion of the vessel at sea.

The three spare windows are associated with spare PLC alarm inputs which are connected to the terminal strip located in the control enclosure.  These are pre-configured as normally-closed, open to alarm inputs.  Each input is equipped with a jumper wire to keep it disabled until such time as it may be used.

Ten Love Controls digital RTD displays with adjustable alarm setpoints are utilized for monitoring the generator bearings and lube oil system temperatures.  Each alarm setpoint may be adjusted individually, and have been preset at a value which is approximately 20 deg. F above the original sea trials test data.

Two Yokogawa model UT320 single loop process controllers are incorporated into the alarm panel to control the lube oil temperature via the lube oil cooler bypass valve, and the cooling water flow to the generator air cooler.  Low temperature alarms for these processes are triggered by these controllers.