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I am an office worker who is studying MARK VIE. I left this message when I was looking at the CUSTMOMER TRIP on the MARK VIE and I didn't know exactly what the TRIP was.
CUSTOMER TRIP is a kind of "catch-all" discrete input that allows Customers (purchasers of Mark* turbine control systems) to connect one <i><b>OR MORE</i></b> inputs to initiate a turbine trip.

For example, let's say the Customer has a natural gas compressor and they want to trip the turbine if the natural gas compressor trips. They would use a normally closed contact that opens when the gas compressor trips connected to this discrete input. The Process Alarm text message should be changed to indicate the trip is being caused by the natural gas compressor tripping, but it rarely ever is.

Worse, let's say the gas turbine exhausts into a HRSG (Heat Recovery Steam Generator). These can have several conditions which would warrant a trip of the gas turbine--low-low boiler drum level, high-high boiler drum level, loss of feedwater pressure, etc. Many times these trips are "ganged" together to the single CUSTOMER TRIP input--which means that when any one of these conditions causes a trip there is no specific indication of which one initiated the trip. And, most site personnel (I&C technicians; operators; site management) don't know all of the conditions which might result in a CUSTOMER TRIP which makes trouble-shooting this trip difficult. Very difficult.

Emergency Stop Push-buttons are occasionally connected to this CUSTOMER TRIP discrete input--incorrectly. E-Stop P/B's should be connected to the E-Stop P/B input channel(s) of the Mark, and each one should have a second contact connected to a discrete input channel to provide a Process Alarm to indicate which E-Stop P/B was actuated to trip the turbine.

Hope this helps! One last thing to know about this "trip" is that it is almost ALWAYS configured as a discrete input to a Mark* turbine control panel--even if nothing is connected to the input. In that case, a hardwire jumper is connected across the discrete input terminals to allow a START. So, even if it's present in the input list, Alarm List and Trip Display, the only way to know if it's actually used or not is to physically (visually) check the discrete input terminals to see if any external circuit(s) is(are) connected.

Isn't this fun?!?!?!
Customer trips are any trip that comes from outside of the turbine control panel. At a combined cycle plant, customer trips can (and should) include low water levels in a boiler drum or high steam temps. Typically there is a screen on the Balance of Plant (BOP) DCS that will show what the customer trips are. There should also be an alarm associated with the BOP DCS. Its not a bad idea to verify the wires from the DCS go to the turbine control panel and the DCS logic has the appropriate low drum level and steam temp set points, this will also wring out if there are other hard wired inputs used for Customer Trips...
Always very useful explanation from CSA, we can add that every trip not being initiated by GT and/or ST mark* (in combined cycle) is a customer trip.Trip could be initiated from other process (BOP), HRSG, Condenser.. other than GT/ST subsystems, in general ESD safety controller.

Best of luck
In general customer trip signal is L4CT, In the other hand we have L4CP customer permissives.

Tip: toggle just their values true--> false and false--> True respectively in case you want to offline water wash, and your boiler is not ready, so far so good.