LM 6000 Excitor not Cutting Off


Thread Starter


Dear friends,

We are facing a problem in LM 6000 GE machine. Machine is controlled by Netcon 5000 controller and excitation control is EX 2000. Earlier once machine is given off command exciter was cutting off in AUTO. But nowadays due to some anonymous reasons we need to switch off the exciter manually after giving STOP command for machine. Can any one explain whats the logic used for cutting of exciter? what are the signal going from and to related to Netcon 5000 and Ex 2000.

Dear PremSagar,

There are only two ways to communicate with an EX2000 exciter--via a coaxial cable (which may include a fiber optic link) using a communication protocol called StatusS, or via hardwired signals (discrete inputs and outputs, and possibly one or more analog (4-20 mA) signals. Since the Netcon and the HMI at your site aren't likely capable of StatusS communication, it's most likely being done using discrete and possibly some analog signals. (EX2000s can be controlled using BOTH StatusS and discrete, hardwired signals, or just by discrete hardwired signals.)

So, if you can find the drawings for the EX2000 and the Netcon you can find the wires and the signal names of the I/O between them, and then look in the programming of the Netcon for details about why it's not "automatically" doing what you think it should be doing, or did in the past.

An exciter shouldn't be "offed" until the generator breaker is open during a normal shutdown or an emergency shutdown. Sorry; I'm not familiar with the names of the modes used with GE LM control systems, but I'm referring a normal shutdown as an operator initiated, orderly reduction in load until the generator breaker automatically opens, and then an orderly reduction in turbine speeds while a "STOP" is issued to the exciter, and fuel is automatically cut off when the control system is programmed to do so, and the unit then coasts to zero speed. My definition of an emergency shutdown is some condition that results in an immediate shut-off of fuel to the turbine, which also results in an opening of the generator breaker, and a "STOP" signal being issued to the exciter.

In addition, it's very common for there to be manual switches somewhere in the plant, or even signals from a DCS or other control system (AGC; etc.) that can send signals to the exciter (usually only generator terminal voltage RAISE- or LOWER signals, but also sometimes manual start/stop or field voltage/current RAISE- or LOWER signals). Are you sure the manual/auto control switch which sets the mode for how you seem to be "stopping" the exciter is in automatic mode when the Netcon is issuing the stop/off command? It may be "blocking" the Netcon stop/off command when it's not in automatic position.

But, your question isn't really clear--and that may just be that I don't recognize the operating modes for GE LM machines and what you're trying to describe. But, I'm fairly confident the communication between the EX2000 and any other control system or control panel at your plant is being done using discrete, hardwired signals (unless there's some kind of module which can take electronic signals from the Netcon and send them over the coaxial cable using StatusS to the EX2000, and vice versa--and that's certainly possible, I've just never seen or heard of it).

Hope this helps!