I have noticed one thing in Gas turbine SOVs. few of them are dual element SOVs like 20CB1, 20FD, 20FB and rest are single element.

Why so? what is the difference? What is "Pull in coil" and "Hold in coil"?

please through some light.

 

The "Pull-in coil" moves the solenoid to its energized state. It uses a higher current coil to do this. The "Holding coil" maintains the solenoid in the energized state, with a lower current. There is an internal switch in the solenoid that transfers from the pull-in coil to the holding coil.

 

Thanks for this useful information.

Will anyone explain in more detail, how does it happen, and other kind of details.

 

Aliya,

You may be making this more complicated than it is. I would add to otised's explanation that the pull-in current is higher because of the need to open or close the valve the solenoid is operating against high pressure differentials (across the valve). Once the valve is opened or closed, the amount of current required to maintain the valve position is much less, so the switch in the solenoid reduces the current drawn by the solenoid. Sometimes, it's just by shorting out a portion of the solenoid windings.

There are only two wires providing current to the solenoid. The switching is done inside the solenoid-operated valve.

Many of these older SOVs are polarity sensitive, meaning it's important to connect the positive supply to the positive lead of the SOV, and the negative supply to the negative lead of the SOV.

Most of these SOVs, when operated by Speedtronic panels, have "slow-blow" fuses in the wiring. These fuses are rated much lower than the pull-in current value, but higher than the holding current value. The high amount of pull-in current drawn during energization occurs for a very short period of time (less than one second, usually), and the internal switch of the SOV then reduces the current to the lower holding value. The slow-blow fuses can withstand the higher pull-in current for this brief period of time, but if the internal switch fails or if the valve fails to open or close in a reasonable period of time (two or three seconds, approximately) then the fuse will protect the Speedtronic panel against the high current being supplied for an excessive period of time. The fuse primarily protects the internal Speedtronic wiring, not necessarily the SOV coil.

Many solenoids do not have to operate valves or other equipment against high pressure differentials, or in applications requiring lots of force. If they do, many solenoids use a "pilot" arrangement, using pressure or flow from the process to assist with providing the force required.

So, there are many different ways to provide the force necessary to operate a piece of equipment. GE has chosen, for a couple of applications, electric solenoids to provide the necessary force and these solenoids use a high current to provide the initial force necessary to operate the valve, and use a much lower force to maintain the valve position once activated. The SOV they chose to use employs an internal switch to provide the force required to initially operate the valve and then the force required to maintain the valve position.

Hope this helps!

 

Aliya... this time I am in full agreement with CSA! Increased Amps yields increased magnetic force.

Regards, Phil Corso

 

Thanks a lot for this information.

As you mentioned, i noticed there is a switch showing in SOV coil in elementary.

Thanks a lot.

One more thing i want to know which i don't get.
In elementary with solenoid circuits, there is a SSFG unit shown connected to both terminal of SOV.
What does it mean and what function of it is?

 

When you write about a problem, please remember that you work daily (or something like that) with the unit at your site and its configuration, but we do not. We don't know anything about the unit you work with, what kind of Speedtronic control system it has, what kind of fuel(s) it burns, what kind/size of turbine it is, whether or not the turbine drives a generator or a compressor, etc.

From the SSFG reference, it would seem the turbine has a Mark IV Speedtronic control system. If you review the first pages of the Mark IV Speedtronic elementary (before sheet 01A), you will likely find some very interesting information about the hardware in the panel, including a drawing of the SSFG function. I don't have access to a Mark IV Speedtronic Elementary at this time, but I believe that components on the card are what GE calls MOVs--Metal Oxide Varistors.

The MOVs are used to shunt the inductive kick from the DC solenoid coils so that they don't burn up the relay contacts; they conduct when the voltage exceeds a certain level. (And, no; I don't know what that level is. You could probably find it out from the nameplate information on the MOV.

That's my best estimate, without being able to examine a Mark IV Speedtronic elementary drawing. And without knowing if the turbine you are referring to has a Mark IV Speedtronic turbine control panel.

 

great....
salute to CSA