in ge mark5 control system, what are these relays: 4-1, 4-2, 4-3 and 4-4, which are connected in series with the external trip inputs in PTBA Terminal Board of P-Processor. Are these physical relays? Where are they located? In TCTG card?

One more thing, is 4-1 for R-Processor and 4- for S and like this?

Also, when the logic signal L4 becomes true for any processor when we execute start command, for starting the gas turbine, is it that its corresponding 4-1 relay gets energised?

When these relays are energised then only 24 V DC supply will be extended to the PTRS and ETRS.

Please, can anyone help me to find out the answer of these questions? It will be a great help for me.

 

The 4-1, 4-2, 4-3, and 4-4 relays you are asking about are located on the TCTG card of a heavy-duty gas turbine Mark V control panel, a TCTS card of a medium steam turbine Mark V control panel, or a TCTL card of a large steam turbine Mark V control panel (or TCTG/S/L, in App. Maual Appendix-ese).

4-1, 4-2, 4-3, and 4-4 are physical relays (usually small, plastic, yellow rectangular relays), with 125 VDC coils. When the hard-wired trip circuit connected to the PTBA card is closed (closed to run, open to trip), the four relay coils are energized, which passes 24 Volts to the P24VR-4 "bus", which is required for the Primary Trip Relays (PTRs) and the Emergency Trip Relays (ETRs) to be energized when "told to."

4-1, 4-2, 4-3, and 4-4 are not associated with any control processor(s) or the L4 Master Protective logic function. They are present in SIMPLEX panels; their function is to remove the P24VR-4 bus from the PTRs and ETRs when the hard-wire trip circuit is opened, thereby de-energizing the PTRs and the ETRs. It's tone of the things which sets a Mark V WAY apart from any PLC (mis)applied as a turbine control system.

The PTR for a Stop/Ratio Valve is usually driven by logic signal L20FG1X (or something similar). Each control processor drives its own independent PTR, an L20FG1X for <R>, one for <S>, and another for <T>. There are two groups of ETRs, and each group of ETRs contains one for <R>, one for <S>, and one for <T>. This is the TOOT (two-out-of-three) voting for the PTRs and the ETRs--yet ANOTHER thing which sets the Mark V FURTHER apart from any PLC (mis)applied as a turbine control system.

Speedtronic turbine control systems "sink" relays driven by logic signals, so supplying 24 VDC to the coil doesn't energize them, but connecting the other side of the coil to COM (ground) completes the circuit and energizes the relay coil. This is still ANOTHER feature which sets Mark V control panels apart from any PLC (mis)applied as a turbine control system. (Get the idea that PLCs shouldn't be used for turbine control systems? They shouldn't; neither should turbine control systems be used to make cardboard boxes or control water treatment systems.)

In order for the ETRs and PTRs to be picked up when "told" to by their driving logic signal(s), there must be power on the P24VR-4 bus. In order for there to be power on the P24VR-4 bus, the hard-wired trip circuit connected to the PTBA card must be closed.

It sounds as if you are having trouble energizing the ETRs or the PTRs or the 4-1, 4-2, 4-3, and 4-4 relays. Which is it? It should also be noted that many early Mark V control panels required a speed signal (of approximately 10% of rated speed) to be applied to the <P> core speed inputs in order to be able to energize the PTRs and ETRs. Later Mark V turbine control panels had a logic signal, L97HP0T_BYP (that's a zero, not an "O") to bypass the speed permissive; check your CSP. Please describe any difficulties you are having with the <P> core relays.

markvguy

 

Thank you very much for your reply, and it clears my doubt regarding 4-s circuit.some more regarding this i want to ask.

1. if i understood correctly, then so long as any hardware trip are not energised (for example manual trip or like that) there is always 125 vdc supply to the 4-s circuit and they are always in energised condition, which results in always 24 vdc supply extended to PTRs AND ETRs,though the turbine is in stopped condition.

2. when the logic signal L20FG1X becomes true for any 2 out of three processors then this 24v will
be applied across the PTR1 of R and PTR1 of S and PTR1 or T. Then 2 out of 3 hardware votings 125 V DC supply will be extended to 20FG solenoid to open the SRV. Is it right?

3. One more thing, I do not understand the meaning of "sink" relays. Please clear me one thing, you told that by applying only 24V DC this sink relay coils will not energise, and the other side must be connected to COM (ground). Ok, fine, this I understood. But I am not able to understand what exactly physically happens when L20FGIX signal becomes true, are these logic signals driving any physical relays? Please clarify my doubt as it confuses me a lot.

Thanks again for your valuable reply.

 

You're very welcome; it's quite nice not to be answering a question about droop or isochronous control for a change!

1. The Emergency Stop Push-button on the door of the Mk V turbine control panel is a normally closed contact, which opens when the button is pushed, or, "actuated." (The E-Stop P/B latches the contact in the open position when it is pushed (actuated), and it must be twisted to release the latch and close the normally closed contact.) You are correct--when the hardwire trip circuit is "made up", or closed, the 4-n relays are energized and the P24VR-4 bus is powered through the contacts of the 4-n relays--even if the turbine is not running. The other side of the PTRs and ETRs are "floating" and are not continually connected to ground.

2. When the logic signal L20FG1X of <R> is true, <R>'s PTR for 20FG-1 is energized. It's energized by connecting one side of the coil to COM (ground)--that's what happens when a logic signal which drives a relay goes to logic "1". With 24 VDC applied to one side of the coil through the 4-n relays via the P24VR-4 bus, when the other side of the relay's coil is connected to COM the coil will be energized and the relay's contacts will change state.

When two out of three control processors' PTR relays are energized AND the ETRs are energized, then 125 VDC will be applied to 20FG-1 (in this example). The negative side of the 125 VDC supply to 20FG-1 passes through the PTRs, and the positive side of the 125 VDC supply to 20FG-1 passes through the ETRs. This can be seen on drawings of the Signal Flow Diagrams for the TCTG card.

3. The answer is yes, even though 24 VDC is applied to the coils of the relays, they are NOT energized because the other side of the relay coil is not connected to anything--until the logic signal which drives the relay goes to a logic "1" and connects the opposite side of the relay coil to COM.

When a one side of a relay coil is continually connected to common/ground and the other side is switched between an open, floating condition and the application of a voltage source, that's referred to as "sourcing" the relay coil. When one side of relay coil is continually connected to a voltage source and the other side is switched between common/ground and an open, floating condition, that's referred to as "sinking."

In a SpeedTronic turbine control panel most every relay--including the ones on the TCRA cards in the digital I/O cores--has a voltage source continually applied to one side of the coil, and when a logic signal which drives a relay goes to a logic "1", that action sinks one side of the relay's coil to COM and the coil is energized and the contacts change state. When the driving logic signal goes to a logic "0", the connection to COM is opened and the relay de-energizes.

The logic signals do drive relays, but they do so by connecting one side of the relay coil to COM, not by applying voltage to one side of the relay coil.

markvguy

 

Greetings! We have three Frame 5 turbines installed in 1970. In looking at the schematics I noticed years ago that the relays are wired in a sinking configuration, and I have always wondered why that was the case. Can you shed some light on this?

Mark 1 User

 

There were some written descriptions of the functionality of printed circuit cards used in Mk I- and Mk II turbine control panels that were not intended to be distributed to Customers, but somehow became quite universally available. They are commonly referred to as "back-sheets." It is believed that one of the contributors to control.com, Rahul P. Sharma, has at least some of the Mk II backsheets.

The back sheets included some "engineers' notes", which were sometimes VERY informative and extremely instructive in understanding why things were done the way there done and some of the information and options that were considered in making the choice to do this or that. This author recalls some information on one back-sheet that detailed the decision to sink relay outputs as opposed to sourcing them. It's been a very long time, and which card was being described can't be recalled--but somewhere that choice was documented "for posterity."

>From other threads on control.com, it seems that sinking output relays is more common in North America, and sourcing output relays is more common in Europe--that's probably a terrible generalization, but it really just seems to boil down to a choice by the circuit designer which seems to have some "geographical" considerations...which doesn't really make much sense, but...

Having said that, GE went to great lengths to "use" the known failure modes of devices and components to design control systems and schemes to maximize reliability. Perhaps that thinking also figured into the decision to sink output relays...

This is another one of those things that's not really necessary to understand to be able to troubleshoot and work on a SpeedTronic turbine control system, but sometimes if the logic and reasoning is understood other related concepts and schemes become clearer, also.

Perhaps somebody who has access to the backsheets can look through them and find that passage and share it with us. This author guarantees that individual that he/she will find other very valuable tidbits of information as well!

markvguy

 

We have a complete set of Mark I backsheets. They were sent to us back in 1979 (I believe by GE). Some years ago I spent a years worth of lunch breaks perusing them at length. I don't remember seeing the explaination you mention, but it was indeed very enlightning!

Mark 1 User