GE Speed Protection


>Can you explain me about protective speed and control speed
>in GT?

For just about any type of turbine it is important to be able to control the speed of the turbine in order to control the power being produced by the turbine. Speed sensors are connected to the turbine control system (the "governor" function of the turbine control system) to sense the speed and control the energy flow-rate into the turbine as necessary to control the speed as necessary to control the power being produced by the turbine and transmitted to the driven device (such as a compressor, or a pump, or a generator). This is the speed control function of the turbine control system (which is technically the governor function of the turbine control system).

It is a required practice that large rotating equipment such as turbines (of any type) have two (2) independent means of protecting against an overspeed condition which could cause catastrophic damage to the equipment and serious physical harm or even death to humans nearby during an undetected overspeed condition. One method serves as a back-up to the other in case of a failure of one of the overspeed detection systems.

The most common means of ensuring independent overspeed sensing and protection is to use separate speed pick-ups (sensors) providing speed indication to an independent method of determining speed and initiating a trip signal to immediately stop the flow of energy into the turbine. This is the protective speed function of the turbine control system.

Some turbine control systems use the speed control speed pick-ups for BOTH speed control as well as overspeed detection--but only as one of the two independent overspeed protection methods. So, the same speed sensors being used for the governor function will also serve as one of the overspeed sensing and protection functions. A separate set of speed pick-ups will be connected to an independent overspeed sensing and protection method. The two overspeed sensing methods are redundant, and provide back-up protection to each other.

Some turbine control system manufacturers actually have the overspeed protection incorporated into the main turbine control system--but is is independent of any other overspeed detection and protection method. Some turbine control system manufacturers supply a completely separate overspeed sensing and protection system, often from another manufacturer, as the overspeed protection method which is in addition to the overspeed protection accomplished with the governor function of the turbine control system.

To sum up, speed control of any turbine (prime mover, actually) is very important--and usually has its own separate speed sensors (pick-ups). Often, the governor function of the turbine speed control system also performs one of the two required overspeed sensing and protection functions. But there must also be a second, independent means of sensing and protecting against an overspeed condition--and that is usually called the "protective" function, and it usually has its own separate speed sensors (pick-ups). Each overspeed sensing method must be independently capable of detecting an overspeed condition AND of initiating a trip to immediately shut off the flow of energy into the turbine (prime mover).

Hope this helps!
In gas turbine, there's generally speed protection (overspeed) relay.
In taking GE Frame 9E for example, which has its normal speed as 3000rpm, there's a mechanical overspeed and electrical overspeed protection relays. The electrical overspeed relay is usually 110% while the mechanical overspeed relay is 113%. (3300rpm & 3405rpm respectively)...

At this speeds, the control system triggers the closure of the gas valves and thus shutting down the GT at emergency.
Actually, in GE Frame 9E with a mechanical overspeed protection device, it's called a "bolt"--which is a piece of metal held in a shaft (usually in the Accessory Gear Box) with a spring. The bolt is slightly "out of balance" such that when the shaft speed gets high enough to overcome the spring tension (due to centrifugal force) the bolt moves out and releases a latch which then dumps oil pressure to the Trip (or Control) Oil system and that in turn causes a mechanical-hydraulic dump valve (sometimes called a "relay" or "trip relay") to operate which prevents high-pressure hydraulic oil from opening the fuel stop valve which is closed by a great big spring. The dump valve (or "relay" or "trip relay") is not an electric or electro-mechanical relay, it's strictly a mechanical-hydraulic device. (See the definition of 'relay'--it can mean many different things. In this case, the dump valve is "relaying" a signal (from the Trip or Control Oil system to the High-pressure Hydraulic Oil system) to shut off the flow of oil to the stop valve actuator to allow the closing spring of the fuel stop valve to close the valve, thereby shutting off the flow of fuel to the turbine.)

The speed at which the overspeed bolt overcomes its retaining spring tension is a function of the adjustment of a threaded spring holder. It's nothing to do with electric or electronic system; it's a tried-and-true, proven technology that is not without its faults (it's not very repeatable; it can stick because of moisture (which causes rust) or varnish build-up (because it's in an enclosed gear box).

Electronic overspeed protection devices, which use electronic speed pick-ups, have proved to be much more reliable and repeatable over the past couple of decades. Most turbine manufacturers, and many existing Customers with older turbines that used mechanical overspeed bolts, are using electronic overspeed protection for "back-up" and have done away with the mechanical overspeed bolt mechanisms. Many insurance companies also prefer electronic overspeed protection--both for primary- and back-up ("emergency") overspeed protection over a mechanical overspeed bolt for back-up ("emergency") protection.

What do you mean by coordinating overspeed and over-frequency?

What would coordinating overspeed and over-frequency produce, or how would it be beneficial?

Do you know what the typical over-frequency setpoint is for generators in your region of the world?