The cooling air is needed for the generator while the barrier air is needed for labyrinth seals of the generator.

Prior Art The present invention is directed to micro gas turbines being a part of a thermoelectric generating set, normally used to produce both electricity and heating. The gas turbine is driven at a high speed and has to be lubricated constantly. The moving parts to be lubricated are furnished with labyrinth seals or the like. To hinder oil leakage barrier air is provided on the outside of the seals and is swept past the parts of the unit to be lubricated. The barrier air is also used as cooling air for the generator.

The gas turbines according to the prior art normally do not have any special fan for cooling air to the generator and barrier air to labyrinth seals or the like. A part of the air of combustion is normally used as cooling air. Furthermore, the gas turbines of the prior art often use a type of seals having a much lower demand for barrier air.

Summary of the Invention The present invention concerns an external emergency system. It is intended for use with a gas turbine. It is especially directed to the provision of air to the generator in case of an emergency stop of the gas turbine.

The generator of the present invention is furnished with labyrinth seals. During normal service the generator and

the labyrinth seals are furnished with air from a three- phase fan arranged in a side channel. In case of a power failure the gas turbine will be stopped, as it is not possible to run it without any load. However, it will take a couple of minutes before the gas turbine has rolled out and during that time period the generator must be cooled and the labyrinth seals must be furnished with barrier air.

One object of the present invention is to furnish the. generator with cooling air and the labyrinth seals with barrier air during roll out of the gas turbine at a power failure.

This is done in that a part of the air from the compressor is led through a separate conduit. The compressor will function and take in air as long as the rotor rotates. In case of a power failure a magnetic valve will open and a restriction will reduce the pressure at the same time as the temperature of the air will go down.

Further objects and advantages of the present invention will be obvious for a person skilled in the art from reading the detailed description below of preferred embodiments.

Brief Description of the Drawing In the enclosed figure the emergency system of the invention is shown schematically.

Detailed Description of Preferred Embodiments In the figure a part of a gas turbine is shown schematically. The gas turbine is part of a thermoelectric generating set. The parts shown are a generator 1 connected to a compressor 2. The compressor 2 takes in air from the environment as long as the gas turbine and, thus, the compressor 2 rotates. The generator 1 is furnished with labyrinth seals 4, indicated in the figure. To hinder oil leakage barrier air is provided on the outer side of the labyrinth seals 4. Furthermore the generator 1 as such is furnished with cooling air. In practice the barrier air and

the cooling air is the same air having the two stated functions.

During normal service the barrier and cooling air is furnished by a fan 8. The air from the fan 8 is led via a conduit 12 to a cooler 7. The function of the cooler 7 is to cool the air to the desired cooling temperature. From the cooler 7 the air goes in two separate conduits 13,14 to the generator 1. The air leaves the generator via two further conduits 15 and 16. In the conduit 12 leading from the fan 8 to the cooler 7 a check valve 9 is placed. The check valve 9 hinders air from going backwards through the fan 8. The air to the compressor 1 is in the normal way taken from the environment of the compressor 1.

In an emergency situation a part of the air from the compressor 1 is led by means of a conduit 10 to a magnetic valve 5. The magnetic valve 5 is normally closed but will automatically be opened during a power failure, in that the solenoid will be out of power. Thus, during normal service there will be no flow in the conduit 10 leading to the magnetic valve 5.

A pressure switch 4 is placed on the generator 1.

From the pressure switch 4 a control line 11 leads to the magnetic valve 5 and the magnetic valve 5 may be opened by the pressure switch 4. The pressure switch 4 will open the magnetic valve 5 if the pressure in the generator exceeds a set value. Thus, the magnetic valve 5 is opened either by a power failure or by the pressure switch 4.

A restriction 6 is placed after the magnetic valve 5.

In the shown embodiment the restriction 6 is a pressure regulator set to a desired value, e. g. 0,3 bar. A person skilled in the art realises that the restriction may have any suitable form, such as a fixed orifice.

If for instance the fan 8 stops to function the pressure in the generator 1 will rise as no cooling air is feed to the generator 1. Due to the increased pressure the

pressure switch 4 will open the magnetic valve 5, and air will be taken in by means of the conduit 10 and fed to the generator 2. Thus, even if the fan 8 stops the cooling and barrier air will be furnished to the generator 1. The restriction 6 will reduce the pressure and the air will be cooled adiabatic, due to the pressure drop. Thus, there is no need for the cooler in the emergency state. Furthermore, the cooler 7 will not function during a power failure.

When the pressure set by the pressure switch 4 is exceeded, the gas turbine will be shut off and will roll out. The roll out time is normally about 3 to 5 minutes.

When the magnetic valve 5 has opened during an emergency state air will be led through the cooler 7, which does not function as a cooler in this situation. From the cooler 7 air will go into the generator through the normal conduit 13. A part of the air will go directly to the other inlet conduit 14 of the generator 1.