Definition of secondary reserve; its role in the electricity system
Secondary reserve is a service in the interest of the system, which means ‘black start’ or built in capacity available for the electricity system and the possibility to use import, which can be used in case of shortages of capacity caused by malfunction, when it is not enough to use the available domestic capacity, surplus capacity and help in co-ordination with foreign partners to restore the balance in capacity. In these cases the National Dispatching Centre of the system operator gives the instruction to use the secondary reserve capacity. In the course of negotiations on the Hungarian electricity system to join UCPTE (since 1998 UCTE, Union for the Coordination of the Transmission of Electricity) at the beginning of the 1990s it was concluded that the reserve capacities to be used quickly in case of malfunction are missing from the composition of our power plants. According to the regulations of UCTE, the systems participating in the union of co-operating systems are bound to have secondary reserves. Secondary reserve is reserve capacity, which can actually be used within a short time – within about 15 minutes and which can be used to provisionally make up for the unexpectedly failing output. It keeps on operating till the shortage is counteracted either by eliminating the failure or by taking into operation some other equipment.
Establishing reserve gas turbine power plants
Fulfilling the conditions for joining the UCTE and in accordance with the energy policy objectives approved by the Parliament, secondary reserve gas turbine power plants were established to ensure the long-term security of power supply in Hungary.
The establishment was preceded by a procedure to carefully select the sites. As a result of this procedure, the sites of power plants to be established are near network nodes at a rather long geographical distance from each other.
- In Litér near the 400/132/35/20 kV and in Sajószöged near the 400/220/132 kV substations, which is perhaps the most important network node between the Western and Eastern parts of the country;
- In Lőrinci – primarily taking into consideration the existing and partly usable power plant infrastructure, the economical aspects and the potential of further development – on the site of the previous Mátravidék Power Plant, which MVM Rt. bought from the Mátra Power Plant Co. in the autumn of 1995.
In the cases of the World Bank and EIB credit lines, the selection was made by means of tenders, where the so called “heavy duty” type gas turbines proved to be the most competitive in terms of investment costs. Thus in Litér and Sajószöged a PG 9171 E type of E.G.T. and in Lőrinci a V94.2. type, open cycle gas turbine unit manufactured by SIEMENS was installed.
The plants in Litér and Sajószöged were put into operation in 1998 with 120 MW capacity each. In Lőrinci the plant with a nominal installed capacity of 170 MW was put into operation in 2000. All three plants are open cycle and use gas turbine oil for fuel.
According to the regulations of UCTE, the secondary reserve capacity of a system should be equal at least with the capacity of the largest unit in the system. Therefore, the Hungarian electricity system should have the same reserve capacity as that of a unit at Paks Nuclear Power Plant (460 MW). This theoretically needed capacity can be ensured by setting the so called peak load operation or the so called “black start”, which is bigger than the nominal capacity.
Local handling of equipment; changes in the operation system as a consequence of amendment in the legal background
The original aim in Litér and Sajószöged was to establish a power plant with remote control, operating basically automatically with no staff in the plant. Based on the agreement with the National Power Line Co. (OVIT Rt.), the special staff to supervise the power plant came from the most qualified experts of the substation, who were trained for the job. Starting and shutting down the power plant happened according to the instruction of the system operator.
In the autumn of 1999 the Government worked out a new energy policy concept to harmonise with the EU requirements. The electricity market was about to open and therefore the electricity industry activities were to be unbundled accordingly in a severe administrative order. As a consequence of all this, MVM Rt. set up its subsidiary, the Gas Turbine Power Plant Operation and Maintenance Ltd. (GTER) as a limited liability company. The company was in charge of managing the equipment in the plants. MVM Rt. commissioned the independent company to manage and supervise the operation of all three gas turbine power plants from 1 June 2000.
The Act on Electricity XC/2001 entered into effect on 1 January 2003. The act regulated the system of legal regulations relating to the operation of the Hungarian electricity sector, which considerably changed the operational pattern of the energy actors. The operation of secondary reserve gas turbines was qualified as a license-bound activity in the related rules of law, so the MVM Rt. was not allowed to have the license to operate the gas turbine power plants in its ownership. powe_quick3.jpgConsequently, the owner as a power generation licensee signed a leasing agreement with GTER Kft. and put the quick-start gas turbine power plants at the disposal of GTER Kft. under the condition that the availability (maintenance, upgrade, necessary development, failure elimination and licenses) remained the responsibility of the owner and which is actually carried out by the Power Plant Subdivision.
GTER Kft. as the winner of capacity contracting tender invited by the MAVIR Rt. is the holder of a capacity contracting agreement for indefinite time with the system operator.
Gas turbines’ principle of operation
Under nominal conditions, the main equipment of the open cycle power plant (outer temperature 15 oC, atmosphere air pressure 1, relative humidity 60 %) provides the prescribed heat and (as in the present case) electricity output. The engine is started, depending on the construction, with the starter motor or the generator of the engine unit (engine operation). The air flowing in through the air inlet is compressed in the compressor to the necessary degree after reaching the specified speed, the high-pressure combustion air and the sprayed fuel oil flow into the combustion chamber. The fuel-air mixture prepared for combustion is then inflamed by electric sparks or pilot-flame. The hot combustion gases flow through the turbine grades and the heat energy will turn into mechanical energy there. When the quantity of fuel is continuously increased, the engine will further accelerate. After the starting equipment is shut down, the engine as a consequence of stable combustion process will accelerate to the timed rotation. Following the automatic timing, the engine takes up the set loading condition and remains in this state of operation till the operation controller gives instruction to shut or to set for another loading condition. In order to decrease the content of pollutant (NOx) in the smoke gas of about 540 oC discharging through the chimney, the combustion area is cooled by means of injecting desalted water. The volume of injected water is the same as the volume of burnt gas turbine oil. The pollutant content of the discharged smoke gas is continuously monitored and registered by the system. The control and regulation of gas turbine unit is performed with a high-reliability (redundant) control technique system. In the system, in parallel with the equipment group doing the controlling tasks, a reserve system is also continuously operating. In case the control system of the plant breaks down, the control of the whole engine unit is taken over by the system operating as “warm reserve” so far.
The most important technical data of power plants
Nominal capacity: 170 MW
Fuel: gas turbine oil
Quantity of fuel: 42 t/h
Manufacturer: SIEMENS AG.
LITÉR – SAJÓSZÖGED
Type: PG 9171 E
Nominal capacity: 120 MW
Fuel: gas turbine oil
Quantity of fuel: 32 t/h