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Gas turbine units PB 4-5

The Alstom gas blocks with a power of 2 × 114 MW operate in a simple open process. Natural gas, extra light fuel oil, or a combination of both fuels can be used for operation. Both units started operating in 2000. The operation of the blocks is environmentally friendly: the concentration of harmful substances (NOX, CO, SO2) in the exhaust gases and the noise they generate in the process are below the regulatory limits.
Already in the phase of commissioning and construction of gas blocks, the focus was on the reliability, flexibility of operation, and suitability of blocks to provide system services in the power system, therefore the blocks enable individual operating regimes that go beyond the usual characteristics of such units:
  • In addition to a normal start-up, they have the option of a fast start-up - in less than 15 minutes from start-up to rated power.
  • Possibility of rapid change of load (up to 25 MW/min).
  • Possibility of remote power control for the needs of secondary regulation in the electricity network.
  • Possibility of frequency regulation with extremely fast power response to the change in the network frequency.
  • Capability of island operation: in the event of the power system breakdown, the blocks can be started without the power from the grid with the help of prestarted PB 1-3 gas blocks. In this case, their capability of island operation can serve to restore the electric power system.
  • Capacity to operate with liquid and gaseous fuels. Switching between the two types of fuel is possible during operation, and operation is also possible with a mixture of both fuels in the ratio of 20: 80% to 80: 20%.
  • High operating stability: in the event of a loss of load during operation (e.g. due to power system breakdown, fault in the switching substation...), the block is maintained at rated speed and powers itself. Consequently, it is immediately ready for synchronization with the network.

Main turbine unit

A 14-stage axial compressor delivers compressed air to the combustion chamber.  With the help of the hydraulic mechanism, stator blades of the first three stages have an adjustable angle, thus regulating the mass flow of air through the turbine. The result is stabilised combustion and high efficiency even at partial loads.
Combustion chamber with burners
The silo-type combustion chamber is installed vertically above the turbine housing. Such a chamber provides an easier and faster access to the burners, the first stage of the turbine, and other most heat-stressed parts of the turbine. At the top of the chamber are 37 circularly mounted burners, and the middle burner is intended for ignition of the fuel at the start-up stage. Each burner can operate on both types of fuel, but only one type at the same time. The number of operating burners and fuel type on a single burner depend on the current load of the block and the share of individual fuels.
Gas turbine
The combustion chamber converts the released energy to mechanical energy and drives the generator. The four-stage turbine and the compressor are located on the turbine rotor which is connected to the generator via a reducer.
A two-pole synchronous generator with static excitation transforms the mechanical work of the turbine into electrical energy. The generator is air-cooled; it is cooled indirectly by heat exchangers via a closed cooling system for the generator and lubricating oil. During the turbine start-up phase, the generator acts as a synchronous electric motor and starts the turbine with the aid of a starting device.
The reducer of 135 MW rated mechanical power is installed between a gas turbine and a generator and is designed to convert the rated turbine rotation speed, 3600 min-1, to the generator rated rotation speed of 3000 min-1. The reducer is lubricated and cooled with the help of a lubricating oil system which is also shared by the turbine and the generator.

Other mechanical systems

They are designed to provide functions that are indispensable for the safe and reliable operation of the gas block:
  • Fuel supply system - natural gas and extra light fuel oil,
  • Ignition system,
  • System for injecting demineralized water into a combustion chamber for reducing NO Xemissions during the combustion of extra light fuel oil,
  • Hydraulic and protective oil system,
  • Lubricating oil system,
  • Generator and lubrication oil cooling system
  • Compressor air filtering and supply system,
  • Exhaust system.

Electrical and control systems

They are designed to manage the following functions:
  • Speed control, bearings temperature, and vibrations of rotating parts,
  • Dissipation of generated electricity,
  • Supply of the necessary auxiliary electricity for the gas block,
  • Start-up of the gas block using a static frequency converter,
  • Open and closed-loop control,
  • Control and protection.

Block transformer
It is intended to adjust voltage levels between the 11.5 kV generator and the 110 kV switchgear.
Transformer of own block use
It provides electricity of 2.1 kV voltage for supplying the turbine start-up system, and 0.4 kV electrical power required for supplying the auxiliary drives of the gas block.
Numerical protection
Generator, generator collectors, generator circuit breaker, block transformer, and transformer of own use of the block are protected by the ABB numerical protection.
Management system
The EGATROL 8 gas block management system is an autonomous system and contains all the control functions required for a safe and efficient start-up, operation and shutdown of the block.
Control system
It is designed for the start-up and handling during the operation and enables:
  • Fully automatic start-up and shutdown of the gas block,
  • Accurate monitoring of the process with short response times,
  • Automatic load, frequency and temperature control during all the operation phases,
  • Automatic operation at various loads with maximum thermal efficiency.