Click here to load reader

Catalogo Thyripol Ingles_excitacao

  • View
    47

  • Download
    5

Embed Size (px)

Text of Catalogo Thyripol Ingles_excitacao

T H Y D ig it a l E x a n d R e g u la t io n

R IP c it V o S y

O L D a t io n lt a g e s te m

f o r s y n c h r o n o u s m a c h in e s

P o w e r G e n e r a t io n

I

E d i o 1 1 /0 9

Thyripol D Digital excitation and voltage regulation system for synchronous machinesIntroduction

T

he THYRIPOL D excitation system is used for the excitation and voltage regulation of synchronous machines fitted with slip rings. In such cases the rotor winding is supplied directly by the Thyripol D by means of static thyristor rectifiers in B6C configuration. Instead of the terminal voltage the system can also perform the reactive power or the power factor regulation.

excitation transformer, which can be a dry type or an oil-immersed one. This transformer is especially designed for supplying fully controlled thyristor rectifier bridges. The protection of the excitation transformer is performed by a fully digital overcurrent relay of the SIPROTEC series of Siemens. The generated voltage is controlled by varying the moments at which the thyristors are fired, that is, become conductive. This way a controlled direct current is supplied to the field winding. The automatic voltage regulator is responsible for automatically matching the excitation current to the actual load condition of the synchronous generator. For the excitation build up (field flashing) auxiliary energy must be taken from the power plant auxiliaries (AC or DC). The energy drain from the auxiliary source is automatically switched off as soon as the main rectifier (thyristor bridge) takes over the field supply, what occurs as the terminal voltage reaches about 15% of its rated value. Anyway the field flashing device is switched off if the generator voltage has not built up during the adjusted time interval.

Due to its outstanding features the dry type GEAFOL transformers of Siemens are the best choice as excitation transformers.

The system takes from the machine terminals the necessary energy for supplying the field winding through a three-phase medium voltage

2

The measuring of the analogical values, the voltage and reactive power regulation, the control of the start up and shut down processes, the setpoint generation for the regulators and the whole system monitoring as well as the alarm generation are carried out by the processor modules in a completely digital way. The CPU modules possess floating point RISC technology microprocessor. No transducers are used for voltage and current measuring. The powerful operating system of the voltage regulator allows defining the several sampling times to be used by the processor. The shortest sampling time of 0.1 ms is associated with the fastest task. Power stage he current is rectified by a fully controlled three-phase rectifier bridge of the Simoreg 6RA70 series. The rectifier is air forced cooled. The thyristors are individually protected by ultra fast supervised fuses. The rectifier bridge is designed for the most severe overload conditions of the generator. The Simoreg converter possesses a complete protection and monitoring system of all thyristors, what also includes junction temperature calculation and indication.

Outward appearance of a 2,000 A rectifier bridge. The compact construction of the unit and the parameterization device on the converter door are noticeable.

T

On request the Thyripol excitation system can be designed with N+1 redundancy, that is, an identical Simoreg unit is additionally supplied in order to increase the system availability. In this configuration, only one Simoreg converter (namely the master channel) is working at a time: the other one (defined as slave channel) stands by and follows up continuously the master unit. If faults involving the master channel occur, the slave channel takes over the excitation field supply immediately, without any oscillations on the generator voltage, so that the generator remains in safe operation.

3

Automatic voltage regulator (AVR)

T

he regulation, monitoring and control tasks of the excitation system are carried out by powerful RISC technology processor modules with floating point arithmetic. This feature allows the processors to work directly with real numbers, what means that there is neither a scale limitation nor the need of scale adjustments. Furthermore, the operational system is multitasking based on priorities: the processor carries out at first the task associated with the shortest sampling time, that is, the task with the highest priority. Immediately afterwards the processor carries out the task associated with the second shortest sampling time and so on. This way the accomplishment of a certain task can be interrupted several times, during its processing, by tasks with shorter sampling times. This way of processing guarantees that the digital regulator performance can be compared to the one of an analogical regulator. The CFC programming language is very friendly and possesses numerous possibilities for on line editing and testing. Furthermore it enjoys the use of all the facilities of the Windows operating system. There are two independent regulating channels: AUTOMATIC (automatic voltage regulator or AVR) and HAND (field current regulation).

The regulation and control software is fully graphic and friendly, what makes the programming and understanding easier.

Both regulating channels (AUTOMATIC and HAND) act on the same rectifier bridge. A bumpless channel changeover from automatic to hand and vice-versa is ensured by a follow up routine. If specified by the client the regulation is configured as double automatic voltage regulators. In such cases two identical and completely independent automatic channels are designed, each one possessing its own hand channel. The power supply for the electronics is always taken in a redundant way, namely from the excitation transformer and from the station battery. Automatic channel

T

he automatic channel corresponds to the automatic voltage regulator (AVR), which compares the generator voltage actual value with the reference value (voltage setpoint) adjusted by the power plant operator.

4

For the measuring of the actual generator voltage the three phases are used. This way any unbalance among the phases is taken into account, leading to a very precise measuring. The generator voltage and current actual value detection is fully digital and does not employ any kind of transducers. The generator voltage setpoint is digitally generated and can be adjusted in the range 90% to 110% of the rated generator voltage. During the operation of the synchronous generator attention must be paid to its capability diagram. For this reason the following limiters act on the AVR: Quick acting excitation current limiter (field forcing limiter) Overexcitation limiter Underexcitation limiter Volt/Hertz limiter Stator current limiter

power (or power factor) of the generator itself or of any point of the plant.ACTIVE POWER (MW) STATOR THERMAL LIMIT STATOR THERMAL LIMIT

STABILITY LIMIT UNDEREXCITATION OVEREXCITATION

ROTOR THERMAL LIMIT

REACTIVE POWER (MVAr)

During the automatic voltage regulation it must be ensured that the generator always works inside its capability diagram. This function is carried out by the limiters.

Hand channel

T

The automatic voltage regulator includes also the power system stabilizer (PSS), which stabilizing output signal is derived from the power and frequency oscillations (accelerating power). Additionally the THYRIPOL D excitation system includes also a reactive power (or power factor) regulator for controlling the reactive

his control channel corresponds to the excitation current regulator. It is extremely useful when performing tests on the generator. In addition the hand channel works as a stand-by regulator allowing continuing of the operation even at failures in the AVR. The setpoint of the excitation current ranges from about 10% up to 110% of the rated excitation current of the generator. By taking an independent power supply for the excitation system (e.g. during tests) the setpoint range stretches from zero to 110%.

5

Channel changeover and follow-up

A

bumpless channel changeover from AVR to excitation current regulator and viceversa can occur at any time. This is possible thanks to the followup routine, which ensures that the selected control channel follows up the settings of the other channel. This way the outputs of both channels have always the same firing angle for the thyristors, what guarantees a bumpless channel changeover at any time. Certain failures involving the AVR cause an automatic changeover to the hand channel. A trip signal is released if failures occur in the hand channel being selected the hand channel. In the double channel configuration (two independent automatic voltage regulators) an automatic changeover to the standby AVR takes place at the occurrence of failures in the operating AVR. In such cases a channel changeover to the hand channel takes place automatically only if both AVRs are simultaneously faulty. Mode of control

but also for remote operation (through the power plant superordinated control system). The color touch screen man-machine interface (MMI) is installed on the regulator cubicle door. This device is also fitted with a keyboard that can be used additionally to the touch screen functionality.

The local control of the excitation system is performed through the integrated touch screen man machine interface.

Through this device commands (Excitation ON /OFF, Channel selection, etc.) can be entered and actual system parameters (excitation current and voltage, generator active and reactive power, generator voltage