SPPA-E3000 Brushless Excitation System (BES, Type RG3)

Transcription

1 / Technical Description / Juni 2014 SPPA-E3000 Brushless Excitation System (BES, Type RG3) Maximum-availability excitation system for synchronous generators with brushless exciters Answers for energy.

2 Table of Contents 1. Introduction Basic circuit Method of operation Automatic voltage regulator (automatic control system) Manual control system (excitation current regulator) Other operating modes Follow-up control Limiters Overmodulation and field-forcing limiter Power system stabilizer (PSS) Open-loop control Power circuit De-excitation Basic modules Basic modules Data exchange with DCS Local operator and monitoring Software Areas of Applicaltion Technical Data Abbreviations Unrestricted Siemens AG All rights reserved

3 1. Introduction The automatic voltage regulator SPPA-E3000 BES Type RG3 (SPPA Siemens Power Plant Automation) for brushless excitation system is suitable for any type of synchronous generator. It is equally suited to hydroelectric, steam, or nuclear power plants. Thanks to its high degree of flexibility, it can be adapted to the conditions of any plant and is an optimal solution both for new plants and for the modernization of existing plants. Depending on the technical aspects of the modernization of existing plants, a number of flexible, project-specific adaptations are possible. The main performance characteristics of the BES excitation system are: High reliability High availability Good adaptability Low maintenance requirements High speed of response Good regulating properties Robust construction Digital open- and closed-loop control Extreme flexibility Compact design Low space requirements Figure 1: SPPA-E3000 BES Type RG3-S (Example) The voltage converter is implemented with a powerful microprocessor which, besides performing voltage control, also assumes all the important limitation and monitoring functions of the excitation system. A high availability factor is achieved by the use of field-proven industrial components. It s completely modular design makes the operation and maintenance extremely user friendly. A brief description of the main components of the excitation system is given below followed by a detailed description of the device and component scope and their functions. 3 Unrestricted Siemens AG All rights reserved

4 2. Basic circuit The voltage regulator RG3 is suitable for brushless excitation system for synchronous generators with an exciter. It can also be connected directly to the slip rings of the generator. Its high flexibility and modular design make it suitable for use in all power plant types, and especially for the modernization of existing plants. Versions of BES available: RG3 DUR is designed especially for small generators with excitation current up to 30 A RG3 S is suitable for all power ratings. This version also offers the full flexibility of the logic as well as in the communication to the control system The power section comprises a transistorized chopper regulator which is connected to the field winding of the exciter or the generator slip rings. The BES excitation system can obtain its excitation power from any of the following: from the permanent-magnet pilot exciter (PMG) from an auxiliary winding in the generator stator (e.g. clamping bolt voltage of laminated core) from the auxiliary power supply of the power plant via a separate excitation transformer This excitation transformer can either be connected to the terminals of the synchronous generator or supplied by the auxiliary power supply. Other redundant power supplies are possible, e.g. battery power supply or UPS system. A redundant power supply from two or more of the sources named above is also possible in order to increase the availability. The modular design, the flexible software of the digital open- and closed-loop control, and the low space requirements make the RG3 especially suited for new plants and for the modernization of existing excitation systems. 4 Unrestricted Siemens AG All rights reserved

5 3. Method of operation 3.1 Automatic voltage regulator (automatic control system) In this operating mode the generator voltage actual value is compared with an adjustable generator voltage setpoint in the automatic voltage regulator. The resulting signal is compared with the outputs of the excitation limit controllers and applied to the input of the PI voltage regulator. The PI voltage regulator, whose gain and time response can be adjusted, supplies an output signal which is used as the current setpoint input (I setpoint) for the lower-level excitation current regulator. The degree of modulation of the pulse-width modulated trigger signals for the power transistors varies depending on the output of the current regulator. The structure of the AVR is represented by the model AC7B in IEEE Manual control system (excitation current regulator) A smoothed setpoint signal is input to the associated P-action control amplifier in the excitation current regulator and compared with the excitation current actual value. The output signal controls the power transistors of the associated output stage by means of pulse-width modulation. This operating mode is especially used during commissioning and testing of the generator and protection system. It is also the emergency operating mode as a backup mode for the AVR. 3.3 Other operating modes Automatic power factor regulation or reactive power regulation on generator leads or net coupling point The power factor regulator compares the actual value with an adjustable power factor setpoint. In the event of a deviation, the setpoint value of the voltage regulator is adjusted until the power factor deviation is reduced to zero. In isolated or no-load operation of the generator, automatic switchover from the power factor regulator to the automatic voltage regulator is performed. The reactive power regulator is working analog to the power factor regulator. Optionally also regulation at the net coupling point is available. Of the three operating modes (chapter 3.1, 3.2 and 3.3), the automatic voltage regulator is normally the one in operation, even during startup and shutdown of the turbine generator. The automatic voltage regulator comprises measured value acquisition, setpoint inputs and the control and monitoring circuits for the following functions: Generator voltage regulation Lower-level control and limitation of the excitation current (excitation current regulation) and/or field-forcing limiter Limit controller for the under-excited range (under-excitation limiter) Delayed limit controller for the overexcited range (overexcitation limiter) Delayed generator current limit controller (stator current limiter) 3.4 Follow-up control The setpoint value of the excitation current controller is continuously updated during operation with the automatic control system, thus ensuring rapid and virtually bumpless changeover to the excitation current regulator (manual control system or the other channel) in the event of a fault. Automatic changeover takes place, for example, when internal monitoring functions for the excitation current respond and in the event of error messages relating to generator voltage actual value acquisition. 5 Unrestricted Siemens AG All rights reserved

6 3.5 Limiters When operating a synchronous generator, it is necessary to observe the permissible combinations of active and reactive power, as shown in the capability diagram. L-M-O O-P P-Q Limit characteristic of the underexcited range Limit characteristic set by the stator temperature rise Limit characteristic set by the rotor temperature rise The underexcitation limiter corrects the reactive power by raising the generator voltage such that, in the case of an excursion beyond limit characteristic L-M-O, the operating point is returned to that characteristic before the generator is tripped by the underexcitation protection. This limiter can be represented by UEL2 model in IEEE Figure 2: Limit characteristics of synchronous generator in The overexcitation limiter ensures that the operating point is always kept within section P-Q of the generator capability diagram in the overexcited range. In response to system voltage drops caused by high reactive power requirements, switching operations or faults, the voltage regulator raises the excitation level so as to keep the generator voltage constant. The overexcitation limiter acts as a safeguard against thermal overloading of the rotor. The overexcitation limiter permits excitation values between the maximum continuous current and the maximum excitation current (field-forcing) for a limited period of time to enable the generator to provide voltage support in response to short-time voltage dips on the power system. The excitation current limiter (field-forcing limiter), in contrast, has the task of limiting the excitation current to the maximum permissible value as quickly as possible. The stator current limiter ensures delayed limiting to the continuously permitted stator current. The task of the stator current limiter is to prevent the thermal overload of the generator stator which can be caused by high reactive power at increased active power. The stator current limiter also permits increased excitation values for a limited period to enable the generator to provide voltage support for the power system. Figure 3: Underexcitation limiter Ceiling current limiter Overexitation limiter Ceiling current limiter Figure 4: Overexcitation limiter and ceiling current limiter 6 Unrestricted Siemens AG All rights reserved

7 3.6 Overmodulation and field-forcing limiter At full modulation, the chopper regulator outputs a higher voltage than is required for excitation to ceiling current. This voltage overmodulation of the field winding shortens the time required for the ceiling current to be reached, thus also shortening the compensation of setpoint deviations of the voltage on the generator terminals. The output voltage of the chopper regulator for the manual control system is limited by the upper value of the setpoint. The output voltage of the chopper regulator for the automatic control system is affected by the modulation limiter of the PI voltage regulator. This reference variable corresponds to the voltage value of the required excitation current. Figure 5: Overexcitation limiter and lower-level excitation current limiter 3.7 Power system stabilizer (PSS) A "Dual Input PSS" according to IEEE type PSS2B is implemented. This feature acquires the frequency or active power changes in the natural frequency range of the generator and the network, and exerts a damping influence through the voltage regulator and the generator excitation. This is achieved by calculation of the integral of the accelerating power from the electrical active power and compensated frequency as input variables into the PSS. Implemented is also the model Hinfinite (PSS3B). A PSS is recommended for networks where steady-state stability is endangered by the presence of long transmission lines and the natural damping properties of the generator are inadequate. 7 Unrestricted Siemens AG All rights reserved

8 3.8 Open-loop control Every operating condition of the excitation system is monitored and displayed. In addition to internal fault indication, the internal monitoring routine makes the following alarms available at the cabinet terminals: Fault with TRIP command Fault in automatic voltage regulator and switchover to manual mode Group alarm triggered by various internal fault signals Status signals are also made available for external indication: Excitation is on Excitation is off Automatic is on Manual is on Power factor / reactive power regulation is on Limiters are active Other detailed alarms status signals are possible as options on customer-specific design for modernization projects. 3.9 Power circuit In the power circuit, SINAMCS S120 or DIGUREG transistorized chopper regulators are used to make the necessary excitation power available via a DC link, i.e. the output stages of the transistorized chopper regulator derive their power from the DC link. The excitation voltage is influenced by the pulse/pause ratio and the excitation current is changed via the field resistor. The excitation current is measured in the output stage and converted for the field current regulator De-excitation When the synchronous generator is shut down or when the protection systems of the generator or unit transformer respond, the generator must be de-excited. The chopper regulator is disabled directly by the de-excitation command for this purpose. The magnetic energy of the field is fed back into the DC link via the integrated diodes in the chopper regulator. The de-excitation process can therefore be performed very quickly. The excitation switch also isolates the power circuit from the power supplies. U DC positive voltage Zero voltage negative voltage 0 t 1 -U DC T Figure 6: Block diagram of transistorized DC link converter Figure 7: Principle of operation of pulse-width modulation 8 Unrestricted Siemens AG All rights reserved

9 4. Basic modules The transistorized chopper (1), and in the case of redundant systems a second transistorized chopper (2), supplies the necessary excitation current for the exciter (5-7) or the generator field (8). Whereas the automatic voltage regulator (3) controls the generator terminal voltage (automatic channel), the excitation current regulator (4) controls the field current of the exciter (manual channel). Thanks to their compact design, these two modules have been integrated in a single device. The excitation power (E) can be supplied by the auxiliary power supply, a power plant battery, an auxiliary winding, a separate excitation transformer or via a pilot exciter. The optional redundant supplies of exciter power, e.g. from the power plant battery, ensure high availability of the excitation system. RG3 can be used for a wide variety of generator types, e.g. for brushless turbine generators with a three-phase exciter and rotating-rectifier diodes (5) and (7), for turbine generators with a direct-current exciter (6) and also for directly excited generators (8). The transistorized chopper regulator is supplied by means of a DC link. The integrated de-excitation resistor, which is connected in parallel to the DC link of the chopper regulator, is used for de-excitation of the generator. In the event of de-excitation, the field power of the exciter is fed back into the DC link of the chopper regulator. Figure 8: RG3 basic modules 4.1 Basic modules Both versions of the BES excitation system are installed in a standard cabinet specially designed for systems combining electronic closed- and open-loop control systems, and power electronics. Modular design and easy access to all components make for simple handling of all the important functions and optimization equipment. The dimensions of the standard cabinet are 800 mm wide, 2200 mm high and 600 mm deep. However, adaptations to a wide range of plant requirements, especially in the case of modernization projects, may necessitate deviations from these dimensions. 9 Unrestricted Siemens AG All rights reserved

10 SIMOTION D435-2 Open / closed loop control incl. communication to DCS Basic Line Module (BLM) Power supply module with DC-Link SINAMICS S120 Single Line Module (SLM) Power module De-excitation resistor Output choke to compensate the cable length NTG-3000 Actual value acquisition Power supply, output to field Figure 9: Main components in RG3-S cabinet - example 10 Unrestricted Siemens AG All rights reserved

11 4.2 Data exchange with DCS Data exchange to/from the excitation system is implemented via a PROFIBUS DP interface and at a standard baud rate of 12Mbit/s. On redundant excitation systems, the PROFIBUS DP interface is also redundantly implemented. The main control commands, feedback signals for operator control and monitoring of the excitation system, as well as fault messages and measured values of the generator and excitation variables are transmitted. Optionally, the signal interface can also be implemented with conventional hardwiring with coupling relays and optocouplers. 4.3 Local operator and monitoring (Option) An operator control and monitoring device SIMATIC TouchPanel can be installed in the door of the regulating and control cubicle for local operation, monitoring of operating states, measured values from the excitation system and for signaling faults and alarms. The main functions and features of this visualization unit are: Simultaneous display of operating and display values of both channels Simultaneous display of 6 analog values per channel Password protection Local operation of the excitation system Figure 10: Local operator panel (example) 11 Unrestricted Siemens AG All rights reserved

12 5. Software User-friendly software tools (SCOUT or Webserver for RG3-S and DIGUREG-Tool for RG3-DUR) are used for easy commissioning and maintenance of the excitation system. The converter and the power section can be parameterized fully with this software. For this, the voltage converter is connected to a PC via the ethernet, from where it is configured. Actual parameters can be monitored directly in the parameter list. A parameter can be changed simply by selecting it and entering a new value. Several predefined parameter lists for various applications (e.g. inputs/outputs) and an entire parameter list are available. It is also possible to compile user-defined parameter lists by entering parameter numbers. The current parameterization can also be stored on data media. This provides a simple method of documenting the actual state of the voltage regulator. The RG3-DUR DIGUREG-Tool can also be used as a local HMI (Human Machine Interface) installed either in the cabinet door or directly in the control room. RG3 features a TRACE memory. The TRACE is an important commissioning, diagnostic and trouble-shooting tool. Up to 8 analog values (measuring channels) of any type can be recorded with the TRACE function as with a storage oscilloscope. Alternatively, each measuring channel can be used to record 16 binary values. An easy-to-use trigger can be used to start recording. A pretrigger can be set to record events before and after the main trigger event. The recording level can be configured. The sampling time between two measuring points is 250µs. Figure11: Trace function for RG3-S Figure12: Trace function for RG3-DUR 12 Unrestricted Siemens AG All rights reserved

13 6. Areas of Application Figure 13: Applications of SPPA-E3000 SES excitation systems Example of a version in the lower power range Dual-channel open- and closed-loop control DIGUREG dual-channel voltage regulator Example for newly built power plant Figure 14: BES-DUR dual-channel excitation system with integrated redundant closed-loop controller Example of a version in the upper power range Dual-channel open- and closed-loop control with local control AC and DC power supply Example for modernization project Figure 15: RG3-S dual-channel excitation system with integrated redundant closed-loop controller 13 Unrestricted Siemens AG All rights reserved

14 7. Technical Data Auxiliary power supply from power plant battery: For signal and controller power supply (24 V DC power supply) Power consumption: < 0.2 kw continuous Accuracy of AVR: Transformers: 0,5% continuously Voltage converters: 3-phase connection to generator voltage Power consumption < 5 VA per phase Rated secondary voltage 100 V to 120 V Current transformer: 1 to 3-phase for measurement of generator current Rated secondary current 1 A or 5 A Power consumption < 3 VA (not including losses on incoming cables) The transformers are not included in the scope of supply of the voltage regulator. Standards: The BES excitation system complies with the applicable IEC, EN, DIN, VDE standards and IEEE-421. Models: according to IEEE AC7B (available in PSS/E version 31 or higher) 14 Unrestricted Siemens AG All rights reserved

15 8. Abbreviations BES DIN EN I E IEC IEEE I EN I EO IGBT I max I setpoint PMG PSS RG3 DUR RG3 S SES SPPA SPPA-E3000 U E VDE Brushless Excitation System (= Rotating Excitation System) Deutsches Institut für Normung e. V. (German Standards Institute) European standard Output current of chopper regulator corresponds to excitation current International Electrotechnical Commission Institute of Electrical and Electronics Engineers Output current for rated load Output current for no-load operation Insulated-Gate Bipolar Transistor Ceiling current Exciter setpoint Permanent magnet synchronous generator Power System Stabilizer BES with DIGUREG as power stage and as closed-loop control BES with SINAMICS S120 as power stage and SIMOTION D4x5-2 as open-loop control Static excitation systems Siemens Power Plant Automation Siemens Power Plant Automation Electrical Solutions Output voltage of chopper regulator corresponds to excitation voltage Verband der Elektrotechnik Elektronik Informationstechnik e.v. 15 Unrestricted Siemens AG All rights reserved

16 Published by and copyright 2014 Siemens AG Power and Gas Freyeslebenstrasse Erlangen, Germany For more information, please contact Siemens AG Fossil Power Generation Division Siemensallee Karlsruhe, Germany Siemens Energy, Inc Ridgeland Parkway, Suite 116 Alpharetta, GA 30004, USA sppa-e3000.energy@siemens.com E3071_DT31_BES_TechnDescription_e_V2-4 AL: N ECCN: N Unrestricted All rights reserved. Trademarks mentioned in this document are the property of Siemens AG, its affiliates, or their respective owners. Printed on elementary chlorine-free bleached paper. Subject to change without prior notice. The information in this document contains general descriptions of the technical options available, which may not apply in all cases. The required technical options should therefore be specified in the contract. 16 Unrestricted Siemens AG All rights reserved