A modern excitation system for medium and large synchronous generators is designed and manufacturing under license of SIEMENS Company. This system is typically of the full redundant type: two identical rectifiers are provided, each one is capable of powering the generator field, and two identical digital regulators each one is capable of controlling indifferently either of two rectifiers. Once one of the two rectifiers and one of the two AVR have been chosen, the system considers the other rectifier and the other AVR as being as standby while any faults occur, the system switches to the standby rectifier or AVR, or both, automatically. The changeover from one rectifier to the other is carried out with a zero transient, while the change over from one AVR to another take place with a very limited transient, due to the alignment function on the regulators. Naturally, the operator can switched from one rectifier or AVR to the other under any operating conditions. Each of the two rectifiers is housed in its own compartment of the excitation cubicle, with a separation diaphragm between it and the other parts of the system. Each rectifier is connected to the incoming line from excitation transformers by means of a three pole disconnecting switch. Excitation control elements include both excitation regulating and stabilizing functions such as underexcitation limiter, overexcitation limiter, stator current limiter, power system stabilizer (PSS), V/Hz limiter, power factor and reactive power controllers.
|Rated output||420 KW|
|Exciter response||1/3 S|
|Rated excitation current IE rated||1,417 A|
|Max. continuous current IE max (= 1.1 x IE rated)||1,558.7 A|
|Impulse test current Ip (10 s)||2,250 A|
|Max. input voltage||520 V|
|Thyristor type||5ST P27 H810|
|Voltage rating factor*||2|
|Redundancy||2 x 100%|
|Rated losses||7.0 kW|
|Required cooling air (3 to 4 fans)||4,800 m³/h|
|Sound pressure level 50 Hz power supply||75 dB(A)|
- Control accuracy ≤ ±0.5%
- Control range 90 ... 110% Urated
- Setting range (manual) 0 ... 110% Irated
- Controller dead band ≤ ±0.1%
- Mean excitation response ≥ 3 s-¹ (dependent on surge factor)
- Surge factor ≥ 1.8 (dependent on input voltage in relation to rated field data)
- Initial excitation time ≤ 10 ms
1- Compact units and individual static excitation units are factory-mounted, wired and checked in cabinets from the 8MT system. They are supplied as ready-to-use units. This significantly reduces startup time and costs at customer sites.
2- Including automatic voltage regulator (AVR)
3- Integrated radial fans dissipate heat; the fans are redundant for the static excitation equipment (single bridges only).
4- The static excitation equipment is able to exchange signals with the instrumentation and control for the purpose of operator control and monitoring as well as for error signaling.
5- Digital SIMATIC S7 and SIMOREG (SEE) are used for all open-loop and closed-loop control tasks; these are 2 well-proven systems for fast open-loop and closed-loop control and arithmetic tasks in drive and power engineering with the following characteristics and features:
- Modular design and subdivision into clear, transparent function diagrams using the STEP 7, with correspondingly transparent documentation
- Option to connect a PC or PG
- Suitable software packages are available to make parameter adaptation easy.
- Self-test routines
- Intelligent operator control and display unit for local control with plain-text messages and time stamp
- Trace memory for recording fast sequences for diagnostics and troubleshooting (complete fault history before and after the event), read out using option to connect PC or PG
6- The medium-voltage converter for gating and monitoring the optocoupler and fiber-optic cable power semiconductors.
7- Mechanical encoders are not required on the rotor for open-loop and closed-loop control. The information required is derived from the electrical generator stator actual values CT and VT (current and voltage).