Hi every body
I'm preparing a bid for a generator of a 120 to 180MW gas turbine ( frame9, V94.2,…), you find her my proposal for the excitation system specification
Can you comment this to enhance it??? Is this applicable for the standardized products on the market specially for this application? Should I add any thing else? is there any particularity between brushless and static exciter?
Can you help me on the spec of the converter to start the turbine?(I can follow you my email if you have any typical specification)
I don't have the IEEE and ANSI standards related here (I was inspired for this spec from the WEB doc's), are they applicable to my application? Is there any equivalent in the IEC standard (other than IEC34)
is there any other standard to include? Are the ceiling values, droop percent, and other values standardized??
Should I ask for any redundancy ?is it compulsory or optional?(on the standardized products on the market)
Thank you in advance
Best regards
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Excitation specification / construction
The excitation system shall be provided with devices which will polarize the main generator field , it's a permanent magnetic generator or transformer on the main duct. If necessary, the station battery insure generator voltage buildup. Means shall be provided to prevent inadvertent backflow of current from the generator field and exciter output circuit through the contactor to the station battery. The scheme proposed by the contractor shall be subject to approval of the Construction Engineer.
The output shall be connected to the generator field through either a conductor and resistor or a free-wheeling diode to allow field discharge on loss of field excitation and to minimize contributions to faults specially iron burning in the event of a generator fault. The preferred method is to reverse voltage the generator field to drive the current to zero. The time constant should be communicated. An alternating-current breaker is required at the excitation system input to allow field circuit tripping for either external system conditions or a failure of the excitation components.
The initial capacity of the rectifiers shall have an allowance to cover any loss in capacity which may be caused by aging. the rectifiers shall have a Peak Inverse Voltage (PIV) rating of not less than four times the maximum root-mean-square voltage of the input.
Field ground detection relay (64F) shall be provided it shall be able to detect grounds at all points of the winding and under all operating conditions.
Excitation systems shall have a minimum ceiling voltage of 150 percent of rated full load field voltage and be classified as a high initial response excitation system as defined in IEEE 421.1.
Ceiling current shall have a transient time capability equal to or greater than the short time overload capability of the generator. See ANSI C50.12, 13, or 14.
The system shall be able to calculate the field temperature and eventually to display it and to present as such a kind of redundant protection
Static Systems shall meet these criteria with 70 percent of generator terminal voltage. The offline generator terminal voltage response shall have an overshoot limited to 20 percent.
Tracking between automatic and manual regulators should insure the smooth transfer between both of them.
A damping filter should ground the high frequency components of the field voltage to avoid the bearing damage due to the shaft voltage induced by the rectifier in the case of a static excitation, and in the case of a rotating rectifier, the shaft will be ground via brushes. It should be possible to control this current.
The system should support network communication with the turbine control panel and the DCS, and also a remote control by ma signal for the grid managing
Automatic Voltage regulator
The regulator must be acting continuously and be able to maintain the generator voltage under steady-state conditions without hunting and within 0.2 percent of any voltage level between 90 percent and 110 percent of the rated generator voltage
Voltage regulators shall have a minimum of the following signal modifiers:
§ Reactive current compensator capable of line drop or droop characteristic (value???????)
§ Minimum excitation limiter: shall limit the decrease of generator excitation below that may result in pullout of the generator. The characteristics shall closely match the manufacturer’s capability curves and shall be such as to permit generator operation from rated kilovolt ampere, rated voltage and unity power factor to the kilovolt ampere rating at rated voltage and zero power factor under excited. This device shall assume control smoothly and maintain excitation in a stable manner.
§ Maximum excitation limiter shall have an adjustable time delay feature to permit short-time operation subject to thermal limitations with ceiling excitation. shall have an adjustable inverse timing range based on the magnitude of the over excitation. This device shall limit excitation smoothly while maintaining stability.
§ Volts per Hertz limiter responsive to both varying voltage and varying frequency.
§ Two levels of over-excitation protection. The first level should provide a forcing alarm and trip the voltage regulator after a time delay to permit short-time operation subject to thermal limitations with ceiling excitation. The second level shall have an inverse time characteristic such that the time-current relationship may be coordinated with the generator short time thermal requirements (ANSI C50.13 or C50.14).
§ A two input Power System Stabilizer (PSS) utilizing Integral of Accelerating Power (of preference) to produce a stabilizing signal to modify regulator output. PSS shall provide a positive contribution to damping for a frequency range from 0.1 hertz through local mode frequency (minimum to 5 hertz).
Power Factor Controller
The controller must be able to maintain a power factor setting within 1 percent of the setting at full load at any set point between 90 percent lagging and 95 percent leading.
Manual voltage regulator
This regulator is based on the field current feedback, it should higher range of voltage control, the maximum and minimum excitation limit should be kept to remain within the generator heating capabilities
