Generator demagnetization protection is a kind of generator relay protection, when the excitation of the generator suddenly disappears or partially disappears to complete loss, the excitation current gradually decays to zero. When the δ exceeds the static stability limit angle, the generator is out of sync with the system, and the generator protection device acts on the generator outlet circuit breaker to make the generator off the grid, prevent the generator from being damaged and protect the stable operation of the power grid.
There are two kinds of impedance circles for the generator stator side impedance criterion, the asynchronous impedance circle or the static boundary circle, and the action equation is:
For the impedance criterion, you can choose to combine it with the reactive power inverse criterion: q
Statically stable circle, asynchronous circle, and the change trajectory of the impedance after demagnetization is measured at the generator end in normal sequence
The process of change of the impedance circle after the loss of magnetization.
The generator loss of magnetism protection debugging project is the major difficulty of generator protection debugging, and the following example illustrates the debugging method of generator loss of magnetism protection impedance circle.
1. A generator protection value list: (partial).
Note: The impedance circle characteristic is set to "1" for an asynchronous circle, and "0" for a static circle.
2. Test wiring:Jibaozhixing-S60 handheld relay protection test systemThe output voltages UA, UB, UC, UN are connected to the terminal voltage terminal row of the generator protection device. The output current of the Relay Star-S60 is connected to the current terminal strip of the generator protection device. The trip exit of the terminal strip of the generator protection device is connected to the opening volume A and the common end of the relay protection star-S60.
Jibaozhixing-S60 handheld relay protection test system
Wiring diagram for loss of magnetism protection.
3. Test software and parameter settingsSelect the impedance characteristic test.
Test item selection: Search for impedance boundaries. Search method setting: two-way search, which means that the action area and the fixed area are searched back and forth to the boundary in both directions. Fault setting: The fault type is generally ABC short circuit, and the current can be set to 5A (if the system is loaded, the short circuit current can be reduced). Time setting: The time before the fault should meet the PT disconnection return, generally set 10 12s, and the maximum failure time is greater than the fixed value of 01s。The interval between the trials is 05s, which is the normal output time. Fault trigger mode: Select Time to trigger. Zero sequence compensation coefficient: Since the three-phase short circuit is selected, the zero sequence compensation coefficient can not be set.
Search center: According to the fixed value, the center can be calculated as 5 ((8 +2) 2=5), the angle is -90°, set z-, and the software automatically converts r-x. Search radius: The radius of the asynchronous circle is 3 ((8 -2) 2=3 from the fixed value, and the radius is greater than 3. The search step size determines the search accuracy. Number of search lines: Determined by the start angle, end angle and angle step, generally set 12 search points.
Tuning parameter setting: the setting impedance is the value on the fixed value sheet, which can be set to 8 and the angle is -90°. Manually set the protection area: the area is selected as a circle characteristic, the setting impedance z in the software is a fixed value asynchronous impedance zb=8, the offset is asynchronous impedance za=-2, and the impedance angle is set to -90° because it is an asynchronous circle. Let the reactive power inverse -qzd be greater than -2.
4. Test methods and results:After starting the test, the loss of magnetism protection action, the corresponding message information is displayed on the protection device, and the action information collected by the Star-S60 opening volume A is marked with a green dot at the corresponding search point, and the asynchronous circle of the loss of magnetism protection is searched.
Loss of magnetism protects asynchronous circle boundaries.
Think: If the impedance circle characteristic is set to "0", that is, it is a static circle, what is the corresponding parameter setting and circle characteristics? At this time, the search center should be set to 3 -90°, the search radius should be 6, which is greater than the static circle radius 5, the setting impedance should be 8, the offset should be 2, and the impedance angle should be -90°.
Loss of magnetism protects the theoretical boundary of the statically stable circle.