Distance protection implementation principle:
The specific implementation of distance protection is achieved by measuring the impedance of the short-circuit point to the protection installation, because the impedance of the line is proportional to the length of the line. BR> In the previous analysis, it is known that the voltage at the protection installation is equal to the point of failure. The voltage plus the line voltage drop, ie UKM=UK+△U; wherein the line voltage drop ΔU is not simply the line impedance multiplied by the phase current, which is equal to the sum of the voltage drops of the positive, negative and zero sequence currents on each sequence impedance. , ie △U=IK1*X1+ IK2*X2+ IK0*X0.
Distance protection range:
Generally, the total length of the protection line in Section I is about 80%-85%, and there is no time limit action. The second paragraph is matched with the first or second paragraph of the adjacent protection, and the action time is 0.5 seconds. The first and second parts constitute the main protection. In the third paragraph, the maximum load current is set as the backup protection, and the time is matched with the adjacent line.
Distance protection and calculation:
Regardless of which relay is used to constitute the current quick-break protection, the principle of setting is to avoid the starting current and the instantaneous overload when the motor starts. The protection setting of the relay's primary operating current is generally calculated as follows: I = KIS where: K — reliability factor. For DL ​​type, take 1.4 ~ 1.6, for GL type, take 1.8 ~ 2.0 IS - motor starting current, generally take 5 ~ 7 times of rated current. In the setting, the reliability coefficient and starting ratio are often easy to cause relay malfunction if it is not well mastered. Or refuse to move, in general, can be mastered according to the following principles. The reliability factor setting mainly considers two factors. First, whether the motor is easily overloaded, it is easy to take a large value of overload; otherwise, it takes a small value. Second, the electrical distance between the motor and the relay current measuring component
The distance protection consists of which parts are generally composed of starting, measuring, oscillating blocking, voltage loop disconnection, coordination logic and exit.
1. Startup section. The startup section is used to determine if the power system has failed.
2. Measurement section. The measurement part is the core of distance protection. The requirement is to quickly and accurately determine the fault direction and distance in the case of system failure, and compare it with the preset protection range. Does not work when there is an out of zone fault.
3. Oscillation blocking part. The oscillations in the power system are not short circuits, and the distance protection should not be operated.
4. The voltage loop is broken. When the voltage loop is broken, the protection measurement power supply will disappear, which may cause the distance protection measurement component to malfunction. In this case, the part is required to be closed.
5, with the logic part. This part is used to achieve the logical cooperation between the various parts of the distance protection and the time coordination between the sections of the three-section distance protection.
6. The exit part of the exit part includes a trip outlet and a signal exit, and the trip circuit is turned on during the protection action and a corresponding signal is sent.Horizontal Plate Pneumatic Mixer
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