With regard to the knowledge of distance protection, distance protection is a device for determining the time of movement based on distance. The rationale for achieving distance protection, as well as the scope of protection in paragraphs i, ii and iii of distance protection, and the method of consolidation and calculation of distance protection, are described below for your information。
I. What is distance protection
Distance protection is a protection device between the point of reaction failure and the place of protection installation (or resistance) and determines the time of movement based on the distance。
When the short-circuit point is close to the protection installation, its measurement is less resistant and has a shorter time frame; when the short-circuit point is far away from the protection installation, its measurement resistance increases and the time of movement increases, thus protecting the selective removal of fault lines。
Ii. Rationale for achieving distance protection
Distance protection is achieved by measuring resistance from short-circuit points to protection installations, where resistance is proportional to route length: the voltage of the protection installation is equal to failure point voltage plus line voltage, i. E. Ukm = uk+u; in which line voltage is not simply route resistance to utility, but is equal to the sum of the pressure reduction of positive, negative, zero-sequent electrical currents in the sequence resistance, i. E. U=ik1*x1 + ik2*x2 + ik0*x0。
Iii. Scope of protection in territories i, ii, iii
Paragraph i acts instantaneously, covering 80 to 85 per cent of the total length of the line; paragraph ii is similar to a time-limited electrical break, and the scope of protection should be within the protection of the next line from paragraph i, with a time frame greater than one t to ensure selective movement。
Paragraph iii, which is similar to electrical current protection, activates resistance to selection by avoiding load parameters for normal operations, with an action time limit of one t higher than the maximum action time for each of the other protections in the protection。
The scope of protection in paragraph ii is the full length of the line and extends to one part of the next line (which should not go beyond the protection of the next distance to protect the i segment), which together constitutes the primary protection of the line. The scope of protection in paragraph iii is the entire length of this and the next line and extends to part of the next line as a back-up protection for the protection of sections i and n。
Iv. Transition and encouragement of protection
Regardless of which relays are used to constitute current break protection, the principle of consolidation is to avoid the start-up current and instant overload at the start of the motor。
The protected constant of the current of a single action by a relay is normally calculated in the following manner: i=kis type: k-reliability factor. For the dl type 1. 4 ~1. 6, for the gl type 1. 8 ~ 2. 0is - motor-activated currents, the normal rated current is 5-7 times fixed, and reliable coefficients and start-up multipliers, if not properly mastered, tend to cause the relay to miss or resist。
It is generally understood that the reliability factor is based on two factors:
The first factor is the ease with which the electric motor is overloaded and overloaded to take a high value; conversely, to take a small value。
The second factor is the electrical distance between the electrical motor and the current measurement element of the relay。
