Bus differential protection function and principle
Bus differential protection device has those functions?
The main functions of bus differential protection are: bus differential protection, bus coupler dead zone protection, bus failure protection, bus coupler charging protection, bus coupler overcurrent protection, line failure protection and PT disconnection.
Bus differential protection What are the requirements? What is the protection principle?
Bus protection needs to meet the speed and selectivity requirements, bus differential protection devices are based on the current differential protection principle.
In general, the principle of current differential protection is still very simple and practical and reliable, in general, we still use the principle of current differential protection to form bus differential protection, bus differential protection device principle we can generally be divided into two categories: Current differential protection; 2 current phase differential protection.
Bus differential protection principle
In the event of a fault on the busbar, the current in each connection unit will normally flow to the busbar. In the event of a fault outside the busbar (on the line or inside the transformer), the current in each connection unit will flow to the busbar and to the busbar. On-line fault bus protection should be action, busbar busbar fault protection should be reliable operation.
1. action current and braking current acquisition
For busbar differential protection with double busbar, the total differential is used as the total starting element for differential protection, which reflects the sum of the current flowing through all the connecting elements of bus I and busbar II to distinguish the busbar fault from the external short-circuit fault.
The I component differential and the II component difference are used as the selection components of the fault bus, which respectively reflect the sum of the I bus and II bus currents flowing from each connecting component, so as to distinguish the I bus fault or the II bus fault.
The total differential is also often referred to as the "total difference" or the "big difference" because the total differential protection covers the bus bars.
Sub-differential because of its differential protection is only a corresponding section of the bus, often referred to as "points difference" or "small difference."
Take the action current as an example to illustrate the method of obtaining the total differential (large difference) and the differential (small difference) current:
① double bus wiring;
② bus of the bypass mode and the double busbar wiring;
③ bypass and bus connection in the form of double busbar.
2. Duplex ratio differential bus protection action criteria:
(1) The busbar differential protection based on the ratio braking principle uses one passing current as the braking current to overcome the differential unbalanced current caused by the TA error of the current transformer in the out-of-zone fault and has been widely used in the high-voltage power network.
Action current and brake current acquisition
Domestic microcomputer bus differential protection generally adopts the principle of full current differential protection.
Full current differential refers to the bus connected to all the components of the current access to the differential circuit by phase. The amount of current that determines whether a maternal differential protection is active is the operating current and the braking current.
Braking current refers to the sum of the absolute values of all connecting element currents on the bus Ires
The operating current refers to the absolute value Id of the sum of the current phasors of all connection elements on the bus.
Ij for each component current quadratic value (phasor), Id for the operating current amplitude, n is the number of lines, Ires for the braking current amplitude.
② duplex ratio differential bus protection action criteria:
Braking current composite brake current:
In the event of a fault in the area due to I d Ⅰ Ires, the composite braking current | Ires-Id | ≈ 0, no braking system protection;
Ⅰres >> Ⅰd in the event of an out-of-area failure, the protection system has very strong braking characteristics.
Figure 1 bus differential protection action logic diagram
Description: large differential components and bus differential components have their own characteristics. The range of differential protection covers the busbar of each section, and in most cases it is not controlled by the operating mode. The small difference is controlled by the operating mode, and its differential protection range is only a corresponding busbar with selectivity.
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