Thorough differential maintenance of the bus is to connect the current transformer of all the connecting elements on the bus to the differential circuit according to the same name phase and polarity, the characteristics and transformation ratio of the current transformer should be the same, if the transformation ratio can not be together, the compensation converter can be used to compensate, satisfactory ΣI=0.
The operating current of the differential relay is calculated and set according to the following conditions, whichever is greater:
1) Dodge the unbalanced current generated when the external short circuit occurs;
2) Avoid the large load current of the load branch in the bus connection element to avoid misoperation when the secondary circuit of the current is broken.
For incomplete differential maintenance of the bus, only the current transformer on the power supply element connected to the bus is connected to the differential circuit, and the current transformer on the non-power supply element is not connected to the differential circuit. Thus there is a problem on the non-power component, and it will act. The non-power components of the current transformer that are not connected to the differential circuit are reactors or transformers.
Advantages of thorough differential maintenance of the busbar:
1. The components and wiring are relatively simple, easy to debug, and easy to grasp by the operating personnel.
2. The use of speed saturation converter can effectively avoid the maintenance malfunction caused by the saturation of the current transformer caused by the DC component in the primary current outside the area.
3. When the components are fixed and connected, the bus differential maintenance has good selectivity.
4. When the bus tie circuit breaker is disconnected, there is still a selection ability for bus differential maintenance; When the two buses are short-circuited successively, the bus differential maintenance can still operate reliably.
Disadvantages of thorough differential maintenance of the bus:
1. When the method is destroyed, if there is a short circuit problem on any bus, the connecting elements on the two busbars will be cut off. As a result, it is less accustomed to changing the way it operates.
2. Due to the use of the current differential relay with speed saturation converter, its action time is slow (about 30-40 milliseconds action delay), and the fault cannot be quickly removed.
3. If the action current of the starting element and the selection element is set according to the unbalanced current when avoiding external short circuit, its sensitivity is low.
What is the fixed articulation method for busbar thorough differential maintenance?
The method of running the double bus together, according to the certain requirements, the lead wire and the branch with power supply are assigned and fixedly connected to the two buses, and this kind of bus is called the fixed connection bus. The differential maintenance of this kind of bus is called the complete differential maintenance of the bus with the fixed articulation method. The requirement for it is that when a bus is faulty, only the components connected to the bus bar are removed, and the other bus can continue to operate, that is, the bus differential maintenance has the ability to select the faulty busbar. When the fixed connection method of the running double bus is destroyed, the maintenance will not have the ability to pick the faulty busbar, and all the connected elements on the double bus will be removed.
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