Busbar differential protection switching operation – Wienal

1. Whether the maintenance scale of the bus differential is confirmed, and whether the maintenance target is unchanged

Generally, differential maintenance includes bus differential maintenance, transformer differential maintenance, generator differential maintenance and line differential maintenance. The basic principle of completing differential maintenance is the same, that is, the current transformer of each side or each element is wired according to the differential connection method, and when there is a fault outside the normal operation and maintenance scale, the differential current is equal to zero, the fault time difference current within the maintenance scale is equal to the fault current, and the action current of the differential relay is calculated and set according to the maximum unbalanced current that occurs when avoiding external faults.

But it should also be very clear that the bus differential maintenance is very different from the transformer differential maintenance and generator differential maintenance: that is, the main junction method of the bus will change the operation method with the reverse operation of the bus, such as the double bus to single bus operation, the double bus side by side operation to double bus segmented side by side operation, bus components (such as lines, transformers, generators, etc.) can be switched from this section of the bus to another section of the bus and so on. In other words, the scale of bus differential maintenance will change (expand or shrink) with the operation of the bus and the change of the bus operation method, and the goal of the bus differential maintenance can also be changed (added or reduced) because of the switching operation of the bus components.

Busbar differential protection switching operation – Wienal

Busbar differential protection switching operation – Wienal

2. Whether the bus differential maintenance must be withdrawn during the bus reversal operation

"When carrying out the reverse operation, the bus differential maintenance must be withdrawn" is wrong, the reason why this error occurs is because some operators have seen, and even in the bus reverse operation, the bus differential maintenance misoperation, but the underlying reason is the lack of correct knowledge of the bus differential maintenance. If the bus reversal operation is carried out in strict accordance with the rules, that is, the equipotential operation when merging and de-arging, the potential difference when operating the isolation switch is reduced as much as possible, the secondary side reverse charging of the bus voltage transformer is prohibited, and the pulling, closing and switching of the low-voltage blocking bus differential maintenance pressure plate are fully considered for bus differential maintenance, etc., which will not cause bus differential maintenance malfunction. Therefore, in the process of inverting the busbar, the operating principle of the differential maintenance of the bus should generally be put into operation if it is not damaged. According to the statistics of the past years, the probability of bus short circuit incident caused by misoperation is still very high. Although in recent years, in order to prevent misoperation, five anti-locking equipment has been installed on the primary and secondary equipment of substations and power plants, some operators still use the master key in violation of regulations to go to the wrong distance, misclose, and pull by mistake. This makes it extremely important to insist on the bus differential maintenance investment when the bus is reversed. Investing in bus differential maintenance and inverted bus can be used to maintain the equipment to remove the fault in case of misoperation and short circuit of the bus, and then prevent the further expansion of the incident, and prevent serious damage to the equipment, loss of stability of the system or personal injury or death.

In fact, it is not so much that the bus reversing operation is easy to cause the bus differential maintenance malfunction, but rather that the bus reversing operation often makes the bus differential maintenance lose selectivity and mistakenly cut the non-faulty bus.

3. After the bus reversal operation, whether to incorporate the non-selective switch of bus differential maintenance into the actual operation

Some operators one-sidedly believe that the bus reverse operation will make the bus differential maintenance lose selectivity, so after the operation is completed, the non-selective switch of bus differential maintenance is closed. The root cause of this misunderstanding is that they don't understand the purpose of setting up this non-selective switch in the bus differential maintenance equipment.

There are many types of bus maintenance, and the operating principle of different types of bus maintenance is different. Some types of bus maintenance have shortcomings due to their operating principles, which will make the equipment lose its selectivity to faulty buses when carrying out bus reversing operations. Therefore, the key to the problem is that the operator should figure out what type of bus maintenance will lose the selectivity of the faulty bus during the bus reverse operation, and how to merge the non-selective switch of the equipment at the appropriate time, and when to pull the non-selective switch of the equipment away, or whether the switch should be kept in the closed state.

Busbar differential protection switching operation – Wienal

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