WHAT IS The Principle of Busbar Differential Protection

Now I come to the principle of bus differential protection:

There are only incoming and outgoing lines on the bus, and under normal operating conditions, the size of the incoming and outgoing currents is equal and phased.

Same. If the busbar fails, this balance is broken. Some protections are used for comparison.

Whether the current is balanced, some protection uses to compare whether the current phase is consistent, and some have both.

Yes, once the bus fault is identified, the protection action element is immediately activated and the bus is jumped.

All circuit breakers. If the two busbars are running in parallel, some protections will selectively jump out of the bus.

Coupling switches and all incoming and outgoing circuit breakers for faulty busbars to reduce the scope of the outage.

Female differential protection includes, microcomputer female differential protection, and ratio braking female differential protection.

The principle of traditional ratio braking bus differential protection is to use the vector sum of the currents of each branch (including bus connection) of the protected bus as the action quantity, and the sum of the absolute values of the currents of each branch is attached to the braking coefficient of less than 1 as the braking quantity. It is reliably immobile in the event of an out-of-zone fault and has considerable sensitivity in the event of an in-zone fault. The algorithm is simple but has poor adaptability, large secondary load, and is easily affected by the complexity of the loop.

However, the microcomputer bus differential protection consists of a split-phase ratio differential element that can reflect single-phase faults and phase-to-phase faults. The double bus wiring differential circuit includes the bus large difference circuit and the bus small difference circuit of each section. The difference is the difference circuit composed of all branch currents except for the bus tie switch and the section switch, and the difference of a certain section of the bus refers to the difference circuit composed of all the branch currents connected to the section, including the bus tie and the section circuit breaker.

The large difference is used to identify the faults within and outside the busbar, and the small difference is used for the selection of the faulty bus.

The biggest difference between these two principles in use is that the concept of large difference is introduced into the microcomputer bus deviation as a fault criterion, reflecting the bus node and current state in the system, which is used to judge whether the bus fault really occurs, which is more reliable than the traditional ratio braking bus differential protection, and can minimize the bus differential protection malfunction caused by the non-corresponding position of the auxiliary contact of the knife switch.

Brother. Pure, give points and wish you a safe family.

Differential protection is an important system equipment to ensure the safe and stable operation of the power grid, and its safety, reliability, sensitivity and rapidity are of decisive significance to ensure the safety of the entire regional power grid. So far, the bus current specific phase differential protection, current phase comparison differential protection, and ratio braking differential protection that have been widely used in the power grid have been widely used in the power grid, and it is generally believed that in terms of adapting to the bus operation mode, fault type, transition resistance, etc., it is undoubtedly the best ratio braking bus differential protection composed of the principle of split-phase current difference.

Comparison of the working principle of ratiometric differential elementsThere is no essential difference in the working principle of conventional ratio differential element and microcomputer mother differential protection, but the braking current of the two is different. The former is taken as the braking amount by the sum of the absolute current values of each component (including the bus connection) on the bus, and the latter takes the sum of the absolute current values of each component on the bus except for the bus connection and segmented current as the braking amount, and the action amount of the differential element is the current vector and absolute value of each component on the bus.

The principle of bus differential protection is to use the vector sum of the current of each branch (including bus connection) of the protected bus as the action quantity, and the sum of the absolute value of the current of each branch is attached to the braking coefficient of less than 1 as the braking quantity.

Female differential protection is an important system equipment to ensure the safe and stable operation of the power grid, and its safety, reliability, sensitivity and rapidity are of decisive significance to ensure the safety of the entire regional power grid.

The bus current ratio phase differential protection, current phase comparison differential protection, and ratio braking differential protection that have been widely used in the power grid have been widely used in the power grid, and it is generally believed that in terms of adapting to the bus operation mode, fault type, transition resistance, etc., it is undoubtedly the best ratio braking bus differential protection composed of the principle of split-phase current difference.

Microcomputer mother-difference protection features.

1. Digital sampling, and mathematical model analysis to form the adaptive impedance-weighted anti-TA saturation criterion.

2. The TA ratio is allowed to be different, and the adjustment coefficient can be adjusted, which can adapt to any change ratio situation in the future expansion.

3. Adapt to different bus operation modes.

4. There is no contact switching between TA circuit and trip outlet circuit, which increases the reliability of action and avoids a series of problems caused by unreliable contact contact.

5. The software logic used in the same device can realize bus difference protection, charging protection, dead zone protection, failure protection, etc., with compact structure and simple circuit.

6. Different configurations can be carried out to meet the needs of different forms of main wiring.

7. The human-machine dialogue is friendly, the background interface communication mode is flexible, and the communication with the monitoring system has a perfect device status message.

8. Support the power industry standard IEC 608705103 protocol, compatible with the fault recording data format output by Comtrade.

Line bus differential protection refers to the line bus differential protection, which is judged and acted in accordance with the principle of early hunger and branch balance. The debusbar is fully differential and incompletely differential.

The complete differential protection of the bus is to connect the current transformer of all the connected elements on the bus to the differential circuit according to the same name phase and polarity, and the characteristics and transformation ratio of the current blind transformer should be the same, if the transformation ratio can not be the same, the compensation converter can be used to compensate to meet the i=0.

The operating current of the differential relay is calculated and set according to the following conditions, and its maximum value is taken

1) Dodge the unbalanced current generated when the external short circuit occurs;

2) Avoid the maximum load current of the maximum load branch in the bus connection element to prevent misoperation when the secondary circuit of the current is broken.

The incomplete differential protection of the bus only needs to connect the current transformer on the power supply element connected to the bus to the differential circuit, and the current transformer on the non-power supply element is not connected to the differential circuit. So in the event of a failure on a powerless element, it will act. The non-power components of the current transformer that are not connected to the differential circuit are reactors or transformers.

Answers]: a, b, c, d

Due to the current differential protection of the fixed ruler connection of the components, when the fixed connection mode is destroyed and the core is taken, the protection loses selectivity, and the failure of any group of buses may cause the removal of two groups of buses. The phase comparison formula, which compares the change of current phase, overcomes the shortcomings of high branch failure of components, and the lack of flexibility of fixed connection protection, and is suitable for bus protection where the operation mode of connecting components often changes. At the same time, the current ratio phase protection is based on the phase comparison, which has nothing to do with the amplitude, and does not need to consider the current error caused by the current transformer protection, and can still be used when the current transformer model and conversion ratio are inconsistent.

The bus protection principle is a power system protection technology that protects the bus by detecting the current and voltage on the bus. When a fault occurs on the bus, the bus protection device will detect the fault by monitoring the current and Peiming voltage on the bus, and automatically cut off the connection on the bus, so as to protect the bus from damage. The bus protection device automatically cuts off the connection on the bus by setting a maximum current value that once the current on the bus exceeds this maximum value.

In addition, the bus protection device can also monitor the voltage on the bus, and if the voltage on the bus exceeds the set maximum value, it will also automatically cut off the connection on the bus. In this way, the busbar can be effectively protected from damage.

Advantages: 1. The components and wiring are relatively simple, the debugging is convenient, and the operators are easy to master.

2. The use of fast saturation converter can effectively prevent the protection malfunction caused by the saturation of the current transformer caused by the DC component in the primary current of the fault outside the area.

3. When the components are fixedly connected, the bus differential protection has a good selectivity.

4. When the bus tie circuit breaker is disconnected, the bus differential protection still has the ability to choose; In the event of a short circuit between the two buses, the bus differential protection can still operate reliably.

Disadvantages: 1. When the mode is destroyed, if a short circuit fault occurs on any bus, all the connecting elements on the two busbars will be removed. As a result, it is less able to adapt to changes in 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 maximum unbalanced current when avoiding external short circuit, its sensitivity is low.