What is the difference between the differential protection of the transformer group and the longitud

The differential protection of the transformer group is to use the sampling value of the CT current on each side for differential, and the differential current of the current on each side is 0 under normal circumstances.

For example, a 220kV transformer has three sides are high, medium and low, each side is equipped with CT, the current used in the protection device is from the CT, under normal circumstances, the current flowing into the main transformer is equal to the current flowing out of the main transformer, if the short circuit occurs inside the main transformer, all the current will flow into the short circuit point, at this time there must be a bad current. (It can be said that it is similar to the mother difference).

The longitudinal differential is set up for the line protection, I will talk about the optical fiber differential: the line has two sides, I call one of the sides this side, the other side is called the opposite side, the protection device on this side samples the secondary current on the side of the line CT, the same opposite side current is the secondary current taken through the side CT, the protection device on both sides is connected by optical fiber, the current on the opposite side is transmitted to the side through the fiber optic channel, and the protection device on the side will receive the current on the opposite side and compare the current on the side. When the differential current is generated and reaches a fixed value, the differential protection action on the local side is the same as the differential protection on the opposite side.

In fact, the principle is to compare the currents on each side, and it cannot be said that the difference is that the secondary current of the differential protection of the transformer group is directly taken from the CT, while the current on the opposite side of the longitudinal differential is transmitted through the channel.

Differential protection of the transformer group.

Commonly known as "machine-variable large differential", it is the application of the principle of longitudinal differential, but the generator differential and the main transformer differential are combined into one, and a set of longitudinal protection equipment is used, and the protection scope is extended to the entire "transformer group".

What is tandem differential protection? What is the definition of longitudinal differential protection: use a certain communication channel to connect the protection devices at both ends of the transmission line longitudinally, transmit the electrical quantity at each end to the other end, and compare the electrical quantity at both ends to judge whether the fault is within the scope of the line or outside the scope of the road, so as to decide whether it is the only line to be protected.

Principle: 1. The longitudinal differential protection device is composed of current transformers and relays on both sides of the transformer, and the two current transformers are connected in series to form a loop, and the current relay is connected to the loop. Therefore, the current of the current relay is equal to the difference between the currents on the secondary side of the current transformer on both sides.

2. When a fault occurs under normal conditions or outside the protection range, the current on the secondary side of the current transformer on both sides is equal in magnitude and the phase is the same, so the differential current flowing through the relay is zero. 3. However, if a short circuit fault occurs in the protected area, the differential current flowing through the relay is no longer zero, so the relay will act to trip the open circuit cavity, so as to play a protective role. Do you understand this explanation?

Summary. Pro, longitudinal current differential protection is a kind of protection method commonly used in high-voltage transmission lines, and its main working principle is as follows:

Pro, longitudinal current differential protection is a kind of protection method commonly used in high-voltage transmission lines, and its main working principle is as follows:

1.Sensor: Converts the current signal into an electrical signal.

2.Comparator: Compare the current signals at both ends to calculate the difference between the currents at both ends.

3.Ratiometric braking like a wheel songner: The differential current signal is compared to the rated current, and if the differential current bend exceeds a set threshold, a protection action is triggered.

4.Time Delay: After the differential current signal exceeds the set threshold, a certain time delay is required to avoid malfunction.

5.Trigger: After the time delay, if the differential current signal still exceeds the set threshold, a protection action is triggered, cutting off the fault circuit.

Difference 1: The protective role is different.

Differential protection is mainly used for the protection of power transformers. Transformer longitudinal protection - the differential relay is installed on the high and low voltage side of the transformer (or the line of the combined relay is connected to the protection CT circuit of the high and low voltage side respectively), and the operation status of the transformer is monitored according to the principle of equal input and output power (no-load loss should be corrected).

2. The principle is different.

Differential protection monitors the operation of the transformer. Once the monitored data on both sides reaches the setting value, the protection device will act on and switch to remove the transformer from the system. The principle of transformer longitudinal protection is to monitor the change of current at two different monitoring points of the protection equipment, so as to find out whether the monitored object is abnormal, and when the abnormal value reaches the setting value, that is, the circuit breaker is used to remove the equipment from the system to prevent the accident from expanding.

There are two types of differential protection: longitudinal difference and cross difference.

3. The performance is different.

When there is a short circuit between phases near the stator lead line or the neutral point, the current in the connection line between the two neutral points is small, and the cross difference protection cannot be operated, and a dead zone appears, and the longitudinal protection can be replaced.

The longitudinal differential protection is the quick-action protection of the whole line, which is to compare the changes in the electrical quantity on both sides of the line at the same time.

Advantage 1) Based on Kirchhoff's current law, the principle is simple and reliable, and the action speed is fast.

2) It has a natural ability to select phases.

3) It is not affected by system oscillation and non-full-phase operation, and can reflect various types of faults, which is the ideal line master protection.

Disadvantage 1) The information transmitted by the protection device through Fibre Channel is required to be synchronized.

2) For ultra-high voltage long-distance transmission lines, the influence of capacitance current needs to be considered.

3) When the line is grounded by large resistance or the remote fault of the heavy-load and long-distance transmission line, the protection sensitivity will be reduced.

Longitudinal differential protection.

The measuring element that uses a differential relay as a protection is used to compare the difference between the current and the phase of each end of the protected element, so as to judge whether a short circuit occurs in the protected area.

Because the longitudinal differential protection only operates when there is a short circuit in the protected area, there is no selective fit problem with the protection of adjacent components in the system, so it can quickly cut off the short circuit at any point in the entire protected area, which is its valuable advantage. However, in order to form a longitudinal differential protection device, a current transformer must be installed at each end of the protected element, and their secondary coils must be connected with auxiliary wires to connect to the differential relay. Due to the limitation of auxiliary wire conditions, the differential protection of longitudinal connection is limited to the first road, and for generators, transformers and busbars, etc., longitudinal differential protection can be widely used to achieve main protection.

Scope of application. The longitudinal differential protection differential protection device has differential quick-break protection and compound ratio differential protection with or without second harmonic braking, which can be used in the occasion of three-side differential current input (three-turn transformer), has a complete and powerful acquisition function for the voltage and current analog and switching quantities of primary equipment, is equipped with standard RS485 and industrial CAN communication interface, and realizes three-turn main transformer differential protection, two-turn main transformer differential protection, two-turn distribution transformer differential protection, generator differential protection, Protection and measurement and control functions such as motor differential protection and non-electric protection.