Selection, installation and commissioning of differential protection device for large power generato
Ships of all sizes, regardless of their type, often encounter some problems that prevent the equipment from operating properly during the construction of the electrical system.
With the development of modern science and technology, the electrification of ships and the degree of automation are also constantly increasing. The higher the tonnage of ships is, the higher the load on ships is. Therefore, due to the factors such as hull structure and installation of piping system, The use of modern ships is increasingly common, how to better strengthen the protection of high-power generators is particularly important. According to the requirements of the classification society, it is proposed that a high-power generator with a load of more than 1400KVA must use a differential protection device.
However, in the actual installation and commissioning of electrical equipment for ships, the phenomenon of incorrect connection is very common. The reasons are many and inevitable. In addition to the phenomenon of easy to damage the equipment, the construction cycle of the ship and the loss of manpower and material resources are incalculable, the author now Jinling Shipyard 8050RO-RO series of ships, for example, talk about high-power generators Differential protection device in the installation and commissioning process failure and troubleshooting.
The generator differential protection device is a kind of protection device that detects whether the line between the generator and the main switch is short-circuited or grounded. The differential protection device is equipped with two current transformers for each phase on the generator side and the distribution board side, and the current of each phase is designed to be overlapped. By using the secondary current detected on the non-inverting generator side and The vector difference of the secondary current detected on the switchboard side enters the differential protection device. The internal circuit of the differential protection device determines whether to issue a command to de-energize the generator according to the differential current (usually not more than 5%) that the generator can withstand, and the tripping board on the main busbar The main switch, the generator in a standby state to protect the generator winding coil damage, to protect the generator to reduce unnecessary losses.
In the actual construction process often appear the following error,
1, the polarity of the transformer on the generator side or the distribution board side is reversed, that is, any one of RS1 and RS2, SS1 and SS2, TS1 and TS2 is reversed (as shown in Figure 2 and R phase for example) , Will change the generator side and distribution board side of the current vector relationship from the secondary current vector difference into a secondary vector and the current relationship between the two sides so that the current superimposed, it will cause the phase current imbalance , While the set value of the differential protection device , resulting in malfunction of the differential protection device , it is difficult to ensure the normal power supply to the grid generator;
2, in the generator or distribution board side, the phase transformer line is wrong, that RS1, RS2 and SS1, SS2 or TS1, TS2 between the mistakes, as shown in Figure 3, this will cause the generator side and The difference of the secondary current, which is not in phase with the distribution board, enters into the differential protection device, but the difference of the secondary current between R phase and S phase, S phase and T phase, or T phase and R phase enters the differential protection Device, easily lead to the current imbalance between the phase, resulting in differential protection device action, it is difficult to ensure the normal power supply to the grid generator.
After the above problems, we usually exclude the method is:
1 Check the connection between the generator side and the switchboard side transformer;
2 Check the wiring of the generator side transformer;
3 Check the wiring of the transformer on the switchboard side.
According to the drawings, you can get the solution. But in actual process, due to the negligence of manufacturers and the internal structure of the equipment, it is often difficult to confirm the polarity of the transformer with the naked eye. Many detours can not find the problem Where you are. The author based on their experience in the field debugging accumulated in this article describes a method: that is, to prepare an ammeter according to the circuit shown in Figure 3 to connect, and then phase by phase measured the difference between the two secondary current vector, according to the current The size of the problem to determine where. There are generally the following situations:
1 has two phases of the secondary current vector difference is almost zero, and the other phase of the secondary current vector difference than this two-phase equal current vector difference, we can determine the phase of the transformer Reverse polarity, as shown in Figure 2, as long as the polarity of this mutual inductor can be changed;
2 one phase of the secondary current vector difference is close to zero, while the other two phases of the secondary current vector difference, then we judge there are three cases,
a The polarity of these two mutual inductors is reversed;
b the two mutual inductor reversed;
c the two mutual inductor reversed, at the same time the polarity is reversed;
3 three-phase current difference between the two currents are not the same, we should take the exclusion method to confirm the same way, with any phase as the standard, change the other two mutual inductor wiring, testing between the phases Of the vector difference current, to compare, according to the size of the current, refer to steps 1 and 2 to find out where the problem lies.
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