Zero-sequence current transformers are used in conjunction with relay protection devices or signals when zero-sequence earth currents are generated in the power system, so that the device components act to achieve protection or monitoring. When an electric shock or leakage fault occurs in the circuit, the secondary side of the transformer outputs zero-sequence current, so that the equipment on the secondary line connected to the protection action (cut off power, alarm, etc.). So, in what areas are zero sequence current transformers applicable? Let's take a look.
1. zero sequence current transformer characteristics of the application
Zero sequence current transformer is cable type, the choice of ABS engineering plastic shell, resin casting into a fully sealed, insulation function is good, beautiful appearance, with high sensitivity, good linearity, reliable operation, easy installation and other features, its function is better than the general zero sequence current transformer.
Wide range of applications, not only to adapt to electromagnetic relay protection, but also to adapt to electronic and microcomputer protection devices, users can according to the system operation method (neutral grounding, neutral point is not grounded, large resistance grounding, small resistance grounding, arc extinguishing coil grounding) to choose the appropriate zero sequence current transformer.
2. the use of zero sequence current transformer principle
Zero sequence current transformer in the power system when the zero sequence grounding current and relay protection devices and signals used in cooperation, so that the equipment components action, to achieve protection or monitoring.
The basic principle of zero sequence current protection is based on Kirchhoff's current law: the algebraic sum of the complex currents flowing into any node in the circuit is equal to zero. In the case of normal lines and electrical equipment, the vector sum of the phase currents is equal to zero, thus the secondary winding of the zero-sequence current transformer has no signal output and the actuating element does not act.
When the ground fault occurs, the vector sum of the current of each phase is not zero, the fault current makes the magnetic flux in the annular core of the zero sequence current transformer, the secondary side of the zero sequence current transformer induced voltage makes the actuating element actuate, drive the decoupling device, switch the power supply network, to achieve the purpose of ground fault protection.
Zero sequence current transformer use scale more widely, not only adapt to electromagnetic relay protection, but also can adapt to electronic and microcomputer protection device, the user can according to the system operation method, neutral point useful grounding or neutral point non-useful grounding of different, choose the corresponding zero sequence current transformer.
3. the zero sequence current transformer installation environment
① the zero sequence current transformer should be installed in a humid environment to prevent corrosion and make the sensitivity decline, resulting in the protection device to refuse to move. If it must be installed in a humid environment, it should be installed in an airtight box to prevent rain and humid air from entering.
② zero sequence current transformer should avoid installation in high and low temperature environment. Because the temperature is too high or too low will affect the magnetic conductivity of the transformer, thus affecting the stability of the action.
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