According to the analysis of relevant national standards and the two main low-voltage reactive power compensation methods mentioned above, the correct selection of low-voltage reactive power protection fuses should be considered and selected separately from the following two aspects:
1. For pure capacitance compensation applications, the compensation components are only low voltage capacitors:
Due to the rationality of the national standard GB/T12747.1-2004, the protection current fuse can be selected by referring to the maximum allowable current requirement in the standard, 1.10×overcurrent capability×capacitor rated current.
An example of a capacitor compensation loop of 25KVAR/400V:
1) The rated current of the capacitor of this circuit is 36A. If the capacitor only meets the 1.3 times overcurrent capability in the standard, the maximum allowable current of the circuit is 1.10×1.3×36=51.5A. The standard current range of the fuses is 50A, 63A, so the correct fuse rating should be 50A.
2) If the capacitor is larger than the overcurrent capability in the standard, such as 1.5 times, the maximum allowable current of the loop is 1.10 × 1.5 × 36 = 59.4A. The standard current range of the fuses is 50A, 63A, so the correct fuse rating should be 63A. .
2. For non-tuning compensation applications, the compensation components include low voltage capacitors and series reactors:
This kind of application is a series reactor with a certain reactance rate in the traditional capacitor compensation loop. It has the advantages of preventing system harmonic amplification, avoiding resonance, and absorbing harmonics in some systems, thus providing reliable reactive power. While compensating for the purpose of improving power quality, it has been increasingly used in industrial and building power distribution systems.
When considering fuse protection in this application, the capacitor and series reactor should be analyzed as a whole, because the compensation loop should allow it to carry a certain amount of harmonics in addition to the normal fundamental reactive current. Wave current.
More importantly, since the rated voltage of the capacitor for this application is much larger than the voltage of the distribution system (such as the application of 14% reactance, the rated voltage of the capacitor is 525V, much larger than the system voltage of 400V), the capacitor can actually carry in the 400V system. The current (including the fundamental and harmonic currents) is greater than its rated current at the rated voltage (eg 525V). Therefore, in this reactive power compensation application, it is the parameters of the series reactor that determine the loop overload capability, that is, the maximum overcurrent capability of the reactor.
Therefore, the choice of fuse should be based on the rated current of the loop and the maximum overcurrent capability of the reactor. An example of a 25KVAR/400V compensation loop with a reactance of 14% is analyzed:
The rated current of the capacitor of this circuit is 36A. If the maximum overcurrent capability of the reactor is 1.8 times of rated current, the maximum allowable current of the circuit is 1.8×36=64.8A, so the rated protection current of the correct fuse should be 63A.
Semiconductor Disc Devices(Capsule Type)
Semiconductor Disc Devices(Capsule Type) is the abbreviation of thyristor, also known as silicon controlled rectifier, formerly referred to as thyristor; thyristor is PNPN four-layer semiconductor structure, it has three poles: anode, cathode and control pole; thyristor has silicon rectifier The characteristics of the parts can work under high voltage and high current conditions, and their working processes can be controlled and widely used in electronic circuits such as controlled rectifiers, AC voltage regulators, contactless electronic switches, inverters, and inverters.
Semiconductor Disc Devices,Inverter Thyristor,Phase Control Thyristor,Capsule Type Semiconductor Disc Devices
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