High speed fuse selection calculator:

1, Fuse Rated voltage U_FU

Fuse Rated voltage refers to the ac sine wave voltage that fuse can withstand when it breaks. The selection follows the following principles: Fuse rated voltage is greater than no-load voltage of rectifying transformer.

The rated voltage of the high speed fuse U_FU is determined by the following formula:

U_fu>K_bU₂= 1180 * 1.05 = 1239 V

Take U_fu= 1250 V

In this calculating formula:

U_fu-- Rated voltage of high speed fuse

U₂-- Valve side voltage=1180V

K_b-- Network pressure rise coefficient, generally =1.05

2,  Fuse Rated current I_fu

The selection of fuse rated current  follows the following principles:

(1) Fuse rated current is generally the root mean square value of AC/DC Circuit, which is proved by the temperature rise test and repeatable load test specified in the corresponding standard;

(2) Consider the influence of load current value, installation conditions and ambient temperature;

(3) Avoid load current and external short-circuit current, and check according to the overload capacity curve provided by the high speed fuse manufacturer.

The rated current of the high speed fuse Ifu is determined by the following formula:

 Ifu>I_{F(AV) * Ki *Ka* F}

In this current calculating formula:

Ifu-- Rated current of fast melting

IF(AV)-- The actual average current flowing, Here IF(AV)= 123.4AMP

Ki -- Current margin coefficient, usually 1.2

Ka-- Environmental temperature coefficient, usually 1.1

F -- Waveform coefficient, 3.46

Calculated: =564AMP

Considering the surrounding conditions, connection conditions, overload current, etc., the selection is as follows:

The rectifier high speed fuse ratings are selected as 630A/1250V.

(4) Verification of high speed fuse

I²T value accounting

The I²T value of high speed fuse is calculated as follows:

(I²T)R<= 0.9 I²_FSMt 

In this formula:

(I2T)R  -- the metling T-value of high speed fuse, refer to the high speed fuse manual:

7.3×105A²s, 19×105A2s, 27.5×105A2s

IFSM-- Diode surge current peak

T -- Half cycle time for diode to withstand surge current, 10ms

All the empirical calculations meet the requirements of the above formula.