QC/T 1174-2022High voltage fuse of electric vehicles (English PDF)

3.10 Rated current

The current value that is used to identify a fuse, which is measured in accordance with a prescribed method.

Note: The continuous working current of the fuse should be lower than the rated current, and the use of derating can be in accordance with Appendix C.

3.11 Rated voltage

The maximum supply voltage applicable to the fuse.

3.12 Prospective current

The current that would flow in a circuit if the fuse is replaced by a conductor of negligible impedance.

3.13 Operation mode

The operation mode is defined as follows:

a) operation mode 1: the fuse is not connected to the cable or copper bar;

b) operation mode 2: the fuse is connected to the cable or copper bar, but not energized;

c) operation mode 3: the fuse is connected to the cable or copper bar and energized.

Note: The installation method of the fuse is in accordance with Figure A.1 in the appendix; the installation torque is in accordance with Table A.1 in the appendix.

5.1 Working environment

Unless otherwise specified, the fuse shall be able to work normally in the following environmental conditions:

a) Temperature: -40 °C ~ 85 °C;

b) Relative humidity: 5% ~ 95%;

c) Atmospheric pressure: 61.6 kPa ~ 106.2 kPa.

5.2 Appearance

The appearance and identification of the fuse shall meet the following requirements:

a) The surface of the enclosure shall be uniform in color, smooth, flat and dry, and shall be free from obvious scratches, burrs, rust, deformation, cracks and other defects;

b) Product nameplates, plates, labels or indications shall be correct, complete, clear, and reliably and permanently attached to the enclosure.

5.3 Dimensions and tolerances

The dimensions and tolerances of the fuse shall meet the requirements of the product drawings.

5.4 Electrical performance

5.4.1 Requirements for internal resistance

Carry out the test according to 6.4.1, and the relative deviation between the measured value and the internal resistance value declared by the manufacturer shall not exceed ±10%.

5.4.2 Requirements for temperature rise

Carry out the test according to 6.4.2. The temperature rise value of the fuse terminal shall not exceed 50 K, and the temperature rise value at the center of the insulator can be determined through negotiation between the supplier and the buyer. After the test, the overall fuse shall not have obvious discoloration, the terminal, terminal plating and label shall not be burnt and peeled off, and the fuse shall meet the requirements of 5.4.1.

5.5 Requirements for environmental adaptability

5.5.1 Requirements for salt spray resistance

Carry out the test according to 6.5.1. After the test, there shall be no problems such as peeling, chipping, blistering, peeling off of the coating or bare basic metal on the fuse coating, and the fuse shall meet the requirements of 5.4.1 and 5.4.4.

5.5.2 High temperature requirements

Carry out the test according to 6.5.2. After the test, the fuse shall meet the requirements of 5.4.1, 5.4.3 and 5.4.4.

5.5.3 Low temperature requirements

Carry out the test according to 6.5.3. After the test, the fuse shall meet the requirements of 5.4.1, 5.4.3 and 5.4.4.

5.5.4 Constant damp and hot requirements

Carry out the test according to 6.5.4. After the test, the fuse shall meet the requirements of 5.4.1, 5.4.3 and 5.4.4.

5.5.5 Requirements for combined temperature/humidity cycle

Carry out the test according to 6.5.5. After the test, the fuse shall meet the requirements of 5.4.1, 5.4.3 and 5.4.4.

5.5.6 Requirements for cold and hot impact

Carry out the test according to 6.5.6. After the test, the fuse shall meet the requirements of 5.4.1, 5.4.3 and 5.4.4.

5.6 Mechanical load

5.6.1 Mechanical vibration requirements

Carry out the test according to 6.6.1. After the test, the fuse shall not have problems such as appearance change, loose screws, cracked and deformed insulators, and the fuse shall meet the requirements of 5.4.1, 5.4.3 and 5.4.4.

5.6.2 Mechanical shock requirements

Carry out the test according to 6.6.2. After the test, the fuse shall not have problems such as appearance change, loose screws, cracked and deformed insulators, and the fuse shall meet the requirements of 5.4.1, 5.4.3 and 5.4.4.

6.1 General conditions of test

6.1.1 Test standard atmospheric conditions

Unless otherwise specified, all tests shall be carried out under the following environmental conditions:

a) Room temperature: 23 °C ± 5 °C;

b) Relative humidity: 5% ~ 95%;

c) Atmospheric pressure: 61.6 kPa ~ 106.2 kPa.

6.1.2 Test equipment

The instruments, equipment and loading conditions in the test shall meet the following requirements:

a) The graduation value of the universal measuring tool for measuring the size shall not be greater than 1 mm;

b) It shall have an appropriate range, where the graduation value shall not be greater than 1 °C, and the calibration accuracy shall not be lower than 0.5 °C;

c) The accuracy of the instrument for measuring resistance shall not be lower than grade 0.5;

d) The accuracy of the instrument for measuring current shall not be lower than grade 0.5;

e) The accuracy of the instrument for measuring voltage should not be lower than grade 0.5, and the internal resistance shall not be less than 1 kohm.

Note: Other equipment or instruments used can be determined through negotiation between the supplier and the buyer.

6.2 Appearance

Samples shall be inspected by visual and tactile methods under sufficient natural or fluorescent lighting conditions.

6.3 Dimensions and tolerances

General measuring tools shall be used to measure the dimensions and tolerances of fuses.

6.5 Environmental adaptability test

6.5.1 Salt spray resistance test

The salt spray resistance test process is as follows:

a) Fuses are tested under the conditions of operation mode 1;

b) Carry out in accordance with the provisions of the severity level (3) in GB/T 2423.18-2012;

c) A test cycle includes 4 spraying cycles, each 2 h; each spraying cycle is followed by a 20 h ~ 22 h damp and hot storage cycle; after 4 cycles, carry out a storage period of 3 days under the test standard atmospheric pressure and relative humidity of 45% ~ 55%.

6.5.2 High temperature test

The high temperature test process is as follows:

a) Carry out the high temperature test according to Figure 4 and Table 5, wherein Tmax is 85 °C;

b) The test current and the cross-sectional area of the test cable are selected according to Table 2. If there is no corresponding current value in Table 2, it can be determined through negotiation between the supplier and the buyer;

c) If there is a problem of interruption during the test, the test can be continued from the point of interruption. The test requires that the continuous test time shall not be less than 96 h. If it is less than 96 h, the test needs to be repeated. The interruption must be indicated in the report.

C.1 Introduction to fuse

C.1.1 Working principle of fuse

The working principle of fuse is that when the current exceeds the specified value for a long enough time, it will fuse through one or several proportionately designed fuses, thereby disconnecting the device connected to the circuit. A fuse contains all the parts that make up a complete electrical appliance.

C.1.2 Fuse structure

The schematic diagram of the fuse structure is shown in Figure C.1. The structural composition and main functions of the fuse:

-- Melt (fuse): Set the perception current, and use the thermal effect of the current to melt or vaporize the conductor, and form a fracture after melting.

-- Narrow diameter of the fuse-element: The position on the fuse-element where the cross section of the conductor is smaller is used to adjust the fusing speed.

-- Quartz sand: By absorbing the arc heat, reducing the arc temperature, wrapping and absorbing the molten metal particles in the fracture, increase the arc voltage, and extinguish the arc. It also isolates and buffers the mechanical impact and high temperature impact on the enclosure.

-- Insulator (enclosure): heat-resistant insulation structure, resistant to arc temperature and mechanical impact, keeping the overall integrity of the fuse.

-- Terminal: conductor connection, providing electrical connection and installation mechanical force.

C.3 Fuse failure modes

The common failure modes of fuses are as follows:

-- The rated voltage selection is too small, and the loop inductance is greater than the standard test conditions: the circuit breaking voltage is higher than the rated voltage of the fuse or the inductance is greater than the standard test conditions, which may cause the fuse to exceed the conditions and cannot be reliably broken, and it is prone to explosion and arc spray.