Overview

Electrical Fast Transient/Burst (EFT/B) refers to transient bursts generated by various electrical appliances (or equipment) within the same power supply circuit during operation (such as switches, relays, etc.). If inductive loads are repeatedly switched, the burst pulses will occur multiple times at corresponding intervals. These pulses feature short rise times, high repetition rates, low energy, and a wide spectral distribution. EFT/B interference can cause performance degradation or malfunction of electrical appliances (or equipment).

The repetitive fast transient test is designed to couple bursts composed of numerous fast transient pulses to the power supply, signal, and control ports of electrical and electronic equipment. The key aspects of the test are the short rise time, repetition rate, and low energy of the transients. Its purpose is to evaluate the immunity of the equipment under test (EUT) to transient bursts generated during operational transient processes (such as disconnection of inductive loads, relay contact bouncing, etc.).

Test Levels

Table 1 lists the preferred ranges of test levels for the electrical fast transient/burst immunity test on the power supply, protective earth (PE), signal, and control ports of equipment.

Note: * "X" denotes an open level that must be specified in the dedicated equipment technical specification.

Test levels should be selected based on the most realistic installation and environmental conditions. During immunity testing, the performance level of the equipment in its intended operating environment should be determined. For the I/O, control, signal, and data ports of the EUT, the test voltage is half of that applied to the power supply ports.

Based on common installation practices, it is recommended to select the test level for the electrical fast transient/burst immunity test according to the electromagnetic environment requirements. Specific test levels are as follows.

(1) Level 1: Well-Protected Environment

Facilities at this level exhibit the following characteristics:

a. Electrical fast transient pulses are completely suppressed in switched power and control lines.

b. Power lines (AC and DC) are separated from control and measurement lines belonging to environments of higher severity.

c. Power cables are shielded, with both ends of the shield grounded at the facility's reference ground plane, and power protection is achieved through filtering.

Examples include computer rooms. For this level, only power lines in type tests and ground lines, equipment cabinets in post-installation tests are used.

(2) Level 2: Protected Environment

Facilities at this level exhibit the following characteristics:

a. Electrical fast transient bursts are partially suppressed only in power and control lines switched by relays (without contactors).

b. All lines are separated from other lines associated with environments of higher severity.

c. Unshielded power and control cables are structurally separated from signal and communication cables.

Examples include control rooms or terminal rooms in factories and power plants.

(3) Level 3: Typical Industrial Environment

Facilities at this level exhibit the following characteristics:

a. No suppression of electrical fast transient bursts in power and control lines switched only by relays (without contactors).

b. Incomplete separation of industrial lines from other lines associated with environments of higher severity.

c. Dedicated cables are used for power, control, signal, and communication lines. Incomplete separation between power, control, signal, and communication lines.

d. Presence of a grounding system provided by conductive pipes in cable trays (connected to the protective earth system), grounding conductors, and grounding grids.

Examples include locations where industrial process equipment is used, relay rooms in power plants and outdoor high-voltage substations.

(4) Level 4: Severe Industrial Environment

Facilities at this level exhibit the following characteristics:

a. No suppression of electrical fast transient bursts in power and control lines switched by relays and contactors.

b. Industrial lines are not separated from other lines associated with environments of higher severity.

c. No separation between power, control, signal, and communication cables. Control and signal lines share multi-core cables.

Examples include outdoor areas of power plant industrial process equipment without specific installation measures, open-air high-voltage substation switchgear, and switching devices with operating voltages up to 500 kV (using typical installation measures).

(5) Level 5: Special Environment Requiring Analysis

Depending on the quality of electromagnetic separation between disturbances and equipment circuits, cables, lines, etc., and the installation quality, it may be necessary to adopt levels higher or lower than those described above. It should be noted that equipment lines of higher severity levels may enter environments of lower severity.