Internal arc release of low voltage switchgear in North America

IEEE C37.20.7-2007/Cor 1-2010IEEE Guide for Testing Metal-Enclosed Switchgear Rated up to 38 kV for Internal Arcing Faults Unlike GB/IEC standards, which have different internal arc test standards for medium voltage and low voltage switchgear, IEC 62271-200 and Appendix A of GB/T3906 only define the internal arc test standards for medium voltage switchgear. GB/T 18859 and IEC61641 are test guidelines for enclosed low voltage switchgear and control equipment in the event of internal faults causing arcs. The ANSI/IEEE C37.20.7 standard is a testing standard for the resistance of metal enclosed switchgear to internal arcing in North America, including low-voltage distribution switchgear, motor control centers, medium voltage switchgear, motor control centers, and other equipment that require internal arcing testing to be carried out in accordance with this standard. Suitable for all metal enclosed switchgear with voltage levels below 38kV, these devices are commonly used in industrial, commercial, and residential distribution systems as critical equipment for power distribution and control. This standard pays special attention to the testing of internal arc faults to ensure that the switchgear can quickly and effectively cut off the circuit in the event of a fault, preventing dangerous situations such as fires and explosions caused by arc faults. --Type 1. Switchgear with arc resistant design or function only located in a freely accessible position at the front of the device. --Type 2. Switchgear with arc resistant design or function only on external surfaces (front, back, and side) that are freely accessible to the device. The preferred value for the test voltage is the maximum rated voltage of the equipment. If it cannot be achieved due to laboratory limitations, a reduced voltage can be used. Suggest reducing the voltage by no less than 60% of the maximum rated voltage of the equipment. It is not recommended to conduct voltage drop testing on equipment with a rated voltage of 5 kV or below. The duration of the short-circuit current is 0.5s.

Unlike IEC standards, internal arc testing focuses on the test itself, as long as it meets the criteria, even if the interior of each compartment in the switchgear is completely destroyed, there is no problem. The C37.20.7 standard focuses more on the structure and the impact of internal arc testing. If it is necessary to verify the instrument room, that is, the instrument room is in normal use, the internal arc test of other compartments should not affect the instruments, etc.

Due to the multi-layered vertical layout of low voltage and medium voltage switchgear in North America, it is required that the vertical parts be fully equipped. The physical models of internal components can be replaced as long as they have the same volume and similar materials as the original item.

The compartments within the vertical cross-section should represent the minimum volume and maximum unsupported wall surface of the largest component used in the design. The sample should include the maximum number of openings designed for equipment ventilation and the minimum number of openings designed for arc fault pressure relief. The North American low-voltage switchgear has distinct compartments, from front to back, including functional unit compartments (including instrument compartments), vertical busbar compartments, horizontal busbar and cable connection compartments. Each compartment cabinet has a separate pressure release channel at the top, and the pressure cover plate is opened before releasing to the horizontal pressure release channel.

Before starting the testing, all ventilation openings designed for equipment cooling and designed to close during overpressure events must be open and functioning properly.

If the equipment is intended to be used with control devices such as relays and instruments installed on exposed doors or covers, representative samples of these devices should be present on the sample. When this is not feasible, the compartment directly behind the installation point should be evaluated to verify that any abnormal pressure generated during the testing process will not cause the installed equipment to shift or be exposed to the arc. The indicator should be placed inside the compartment to verify that the impact of the fault will not enter the compartment.

Pressure relief device for low voltage switchgear in North America

Any opening created by the manufacturing, assembly, or modification of the equipment, if intentionally covered, blocked, or similar devices, may be installed. In this test, openings that are not intentionally covered must not be blocked under any circumstances. The pressure relief channel is a common application for low voltage switchgear and motor control cabinets in North America that are resistant to internal arc levels. Through the pressure relief channel, the internal arc pressure flame of the switchgear is released to the safe space outside the distribution room, minimizing damage to other equipment in the distribution room.