Stability of short-circuit current
For current-limiting fuses, the dynamic and thermal stability checks do not need to be conducted; for non-current-limiting fuses, the dynamic and thermal stability checks must be carried out.
Thermal stability check: I² chTre≧Qt
Dynamic stability check: Idei ≥ ch (3)
Where:
ich (3) – Peak short-circuit current
I ch – Effective value of steady-state short-circuit current
Fuse of the voltage transformer
It needs to be selected according to the rated voltage, breaking capacity, and rated current.
Check the sensitivity of the fuse
Idm > 4Ie means that the minimum short-circuit current of the power grid is greater than 4 to 7 times the rated current of the fuse. ==================================
The usage method of vacuum circuit breakers
A vacuum circuit breaker is a type of protective equipment with excellent performance, which can play an important role and value during use. It is mainly used to test high-voltage electrical equipment with a ground voltage of 250V or above. Vacuum circuit breakers have different forms and types in use. Currently, the widely adopted types include the luminous high-vacuum circuit breaker, the sound and light vacuum circuit breaker, and the windmill-type vacuum circuit breaker. They are generally composed of three major parts: the detection part (indicator part or windmill), the insulation part, and the handshake part. The insulation part refers to the part from the lower metal connecting screw of the indicator to the protective ring. The handshake part refers to the part below the protective ring. The lengths of the insulation part and the handshake part vary according to the voltage level.
Before using a vacuum circuit breaker, it is necessary to conduct a proper inspection to ensure that it can play an important role and value during use. When using a vacuum circuit breaker for electrical testing, it is essential to strictly follow the operation supervision system. One person operates while another supervises. The operator is in front and the supervisor is behind. When using a vacuum circuit breaker, it is necessary to pay attention to the rated voltage of the circuit breaker should be compatible with the voltage level of the tested electrical equipment. Otherwise, it may endanger the personal safety of the operator or cause incorrect judgments. During the electrical testing, the operator must wear insulating gloves and insulating boots to prevent step voltage or contact voltage from harming the human body. The operator should hold the hand-holding part below the protective ring and first test the energized equipment. During the testing, gradually approach the energized equipment until it lights up or makes a sound to verify the integrity of the tester. Then, test the equipment that needs to be tested. When testing multiple layers of lines on the same pole, test the low voltage first, then the high voltage, the lower layer first, and the upper layer later. It should be particularly noted that during storage and transportation, do not subject it to strong vibration or impact. Do not擅自adjust or disassemble it without permission. Any environment with rain， snow， etc. that affects the insulation performance must not be used. Do not expose it to the open air under the scorching sun. It should be stored in a dry and ventilated place. Do not use corrosive chemical solvents and detergents for wiping or contact.
Before using a vacuum circuit breaker for electrical testing, it is essential to carefully read the user manual and check whether the test period has expired, whether the appearance is damaged or torn. For example, when taking out the GDY type vacuum circuit breaker from the package, one should first observe whether the electric rotation indicator blade has a disengaged shaft phenomenon, and whether the alarm emits an audible signal. Those with a disengaged shaft shall not be used. Then, gently shake the electric rotation indicator in your hand, and its blade should have a slight movement, indicating that it is in good condition. Next, check the alarm part to ensure that the audible signal is good. For the GSY series of high-voltage sound and light type vacuum circuit breakers, before operation, the indicator should undergo a self-check test. Only after the indicator is rotated and fixed on the operating rod and the operating rod is stretched to the specified length can a second self-check be conducted before proceeding.