1. Equipment overview and introduction
X device UPS is dual-machine dual-circuit configuration, the UPS adopts X9305 model, the capacity is 20KVA.
The UPS host and battery cabinet are located in the substation. The input switch of the UPS is 50A, and the output of the UPS is routed to the power distribution cabinet of the instrument between cabinets through cables. The two main switches in the power distribution cabinet use X NS100N-MA50 amp plastic-case circuit breaker. The lower side of the main switch is equipped with a static interswitching switch directly connected to APC AP7723-16A, and the static intercutting two power supplies have no circuit breaker protection. Each main switch is equipped with 12 Schneider IC65N-K C10A MCB loads, and the static intercutting switch is also equipped with 5 MCB loads of the same model.
picture
MTBE instrument power wiring diagram
Second, the fault process
1. Time: 7:46 on November 15, 202X
2. Location: between X cabinets
3, after: November 15, 2020 at 7:46, X pump room video monitoring point, due to the aging of the line short-circuit, resulting in the overall power loss of the instrument.
Iii. Reason analysis
(1) Process inspection and analysis
It is found that after the instantaneous speed break and trip of the upper main circuit breaker of the control power supply, the static intercutting switch detects the voltage loss and switches to the other power supply. At this time, the short circuit fault does not disappear, and then causes the other main circuit breaker to trip, resulting in the loss of power of the X device instrument.
picture
Main circuit breaker instantaneous speed trip The other main circuit breaker is tripping
picture
The other main circuit breaker is tripping
picture
MA Thermal magnetic trip unit
picture
C-type trip curve
picture
Comparison of ampere-second characteristics of IC65N-C10 and NS100N-MA50 circuit breakers
(2) The root cause of the failure
1, the direct cause: the branch load with the UPS short-circuit fault, causing the main circuit breaker over the instantaneous speed break protection action.
2, indirect cause: the main circuit breaker and the lower branch circuit breaker protection does not match, the main circuit breaker only instantaneous speed break protection, the characteristics are better than the branch switch to jump open; The static intercutting switch power supply is taken to the lower side of the main switch in the power distribution cabinet without circuit breaker protection. After the first main circuit breaker breaks and trips at an instant speed, the intercutting switch detects the voltage loss and switches to the other power supply. At this time, the short circuit fault does not disappear, causing the other main switch to trip.
3, management reasons: maintenance and overhaul process failed to check the upper and lower switch protection does not match, technical management is missing; When purchasing the instrument power distribution cabinet, the technical agreement does not specify the specific requirements of upstream and downstream switch protection, and it is not checked during inspection, and there is a lack of technical management; As an important equipment, UPS power distribution cabinet is put into use without short-circuit crossover test before putting into use, and there is a lack of technical management. The non-continuous control instrument load such as the information camera is connected to the instrument power supply cabinet, and its failure will affect the operation of important equipment, and the hidden dangers are not identified in time, and there is a lack of technical management.
4. Rectification measures
1. Separate the information load caused by the failure from the continuous control instrument load and move it out of the distribution cabinet to avoid secondary failures.
2. Check the load carried by the UPS, strip the load with non-control instruments, and set a separate UPS power supply according to the importance of the load.
3. Check the protection match of the main circuit breaker and branch circuit breaker of the existing power distribution cabinet, formulate a plan for the mismatch and rectify it.
4. Prepare the standard configuration diagram of the UPS dispensing power cabinet, implement it in the technical agreement of the new reconstruction project, and do short-circuit crossover test before putting into use.
V. Summary and enlightenment
1. Professional technology lacks the check of switch protection matching at all levels of UPS, and whether the protection is matched cannot be found in time.
2, before the new reconstruction project equipment is put into use, it must be tested to ensure that the expected purpose is achieved before it can be put into use.