What Is Load Shedding?

Low-voltage automatic load shedding refers to the use of low-voltage load shedding devices to bring the entire system back to normal as soon as possible when an accident occurs in the power system. When the frequency and voltage drop due to active and reactive power shortages in the power system, the low-cycle and low-voltage load shedding device will automatically cut off part of the power user s load according to the frequency and voltage reduction values, so that the system s power and load are rebalanced to prevent frequency, The voltage collapse accident brought the whole system back to normal as soon as possible.

In the power system due to active and reactive power shortages, the frequency,

When the power system frequency changes, the power consumed by users will also change. The sensitivity of power system loads to frequency changes varies with the nature of user loads. The active power absorbed by the first type of users has nothing to do with frequency, such as electric heating equipment, lighting loads, rectification equipment, etc .; the active power of the second type of users is proportional to the frequency, and the load with a resistance moment equal to a constant falls into this category, such as hoists, grinding Coal machines, cutting machine tools, etc .; the power consumed by the third type of users is a function of frequency higher than the first power. Users belonging to this category include feed pumps, air pump motors, etc. The relationship between the load power and frequency of the entire system can be used to comprehensively analyze the load static low frequency low voltage automatic load shedding device circuit analysis

The dynamic frequency characteristic of a power system is the process of decreasing frequency when an accidental deficit of active power shortage occurs. When considering the dynamic characteristics of system frequency drop, it is generally considered that the system can be considered as a whole of mechanical energy and electrical energy conversion. Its mechanical moment of inertia includes all rotating parts of the system such as steam turbines, hydraulic turbines, generators, synchronous compensation machines, The mechanical moments of inertia of the motor and the machinery being driven by the motor all work at the same equivalent speed, that is, under the same changing mechanical value.

According to the needs of actual operation, the UFV-2 microcomputer low-frequency and low-voltage automatic load shedding device is used to realize the functions such as jumping the middle and low voltage side of the main transformer, 110, 35, and 10 kV feeders. However, due to the many trips of the feeder during operation, when the bypass switch operates on behalf of the feeder switch, the corresponding low-frequency setting value switching is more complicated. The setting value must be adjusted by the small switch in the device plug-in. The entire low-frequency and low-voltage load shedding automatic device is used, and it also causes significant hidden dangers to the safe operation of the system during the setting process. After careful exploration and practice, in accordance with the principles of safety, convenience, and practicality, the small switch W4 of the bypass exit dial in the device was improved, which fundamentally solved the contradiction that the setting must be deactivated and the level of safe operation Greatly improve ^[2]

The improved device is in good working condition, and it is proved that the improvement of the dial switch is feasible. When the bypass switch replaces the feeder switch, it is safe, convenient and flexible to switch in low-cycles.