Lonely networks are the abbreviation of isolated grids, and generally refer to small-capacity grids that are separated from large grids. The grid with the largest single capacity less than 8% of the total grid capacity can be called a large grid; grids with a capacity greater than 8% of the grid capacity are collectively referred to as small grids; isolated networks that operate in isolation are called orphaned grids. There are several units in the network running in parallel, and the ratio of single machine to grid capacity is more than 8%, which is called small network. Only one generator in the grid supplies power and becomes single machine with load; , is a special case of stand-alone load. Solitary Network Operation Features The most prominent feature of the isolated network operation is that it is changed from the load control to the frequency control, and the speed regulation system is required to have the required static characteristics, good stability and dynamic response characteristics, so as to ensure that the grid frequency is automatically maintained under the change of the user load. The stability, which is commonly referred to as a FM function. The problem that the operator is concerned with is no longer adjusting the load, but adjusting the frequency of the isolated network to maintain it near the rated frequency. This adjustment is accomplished by operating a given mechanism of the speed control system to become secondary frequency modulation. Because of the small capacity of the isolated network, the kinetic energy stored by the rotating inertia and the thermal potential energy of the boiler group are all small, and the unit's speed control system is required to have higher sensitivity, smaller sluggish rate and faster dynamic response. Solving the problem of isolated-network operation of turbo-generator units: 1. The voltage, frequency and engine speed of the turbo-generator are not stable. The changes will be tracked according to the changes in the load. The quality of the power supply is poor and the safety factor is low. 2. Under heavy load changes, the load has a great impact on the turbine. Long-term operation will cause damage to the turbine governor and even flush out the normal operation of the turbine. 3, frequent exhaust, noise, a serious waste of heat and water resources. Technical measures to ensure the operation of isolated networks 1. In order to meet the power quality requirements of the load side of single-machine with isolated-network operation and the voltage stability requirements of the power system of the plant, the terminal voltage of the generator should be kept basically unchanged, and the automatic excitation system is required to be automatically operated when the generator is isolated. The voltage control function adjusts the excitation current of the generator with the change of the reactive current to maintain the stability of the generator terminal voltage. 2. In the stand-alone operation with isolated network, the active change of the load side of the isolated power grid is uncontrollable. If the PSS (Power System Stabilizer) is put into use, the reactive power will follow the active fluctuations, which will affect the stability of the terminal voltage. Therefore, the PSS function of the excitation system should be cut off when the isolated network is running. 3. In the case of isolated-network operation, when the external load changes, the adjustment direction of the power-frequency electro-hydraulic control system is opposite to that of the external load, ie, the frequency will be reversed. After a frequency modulation operation of the unit, the valve opening of the turbine is the sum of the power feedback control of the power-frequency electro-hydraulic control system and the effect of the primary frequency modulation control. Since the normal unit frequency modulation adjustment is small, the isolated network sometimes cannot rebalance power and frequency. . By switching the power control mode of the unit to the valve control mode, the isolated network can operate stably for a long time. 4. When a lone network is running, the fluctuation of the load in the lone network and the large change in the load caused by the fault all require a large and fast adjustment of the primary frequency to ensure the stability of the lone network. 5. When an orphaned network runs, once an FM fails to effectively suppress the rise of the orphan frequency in time, it will cause OPC actions, which will bring huge impact to the isolated network. The most likely consequences of OPC actions include: Repeated frequent changes in frequency, repeated large-scale operation of a frequency modulation, unit valve oil pressure is too low to cause the unit to trip; OPC action causes the unit to turn off the door, due to various reasons can not be opened or fully open, resulting in orphan The network frequency dropped too much and eventually lost stability. Therefore, the OPC operation of the unit should be avoided during the operation of the isolated network. Measures include increasing the frequency modulation limit, increasing the OPC operation delay, increasing the OPC operation speed, and canceling the OPC exit function. At the same time, after the OPC operation to ensure the stable operation of the unit accident handling plan, such as OPC action, quickly take the small adjustment gate, fully open bypass, timely start high-power auxiliary and so on. 6. When the isolated-grid operation is in progress, increasing the frequency-adjusted dead zone can prevent the unit from being adjusted too frequently, causing the unit to trip due to a decrease in the oil pressure of the valve or difficulty in controlling the water level at the furnace side. However, once the FM dead time increases, when the fault causes part of the load to be lost, the FM operation is relatively late and the OPC operation is more likely to occur. Therefore, the increase in dead time should be modest. 7. The valve operation mode of steam turbine was changed to single-valve control. The steam turbine was operated under the sequential valve control mode. It was easy to cause the vibration of the turbine due to the overlap of the high-pressure control door, and it was changed to a single-valve control. Operational control measures when isolated network 1. Electrically ensure that the power outage of the neighboring power grid does not affect the normal operation of the isolated network unit. Since the isolated network cannot withstand the impact of the power switchover of the neighboring power plant, the plant security power supply should be ready in time for the isolated network unit to trip. Switch to plans and measures for neighboring power grids. 2. Ensure that the boiler is stable in combustion and ensure that the fuel system can be put into production and use. When the combustion condition of the furnace is unstable, it is required to adjust the combustion of the boiler in a timely manner. If necessary, the oil gun can be stabilized and the boiler should not be extinguished. Pay attention to the operation of the pulverizing system. Start and stop the process to make good combustion measures in advance to ensure that the coal bunker is in the proper range. Boiler operation personnel should strengthen the monitoring and adjustment of the main parameters, and maintain communication with the turbine operation personnel at any time to understand the changes in the unit load, and timely follow-up adjustments to avoid shutdown accidents caused by parameter overruns. 3. During the operation of the isolated network, the water level can be maintained at a slightly higher level, the water level can be increased, and the buffer capacity of the steam drum can be prolonged. In unexpected accidents, it can sometimes play an unexpected role. In addition to the conventional parameter monitoring, the system voltage and turbine speed should be monitored to ensure the power quality of the isolated network system. In particular, the heat pressure of the heating network and the change of the heating flow should also be closely monitored because of sudden changes in heating supply. For turbine speed and generator load, there will also be a great impact. 2 Burners Stainless Steel Top 2 Burners Stainless Steel Top,frigidaire induction range,cooktop gas,portable cooktop,glass cooktop Vast Dragon Trading Limited , https://www.lgstove.com