Energy is getting tighter Today, energy shortage has become an important factor restricting China's social and economic development. The concept of energy conservation is increasingly accepted by people. Electricity is the most important secondary energy in the world today, and the economic operation of the power system is particularly important. The power system loss is related to the active power loss of the equipment, and is related to the reactive power loss of the equipment. The reactive power consumed by the equipment is also supplied by the power system. The reactive power is stored, so that the current in the power system increases, which causes an increase in active power loss in the power system, and the system efficiency is also greatly reduced.
At present, the main method for solving this problem is to use KVM switch for reactive power compensation. Among them, the KVM switch method in the power system is widely used because of its advantages of simple installation, convenient maintenance, small active loss, and flexible use.
- The necessity of using a KVM switch
There are many advantages to using the KVM switch for powerless compensation in power systems. When these KVM switches are connected to the grid, large and high frequency inrush currents are generated instantaneously. The peak value is called the surge current peak and KVM switching can be achieved. The rated operating current is about 180 times.
At present, advanced reactive power compensation devices are automatically controlled. This control method automatically controls the size and number of KVM switch units put into the power factor control setting range.
The control KVM switch input actuator is usually a contactor. Generally, the KVM switch can easily cause the main contact to be welded under the impact of the surge current.
If the main contact of the contactor is welded, there may be a loss of compensation equipment. Whether the contactor works reliably or not will directly affect the reliability of the reactive power compensation system. A dedicated KVM switch is specifically designed for this purpose. This kind of dedicated KVM switch is generally equipped with a device for suppressing inrush current, which can effectively reduce the surge current generated during the closing of the capacitor bank, reduce the overvoltage generated during operation, and also avoid the fusion welding phenomenon of the KVM switch.
Second, KVM switch selection principle
To ensure reliable operation of the reactive power compensation system, the KVM switch must meet the following two basic conditions:
1) The rated operating current of the KVM switch must continue to reach 1.5 times the rated operating current of the switch. Harmonics and network voltage errors can cause a continuous flow current in the circuit, which is about 1.3 times the rated current of the KVM switch. Considering manufacturing errors, the actual power of the KVM switch should be 1.15 times its rated power. The maximum thermal current of the KVM switch specified in GB3938.1 and IEC831-1 is:
Where, IT is the maximum thermal current of the switch; In is the rated operating current of the KVM switch.
(2) The KVM switch contacts must be able to withstand a brief and large peak current, ie, surge peak current. The magnitude of the surge current peak is related to many factors such as power network inductance, transformer capacity, short circuit voltage, and power factor compensation type. Among them, there are two main types of power factor compensation:
The first is that the KVM switch group input is a one-step fixed power factor compensation. In this case, the peak value of the inrush current when the KVM switcher is plugged in can reach approximately 30 times the rated capacity of the KVM switch, and the peak value of the inrush current can be estimated by the formula.
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