1、 Electromagnetic current transformer is the most commonly used measuring equipment in power systems, with mature technology, low cost, and very high accuracy. It is currently the most commonly used measuring equipment. However, electromagnetic current transformers have many limitations: 1. The difficulty of insulation, especially above 500kV, increases the volume, quality, and price of the transformer due to insulation; 2. When the dynamic range is small and the current is high, the CT will experience saturation, which will prevent the secondary protection from correctly identifying the fault phenomenon; 3. The output signal of the transformer needs to be laid with cables to the secondary equipment and converted into digital quantities in the secondary; 4. CT open circuit can generate high voltage, endangering personal and equipment safety; 5. Easy to generate ferromagnetic resonance; 6. A current transformer has high accuracy at the specified operating frequency, but it can adapt to a narrow frequency range, especially when it cannot transmit direct current. In addition, there is excitation current during the operation of the current transformer, so it is an inductive component with the same drawbacks as a shunt. 2、 Hall current sensor Hall current sensor can measure both DC and AC currents. Ordinary current transformers can only measure AC currents, while ordinary current transformers cannot open circuits on the secondary side during use. Hall current sensors can open circuits. The output voltage of the Hall current sensor is proportional to the magnitude of the current flowing through the primary side. The direction of the primary side current changes and the output polarity also changes, so it can measure AC and DC currents without special requirements for waveform; The applicable frequency range is also relatively wide. Generally used in electronic circuits, such as frequency converters. AC transformers can only measure AC, and the frequency must be the rated frequency. For example, a 50Hz transformer has a large error when measuring 60Hz, and the output signal cannot be directly fed into the electronic detection circuit. 3、 A shunt is a resistor that is connected in parallel with the current circuit of a measuring instrument to expand its measurement range. A shunt is made based on the principle of generating voltage at both ends of a resistor when direct current passes through it. In reality, a shunt is a resistor with a very small resistance value. The measurement is simple, and the DC measurement accuracy can reach a relatively high level. The biggest problem with diverters is the lack of electrical isolation between input and output. In addition, when using a splitter to detect high-frequency or large currents, there is inevitably electrical inductance, so the connection of the splitter not only affects the measured current waveform, but also cannot truly transmit non sinusoidal waveforms