Current Transformers Do Not Need Protection
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Current transformers are widely used to measure current and monitor grid operation. The need for a current transformer is for two reasons: it isolates the protection system from high voltages and currents, thereby reducing the size and cost of the protection device; the output of the current transformer is standard (i.e. 1A or 5A) and no protection device is required, e.g. relays with different operating values.
1. One of the functions of the current transformer is to measure, which is often used for billing or measuring the current of equipment in operation. When measuring large AC current, in order to facilitate the measurement of the instrument and reduce the risk of directly measuring high-voltage electricity, it is often necessary to use a current transformer to convert it into a more uniform current. Here, the working principle of the current transformer is to play the role of current conversion and electrical isolation. The current transformer converts a large current into a small current proportionally as required, and is used to connect the primary side of the current transformer to the primary system and the secondary side to the measuring instrument or relay protection device during measurement.
2. The second function of the current transformer is to protect it. It is usually used in conjunction with a relay device. When the line is short-circuited or overloaded, the current transformer will send a signal to the relay device to cut off the faulty circuit and achieve the purpose of protecting the safety of the power supply system. Current transformers for protection are different from current transformers for measurement. It can work effectively only when the current is several times or tens of times larger than the normal current, and requires reliable insulation, a large enough precise limit coefficient, and sufficient thermal stability and dynamic stability.
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