FAQ | Feb 28,2023
According to their purpose, current transformers can be roughly divided into two categories:
Current transformers for measurement (or measuring windings of current transformers) : provide current information of the power grid to measuring and metering devices within the normal working current range. When measuring the high current of alternating current, it is necessary to convert it to a relatively uniform current for the convenience of secondary instrument measurement (China stipulates that the secondary rating of the current transformer is 5A or 1A). In addition, the voltage on the line is relatively high, so direct measurement is very dangerous. The current transformer plays the role of changing current and electrical isolation. It is a sensor used by measuring instruments, relay protection and other secondary devices in power system to obtain the current information of the primary circuit. Current transformer converts high current into low current proportionally. Current transformer is first side connected to the primary system, and second side connected to measuring instruments and relay protection.
Current transformer for protection (or protection winding of current transformer) : in the state of power grid fault, to provide the relay protection device with power grid fault current information. The protection current transformer mainly works with the relay device. When the line fails, such as short circuit and overload, it provides signals to the relay device to cut off the faulty circuit, so as to protect the safety of the power supply system. The working condition of the protection current transformer is completely different from that of the measurement current transformer. The protection current transformer only starts to work effectively when the current is several times and dozens of times larger than the normal current.
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