High-sensitivity current measurement and control device

Abstract

The invention discloses a current measurement and control device which consists of a mutual-inductance transformer and a simple electronic adjuster. The mutual-inductance transformer can be used as a medium device for isolating a transfer voltage (current) to provide an over-current measurement and control signal on one hand, and a voltage (current) on a secondary coil is turned into a direct current through rectifying and filtering on the other hand so as to directly push the switch-on and the switch-off of a relay to omit a direct current voltage-stabilized power source of the current measurement and control device in the prior art and reduce the production cost by more than 10 times. Because of less elements of the current measurement and control device, less steps of circuit conversion, high response speed, high accuracy of current detection, reliability of load loop detection and protection and improved stability, the defects of more electronic elements, high price and poor stability of the traditional electronic current measurement and control device are made up, thereby the high-sensitivity current measurement and control device has high production effect and practical value and is suitable for alternating current motors and protection systems related to over-current, overload, short circuit and the like of an alternating current control system.

Description

technical field [0001] The invention relates to a relay protection device for an AC power system, in particular to a current measuring and controlling device used in an AC motor or a related AC control system to cut off a faulty circuit when faults such as overcurrent, overload, phase failure, and short circuit occur. Background technique [0002] The current measuring and controlling device is connected to the protection system of the AC motor and the related AC control system for overcurrent, overloading, phase failure, short circuit, etc. When there is a fault, a signal is provided to the relay to cut off the fault circuit to protect the safety of the power supply system. [0003] The current current measuring and controlling device can be roughly divided into two types of structures: one is a mechanical adjustment structure, which is composed of mechanical contacts such as magnetic induction coil springs and screws, and the other is an electronic adjustment structure. f...

AI Technical Summary

Problems solved by technology

It is known that the secondary coil of the current transformer is in an approximate short-circuit state during normal operation, which teaches people that the secondary coil of the circuit transformer cannot be connected to a load with a large impedance. The above-mentioned current measuring and controlling device of the electronic adjustment structure also follows this principle It is taught that the current transformer is only used as a medium device for isolating and converting the induced voltage, and its induced voltage is very small (when measuring the large current of the alternating current, it needs to be converted into a relatively uniform current for the convenience of the secondary instrument measurement. The secondary coil of the current transformer is rated at 5A or 1A, the primary coil has only a few turns, the cross-sectional area of ​​the wire is large, and it is connected in series to the circuit under test. The current coil of the meter) constitutes a closed circuit, and the output voltage is very low), which is not enough to drive the electronic regulator and relay in the subsequent stage. Therefore, an external power transformer and rectifier regulator must be connected to start the relay. Although the current measurement and control of the electronic regulation structure The adjustment of the device is simple, accurate, sensitive and stable, but the price is 2 to 3 times higher than that of the current measurement and control device with the mechanical adjustment structure. Therefore, people would rather use the former than the latter, so that the current measurement and control device with the electronic adjustment The application of the device is limited

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