The electromagnetic coil of the under voltage relay is connected in parallel with the protected or detection circuit, and the auxiliary contact is connected to the control circuit. When the circuit is working normally, the normally open contact is closed, and when the voltage is low to its set value, due to the electromagnetic force generated by the electromagnetic system Under the action of the return spring, the normally open contact is disconnected, and the normally closed contact is closed, so that the control circuit is powered off, and then the main circuit is controlled to be powered off, so as to protect the electrical appliances from being damaged under low voltage.
The under voltage relay realizes the combination of DC system overvoltage and under voltage protection and voltage display, and the integration degree of the device is very high. The electronic integrated chip is used, which has high reliability, low power consumption, and the threshold setting has a display. This set of devices adopts the method of complete isolation from the measured circuit, and the interference to the main circuit is extremely low. The technical scheme of the utility model is that a large-scale integrated circuit integrating A/D conversion, driving, display and memory is adopted, and a multi-way switch is used to selectively display the voltage and constant voltage of the line. Its composition includes a sampling device, a multi-way switch, a comparison circuit, a threshold setting unit, an A/D conversion unit, an alarm driving unit, a selection button, and an over-voltage and under-voltage alarm unit.
1. Under voltage relay
Under voltage relay is an electronic control device, it has a control system (also known as input circuit) and a controlled system (also known as output circuit), usually used in automatic control circuits, it actually uses a smaller current to control a larger An "automatic switch" for high currents. Therefore, it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit. It is mainly used in the relay protection devices of generators, transformers and transmission lines as the starting element for overvoltage protection or low voltage blocking.
The voltage relay connects or disconnects the circuit according to the voltage signal at both ends of its coil. In actual use, the coil of the voltage relay is connected in parallel with the load. There are two commonly used under (zero) voltage relays and overvoltage relays.
Under voltage relay: When the circuit is working normally, the under voltage relay pulls in, and when the circuit voltage drops below a certain set value (40%~70%UN), the under voltage relay releases to realize under voltage protection for the circuit.
Overvoltage relay: When the circuit is working normally, the overvoltage relay does not act. When the circuit voltage exceeds a certain set value (generally 105%~120%UN), the overvoltage relay pulls in to realize overvoltage protection for the circuit.
Zero-voltage relay: release when the circuit voltage drops to 10%-35% UN, and realize zero-voltage protection for the circuit.
2. Detailed explanation of DC overvoltage and under voltage relays
The DC overvoltage and under voltage relay is specially designed for the DC system. It is assembled with the imported large-scale integrated circuit as the core, and the modules and some peripheral components developed by our factory. It has the characteristics of good versatility, strong interchangeability, long life, beautiful appearance, stable and reliable performance, etc. The relay is not only an overvoltage and under voltage relay, but also a precision digital voltmeter, which can be widely used for voltage monitoring of DC panels or DC systems. Because the relay directly displays the measured value and set value, it brings great convenience to the staff for debugging.
2.1 Technical parameters
2.1.1 Rated DC overvoltage and under voltage: DC48V, 110V, 220V (common)
2.1.2 Return coefficient: overvoltage 98-99%, under voltage 101-102%
2.1.3 Measurement (setting) accuracy: <±2 digits
2.1.4 Setting range: any value within the allowable working voltage range
2.1.5 Output contact capacity: AC 220V 5A (10A) (resistive)
2.2 How to use
The DC overvoltage and under voltage relays are mounted on the front of the board. The relays have overvoltage and under voltage value setting and display, and can also display the monitored data.
2.2.1 Overvoltage setting:
Press the selection key to make the overvoltage setting indicator light on, and the meter displays the overvoltage setting value at this time, adjust the overvoltage setting potentiometer to make the digital meter display the required value, and the overvoltage setting is completed at this time.
2.2.2 Under voltage setting:
Press the selection key to make the under voltage setting indicator light on, and the meter displays the under voltage setting value at this time, adjust the under voltage setting potentiometer to make the digital meter display the required value, and the under voltage setting is completed at this time.
2.2.3 After the overvoltage and under voltage values are set, press the selection key to display at the desired position.
2.2.4 When the relay enters the working state, no matter which position is selected, it will automatically return to the measurement position in case of power failure and power on again.
If it is necessary to check the working conditions of overvoltage and under voltage, first measure the monitored voltage value, and then use the setting potentiometer to adjust the under voltage value to be higher than the monitored voltage value. That is to say, the voltage has been under-voltage, and the relay should act at this time. The overvoltage inspection method is just the opposite of the under voltage inspection, that is, the overvoltage setting value is adjusted to be lower than the monitored voltage value.
2.3.1 Pay attention to the correct wiring when installing, and the positive and negative polarities cannot be reversed. The machine is equipped with protection components, and it will not work when the power supply is reversed, but the relay will not be damaged.
2.3.2 In the wiring diagram, the overvoltage contact is normally open and closed when overvoltage occurs. The under voltage contact is normally closed, normally open when the voltage is normal, and normally closed when under voltage or power-off.