Research on a Novel Voltage Sampling Motor Protector

Research on a Novel Voltage Sampling Motor Protector

Qian Jinchuan and Zhu Shoumin (Zhejiang Taihua Electric Co., Ltd. 325604)

introduction

In the use of three-phase AC motors, more and more are used for three-phase irreversible transmission equipment (such as water pumps, fans, air compressors, elevator motors, etc.). In order to protect the motor in time under the conditions of phase failure, phase sequence, overvoltage and undervoltage, the corresponding protector should have the above protection functions to ensure the normal and safe operation of the motor and equipment. In the voltage sampling type protector, the working voltage of the motor is usually monitored through the protector to determine its voltage status (such as overvoltage, undervoltage, phase sequence, phase error, and the above fault indication is displayed on the protector panel), such as If there is a fault, the protector controls the control appliances (such as AC contactors) in the three-phase power supply circuit, and cuts off the main circuit power supply, thereby effectively protecting the motor and transmission equipment.

Compared with the current sampling type, the voltage sampling protector has the biggest feature: it has nothing to do with the power of the protected electrical equipment, but only protects it according to the power quality of the power grid, so that the protected electrical equipment can avoid damage due to poor power quality. Especially in the three-phase irreversible equipment or feeder circuit, after the phase sequence is determined, when the power supply line is connected with the original phase sequence due to maintenance or modification, the protector can identify the original phase sequence, so as to improve the motor And the corresponding equipment for protection.

1. The main technical parameters of the protector

1.1 Working voltage: AC three-phase 300V～460V 50Hz;

1.2 Overvoltage protection: adjustable from 380V to 460V, and adjustable for delay of about 0.5S to 5S;

1.3 Undervoltage protection: 300V～380V adjustable, delay time is about 1S～10S adjustable;

1.4 Phase failure and phase sequence protection: action time ≤ 0.2S;

1.5 Protective contact capacity: AC220V 5A (resistive);

1.6 Power consumption: <3VA;

1.7 Undervoltage and overvoltage action characteristics of the protector (Figure 1, Figure 2)

In Figure 1 and Figure 2, the characteristic line 1 is a single-phase over-under-voltage characteristic line; the characteristic line 2 is a two-phase over-under-voltage characteristic line; and the characteristic line 3 is a three-phase over-under-voltage characteristic line.