Application of WPJ electronic motor protection relay in oil field power distribution system

1 Current Status of Motor Relay Protection in Metering Stations and Heating Stations

As the main power equipment for oilfield production, the normal operation of motors is directly related to whether oilfield production can operate safely and reliably. In the past, thermal relays were often used as overload thermal protection to realize motor protection functions. Due to the disadvantages of thermal relays themselves, the operation and maintenance management of oilfield motors have brought many inconveniences. With the continuous development of new power electronics technologies and the conversion of new power electronics achievements, new products that integrate motor overload, overcurrent, phase loss, no-load, and low voltage protection and use intelligent control technology have been gradually developed. As an application technology, WPJ electronic motor protection relays are increasingly showing their reliability and practicality. The performance comparison between thermal relays and WPJ is shown in Table 1.

2 Working principle

of WPJ Microelectronics and sensor technology are used to sense and judge the operating conditions of the motor. Through sensors, the motor winding temperature is directly obtained. The tripping element responds to the thermistor installed on the motor winding to monitor the operation of the motor at all times to achieve the purpose of protecting the motor and other equipment.

3 WPJ panel operation function selection

WPJ panel operation function selection is shown in Table 2.

4 WPJ protection's three main protection functions
4.1 Overload protection
Overload means the operation of overcurrent in a circuit without electrical damage. The WPJ action characteristic is inverse time, that is, the action time of the protector decreases with the increase of the overcurrent multiple, see Figure 1.

4.2 Undercurrent protection

Undercurrent means that the running current of the motor is lower than the rated current value when it is unloaded. In order to prevent the motor from idling, the low current of the motor is controlled. The WPJ undercurrent action characteristic is inverse time, that is, the action time of the protector decreases with the increase of the overcurrent and undercurrent multiples, see Figure 2.

4.3 Three-phase unbalance and phase loss protection

Phase loss means that one phase of the three-phase power supply is disconnected, and phase imbalance means that the high-voltage side of the power supply transformer is disconnected, causing the three-phase voltage on the low-voltage side to be different. The action characteristic is basically the same as overload.

5 Operation effect evaluation

The successful application of WPJ in place of thermal relays in the motors of heavy oil pumps at oilfield metering stations, air compressors at heating stations, and water treatment water supply centrifugal pumps shows that it can fundamentally overcome the low current setting accuracy, narrow current coverage range, large influence of ambient temperature, inability to achieve low-load phase loss protection and three-phase unbalanced protection, inability to display fault types, and the need for regular disassembly and calibration of current accuracy and tripping characteristics of bimetallic thermal relays, especially the inability to identify which products in operation are in an effective protection operation state, and the innate shortcomings of being unable to automatically exit operation when protection fails. Since WPJ has a complete and sensitive protection function, in actual application, it may cause frequent pump and production stoppages. To resolve this contradiction, it is necessary to further improve the fault alarm and early warning system in combination with oil production technology.

6 Economic benefit evaluation

A total of 100 sets of wPJ electronic motor protection relays were installed in 38 metering stations and 2 heating stations in the original 7th, 10th, and 15th teams. After nearly 5 years of operation, according to on-site investigation, its protection rate has reached more than 95%, effectively inhibiting motor burning and unnecessary wear of pumps and air compressors. The project investment is 18×10,000 yuan. According to statistics, it reduces the damage of 30 sets of large and small pumps and motors per year, saves 15×10,000 yuan in equipment and labor costs per year, and its cost can be recovered within 1.2 years. The average benefit of 5 years is 11×10,000 yuan/a. If it is further promoted, its annual economic and social benefits will be more considerable.