Design of submersible electric pump protector
The design of submersible electric pump protector is divided into hardware and software. The hardware design includes power supply, signal acquisition, digital input and output, and communication circuit. The software design mainly includes software architecture, measurement algorithm, protection algorithm and control algorithm.
4.1 Hardware Design
Since the working voltage of the commonly used submersible electric pump is from AC 200V~AC2000V, it is not suitable to use the working power supply of the submersible electric pump as the working power source for the protection of the submersible electric pump. The conventional method is to convert the working voltage of the submersible electric pump into an isolation transformer. AC 110V control voltage. In response to this situation, the submersible pump protector power supply uses a switching power supply. This is because the switching power supply has a wide operating range and high efficiency, which is suitable for this situation.
Signal acquisition includes voltage, current and other electrical parameter acquisition. In order to ensure the reliability of the acquisition, TV and TA are usually used as isolated converters for voltage and current signals. When selecting TA, pay attention to the TA voltage level. The conventional TA voltage level is 0.66KV, and when the working voltage of the submersible electric pump reaches AC 1000V or even AC 2000V, the TA of 3.3KV class should be selected to ensure isolation safety.
The design of the digital input and output and the communication circuit is a conventional design without any special features.
Reliability design includes electromagnetic compatibility and safety design. In the initial stage of electromagnetic compatibility design, it is necessary to fully consider various possible problems and plan for reserved measures. Commonly used anti-jamming methods include: adding a EMC filter to the power supply; adding a filter circuit to the signal acquisition part; adding a port protection circuit at the input port of each chip of the signal processing; adding a tantalum capacitor at the input of the chip power supply.
4.2 Software Design
Common sampling algorithms are DC sampling and AC sampling. AC sampling can measure non-sinusoidal signals and is therefore widely used in electrical parametric measurements. Common measurement algorithms include algorithms based on sinusoidal signals and non-sinusoidal based algorithms. Algorithms based on sinusoidal signals include maximum absolute value algorithm, half-cycle absolute integration algorithm, first-order derivative algorithm, second-order derivative algorithm, sample-value product algorithm, three-sample value algorithm, etc. in half-cycle; non-sinusoidal-based algorithms include Fourier Algorithm, first-order differential second half-wave Fourier algorithm, true RMS algorithm, etc. Various algorithms have their advantages and disadvantages. Although the algorithm based on sinusoidal signal is simple and consumes less resources, the measurement is inaccurate when there is harmonic or waveform transformation. However, the algorithm based on non-sinusoidal signal is more complicated, but the correctness of the measured value can be guaranteed.
Because it is difficult to design the inverse time curve algorithm in the protection algorithm, some products are marked as inverse time, but the actual time is the time limit segmentation, such as: (1.2-1.5) times, 60s protection, (1.5-2) times, 40s Protection, more than 2 times, 10s protection. This violates the basic principle of the inverse time curve. If the signal jumps up and down at the critical point, the action time will be inaccurate. The real inverse time limit has a continuous inverse time curve, which is really fast and large, and the small multiple is slow.
In software design, in addition to the need to select a reasonable algorithm, we must also pay attention to the standardization of software design. The basic principles of software design are information concealment and module independence. Good software requires high cohesion (cohesion is a measure of module strength) and low coupling.
Software testing is an indispensable part of software design. Its purpose is to verify whether the software meets the requirements. During the development process, the Chinese medicine follows the principle of early testing and early correction. After the unit test is passed, the integration test, confirmation test and acceptance test are carried out.
Concluding remark
The submersible electric pump is a new type of motor protector derived from the conventional motor protector product. It is more suitable for submersible pumps, adding anti-time protection such as underload, overvoltage, undervoltage, current imbalance and voltage imbalance. At the same time with current, voltage, power, frequency, electrical energy, residual current and other measurement functions, more in line with customer requirements.
