Brief Analysis on Ensuring Reliability of DCS Power Supply System in Thermal Power Plant

1 Introduction

With the advancement of modern control technology and the development of industrial production, DCS systems have been widely used, and a corresponding power supply system is needed to support the safe and reliable operation of this large network. The requirements for power quality are getting higher and higher, and the design layout is becoming more and more perfect. In the design of important occasions, UPS power supply, security power supply double-cut power supply or dual-channel UPS double-cut power supply are used to greatly improve the safety and reliability of power supply. However, in actual applications, it is found that since DCS systems are sensitive electricity users, they have high requirements for power supply. There are still new problems in actual use.

2 Problem Analysis

2.1 Design risks of dual-path single-cut

The power supply configuration uses a dual-circuit automatic switching circuit , one for UPS and one for factory power. Under normal circumstances, K1 and K2 are closed, and the working power is supplied by the UPS, as shown in Figure 1. The problem with this design is that all loads are added to one UPS, and only when the UPS power fails (CI contactor loses power) will it switch to factory power. This design has a risk concentration problem.

2.2 Risks of dual-path dual-cut design

The power supply configuration uses a dual-channel automatic switching circuit: one UPS and one factory power supply. Under normal circumstances, the two sets of power supply are used simultaneously, as shown in Figure 2. The problem with this design is that the current switching contactor itself cannot meet the needs (the contactor model in Figure 2 is LC1D65008M5). When the power supply voltage drops, no active remedial measures are taken, which makes the quality of the power not guaranteed. In other words, when the system is impacted, the voltage drop (the voltage value of C1 has not reached the contactor pressure loss return position) has become an important factor affecting the power quality. The power provided by the factory power supply sometimes even reaches the range where the power supply equipment cannot work normally, and the power supply system cannot provide reliable and effective power supply. The consequences are obvious.

Figure 2 Dual-path dual-cut circuit

3 Problem Solutions

For the power supply mode of using factory power, since the current market cannot provide fast on-off contactors with relatively small hysteresis, necessary measures should be taken to monitor the quality of factory power during design, such as using undervoltage protection switching, alarm, and using a third power supply, etc. As shown in Figure 3.

Figure 3 Three-way single-cut circuit

3.1 Reasonable layout of power load distribution

Most of the current DCS systems have redundant power supply devices, cards, and main controls. Some servers also have dual power supplies. How to deal with equipment without dual power supply control? Grasp the principle: the layout of main and auxiliary equipment and operator stations should be carried out in a risk-dispersed and centralized manner. Because of the different systems and scales, it is no longer shown in the figure. Reasonable layout should be carried out according to the specific situation.

3.2 Choose online UPS power supply

At present, there are many types of UPS power supplies, with large price differences and performance advantages and disadvantages. The UPS power supply selected for the DCS system must be online, that is, when the power supply to the UPS fails, the UPS can use its own battery to ensure that the system has a certain power supply time (minimum not less than 30 minutes); the output power quality of the UPS device must meet the requirements. We found such a problem in use: after the magnetic saturation voltage-stabilized power supply is powered by a certain type of UPS, its measuring instrument output has a ±0.3 swing. Of course, if the selection is appropriate, using a dual-channel UPS power supply is a more reasonable way.

3.3 Three-way UPS power supply solution design

Now according to relevant safety requirements, a three-way UPS power supply is used. This is good, but the investment is large and the circuit is relatively complicated.

4 Conclusion

There are many reasons for the loss caused by the failure of the DCS power supply system, which has attracted the attention and attention of the design institute and users. The anti-accident measures of the State Power Corporation should be strictly implemented. From the early design to the construction, and the later maintenance and improvement, it is possible to ensure that the DCS power supply is truly safe and reliable.