Install instruments and DCS

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Abstract: The installation and commissioning of Distributed Control Systems (DCS) play a crucial role in ensuring that the unit can complete its 168-hour trial operation successfully, be handed over for production, and become a high-quality project. By analyzing the common problems that occur in the operation of DCS systems in several power plants, some targeted improvement measures are proposed. 　　& t) |5 X' r2 I0 Q1 K: b5 C 　　Looking at the development trends in thermal control technology, future new and upgraded large-scale power units will all adopt Distributed Control Systems (DCS). The installation and commissioning of DCS start before power is supplied for plant use and continue throughout the unit’s commissioning process, playing a vital role in ensuring that the unit completes its 168-hour trial operation successfully, is handed over for production, and becomes a high-quality project. This article focuses on the common problems that arise during the installation and commissioning of DCS, as well as the improvement measures. 7 e0 X" O5 T. H. v+ T5 } 　　* K( x: C3 G; |! c/ e( m$ O 　　I. Installation requirements for DCS% A _% F# T: L- @/ Q; t% L 　　1.1 Environmental requirements for DCS 　　When installing DCS equipment, the installation environment has a significant impact on its operational performance; therefore, great attention must be paid to the environment in which the DCS equipment is installed. The installation of DCS equipment must begin only after the interior finishing, fire protection systems, air conditioning, and other related installations at the installation site have been completed, the environment is clean, the temperature and humidity are appropriate, and air conditioning is available if necessary. This is to avoid potential issues in the equipment’s operation caused by temperature damage or dust accumulation. Large-powered electrical equipment should not be placed near computer systems, and high-power walkie-talkies, mobile phones, etc. should not be used in computer rooms; in other words, the intensity of the magnetic field in the environment should be kept below the minimum level permitted by the specifications for computer systems. During the commissioning of Unit 1 in the second phase of Huaneng Fuzhou Power Plant, signal fluctuations occurred due to the use of walkie-talkies in the electronic equipment room. ?3 ?" i/ W8 g1 m+ Y* `& z2 W% I% M 　　1.2 Requirements for DCS grounding 6 F; ^+ W9 W1 `. ]) B0 c" Q 　　The grounding of a control system is intended to provide the entire system with a unified, common reference voltage level with the earth as zero. In the event of a power supply or equipment failure, the overload current is absorbed by an effective grounding system and quickly conducted to the ground. It can also provide shielding for DCS devices to eliminate interference. Therefore, proper grounding is one of the keys to ensuring the stable and safe operation of control systems. DCS has very strict requirements regarding grounding. Experience shows that during the commissioning and trial operation phases, many failures in thermal control systems are caused by improper grounding. ' A- N4 A- I/ | In grounding systems, common problems include: (1) Weak or incomplete soldering at the connections, resulting in poor solder joints ； (2) The bolt connections become loose due to vibration ； (3) Poor contact at the connection point due to corrosion ； (4) The resistance of the grounding electrode increases, and the grounding electrode becomes disconnected from the power grid ； (5) The ground wire wiring is unreasonable. ) H0 \; Y7 F4 L 　　1.3 Requirements for cable installation 　　During the commissioning of Unit 1 in the first phase of Xinjiang Hongyanchi No.2 Power Generation Co., Ltd., it was found that there was an elevated voltage at the common terminals of the DCS cabinet; in addition to the normal operating voltage, there was also an alternating current induced voltage of 80–180V, which prevented some equipment from functioning properly, and even caused normally operating equipment to trip unexpectedly. After careful analysis and inspection, it was found that the switch status line of the electric door acquired a very high induced voltage because it shared a single cable with the 220V operating power line. After consulting with various departments, the issue was fully resolved by placing the switch status wire for the electric door in a separate cable, apart from the power supply for operation. 8 w’ U/ k+ R, v Practical experience has shown that electromagnetic interference has become an important factor affecting the proper functioning of instrument displays, automatic activation, and protection systems. Among the various methods for resisting electromagnetic interference, one effective measure is to install and lay cables strictly in accordance with the principle of separating strong-current and low-current cables. Additionally, the cable should be routed as far away from heat sources as possible to avoid damage to the cable. 　　1.4 Requirements for wiring connections and modifications The work of connecting and modifying wires in a DCS is an important aspect in achieving automation of all equipment in the plant. To ensure the smooth progress of wiring connections and modifications, the following points must be noted: (1) All external wiring connections and modifications for the DCS are carried out by the construction party, while internal wiring connections and modifications are done by the DCS manufacturer ； (2) The construction unit shall notify the commissioning unit to remove the relevant modules before connecting or modifying the lines ； (3) For wiring that has already been connected, the construction party must obtain the approval of the commissioning party before making any changes. * q, F, g& e4 S8 |% Q0 ? 　　1.5 Requirements for the power supply system8 `$ p8 `1 v- s/ w 　　Some small systems often overlook this aspect; in fact, some control systems have only one power supply channel. For example, the FSSS of Unit 1 at the Xinjiang Hongyanchi No. 2 Power Plant had only one power supply; it was only under strong insistence from the commissioning unit that the manufacturer made improvements to the power supply system. The most basic requirement of the thermal control system for the power supply system is that there must be two power supplies, with the ability to switch between them properly. Only in this way can the normal operation of the control system be ensured. 4 |1 {" ( ?' T- c2 ^1 x 　　(3) Modules that have not been subjected to transmission or system calibration should not be placed in the insertion position. + l# C; O: V: T3 v2 T 　　(4) Try not to plug or unplug modules while they are powered on. / n* M4 Z3 _0 V: W" {' B1 \# n. ] 　　(5) Strengthen coordination between installation and commissioning to avoid concurrent operations on the same system. 　　2.2 Dynamic Commissioning of DCS 　　2.2.1 The Problem of Computer Crashes – i2 Q2 S |1 A% E% G8 Z. { 　　During the commissioning of Unit 1 at Guohua Zhungeer Power Generation Co., Ltd. and Unit 1 at Ningxia Guodian Shizuishan Power Generation Co., Ltd., crashes of the AP in the SIEMENS TXP system occurred. The main reasons are: (1) A large number of modifications were made during the debugging process, resulting in a large amount of garbage accumulating within the AP ； (2) Some functional areas are improperly allocated, resulting in excessive computer load, etc. Therefore, during the dynamic commissioning of the unit, no modifications to the configuration should be made as much as possible; if modifications are indeed necessary, approval from the commissioning command center must be obtained before proceeding. Any changes to the configuration must be documented and carried out by the DCS manufacturer. Furthermore, since the TXP system generates some junk files during operation, system administrators are required to clean the system regularly. " W( l& ^$ e w: p' V) M9 O 　　2.2.2 Defect Handling 　　During the 168-hour trial operation of Unit 1 at Huaneng Shang’an Power Plant, one member of the installation unit’s thermal control tuning team went to the site to handle a temperature sensor on the blower. Accidentally, he disconnected the wire connected to another, functioning temperature sensor, which caused the unit to trip. It is evident that handling defects during the unit’s operation must be handled with great care. Before addressing a defect, a defect handling form should be filled out first; contact the operators and obtain approval before proceeding with the resolution. 　　2.2.3 Signal isolation 0 t8 ] |: ~0 x1 x, J 　　During debugging in many field applications, it has been found that for electric control valves equipped with on-site electric actuators, isolators must be installed in the control circuit. The main reason is that the power ground for the commands in the DCS is directly connected to the earth, while the ground wire of the electric control valve is not grounded; this power mismatch prevents the valve from operating properly. After installing the isolator, the power supply of the DCS becomes floating, matching that at the local site. Common examples include the fan impeller blades, the exhaust fan stator blades, and the primary fan guide vanes, all of which require the installation of isolators. 　　2.2.4 Logical Issues (1) Signals for \"high/low water level in the drum\" and \"high/low pressure in the furnace\" should trigger an MFT signal; it is advisable to include a delay of 2–5 seconds. Its main purpose is to prevent the signal from being interfered with, and moreover, adding a short delay will not cause any harm to the equipment. $ L+ B* R5 W! H! r) T 　　(2) In the MFT logic, an MFT signal is often generated when both flame detection cooling fans trip; there is also an interlock relationship between these two fans – the most basic principle being that if one flame detection cooling fan trips, the other fan will start up automatically. However, if one fan trips, it can cause both fans to trip momentarily during the process of starting the other fan, which may lead to an MFT occurrence. Therefore, a delay needs to be added to the MFT signal generated when \"both flame detection cooling fans trip.\" The duration of this delay should be the shortest time sufficient to ensure proper interlocking between the two fans. Similar situations exist for devices such as sealed fans and air preheaters, whose own tripping can affect the operational safety of other equipment; careful attention must be paid to the logic involved in these devices. 5 Y; v, f1 @5 E) e+ {, y( Q 　　(3) One of the main tasks of the thermal control team during the commissioning period is to identify and analyze problems that occur after equipment trips. To quickly and accurately identify the source of the problem, it is recommended that important auxiliary machines be equipped with a \"first-failure logic,\" which primarily applies to devices with numerous shutdown conditions such as the MFY logic, ETS logic, feedwater pump shutdown logic, and coal grinder shutdown logic. This will facilitate accident analysis and enable the unit to start up quickly. Additionally, once the issue is identified, it should be reported to the on-duty project manager as soon as possible. , R. L3 U( |( k5 w+ G1 | 　　2.2.5 Other common issues ( D+ M* C6 K5 l. u' ` 　　(1) Problems with the display of the drum water level. In many sites, it is observed that under rated operating conditions, there is a significant discrepancy between the drum water level displayed by the DCS and that shown by the electrical contacts, ranging from 50 to 100 mm. The values displayed in the DCS, after pressure and temperature corrections, should be the most accurate. Inaccurate readings can be caused by the electrical contacts not being adjusted, as well as possible contamination of the electrodes that may lead to damage. 3 y ' R 　　(5) Fire detection issue. The quality of the flame detector is crucial for ensuring that flame protection can be put into use. The flame detectors currently in use have several issues; primarily, there are serious problems with these detectors ‘seeing’ the flame incorrectly or failing to detect it at all, and the output signals from these detectors become unstable as combustion conditions change. As a result, some of the main protection systems in the boiler cannot function properly. To resolve this issue, the flame detector must be continuously adjusted during debugging in order to achieve the most optimal results. For oil flame detectors, it is better to \"miss\" a flame rather than \"detect\" an incorrect one; in other words, the stability of these detectors should be improved by reducing their sensitivity, so as to prevent fuel from being injected into the furnace when it has not ignited. For coal flame detectors, it is better to have them \"peek\" rather than miss anything; in other words, the sensitivity of these detectors should be increased appropriately, as the furnace temperature is usually high during coal feeding, and the coal powder almost always catches fire. Additionally, the ‘peek’ display logic of the coal flame detector can be slightly modified: the CRT will display that a flame is detected by the coal flame detector only when there is an ‘AND’ condition between the signal indicating the operation of the coal feeder and the signal indicating that a flame has been detected by the detector’s probe; otherwise, it will indicate no flame. It solves the issue of \"peeking\" in display from a control logic perspective, thereby avoiding misjudgments by operators to some extent. The above methods have been successfully applied at Baoji No. 2 Power Plant, Huaneng Fuzhou Power Plant, Xuzhou Pengcheng Power Plant, and others