With the maturing of automation systems, domestic DCS platforms in China have also matured: EDPF-NT from Guodian Zhishen and MAC-II from HollySys hold half the small/medium-unit market on price; XDPS-400 from Shanghai XinHua already serves 300MW units; imported WDPF, Bailey and Siemens systems equip large and medium units. But advanced control systems alone are not enough — MCS functions are ultimately executed by the field devices, and the accuracy of actuator commissioning directly affects automatic-loop performance and control quality. This case describes the DCS and actuators of Xin'an Power Plant.
Xin'an Power Plant phase: 2×135MW, main design by Northwest Electric Power Design Institute, installation and commissioning by Henan No.2 Thermal Power Construction Company. The boilers are HG-440/13.7-L.PM4 single-drum natural-circulation, once-reheat, semi-outdoor, solid-bottom-ash, superhigh-pressure CFB boilers by Harbin Boiler Works, with high-temperature cyclone separators, combined on-bed/off-bed startup and bell-type tuyeres.
The DCS is EDPF-NT by Beijing Guodian Zhishen: 1 main cabinet, 5 boiler cabinets, 3 turbine cabinets and 1 electrical (ECS) cabinet; operator interface comprises 1 engineer station, 1 history station and 4 operator stations on a redundant ring Ethernet.
The 135MW units use only two pneumatic control dampers (fuel-oil pressure and flow, WuZhong products); the important control loops use SIPOS 5 Flash electric actuators, covering superheater/reheater spray attemperation, feed-water bypass control valves, cone ash-extracting valves and HP/LP bypass control valves. The SIPOS 5 Flash series originates from Siemens technology (SIPOS Aktorik, Germany), with 220VAC and 380VAC supply options — compact yet powerful, low noise, stable, and of modular construction for easy dismantling and maintenance.
An electric actuator is a deep-negative-feedback servo system with a built-in servo amplifier: the motor drives the output shaft through a gear reducer, and the shaft angle θ is the actuator output; a position transducer emits feedback current If proportional to θ. When the difference between command Ii and If falls below the amplifier dead band ΔE (about 0.16mA is suitable — too small causes hunting and motor heating), the motor de-energizes and the shaft rests at the corresponding position; a decreasing command drives reverse rotation to a new balance.
a. Complete cable connections first: 220VAC supply, 4~20mA command, 4~20mA feedback. The local panel uses non-contact magnetic buttons — well sealed and easy to operate; through the transparent window the LCD handles local/remote switching, setting and diagnostics.
b. After power-up the main menu offers Language setting, Commissioning, Observing and Diagnosis. First-time setup uses password "9044" to unlock Commissioning parameters, then sets the open/close directions, closing mode and torque values — normally, for tight shut-off, the closing limit is torque-dependent and the opening limit travel-dependent; for smooth opening the opening torque should be one class above the closing torque.
First end-position setting: manually adjust the full-open position, or hold the open button for two seconds until the actuator runs to "until TL reached"; jog close to confirm the open position; adjust the signal gear unit until deviation is 0. Then hold the close button for two seconds — since closing is torque-dependent, the display shows "adapting cl.pos.-busy!"; after a few seconds "adjustment OK!" completes the setup; "increase it!" or "decrease it!" means the signal gear ratio must be changed and the setting repeated.
c. On faults, enter the self-diagnosis menu and follow the prompts; after clearing a fault the end positions can be re-set.
a. Compared with the control valve, an extra emergency-switch cable is wired.
b. End-position setting is the same; the difference is the valve-speed setting — set the emergency speed to maximum. When the turbine demands a fast bypass action, energizing the emergency contact opens or closes the valve rapidly, protecting the turbine.
c. One valve serves both control and trip duty, saving a dedicated trip valve and its maintenance.
The power plants commissioned by the author's company around 2003 — Kaifeng, Xin'an, Wanfang and the then-under-construction China Resources Dengfeng — all used SIPOS 5 Flash actuators on their important control loops. This article is shared with fellow engineers.
See also: our SIPOS brand column; the manual collection hosts the official SIPOS 5 Flash manuals.
