Woodward CPC-II electro-hydraulic current pressure converter

Woodward CPC-II electro-hydraulic current pressure converter: technical selection and implementation points for replacing and upgrading CPC and Voith E360 I/H after discontinuation

Industry Pain Point: Oil Pollution - The Number One Issue in Turbine Control Reliability

In the steam turbine control system, the electro-hydraulic current to pressure converter (I/H Converter) is the core component that converts the current command output by the controller into a hydraulic pressure signal, and then drives the actuator of the regulating valve (throttle valve). The throttle hole and precision valve port of this component are extremely sensitive to the cleanliness of the oil. The deposition of particles and sludge in the oil during long-term operation can cause jamming, delayed response, decreased control accuracy, and even force unplanned shutdown of the unit for filter replacement and component cleaning.

Woodward explicitly states in his application technology literature that oil pollution is the top reliability issue in the steam turbine market. The traditional coping methods are frequent maintenance of precision filters and regular cleaning of converters, but this not only increases operation and maintenance costs, but also introduces additional pressure drop and potential failure points due to the presence of filters themselves. In response to the pain points in this industry, Woodward has launched the second-generation Current to Pressure Converter CPC-II (Generation 2) and simultaneously launched an upgrade plan for old CPC and Voith E360 I/H users.

Special attention should be paid to the timeline: CPC products have been discontinued since July 2012, and the official recommended replacement model is CPC-II. Power plants and equipment owners who are still operating CPC devices online should develop spare parts and upgrade strategies as soon as possible to avoid the passive situation caused by shutdown and supply interruption.

Analysis of CPC-II Core Technology

2.1 Dirt Buster and Silk Buster Anti pollution Technology

The core innovation of CPC-II is the "Dirt Buster" technology, which is reflected in two aspects of hardware enhancement:

The driving force of the actuator is increased by 4 times: the stronger electro-hydraulic actuator can still reliably operate when particles invade, and will not be stuck by 40 μ m level dirt;

Self cleaning valve core design: The valve components have self-cleaning characteristics during operation, and with the patent application's "Sill Buster" sludge cleaning technology, it can remove sludge accumulation without interrupting operation or damaging the integrity of operation - this means that there is no need to shut down and drain oil for cleaning, and the continuity of operation is fundamentally guaranteed.

The practical application effect is that CPC-II can directly "pass through" 40 μ m sized pollutants, thereby reducing or even completely eliminating the front-end filter and its maintenance workload of the converter. For old units with difficulties in purchasing filter spare parts and tight maintenance windows, this characteristic has significant economic value.

2.2 Control performance advantages

CPC-II integrates Woodward's industry-leading control point algorithm, advanced diagnostic capabilities, and PC based service tools, with performance advantages reflected in:

Pressure output is "quiet" and stable: Traditional I/H converters generate excessive pressure "noise", leading to increased wear and tear of the servo system; The dynamic characteristics of over damping also result in delayed response. CPC-II achieves stable pressure output while balancing low wear and fast and accurate command response;

Bumpless precision throttle valve control: ensures control stability under normal operating conditions, achieves disturbance free switching during plant upsets, and minimizes process overshoot and overshoot to the greatest extent possible;

Step response approaching ideal: From the performance comparison curve, it can be seen that during the process of pressure decreasing from about 4.8 bar to 2.7 bar and then rising again, the output transition of CPC-II is smooth, and the servo position response of the steam valve is close to the ideal step characteristic, while traditional I/H converters are accompanied by significant fluctuations and steady-state deviations.

2.3 Functional Capability Comparison

Compared with the older generation CPC and Voith E360 I/H, CPC-II is comprehensively ahead in terms of functional matrix:

Ability/Function CPC-II CPC Voith E360

Oil pollution tolerance ✓——

Resistance to silt accumulation ✓——

Valve linearization compensation ✓——

Corrosive pollution tolerance ✓ - x

Viscous (high friction) mouth compensation ✓ - x

Accept redundant pressure set point input ✓——

Accept redundant pressure sensor input ✓——

Accept external cylinder position sensor ✓——

Internal health monitoring ✓——

Manual Stroking Function ✓ - x

Input/output isolation ✓——

Performance Trend Tool ✓——

Performance/stability adjustment ✓ x -

In addition, CPC-II has increased the inlet pressure option to 25 bar (with an expanded range compared to the previous generation), providing optimal flexibility for redundant control configuration through isolated input-output, advanced redundancy management, and performance monitoring management capabilities. The introduction of redundant set point inputs and redundant pressure sensor inputs enables the seamless integration of CPC-II into a dual channel regulation system with high availability requirements.

Summary of Performance of CPC-II

Based on the original data, the performance improvement of CPC-II compared to traditional I/H systems can be summarized into four points:

Quiet and stable output, significantly reducing servo system wear and tear;

The dynamic response is fast without damping, and the step response is close to ideal;

The disturbance free control capability covers the disturbance conditions of the unit, reducing overshoot/underregulation;

Stable pressure output brings fast and accurate command tracking.

For power plants with throttle valve control accuracy and unit availability as the core assessment indicators, these indicators directly correspond to economic benefits.

Upgrade replacement path and model comparison

4.1 Upgrading from CPC: Real Direct Replacement

CPC-II is a direct replacement for CPC: the external dimensions of the installation base and the manifold of the oil circuit interface remain unchanged, without the need to modify the basic installation surface and pipelines. The precise installation dimensions can refer to Woodward product specification 03352.

4.2 Upgrading from Voith E360 I/H: Adaptation Kit Solution

For users of the original Voith E360 I/H throttle control unit, Woodward offers a separately sold Adapter Kit with order number 8928-7240. The installation of the Voith converter to CPC-II can be completed through this kit.

4.3 Comparison Table of Explosion proof Areas and New and Old Models

When selecting, it is necessary to check the classification of hazardous areas on site. The comparison table is as follows:

The original CPC model area classification control pressure range has been upgraded to CPC-II model

8901-456 / 8901-457 / 8901-459 / 8907-1102 / 8907-1106 Class I, Division 2 / ATEX Zone 2 0~10bar（ Corresponding to 8901 series/0~25bar (corresponding to 8907 series) 9907-1200

9907-046 / 9907-477 Class I, Division 1 0~10bar / 0~25bar 9907-1199

9907-802 / 9907-803 / 9907-1100 / 9907-1103 Class I, Division 2 / ATEX Zone 1 & Zone 2 0~10bar（9907-802、9907-803）/ 0~25bar（9907-1100、9907-1103） 9907-1197

Summary of selection points:

Zone 2/Division 2 applications: corresponding to CPC-II models 9907-1200 (0~10 bar) or 9907-1197 (0~25 bar);

Division 1 application: Corresponding to CPC-II models 9907-1199 (covering 0~10 bar or 0~25 bar);

Pressure level selection: It is necessary to match the corresponding new model with the rated control pressure range (0~10 bar or 0~25 bar) of the original CPC, and cannot be substituted across pressure levels.

Implementation suggestions for upgrading projects

Current situation inventory: Verify the specific ordering model (nameplate information) of the CPC in service on site and the classification of the explosion-proof area on site, and determine the replacement model according to the table above; If it is Voith E360 I/H, include the adapter kit 8928-7240 in the procurement list;

System side confirmation: If the unit regulation system has adopted or plans to adopt a redundant pressure set point/sensor scheme, its redundant input management capability can be activated when upgrading to CPC-II to improve channel reliability;

Adjustment of oil quality management strategy: After the CPC-II is put into operation and verified to be stable, the maintenance cycle of the front-end filter can be evaluated for cancellation or extension, and the operating procedures and checklist can be updated synchronously;

Debugging tool preparation: Use Woodward's PC based service tool for parameter configuration, manual stroke testing, and performance trend recording, establish baseline data for subsequent state monitoring;

Normalization of health monitoring: Utilize the internal health monitoring function of CPC-II, incorporate the converter into the predictive maintenance system, and avoid relying on regular disassembly and inspection.