ZCHDE Increased Safety Motor Pre-Purging Control Device

ZCHDE Increased Safety Motor Pre-Purge System offers wide applicability in hazardous environments. Constructed with a composite explosion-proof design, it complies with the Chinese national standard GB/T 3836,carrying the explosion protection marking"Ex db eb mb IIC T4 Gb". It is suitable for Zone1 and Zone2 areas where explosive atmospheres from Group IIA, IIB, or IIC gases or vapors may occur. Pre-purging is mandatory when motors carry risks of sparking or electrostatic discharge, particularly in industries such as petrochemicals, coal chemistry, offshore platforms, and underground mining. Typical applications include main blowers and pumps with increased safety motors in refinery installations, and explosion-proof motors on offshore platforms requiring gas displacement before start-up.
ZCHDE System ensures operational compliance and asset safety in explosive atmospheres. Using pneumatic logic control, two-stage filtration, and flow-interlocked purge timing, it enables fully automated and highly reliable operation. The system can use clean, dry air or inert gas as the purge source and is equipped with a ZTXe pressure relief module. With support for both remote and local control, the system simplifies procedures, reduces human error, and improves management efficiency in hazardous areas. Operating temperature range: -20℃ to +60℃.

Product Description

Series IntroductionProfessional

● Composite Explosion-Proof Structure & High-Level Protection: Complies with Chinese National Standard GB/T 3836. Explosion-proof marking: Ex db eb mb IIC T4 Gb.
● Pneumatic Logic Control for Enhanced Intrinsic Safety: The purge timing sequence is governed by a pneumatic logic valve group. All field indicators are pneumatic-operated, eliminating the need for electrical power.
● Two-Stage High-Precision Air Filtration & Regulation: Filtration levels: 50μm (primary) and 5μm (for logic control). System response time: <100 ms.
● Precise Control of Flow and Pressure Parameters: Purge flow sensor set pressure: 300–450 Pa. Required main air supply pressure: 100–1800 Pa.
● Strict Flow-Interlocked Purge Initiation: The start signal for timing is triggered by the purge flow sensor, and the timer begins only when the minimum flow rate is reached. The timing module resets and counts continuously to ensure a thorough and effective purge of the enclosure.
● Standard-Compliant Pressure Relief Module: The relief module safely vents purge air through an integrated spark arrestor. It provides overpressure protection, spark containment, and safe pressure relief, with the relief pressure set at 0.35 MPa.
● High-Protection Electrical Interfaces: Increased Safety (Ex e) terminal box rating: Ex e II T6, IP65. The remote indicator switch is Flameproof (Ex d) type, Ex d IIC.
● Operating Temperature Range: -20 ℃ to +60 ℃.

Series advantagesdescription

● Compliant & Asset-Safe Operation: The ZCHDE device complies with Chinese and international standards, performing thorough and effective gas purging prior to motor start-up. This ensures operational compliance in explosive atmospheres, mitigates safety risks, and safeguards high-value Increased Safety (Ex e) motors.
● Reliable Design, Lower Operating & Maintenance Costs: The core control logic uses pneumatic controls, and all field indicators are pneumatic, minimizing electrical failure risks. With dual-stage air filtration (50μm and 5μm) and pressure regulation, the system ensures long-term stability of control operations.
● Automated Process & Safety Interlock, Minimizing Human Error: Once activated, the purge sequence runs automatically. The timer starts continuous counting only when the purge flow reaches the minimum required rate. A mandatory safety interlock prevents erroneous start signals during insufficient purging.
● Remote Centralized Management for Improved Operational Efficiency: The unit is equipped with an explosion-proof "Ex d IIC" switch and corresponding electrical signals connected to the Increased Safety terminal box. This allows monitoring and start-up operations from a remote control room, optimizing human resource allocation.

The introduction of each product in the series

The ZCHDE Increased Safety Motor Pre-Purging Control Device: This device is suitable for hazardous areas within industrial plants with a potential presence of explosive atmospheres from flammable gases or vapors (Groups IIA, IIB, IIC) mixed with air. It ensures continuous and effective internal cavity gas purging prior to starting an Increased Safety motor, providing automated safety assurance for this critical process.

USE cases

Case Study: High-Voltage Liquid-Resistance Soft Starter System Upgrade

1. Project Background
The high-voltage motor system at Shaanxi Yangxian Yuhu Chemical Co., Ltd. had been operating with liquid-resistance soft starters for more than a decade. As the existing equipment aged, several pain points became evident:
The liquid-resistance cabinets were bulky and occupied excessive floor space.
Their complex design demanded frequent maintenance of electrolytes, electrodes, and mechanical parts, resulting in significant O&M workload and high costs.
Startup performance was limited—low accuracy and the inability to support frequent restarts within short intervals—constraining production scheduling flexibility. The customer urgently required a high-efficiency, low-maintenance, and intelligent high-voltage soft-start solution.

2. Hengda's Solution：
Having reliably used Hengda’s excitation systems for more than a decade, the customer had full confidence in our product quality and service support. Based on this established trust, the customer directly selected the HDGR solid-state soft starter cabinet for this critical upgrade.
The solution delivered transformative results:
Lower O&M Costs & Space Optimization: The fully solid-state, modular design occupies significantly less space than the former liquid-resistance cabinet. Eliminating the need for electrolytes and mechanical upkeep, the maintenance frequency and costs were drastically reduced, achieving truly “low-maintenance or maintenance-free” operation.
Improved Startup Performance & Productivity: Leveraging high-precision thyristor control technology (as HDGR is solid-state), the system ensures smooth starting, completely eliminating mechanical and electrical shock during startup. It also supports rapid, repetitive starts and stops, significantly increasing the operational efficiency of the production process. The system's integration enables remote monitoring and condition diagnostics, further aligning with the customer's requirements for a digitalized and intelligent factory upgrade.

3. Client Feedback
The Operations and Maintenance (O&M) Department spoke highly of the benefits of the HDGR's minimal maintenance needs and high starting accuracy. They reported that the new equipment's performance stability and reliability significantly exceeded expectations, effectively guaranteeing the full life-cycle operation of critical assets. This retrofit not only addressed the client's core O&M pain points but also—via advanced solid-state technology—achieved a dual enhancement in production efficiency and reliability in a critical industrial segment.

Hubei Sanning Group: Eliminating Recurrent Failures in Synthesis Reactor Electric Heating with WDTJ

● Customer Challenge
The original temperature control system for Hubei Sanning Group's synthesis reactor relied on analog, non-microprocessor-based circuitry (using resistors and capacitors) to adjust the thyristor firing angle. This caused significant three-phase output imbalance. The resulting uneven heating of three-phase resistor elements led to frequent filament cracking, breakage, and short circuits, repeatedly forcing production line stoppages.

● Our Solution
Since 1997, we have supplied the first-generation WDTJ AC voltage and power regulation cabinet to address this issue. By implementing high-performance industrial control chips and digital synchronous phase-shifting technology, we entirely replaced the unstable analog control, achieving precise digital regulation of the firing angle.

● Long-Term Results
After the upgrade, the system immediately delivered accurate three-phase voltage triggering and stable output current. This completely eliminated unplanned downtime caused by three-phase imbalance at Hubei Sanning Group, ensuring continuous production.

● Built on this long-term trust and proven operational performance,Hubei Sanning Group has since adopted nearly 20 sets of our latest WDTJ AC voltage and power regulation cabinet across five newly built chemical plants. All WDTJ cabinets have been maintaining precise control and stable operation, consistently supporting the development of Hubei Sanning Group's chemical industry.

Case Study:Electrostatic Precipitator Upgrade at Hubei Sanning Chemical

● Customer Challenges
Hubei Sanning Chemical’s electrostatic precipitator (ESP) system had been operating for years with increasing failures and declining dust collection efficiency. Key issues included:
-Failure to reach target high-voltage levels
-Poor voltage control accuracy
-Inability to effectively limit discharge spark frequency
These shortcomings not only risked non-compliance with environmental standards but also undermined production stability.

● Our Solution
We delivered a customized WGT-series high-voltage control power supply featuring:
-Highly precise voltage regulation and improved step-up characteristics
-Microprocessor-controlled monitoring and limitation of spark rate (sparks per minute)

● Results Achieved
-Operating voltage increased by 10%, significantly improving dust removal efficiency
-Stable and accurate voltage output with tightly controlled sparking
-Markedly improved system reliability and reduced failure rate
-The system has now operated flawlessly for three years, earning consistent positive feedback from the custome