Precision DC Hipot Testing for Water-Cooled Generators: The ZGF-S Series

In the power generation industry, the insulation integrity of large water-cooled generators is critical to operational reliability. Traditionally, performing a high-voltage DC withstand test on these generators required extensive drying and blow-down procedures to remove water from the coils. This process was not only time-consuming but also carried the risk of internal arcing due to residual moisture.

The ZGF-S Series DC Hipot Test Set is a specialized instrument engineered to solve these challenges. Designed specifically for water-cooled generators, this unit allows for precise DC voltage withstand and leakage current testing while water is still present in the cooling system. This article provides a technical overview of its functionality, key features, and specifications relevant to electrical testing professionals.

Core Technology and Application
The primary technical advantage of the ZGF-S series lies in its ability to perform "wet testing"—applying high voltage to generator windings while they are filled with water. This capability overcomes the limitations of traditional testing by:

1.Eliminating Extended Dry-Out Times: Bypassing the lengthy process of blowing out and drying the water from the bottom of the stator bars.

2.Preventing Coil Arcing: Mitigating the risk of flashover or arcing that can occur when trying to dry internal moisture unevenly.

3.Integrated Polarization Compensation: The unit features a built-in circuit for outputting polarization compensation voltage directly from the case, ensuring accurate measurement of absorption current and reducing testing errors caused by residual moisture.

Technical Features and Operational Benefits
From a technician's standpoint, the ZGF-S series combines high-precision measurement with robust safety features:

1.Direct Reading & Precision: The control panel displays voltage and current data directly, eliminating the need for external conversion calculations. Measurement accuracy for both voltage and current is ≤1.0% ±1 digit, ensuring reliable data for insulation assessment.

2.Integrated Timing Function: The unit includes a one-minute timing and tip function, allowing technicians to perform standardized time-resistance tests without needing an external stopwatch.

3.Dual-Layer Protection System:

⑴Internal: Features perfect over-voltage and over-current protection to safeguard the test set itself.

⑵External: Includes a zinc oxide (ZnO) over-voltage protection circuit specifically designed to protect the generator's insulation from damage during testing.

4.Output Purity: The equipment maintains a ripple coefficient of ≤3.0% and voltage stability of ≤1.0%, ensuring a clean DC output for accurate leakage current analysis.

Technical Specifications Overview
The ZGF-S series offers a range of models to accommodate different generator sizes and testing requirements. Key electrical parameters include:

1.Output Voltage: Ranges from 50 kV to 80 kV depending on the model.

2.Output Current: Available from 100 mA to 200 mA, with power outputs reaching up to 16,000 W.

3.Power Supply: Models are available for standard AC220V or industrial AC380V (3P4W) supplies, ensuring compatibility with various field power sources.

4.Measurement Error:

⑴Voltage/Current: ≤1.0% ±1d

⑵Over-Voltage Setting: ≤1.0%

Portability for Field Service
Recognizing the logistical challenges of power plant maintenance, the ZGF-S series is designed with a portable, four-part separation structure. The control unit, intermediate frequency transformer, voltage doubler, and accessories are each housed in dedicated, shockproof aluminum alloy cases. This modular design keeps the heaviest individual component (the cylinder) at a manageable 70 kg, while the control unit carrying box remains lightweight at 25 kg, facilitating easy transport and setup in confined turbine halls.

Conclusion
For electrical maintenance professionals, the ZGF-S Series represents a significant advancement in generator testing technology. By enabling safe, accurate DC hipot testing in the presence of cooling water, it drastically reduces maintenance downtime and enhances the safety of the insulation diagnostic process. Its combination of precision metrology, robust protection, and field-ready portability makes it an essential tool for modern power plant electrical testing regimes.

GDZX is a manufacturer of power detection equipment, offering a diverse range of products with comprehensive models and providing professional technical support. Contact us at +86-27-6552607 or +86-17396104357.Website: http://en.gdzxdl.com/