Description

Industry Background and the Misselection Problem in Switchgear Projects

Switchgear projects across the power distribution sector routinely encounter a recurring and costly problem: insulators and earthing components selected based on appearance or thread size alone, without reference to voltage class or fault-current duty. This practice leads directly to insulation mismatch, certification failures, and field failures once equipment is energized. EPC contractors face a related but distinct challenge — multi-category procurement and delivery pressure across low-voltage, medium-voltage, and high-voltage equipment simultaneously. Meanwhile, new energy applications are placing higher insulation performance demands on switchgear components than conventional distribution networks. Maintenance buyers, for their part, often struggle to source dimensionally compatible replacement parts for existing ABB, Siemens, or Schneider equipment when original components become obsolete or unsupported.

Yueqing Duwai Electric Co., Ltd., operating under the brand DOWE (Duwai), was founded in 2012 and is headquartered in Liushi Town, Yueqing City, Zhejiang Province — widely recognized as China’s Capital of Electrical Appliances. The company has built an export network covering 60+ countries and regions across six continents. Rather than pursuing a broad product catalog, DOWE has positioned itself as a focused manufacturer of LV, MV, and HV busbar insulators and associated switchgear insulation components, anchored by a proprietary three-level voltage classification specification designed specifically to prevent insulator misselection. This background frames why the technical detail behind indoor high voltage earthing switches deserves closer examination.

Authoritative Analysis: Why Fault-Making Capability and Interlocking Matter

The necessity for a properly specified earthing switch stems from a basic safety requirement: maintenance work on de-energized equipment requires verified grounding to protect personnel from induced or back-fed voltage. Portable earths introduce risk because they can be applied to the wrong circuit or require a technician to reach into a compartment not yet proven dead. A slow or weak earthing switch may fail to close onto a live circuit, and leaving a single phase un-earthed can be invisible from outside the panel, creating a hidden downstream hazard.

The principle logic behind DOWE’s earthing switch designs addresses these risks directly. Three-pole simultaneous operation drives all three phases from a single shaft, removing the possibility of an un-earthed phase. Mechanical interlocking with the circuit breaker and cable compartment door enforces the safe operating sequence in hardware: the breaker must be open and withdrawn before the earthing switch can close, the earthing switch must be closed before the cable compartment door can open, and the breaker cannot be racked in while the earth is applied. A direct-driven mechanical position indicator shows actual blade position rather than a mechanism proxy.

These designs are benchmarked against IEC 62271-102 type test certification and GB 1985 compliance, applied to three product lines. The JN15A-12 Indoor Earthing Switch is a three-pole 12 kV device installed in the cable compartment of KYN28 metal-clad panels, rated for 50 kA peak making current and 20 kA short-time withstand for 4 seconds. The JN17 Series, available in 12 kV (JN17-12) and 24 kV (JN17-24) ratings with manual or motorized operation, offers higher-duty performance: 80 kA peak making and 31.5 kA short-time withstand on JN17-12, and 63 kA peak making and 25 kA short-time withstand on JN17-24. The JN22B-40.5 High-Speed Vacuum Earthing Switch, built for 35 kV and 40.5 kV systems, uses sealed vacuum interrupters as making elements and delivers 63 kA / 80 kA peak making current with 25 kA / 31.5 kA short-time withstand for 4 seconds.

Deep Insights: Trends in Fault Current, Remote Operation, and Voltage Classification

Several technical trends are shaping how earthing switches are specified. Networks located close to source transformers or with in-plant generation can carry prospective fault current above 50 kA peak, which is why the JN17 series was developed as a higher-duty alternative. Unmanned substations increasingly require remote earthing operations from a control room or SCADA system without dispatching a crew — addressed through motorized variants running on AC/DC 110 V or 220 V. At the 40.5 kV level, required clearances and fault-close energy make open-air earthing switch designs large and slow, a limitation the JN22B-40.5 addresses by containing the arc inside sealed vacuum interrupters and using a spring-driven mechanism that fixes closing velocity independent of operator technique.

On the market side, EPC contractors continue to face pressure from multi-category procurement spanning LV, MV, and HV equipment, while renewable generation collection substations stepping up to 33 kV or 35 kV are driving demand for fault-making earthing switches rather than simple isolation earthing. Retrofit scenarios — where an existing 50 kA earthing switch is inadequate for an increased network fault level, or where original equipment from other manufacturers is no longer supported — represent a recurring procurement pattern.

A notable risk in the industry is specifying making capacity below the site’s actual prospective fault current, described as a common and dangerous procurement error. Dusty or humid switchgear compartments can also degrade conventional microswitches, producing false earth-applied indications, which is why encapsulated position sensors are used on select models to provide reliable open and earthed status to protection relays and SCADA systems.

Company Value: How DOWE Electric Supports Switchgear Reliability

DOWE’s technical accumulation is reflected in self-developed earthing switch designs spanning 12 kV, 24 kV, and 40.5 kV voltage classes, with peak short-circuit making current options of 50 kA, 63 kA, or 80 kA and short-time withstand current of 20 kA, 25 kA, or 31.5 kA for 4 seconds depending on model. These products are engineered for installation in KYN28-12, KYN28-24, and KYN61-40.5 metal-clad panels and equivalent assemblies, covering utility distribution substations, industrial plants such as mining, metallurgy, cement, and petrochemical facilities, renewable generation collection substations, compact and packaged substations, and retrofit projects in aged switchgear.

Independent verification underpins this positioning: the JN15A-12, JN17 series, and JN22B-40.5 have each received IEC 62271-102 type test certification and comply with GB 1985. Combined with the company’s proprietary three-level voltage classification specification, this gives EPC contractors, utilities, and maintenance buyers a documented basis for matching equipment to site requirements rather than relying on appearance-based selection. The company’s stated brand philosophy, "Do What We Can, Do It Well," is consistent with its focused rather than broad product strategy.

Conclusion and Industry Recommendations

Selecting an indoor high voltage earthing switch for power distribution is not simply a matter of matching a voltage label. It requires confirming that peak making current and short-time withstand current exceed the site’s prospective fault level, verifying that mechanical interlocking enforces a safe operating sequence, and checking dimensional and functional compatibility during retrofit work. Buyers evaluating equipment for unmanned or remotely supervised substations should also weigh whether motorized operation and reliable position feedback are needed to remove travel time and operator exposure from the switching process. Reference to third-party type test certification such as IEC 62271-102 and compliance standards such as GB 1985 remains a practical way to validate supplier claims before specification is finalized.