An international tender may specify a 30kV distribution network, while Chinese manufacturers commonly organize comparable products under a 35kV system class and a 40.5kV highest equipment voltage. This difference in naming can create uncertainty for buyers: is the Chinese product compatible, oversized or simply described under another convention?
The answer depends on more than the number printed in a catalog.
During technical review for a Burundi overhead line package, Younxin had to reconcile project descriptions, drawings and Chinese product categories before preparing the supply proposal. The process offers a useful checklist for other EPC and utility projects.
Start with three different voltage terms
The following values should not be confused.
Nominal system voltage
This is the voltage used to identify the network, such as 30kV or 35kV. It is a system designation and may follow local utility practice.
Highest voltage for equipment
This is the maximum system voltage for which the equipment is designed. Chinese 35kV-class switchgear and line apparatus are commonly associated with a 40.5kV equipment rating.
Rated withstand levels
Equipment must withstand specified power-frequency and lightning impulse voltages. Two products described with similar nominal voltage labels may still have different insulation levels.
For this reason, a supplier should not convert every occurrence of “30kV” to “35kV” without checking the technical schedule.
Equipment that must be reviewed separately
Isolators and load-break switches
Confirm the rated voltage, rated current, short-time withstand current, operating method, pole-mounting arrangement and whether the device is designed only for isolation or also for load switching.
A gang-operated isolator provides a visible open point. It is not automatically a circuit breaker and may not be suitable for interrupting fault current.
Fuse cutouts
For a drop-out fuse, check the voltage class, continuous current, breaking capacity, creepage distance and fuse-link rating. The fuse link should be selected according to transformer size, inrush current, feeder duty and protection coordination—not simply because it fits the fuse tube.
Surge arresters
The arrester selection requires more than a nominal voltage. Confirm rated voltage, maximum continuous operating voltage, nominal discharge current, grounding arrangement and system earthing method.
An arrester intended for a 10kV system cannot be assumed suitable for a 30kV line. A mixed-voltage BOM should be treated as a technical query, not quoted without clarification.
Insulators and insulator strings
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- power-frequency and lightning impulse withstand levels;
- creepage distance and pollution class;
- mechanical failing load;
- number of insulator units per string;
- connection standard and fitting arrangement;
- use on tangent, angle or terminal poles.
Pollution, altitude and humidity can change the required external insulation even when the voltage class remains the same.
Cables and terminations
A description such as “3 × 1 × 150mm² MV cable” gives the conductor arrangement and cross-section, but not the insulation class. The buyer should confirm whether the cable is 12/20kV, 18/30kV, 26/35kV or another rating.
The termination must then match the cable's conductor material, insulation diameter, screen structure, armor and indoor or outdoor application.
Transformers and LV boards
The transformer high-voltage winding, low-voltage winding and downstream distribution board must form one coherent system. In the Burundi project review, a 400V, 650A low-voltage board made it essential to verify the transformer's stated secondary voltage rather than copying an ambiguous line from the source document.
Mechanical matching is equally important
Voltage compatibility does not guarantee installation compatibility. Pole-top equipment must also match:
- crossarm hole spacing;
- steel-pole diameter at the installation height;
- mounting bracket geometry;
- phase spacing and electrical clearance;
- conductor sag and mechanical tension;
- operating-rod length and access from ground level.
When a reference drawing was originally developed for a concrete or timber pole, the mounting system should be redesigned for the actual steel pole. Reusing the same drawing without reviewing clamps and brackets can create unsafe site modifications.
A practical confirmation table
Before approving a substitute or equivalent product, compare the following:
| Item | Project requirement | Proposed product | Confirmation needed |
|---|---|---|---|
| System | Nominal voltage and earthing method | Applicable system class | Client/utility approval |
| Equipment voltage | Highest voltage | Rated voltage / Um | Must be equal or higher as required |
| Insulation | Impulse, power-frequency, creepage | Test values | Must meet project standard |
| Current | Continuous and fault duty | Rated current and withstand | Check operating duty |
| Mechanics | Load, dimensions, interfaces | Product drawings | Check pole and conductor fit |
| Standard | IEC, EN, local or utility rules | Test standard | Confirm equivalence |
| Accessories | Brackets, links, fuse links, bolts | Included scope | Avoid installation shortages |
When should the client issue written approval?
Written technical approval is especially important when:
- the proposed voltage designation differs from the tender wording;
- the original model is unavailable;
- pole material or geometry changes;
- insulator type or number of units changes;
- a cable or termination class is inferred from incomplete data;
- a protection-device rating is revised.
The approval record should identify both the original requirement and the proposed equivalent. This protects the buyer, supplier and installer from later misunderstanding.
Send the whole technical package, not one line from the BOQ
The most reliable equipment selection comes from reviewing the BOQ together with drawings, the single-line diagram and utility requirements.
Younxin can help international project buyers translate mixed-language technical lists, compare Chinese equipment classes and prepare a clarification schedule before quotation. Send your 30kV project documents and we will identify the parameters that require confirmation.
FAQ
Is 40.5kV equipment the same as a 40.5kV operating network?
Not necessarily. In many product systems, 40.5kV is the highest voltage for equipment associated with a nominal 35kV network.
Can a supplier choose the fuse link from transformer capacity alone?
Transformer capacity is important, but protection coordination, inrush current, system voltage and upstream/downstream devices must also be considered.
Why must cable terminations match the exact cable?
Termination components fit specific insulation diameters, screens, conductor sizes and cable constructions. Voltage and cross-section alone do not guarantee a correct fit.
