Why Is 126kV Equipment Used in a 110kV Power System?

Open a 110kV substation specification and the primary-equipment schedule may list a 126kV disconnector, a 126kV circuit breaker or even a 126kV GIS bay. For an engineer, the question is not simply why 126 is greater than 110. The real question is whether the system voltage, the selected equipment class and the required insulation withstand levels belong to the same approved voltage schedule.

Those three items must be checked together. A tender that says only "110kV switchgear" is incomplete for procurement: it should also state the equipment rating, power-frequency and lightning-impulse withstand levels, short-circuit duties, service conditions and the product standard for each device. This is especially important when comparing CIS, African and Middle Eastern tenders that may combine national practice, utility specifications and IEC references.

110kV and 126kV Describe Different Design References

This is why a purchase specification should state both the nominal system voltage and the required equipment rating. Writing only "110kV disconnector" can leave room for different interpretations, especially when suppliers are comparing national practices or tender schedules from different regions.

Why Is the Equipment Rating Higher Than the Nominal System Voltage?

·System voltage is not perfectly constant. Network regulation, loading and operating conditions can move the actual voltage above or below the nominal value while remaining within the system's permitted limits.

·Equipment must be coordinated with the system's insulation requirements. The equipment voltage class is used together with specified power-frequency and impulse withstand levels. The 126kV figure alone does not replace those dielectric values.

·Standardized voltage classes simplify equipment coordination. Disconnectors, circuit breakers, instrument transformers, surge arresters, bus supports and other primary equipment must be selected from a compatible project voltage schedule.

·National and project practices differ. A 126kV equipment class is used in some 110kV specifications, while another standardized value may appear in a project governed by a different national or international practice.

Which IEC Standards Define the Selection Framework?

A high-voltage equipment schedule normally uses a group of standards rather than one document. The following references answer different engineering questions. Their inclusion here describes their published scope; it does not claim that the Fengyuan Power GW4-126 is certified or type-tested to these current editions.

Official IEC scope pages: IEC 60038:2009+A1:2021 | IEC 60071-1:2019 | IEC 60071-2:2023 | IEC 62271-1:2017+A1:2021 | IEC 62271-102:2018+A1:2022 | IEC 62271-203:2022

Is 126kV Universal for Every 110kV Project?

No. A supplier should not assume that every 110kV project automatically requires 126kV equipment. The correct value comes from the tender, the utility standard and the applicable national or international voltage schedule. Some 110kV documents may use another equipment voltage value, and 123kV and 126kV equipment should not be treated as interchangeable without the purchaser's technical approval.

For IEC-governed tenders, the purchaser should identify the selected voltage value and insulation levels in the technical schedule. For CIS, African and Middle Eastern projects, it is especially important to review the complete tender instead of translating the system voltage directly into an equipment model. The quotation should repeat the requested voltage class and list every deviation or clarification.

Which Substation Equipment May Carry a 126kV Rating?

When a project adopts the 126kV class for a 110kV installation, the designation may appear across several primary-equipment schedules, including:

·Outdoor disconnectors and earthing switches.

·High-voltage circuit breakers.

·Current transformers and voltage transformers.

·Surge arresters and associated insulation assemblies.

·Busbar supports, bushings and other equipment whose insulation coordination must match the substation design.

The same voltage label does not mean these products perform the same function. A disconnector provides visible isolation and is not a substitute for a circuit breaker. Each device must be selected against its own product standard, switching duty and test requirements.

GW4-126 Outdoor Disconnector as a Practical Example

A practical example is the GW4-126 outdoor high-voltage disconnector. Its source data identifies a 110kV nominal system application, a 126kV equipment rating, 50Hz frequency and rated-current options of 630A, 1250A, 1600A and 2000A. The disconnector is intended to make or break energized circuits only under no-load conditions and to provide a visible isolation gap for inspection and maintenance.

GW4-126 outdoor high-voltage disconnector

The rated peak and short-time withstand current vary with the selected rated-current version. They must be checked against the exact GW4-126 data table and the purchaser's short-circuit schedule rather than inferred from the 126kV voltage rating.

Engineering Case Note: Azerbaijan 110kV Substation Expansion

The available project record identifies an Azerbaijan 110kV substation expansion for an EPC contractor. It confirms the following supplied primary equipment:

Engineering interpretation: the same 110kV expansion record uses both 110kV and 126kV labels across different equipment lines. That is exactly why a project-level voltage and insulation schedule is more reliable than selecting by a product name alone. Because the outdoor disconnect switches were specified at 2000A, the approved schedule would also need to coordinate their continuous-current and short-circuit duties with the switchyard design.

How to Select a 126kV Outdoor Disconnector

Voltage class is only the first filter. Send the following information to the manufacturer before confirming a model or quotation:

·Applicable standard and voltage schedule. State the nominal system voltage, required equipment rating and specified insulation levels.

Rated current. Confirm continuous-current duty and the required terminal arrangement.

·Short-circuit withstand duty. Provide the peak withstand current, short-time withstand current and duration.

·Earthing-switch arrangement. Specify no earthing switch, Type I, Type II or the purchaser's required equivalent, together with interlocking requirements.

·Insulator and pollution requirements. Confirm porcelain or composite insulation, creepage-distance requirement and site pollution severity.

·Operating mechanism. Specify manual or motor operation, control voltage, auxiliary contacts and local/remote control requirements.

·Site conditions. Provide altitude, minimum and maximum temperature, wind, icing, seismic and other environmental data.

·Mechanical and interface data. Confirm phase spacing, terminal loads, connectors, support steel and the approved general-arrangement drawing.

·Documentation. List the required drawings, test reports, certificates, inspection plan, language and destination-country requirements.

Common Selection Mistakes

·Treating 126kV as the normal operating voltage of the network.

·Assuming that 126kV is mandatory for every 110kV project.

·Selecting the product by voltage and rated current while ignoring short-circuit withstand and insulation levels.

·Expecting a disconnector to interrupt load current or fault current like a circuit breaker.

·Copying an old standard number into the offer without checking the tender's current applicable edition.

·Using a generated application image as proof of an actual project installation.

FAQ

1. Is 126kV the same as 110kV?

No. In this context, 110kV is the nominal system voltage and 126kV is the equipment voltage rating selected by the project. They describe related but different design references.

2. Can 126kV equipment be used in every 110kV system?

Not automatically. The equipment rating, insulation levels and applicable standard must match the purchaser's specification and utility practice.

3. What is the difference between 123kV and 126kV equipment?

Both values may appear in documentation for 110kV-class projects under different standardization practices. They should not be substituted for one another without reviewing the tender, insulation schedule and purchaser approval.

4. Can the GW4-126 interrupt load current?

No. The supplied product data describes the GW4-126 as a disconnector for operation under no-load conditions and for providing visible isolation. Load and fault-current interruption must be performed by the appropriate switching device, normally a circuit breaker.

5. Which GW4-126 configurations are available?

The supplied information confirms porcelain and composite insulator options, Type I and Type II earthing-switch arrangements, CS17 manual and CJ6 motor mechanisms, and a pollution-resistant version. Final availability must be confirmed for the ordered rating and project conditions.

6. What should be included in an inquiry?

Send the project specification, rated voltage, rated current, peak and short-time withstand duty, insulation levels, earthing arrangement, mechanism, control voltage, site conditions, quantity, destination country and required documents.

Conclusion

A 126kV equipment rating in a 110kV project is not a contradiction, but neither is it enough to approve an offer. An engineer should be able to trace the selection from the system voltage schedule to the equipment class, insulation levels, current and short-circuit duties, switching function, service conditions, interfaces and supporting test evidence. That traceability is more important than the model number alone.