Voltage Levels in Central Asian Grids: 10kV, 35kV and 110kV Infrastructure Guide

Central Asian power grids — Kazakhstan, Uzbekistan, Tajikistan, Kyrgyzstan and Turkmenistan — inherited their voltage structure from the Soviet GOST system. That structure differs from Western IEC norms in key ways: 10kV where the West uses 11kV, 35kV as a dominant sub-transmission level that barely exists in other regions, and 110kV as the standard regional transmission backbone. Understanding these distinctions is the starting point for correct equipment procurement.

The CIS voltage hierarchy

Post-Soviet Central Asian grids typically operate at four main levels:

• Low voltage (0.4kV): 380/220V three-phase, the distribution endpoint for consumers. Largely unchanged from Soviet practice and compatible with IEC 60038.
• Medium voltage — distribution (6kV and 10kV): 10kV is the dominant urban distribution voltage; 6kV is still found in older urban areas and industrial installations but is progressively being retired.
• Medium voltage — sub-transmission (35kV): A Soviet-specific level used to feed 10kV substations from 110kV networks. There is no direct Western equivalent — most IEC countries jump from 11/33kV to 110kV without a 35kV intermediate.
• High voltage — transmission (110kV, 220kV, 500kV): 110kV is the workhorse of regional transmission. 220kV and 500kV serve inter-regional and export lines.

Why 10kV and 35kV matter for equipment specification

The 10kV distribution level is where most substation metering, protection and distribution equipment is concentrated. A typical 10kV substation in Kazakhstan or Uzbekistan will contain: combined instrument transformers (CT+PT) for revenue metering, dropout expulsion fuses for feeder protection, surge arresters for lightning and switching transient protection, and oil-immersed distribution transformers stepping down to 0.4kV.

The 35kV level adds a further set of instrument transformers and switchgear. Because 35kV is uncommon outside the CIS, Western catalogues often don't list it — procurement teams need to specify GOST or IEC equivalents explicitly.

IEC modernisation: what's changing and what isn't

Central Asian utilities are progressively adopting IEC standards alongside GOST, particularly for new-build substations and World Bank / ADB-funded grid rehabilitation projects. This creates a dual-standard environment: existing installations continue under GOST while new equipment must often meet both. The practical result is that IEC-rated equipment (10kV, 35kV class) with documentation covering both GOST ÏÀÑÏ and IEC 60044/60186 is increasingly preferred.

Combined instrument transformers for CIS 10kV and 35kV metering

Revenue metering at medium voltage requires both current and voltage measurements in a single metering circuit. Two product types serve this need:

• Dry-type combined units (JLSZV-10, JLSZV-35): Epoxy-cast CT+PT in one housing, maintenance-free, suited to indoor and sheltered outdoor locations where oil-spill is a concern.
• Oil-immersed combined units (JLS-10): Mineral-oil-insulated, higher thermal stability, better performance in the −40°C winters common in Kazakhstan and Kyrgyzstan. The polished stainless tank withstands condensation and thermal cycling.

Both types are manufactured to IEC 60044 and are available in the CT ratios (100/5A, 200/5A, 400/5A etc.) and PT ratios (10,000/100V, 35,000/100V) used across CIS grid metering practice.

Surge protection and feeder protection at 10kV

Central Asian grid operators deal with significant lightning exposure, particularly in the mountainous areas of Tajikistan and Kyrgyzstan, and with switching transients on the long rural feeders of Kazakhstan. Station-type and line-type surge arresters (polymer-housed, IEC 60099-4) are required at every transformer incoming and along overhead lines. Expulsion dropout fuses (10kV, 35kV) protect the feeders and allow manual isolation for maintenance in low-density areas where automated switching is not available.

Low-voltage equipment and grid end-use

At 0.4kV — where the distribution transformer feeds the consumer — the requirements are largely universal: three-phase 4-wire 380/220V, energy meters for billing, protection devices, terminal blocks and flexible busbars for panel assembly. Multi-rate DIN-rail energy meters with RS-485 outputs have become the regional standard for both commercial and industrial tariff measurement.

Procurement checklist for Central Asian projects

• Confirm system voltage: 6kV, 10kV or 35kV; single-phase or three-phase configuration
• Specify standards: GOST only, IEC only, or dual-certified
• State ambient temperature range — critical for oil vs dry-type selection
• Provide CT ratio and accuracy class required by the metering authority
• Confirm if equipment will be installed indoors, in an enclosure or directly exposed

Frequently asked questions

Do you stock 35kV-rated combined instrument transformers?

Yes. The JLSZV-35 is a dry-type combined metering unit rated at 35kV, available in standard CIS CT and PT ratios. The JLS-35 oil-immersed variant is also available for outdoor installation.

Can your products be certified to GOST standards?

Our products are manufactured to IEC. For projects requiring GOST certification, we can provide IEC test reports and work with the local certification authority for equivalence assessment. Contact us with the project specification for a direct answer.