What a 110kv Power Transformer Does in the Grid

A 110kv power transformer is the core equipment of the medium-to-high voltage layer of an electrical network. It connects the 110 kV transmission system with lower-voltage sub-transmission and distribution networks, typically stepping 110 kV down to 35 kV, 10 kV or 6 kV, and in power plants or renewable energy projects stepping generator output up to 110 kV for grid connection. Because it sits between bulk transmission and end users, its efficiency and reliability have a direct influence on the operating economics of the whole network.

In most projects the 110kv power transformer is a three-phase oil-immersed unit, with common rated capacities in the range of 6.3 MVA to 180 MVA, and voltage regulation provided either by an off-circuit tap changer or an on-load tap changer (OLTC). Two-winding designs are the norm for simple step-down duty, while three-winding designs are used where a station needs to feed two different voltage levels at the same time.

Main Types and Configurations

• Oil-immersed, on-load tap changing: the standard choice for substations that must regulate voltage under load; cooling is normally ONAN, ONAF or OFAF depending on capacity.
• Oil-immersed, off-circuit tap changing: a cost-effective option for stations with stable load profiles and infrequent voltage adjustment.
• Three-winding units: used in hub substations and industrial plants where 110 kV, 35 kV and 10 kV levels must be supplied simultaneously.
• Autotransformers: selected where the voltage ratio is close and higher efficiency with lower material consumption is required.
• Mobile and skid-mounted units: applied as emergency or temporary capacity in refurbishment and disaster-recovery projects.

Although dry-type transformers dominate indoor distribution duties, the 110 kV class is almost exclusively oil-immersed because of insulation strength, heat dissipation and cost per MVA.

Key Components and Materials

Understanding the build helps buyers compare quotations fairly, because two units with the same nameplate rating can differ substantially in material content and service life.

• Core: grain-oriented silicon steel, stacked or wound, determines no-load loss and noise level. High-grade, low-loss silicon steel with step-lap or wound-core construction reduces both.
• Windings: copper conductors with paper insulation are standard; winding arrangement and clamping control short-circuit withstand capability.
• Insulation system: transformer oil plus insulating pressboard and barriers; oil quality and processing directly affect dielectric strength.
• Tap changer: OLTC or off-circuit switch mounted on the tank, often the most maintenance-sensitive component.
• Bushings, cooling equipment, protection devices: bushings, radiators or coolers, fans, oil pumps, Buchholz relay, pressure relief valve, oil level gauge and temperature indicators.

Standards, Loss Levels and Test Documentation

Procurement should always be tied to recognised standards. For the 110 kV class the usual references are IEC 60076 and the GB 1094 series, together with national energy efficiency limits that set maximum no-load and load loss values. A supplier that cannot state which efficiency grade it is offering, or that quotes a loss figure below any realistic value, is usually cutting material content somewhere.

Every unit should arrive with the following documentation:

• Routine test reports: winding resistance, voltage ratio and phase displacement, insulation resistance, dielectric tests, no-load loss and current, load loss and impedance, temperature rise.
• Type test reports for the design family, including lightning impulse and short-circuit withstand evidence where applicable.
• Oil test certificate, nameplate and rating plate data, plus installation and maintenance manuals.
• A factory acceptance test (FAT) opportunity, or at least a full record of the tests actually performed.

Independent third-party inspection can be arranged for larger contracts and is a normal expectation in international tenders.

How to Evaluate Total Cost, Not Just Price

Purchase price is only part of the story. Loss evaluation is standard practice in serious procurement, because a 110kv power transformer runs continuously for decades. The two figures to compare are no-load loss, which occurs 24 hours a day, and load loss, which follows the load curve. A unit with a slightly higher price but lower loss can repay the difference within a few years of operation.

• Capitalised loss value: multiply no-load and load losses by the capitalisation factors used by your utility or owner.
• Material choice: copper versus aluminium conductors, and high-grade versus standard silicon steel, change both price and efficiency.
• Tap changer brand and cooling design: they affect maintenance intervals and spare parts availability.
• Delivery, transport and site assembly: large units require heavy-haul logistics and oil filling on site, which add real cost.
• After-sales support: commissioning assistance, spare parts, and lifelong quality tracking reduce long-term risk.

Common Selection Mistakes to Avoid

• Choosing capacity by habit rather than by calculated load growth and duty cycle, resulting in either overload risk or idle capital.
• Ignoring impedance voltage, which influences short-circuit current levels and downstream switchgear ratings.
• Accepting a quotation with no defined loss level or efficiency grade.
• Overlooking site conditions such as altitude, ambient temperature, humidity and seismic requirements, all of which affect insulation and cooling design.
• Buying on price alone from traders, without verified manufacturing capability or test documentation.

Installation, Operation and Maintenance Basics

After delivery, the unit should be inspected for transport damage, oil level and gas accumulation before energisation. During service, routine checks cover oil level and leakage, silica gel condition, bushing cleanliness, tap changer operation counts, and dissolved gas analysis (DGA) of the oil. Periodic DGA and oil dielectric testing are the most effective early warnings of internal faults, and planned maintenance of the OLTC prevents most forced outages.

Sourcing from a Manufacturer

Buying directly from the production facility removes intermediary mark-ups and shortens the communication chain on technical clarifications. Working with an established power transformer manufacturer also makes it easier to obtain complete documentation, customised designs and consistent spare parts support.

Runsheng Transformer Co., Ltd. manufactures oil-immersed transformers, dry-type transformers, amorphous alloy transformers, mining and rectifier transformers, custom special transformers, compact substations and high/low-voltage switchgear, and supplies each unit with manuals, inspection reports and test certificates backed by lifelong quality tracking. Units are built to national standards and offered at factory-direct prices, which makes a useful reference point when comparing quotations for your project.

If you are preparing a specification or need a budget figure for a transformer project, contact the team for technical data and pricing: phone +86 13406394988, e-mail runsheng@7813transformer.com, WhatsApp 008613508930968.