Capacitive Voltage Transformer Applications in High-Voltage Grids
2026-09-22 17:40:26
Capacitive voltage transformers (CVTs) are purpose-built instruments used in high-voltage grids to convert transmission-level voltages—typically 110kV and above—into low, standardized signals suitable for metering, protection relays, and carrier communication. Unlike conventional electromagnetic voltage transformers, a capacitive voltage transformer uses a capacitor divider stack combined with an intermediate electromagnetic unit, which significantly reduces physical size and cost at high voltage levels. In 110kV substations, CVTs serve as the primary interface between the power grid and its measurement and protection systems, making their accuracy, long-term stability, and transient performance directly relevant to grid safety.
Understanding Capacitive Voltage Transformer Fundamentals
How a CVT Works
A capacitive voltage transformer splits the line voltage by a stack of series capacitors. The lower voltage is then sent to a step-down electromagnetic transformer. Standard secondary voltages, usually 100V or 110V, are sent out of the output and are used by protection relays, energy meters, and SCADA systems. This design lets CVTs work at voltage levels where electromagnetic voltage transformers can't because they are too expensive or too big.
Core Applications in High-Voltage Systems
In 110kV substations, CVTs do three main things: they measure voltage accurately for billing and grid tracking; they also receive signals for distance and differential protection relays; and they couple carrier frequencies for power line communication. How well these functions work has a direct effect on how fast the grid is protected and how much energy is recorded. IEC 61869-5 says that CVTs that are used for security must meet certain transient reaction limits so that relays don't work wrong when there is a fault.
Why CVTs Are Cost-Efficient at 110kV
When the voltage is 110kV or higher, electromagnetic voltage transformers need to be insulated, which adds a lot of weight and material costs. That's because a capacitive voltage transformer puts the primary insulation work on the capacitor stack, which is cheaper to make and ship at these voltage levels. This structural benefit also makes it easier to lay out substations, lowers the loads on the foundations, and speeds up the installation process on EPC projects.
Comparing Capacitive Voltage Transformers with Alternative Technologies
CVT vs. Electromagnetic Voltage Transformer
Because it responds more quickly to changes and is more accurate at low frequencies, the electromagnetic voltage transformer (EVT) is preferred by some engineers for sensitive differential protection at lower voltages. The size, weight, and cost of an EVT become too high at 110kV, though. Today's CVTs, like those from Xi'an Xikai, have improved damping circuits that allow them to achieve 3PT1-level transient reaction with residual voltage below 2% as a capacitive voltage transformer. This closes most of the performance gap with EVTs for fast relay uses.
CVT vs. Optical Voltage Transformer
Optical voltage transformers (OVTs) use the Pockels effect to measure voltage without touching anything electrical. They can handle ferroresonance and have a very large bandwidth. They are still a niche product, though, because they are expensive per unit, sensitive to changes in temperature, and don't have a lot of field-service infrastructure. If you need to buy a normal 110kV substation for a State Grid or Belt and Road project, CVTs are still the most realistic and standards-compliant option.
Selecting the Right Technology for Your Project
There are three main things that affect the choice of a voltage transformer for a 110kV substation EPC project: the accuracy class needs (0.2 for metering and 3P for protection), the expected level of environmental severity (pollution level, altitude, seismic zone), and the total lifecycle cost, which includes spare parts and calibration intervals. A CVT that is certified by GB/T and meets the requirements of IEC 61869-5 can be used for most domestic and Belt and Road projects without needing any extra qualification tests.
Practical Guide to CVT Installation, Maintenance, and Operation
Installation and Commissioning Steps
Before fitting, make sure the capacitance ratio and dielectric loss (tan δ) numbers match the factory test report. This is the first step in installing a CVT correctly. To keep the capacitor stack from being stressed mechanically, the unit must be plumb to within the manufacturer's limits. Before turning on the relay, the secondary wiring's polarity and burden impedance must be checked against the settings. Xi'an Xikai helps substation workers with every step of the way by giving them full commissioning datasheets and online technical support.
Routine Maintenance Practices
CVTs usually need to be serviced every one to three years, but this depends on how polluted the area is. Some important checks are using infrared thermography to find hot spots in the secondary terminal box, measuring tan ε and capacitance with a precision bridge to see how the capacitor is aging, and looking for cracks and tracking in the porcelain or composite insulator. By keeping track of changes in capacitance over time, engineers can guess how long the parts will last and schedule replacements before measurement drift causes problems with the relays.
Managing Environmental and Load Challenges
Salt fog and chemical layers on the top of the insulator can cause flashovers in coastal or industrial areas. This risk is directly dealt with by CVTs that have anti-pollution coatings that meet IEC 60815 standards and extended creepage distances of more than 25 mm/kV. At elevations above 2,000 meters, the dry arc distance needs to be lowered. Xi'an Xikai's equipment is designed to work at elevations of up to 4,000 meters, which is great for Belt and Road projects in mountainous areas.
Procurement Considerations for Capacitive Voltage Transformers
Evaluating Suppliers and Their Capabilities
Siemens, ABB, Schneider Electric, and other well-known companies, as well as experienced Chinese companies like Xi'an Xikai, sell high-voltage instrument transformers all over the world. When teams are looking at different capacitive voltage transformer suppliers, they should make sure that the factory test results come from accredited labs, that the production site is ISO 9001 certified, and that the seller has a history of delivering similar-sized projects. As a company that has been certified by ISO 9001, ISO 14001, and ISO 45001, Xi'an Xikai has provided CVTs to State Grid projects in several provinces.
Key Procurement Factors for 110kV Projects
Before making an order for a CVT for a 110kV substation, technical and procurement teams should think about the following main points:
- Accuracy class and terminal configuration: Confirm that metering terminals meet 0.2-class requirements and protection terminals meet 3P-class requirements per IEC 61869-5.
- Lead time and project schedule: For EPC projects requiring 3–15 units, typical production lead time ranges from 8 to 14 weeks. Confirm this against the substation energization date.
- Warranty and after-sales support: A minimum two-year warranty covering capacitor stack integrity and secondary terminal performance is standard. Verify whether the supplier offers on-site troubleshooting support.
- Compliance documentation: Projects under State Grid or China Southern Grid procurement rules require GB/T certification. Export projects to Belt and Road countries often require IEC certification and may require CE marking.
All of these things together show whether a CVT procurement decision lowers project risk or causes problems with schedules and performance later on. By taking care of every issue during the bidding process, you can escape expensive change orders during building.
Case Studies: Successful CVT Implementations in High-Voltage Grids
110kV Substation EPC Project, Domestic State Grid System
An EPC company in the region bought 12 Xi'an Xikai 110kV CVTs for a new 110/10kV substation that will serve an industrial park. The project requirements called for 0.2-class accuracy in the meters and 3P protection class. The factory acceptance test showed that the tan µ was less than 0.08% and the partial discharge was less than 5pC. The substation was turned on when it was supposed to be, and the coordination tests for the safety relays passed on the first try. During the first 18 months of operation, there were no transient-related relay trips.
Renewable Energy Grid Connection Project
At the 110kV point of common coupling, a 100MW wind farm had to connect to the power grid using four CVTs. Voltage fluctuations happen a lot because wind power is irregular and changes all the time. The CVTs used in this project had ferroresonance suppression built into the damping circuit, which kept the secondary output stable during generation step changes and fault ride-through events. This allowed for accurate generation metering for settlement purposes.
Belt and Road Infrastructure Project
As part of the Belt and Road building deal, a 110kV substation had to be built overseas. It needed CVTs that were rated for a tropical coastal climate with pollution level IV according to IEC 60815. The units that Xi'an Xikai sent to the client passed their salt fog acceptance test because they had composite insulators and longer creepage distances. The project team chose a provider based on how easily they could get test paperwork that met IEC standards.
Conclusion
A capacitive voltage transformer plays an essential role in modern 110kV substations by providing reliable voltage measurement, protection signals, and carrier communication interfaces. Its capacitor-divider structure offers practical advantages in size, insulation requirements, installation, and lifecycle cost compared with conventional electromagnetic solutions at high voltage levels. However, reliable performance depends on selecting the correct accuracy class, transient characteristics, insulation design, and environmental suitability. Proper commissioning, routine capacitance and dielectric-loss testing, and complete supplier documentation are equally important for long-term operation. By evaluating technical compliance, project conditions, testing records, and after-sales support together, engineers and EPC teams can select a CVT that supports accurate metering, stable protection, and dependable high-voltage grid operation.
FAQ
1.What accuracy class should I specify for a 110kV CVT used for both metering and protection?
Most 110kV substation standards call for separate secondary connections for metering and security. The IEC 61869-5 says that the metering terminal should have an accuracy class of 0.2 for billing energy. The safety terminal needs to meet the 3P class, which limits the response time during transients instead of the steady-state ratio error. The 110kV CVT from Xi'an Xikai offers both classes on a single unit, which cuts down on the number of devices that need to be stored in each bay.
2.How does capacitor aging affect CVT measurement accuracy over time?
The main long-term stable issue for CVTs is capacitor dielectric aging. Capacitance numbers change over time as the dielectric breaks down, which causes the voltage ratio to shift. Maintenance teams can spot early signs of wear and tear by comparing capacitance and tan δ measurements to the factory standard once a year. The ultra-low-loss dielectric material used by Xi'an Xikai has a tan ´ value of less than 0.08%. This slows down the rate of aging and increases the calibration interval.
3.What documentation should I request when comparing CVT supplier quotations?
As you compare suppliers, make sure you get the type-test report that includes impulse withstand, partial discharge, accuracy, and transient response, as well as the routine test report for your order and the ISO certification scope. For Belt and Road projects, make sure the IEC 61869-5 type test was done at a recognized lab. These papers are the most important scientific tools for comparing capacitive voltage transformer suppliers, even more so than price.
Partner with Xi'an Xikai for Your Next CVT Project
Xi'an Xikai is a reliable company that makes capacitive voltage transformers. They have more than 40 patents in the areas of CVT damping and insulation technology, and they work on State Grid projects, industrial substations, and Belt and Road building programs in Asia, Europe, and Africa. We have full factory test records for all of our 110kV CVTs that show they meet IEC 61869, GB/T, CE, and RoHS standards. To get specs or a quote for your unique project, please contact our engineering team directly:
References
1. IEC 61869-5: Instrument Transformers – Additional Requirements for Capacitor Voltage Transformers. International Electrotechnical Commission, 2011.
2. IEEE Std C57.13: Standard Requirements for Instrument Transformers. Institute of Electrical and Electronics Engineers, 2016.
3. Kundur, P. Power System Stability and Control. McGraw-Hill, 1994.
4. Glover, J. D., Sarma, M. S., & Overbye, T. J. Power Systems Analysis and Design. Cengage Learning, 2012.
5. CIGRE Working Group C4.307. Resonance and Ferroresonance in Power Networks. CIGRE Technical Brochure 569, 2014.
6. IEC 60815-1: Selection and Dimensioning of High-Voltage Insulators Intended for Use in Polluted Conditions. International Electrotechnical Commission, 2008.
