RIP Transformer Bushing: Design, Application and Selection Guide for Power Systems
What is an RIP Transformer Bushing?
A Resin Impregnated Paper (RIP) bushing is a type of high-voltage condenser bushing widely used in power transformers, switchgear, and reactors. Its main insulation consists of a core wound from kraft paper with aluminum foil electrodes inserted between layers. This core is then dried under vacuum and impregnated with epoxy resin, resulting in a solid, mechanically strong, and moisture-resistant insulating body. The outer insulation is typically provided by a porcelain or silicone rubber weathershed housing.
The RIP design offers several inherent benefits over older oil-impregnated designs, making it a preferred choice for modern substations and demanding electrical environments.
How RIP Bushings Compare with OIP and RIS Types
To select the right bushing, it is helpful to compare the three main condenser bushing technologies:
OIP (Oil Impregnated Paper): The classic design where the paper core is impregnated with insulating oil. Requires an oil-filled housing and regular monitoring of oil level and dielectric properties. Excellent long-term performance but with higher risk of leakage and fire.
RIP (Resin Impregnated Paper): The paper core is impregnated with epoxy resin, making the capacitor body solid and dry. No oil is used inside the core. Lower maintenance, reduced fire risk, and better mechanical strength. Often lighter than OIP equivalents for the same voltage class.
RIS (Resin Impregnated Synthetic): Similar to RIP but uses synthetic fabric instead of kraft paper. This can provide even higher partial discharge resistance and is sometimes chosen for very high voltage or special frequency applications. However, RIP remains the most common “dry type” bushing for standard high-voltage grids.
Thanks to the solid insulation, RIP bushings can be mounted at various angles without oil-level concerns, offering more flexibility in transformer design.
Key Advantages of RIP Bushings in Transformer Applications
Buyers and plant engineers often consider the following strengths when choosing RIP bushings:
Fire Safety and Environmental Protection: As a dry, oil-free design, RIP bushings significantly reduce fire load and the risk of oil spills in case of a major failure. This is especially valued in sensitive environments and indoor substations.
Low Partial Discharge and High Dielectric Stability: The vacuum impregnation process ensures a homogeneous insulation with very low partial discharge levels. The solid resin bonds eliminate the problem of oil contamination or moisture ingress over time.
Mechanical Robustness: RIP bushings have high cantilever strength and seismic withstand capability. This makes them suitable for regions with earthquake risks or for installations exposed to strong winds and vibrations.
Reduced Maintenance: Without oil to track or sudden pressure risks, field maintenance is simplified. The bushing's condition can be verified through capacitance and dissipation factor tests, as with other condenser types, but routine oil sampling is eliminated.
Compact Dimensions: For many ratings, RIP bushings can be designed with shorter creepage distances and smaller overall dimensions than OIP types, which aids in compact substation layouts.
Typical Voltage Classes and Applications
RIP transformer bushings are available across a wide range of system voltages, from around 12 kV up to 550 kV and beyond, with current ratings from several hundred amps to more than 4,000 amps. They are commonly used for:
Generator step-up (GSU) transformers
Large power transformers in transmission substations
HVDC converter transformers (often with extra DC performance requirements)
Shunt reactors and phase-shifting transformers
Medium-voltage distribution transformers where fire safety is a priority
In HVDC applications, special RIP designs have been developed to handle the combined AC/DC voltage stress and the risk of space charge accumulation. Standard AC RIP bushings should not be directly applied to HVDC without confirmation of the manufacturer's test program.
Selection and Specification Considerations
When specifying an RIP bushing for a transformer, the following technical parameters should be clearly defined:
Rated maximum voltage (Um) and basic insulation levels (BIL and SIL)
Rated current and short-time thermal current requirements
Creepage distance according to the site pollution level (e.g., 25 mm/kV, 31 mm/kV)
Ambient temperature range and altitude
Test tap or potential tap configuration
Flange mounting type and required cantilever strength
Partial discharge acceptance criteria (usually < 10 pC at specified voltage)
Procurement teams should also verify that the bushing conforms to recognized international standards such as those from IEC or IEEE. Type test reports for dielectric, thermal, and mechanical performance are normally required. A reputable supplier will provide a full routine test certificate for each individual bushing.
Installation, Handling and Maintenance Best Practices
Proper handling is critical for RIP bushings because damage to the porcelain or composite housing or stress on the flange area can occur during transport and storage. Best practices include:
Keep the bushing in its original packaging until installation, stored in a dry, clean area.
Use the designated lifting points and spreader beams to avoid bending forces.
Ensure the transformer tank opening and mounting flange are clean and flat. Tighten bolts gradually in a diagonal pattern to the specified torque.
After installation, perform capacitance, dissipation factor (tan δ) and partial discharge measurements to establish baseline values. These results should match the factory test data within defined tolerances.
For bushings with a silicone rubber housing, periodic inspection of the hydrophobicity and any signs of tracking or erosion is recommended in heavily polluted environments.
Because the main insulation is solid, neither oil leaks nor the internal pressure monitoring needed for OIP bushings are applicable. This saves time during commissioning and periodic overhauls.
How RIP Bushings Support a Reliable Transformer Fleet
Asset managers increasingly value RIP bushings for their predictable aging characteristics and operational safety. The solid resin-bonded paper core does not degrade through exposure to small amounts of moisture and oxygen as oil-paper systems can. This translates into a long electrical life with stable capacitance and dissipation factor over decades of operation, provided the external insulation remains sound.
For retrofitting projects, RIP bushings can often replace older OIP types without major modifications to the transformer tank, though flange adapters or draw-rod adjustments might be needed. The weight difference can also affect the transformer's center of gravity, so a review of seismic calculations is advised.
WishPower's RIP Bushing Offerings
WishPower provides a comprehensive range of RIP transformer bushings covering voltage classes from 12 kV to 550 kV and beyond, suitable for both AC and special DC applications. Our design closely follows internationally accepted standards and utilizes high-quality epoxy resin systems and carefully controlled winding and impregnation processes. Each bushing undergoes a full routine test program, including PD measurement and dielectric loss tests, before leaving the factory. With options for porcelain and silicone rubber housings, various creepage distances, and custom flange configurations, we help power utilities, EPC contractors, and transformer manufacturers specify the right bushing for their project requirements. Contact our engineering team to discuss your next transformer bushing specification.