TRANSFORMER BUSHINGS

1. Technical Seminar On
Built-in Novel Insulation
Monitoring Function for
RIF Paperless Transformer
Bushings
PRESENTATION BY :
GURURAJ B
RAWOOR

2. OVERVIEW OF SEMINAR
 Objectives
 Types Of Bushings
 Distinctive Features Of RIF Bushings
 Necessity of developing new monitoring approaches
 Principles and Construction of N-RIF Bushings
 Characteristics of N-RIF Bushings
 Conclusion
 Bibliography

3. OBJECTIVES
• Transformer Bushings are used to insulate high voltage
conductors where they feed through steel tank of a power
transformer.
• Compares the existing types of transformer bushings.
• Distinctive features of RIF paperless condenser bushings.
• Principles, construction, characteristics and applications.
• The construction of RIF insulation would delay the propagation of
a core insulation breakdown after the onset of an initial insulation
defect, this type of real time monitoring of core insulation
condition provides a novel tool to manage bushing defects without
any sense of urgency.

4. • Three major types of high voltage transformer bushings are
1) Oil-impregnated paper insulation transformer bushings (OIP
bushings)
2) Resin-impregnated paper insulation transformer bushings (RIP
bushings)
3) Resin impregnated fiberglass insulation transformer bushings (RIF
bushings).
• Resin Impregnated Fiberglass bushings are innovative products that
have been operating in the field for 10 years from 15kV to 245kV
according to IEC60137 and IEEE 57.19 Standards requirements.
• In recent years, an evolution of RIF bushings, N-RIF bushings,
with built-in insulation monitoring function, are able to conduct in
real time, on-line monitoring of their own insulation conditions.
CONTD…

5. OIP Bushings
• Oil as its basic insulating medium.
• Porcelain insulators are usually fitted
as outer insulation.
• Use of oil has many severe
drawbacks in bushing life,
1. such as being susceptible to
moisture ingress
2. oil leakage due to worn out seals.
3. can trigger explosive failure.

6. RIP bushings
• Dry type paper based transformer bushings. Their cores are made
by winding insulating paper.
• Impregnated with epoxy resin & eliminating the need for insulating
oil.
• Composite insulators(“Silicone Composite insulator”), must be
used outside the bodies as outer insulators.
• Insulating paper is sensitive to moist, so if phenolic resin is used.
• As a result, the oil side of RIP bushings (i.e. fitting inside the
transformer) must be protected during transportation and storage
with a protective sleeve filled with dry nitrogen.

7. RIP Bushing

8. RIF Bushings
• RIF bushings, introduced in 2002. Their paperless condenser
bodies are wrapped with fiberglass-based composite and
conducting layers.
• The outer insulation is made of silicone rubber directly fitted to
the condenser structure’s core, without any gap between the two
components.
• This type of bushings has very high mechanical characteristics,
along with a simple construction, requiring a very limited number
of sealing procedures.
• Simpler manufacturing processes & the pricing remains similar to
RIP bushings.

9. RIF Bushings

10. Distinctive Features Of RIF Bushings
• A Solid Material System.
• High Mechanical Strength and Seismic Capability.
• Maintenance is optional.
• Track Record and monitoring.

11. Necessity of developing new monitoring
approaches
• Users have long been expecting on-line monitoring of
transformer bushing’s insulation conditions.
• The insulation condition can be assessed with sensitivity and
accuracy by reporting changes of capacitive current of the
condenser structure.
• If we can spot insulation faults early, as they appear, and manage
them in time, catastrophic failures such as fire and explosions can
be prevented.
• Therefore, safe operation of the grid can be greatly improved
when bushing insulation monitoring can be conducted
continuously and reliably.

12. Principles and Construction of N-RIF Bushings
• HV is the high-voltage terminal that is
connected to the grid
• C1 is the capacitance of the bushing’s main
insulation and C2 the capacitance of the
added grading layer;
• C2 has a much larger value than C1.
• Parts a and b are monitoring terminals
connected to the two layers of C2, and to
intelligent equipment that conduct insulation
monitoring.

13. • After the grading layer terminals of the bushings are connected,
the ground layer lead can grounded reliably; users can
conveniently conduct on-line monitoring of insulation condition
using appropriate equipment.
• Capacitors C1 and C2 are connected in series to withstand the
voltage applied to the bushing.
• As capacitance C2 is much larger than C1, the Externally
connected monitoring equipment will under no circumstances
affect the bushing’s main insulation, even in case of short-
circuit and open-circuit.
CONTD…

14. • At the same time, determination of C2 takes into account the
impedance of the external monitoring equipment so as to ensure
that almost all of the capacitive current passing through C1 also
reaches the monitoring equipment.
• Thus, in the case of a core insulation fault the C1 capacitance
increases, the capacitive current increases, and the monitoring
equipment detects the increased capacitive current to trigger an
early warning.
• The built-in construction of N-RIF bushings and that of RIF
bushings are the same, with the difference being that the
measurement terminal is changed into a monitoring terminal.
CONTD…

15. • The case in which the monitoring
terminal is externally connected to
an indicator light. No external
power source is needed for the
indicator.
• The light remains off when the
bushing is in normal operation and
will come off only when a
breakdown happens to a
predetermined number of capacitive
layers.
• The maintenance crew can then
conduct testing and investigate the
cause without a sense of urgency
CONTD…

16. • A comparison of the bushings
with and without monitoring
terminals.
• The connection interface is
simple with a pluggable
indicator located on the flange.

17. Characteristics of N-RIF Bushings
• High Safety and accuracy
• Greatly Improved Interference Resistance
• Easy Connection with Insulation Monitoring Systems
• Experience
• Application prospects of N-RIF Bushings

18. CONCLUSION
• RIF have distinctive advantages over conventional OIP and RIP
bushings, and their mature track record over 10 years show a solid
reliability.
• N-RIF bushings have been developed to provide a new, safe and
reliable on-line insulation monitoring of its core structure.
• Provides high performance condenser insulation with full
continuous visibility of its condition.
• As breakdown of RIF insulation would not happen instantaneously
It provides ample time to deal with any fault detection on a
scheduled basis.
• This makes installation and operation of bushings easier, and most
importantly its initiates bushing generated transformer failures.

19. • IEC 60137:“Insulated bushings for alternating voltages above 1000 V”
• CIGRE Working Group 12.05, “An international survey on failures of
large power transformers in service”. Electra. No. 88,pp. 21-48, 1983.
• IEEE Standard C.57.19.00, “General Requirement and test procedure
for power apparatus bushings”, 2004.
• IEEE Standard C.57.19.01, “Performance characteristics and
dimension for outdoor apparatus bushings”, 2000.
• IEEE Standard 21-1976, “IEEE General Requirements and Test
Procedure for Outdoor Apparatus Bushings”, Published by the Institute
of Electrical and Electronic Engineers, Inc.
• NTPC Ltd, “Transformers Failure Data Bank”.
BIBLIOGRAPHY