Technical Seminar On

Built-in Novel Insulation Monitoring Function for

RIF Paperless Transformer Bushings

PRESENTATION BY :GURURAJ B RAWOOR

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

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.

• 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…

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.

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.

RIP Bushing

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.

RIF Bushings

Distinctive Features Of RIF Bushings

• A Solid Material System.

• High Mechanical Strength and Seismic Capability.

• Maintenance is optional.

• Track Record and monitoring.

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.

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.

• 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…

• 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…

• 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…

• A comparison of the bushings with and without monitoring terminals.

• The connection interface is simple with a pluggable indicator located on the flange.

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

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.

• 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