Approximately 100 years ago the first transformer bushings were installed. In recent years, increasing demand for limited energy resources means transformer manufacturers and owners should use energy efficient bushings. Energy efficient bushings are defined as those that reduce electricity losses by more than forty percent, relative to equivalent bushings on the market. In this blog we explore how each installation of bushings on a transformer may exclude as many as sixteen households from an electricity grid.
Although bushings operate on the power grid equivalent of data network switches, and consume significantly more power than network switches, it is surprising that there is no energy efficiency bushing standard to similar to IEEE 802.3bj™ “Standard for Ethernet Amendment 2: Physical Layer Specifications and Management Parameters for 100 Gb/s Operation Over Backplanes and Copper Cables.” Instead, current bushing specifications present several challenges to be addressed by any manufacturer, owner, user, buyer and designer of bushings which are: (a) to provide sufficient insulation to the bushings so that they will withstand voltage conditions in which the bushings operate or are indicated in standards, (b) to prevent the bushing from overheating or operating at too-high temperatures, (c) to manufacture bushings with low losses, (d) to produce bushing designs that can be manufactured, (e) to minimize bushing total ownership cost, (f) to minimize bushing weight, (g) to minimize corona discharge, (h) to maximise water hydrophobicity, icephobicity and pollution repellence, (i) to ensure human safety, (j) to protect other substation assets near the bushings and transformer, (k) to protect the environment, (l) to withstand vibrations of the transformer, earthquakes and other significant forces, (m) to minimise heating of the transformer caused directly by the bushings, (n) to withstand solar radiation in the form of heating and ultraviolet radiation without degrading, (o) to withstand loading and interaction with winds as high as 160km per hour, rain, snow, dust, fog, acidity, alkalinity, pollutants, and combinations of these, (p) to be vandal resistant, (q) to keep installation, maintenance and storage simple and infrequent, (r ) to ensure a lifespan of the bushing of 30 year, (s) to make monitoring and testing equipment and maintenance equipment and processes inexpensive, (t) to ensure products remain compliant with ever more stringent with environmental and health and safety legislation, (u) to seal the transformer effectively, even under faults so that oil does not leak out of the transformer,(v) not to be the weakest link in the relation to other components close-by in the network including the transformer, circuit breakers and surge arresters.
Designers, manufacturers and owners of bushings seek compliance and technical guidance related to bushings’ mechanical performance requirements, pollution resistance performance, and electric stress performance from eighteen specifications as follows:
- ANSI IEEE Std C57.19.01™-2000, IEEE Standard Performance Characteristics and Dimensions for Outdoor Apparatus Bushings
- IEC/IEEE 65700-19-03, Bushings for DC application
- IEC 60137 Insulated Bushings for alternating voltage above 1000V
- IEC 60076-7 Loading guide for oil-immersed Power Transformers
- ANSI IEEE C57.91-2011 – Guide for Loading Mineral-Oil-Immersed Transformers and Step-Voltage Regulators
- ANSI IEEE C57.12.00-2015 – General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers
- IEC 60296, Fluids for electro-technical applications – Unused mineral insulating oils for transformers and switchgear
- IEC 60376, Specification of technical grade sulfur hexafluoride (SF6) for use in electrical equipment
- IEC 60480, Guidelines for the checking and treatment of sulphur hexafluoride (SF6) taken from electrical equipment and specification for its re-use
- IEC 60836, Specification for unused silicone insulating liquids for electro-technical purposes
- IEC 60867, Insulating liquids – Specifications for unused liquids based on synthetic aromatic hydrocarbons
- IEC Guide 109, Environmental aspects – Inclusion in electro-technical product standards
- ANSI IEEE Std C37.23™-2008, Metal-Enclosed Bus
- IEC 60076-18 Measurement of frequency response
- IEC 61463 Seismic Qualification of Transformer High Voltage Bushings
- IEC 60815 Guide for Selection of Insulators in Respect of Polluted Conditions
- IEC 60815-3 Polymer insulators for a.c. systems
- BS EN 13601:2002 Copper and copper alloys. Copper rod, bar and wire for general electrical purposes
Importance of energy efficiency
Energy efficiency of bushing is one of the most important factors to consider during design and selection of bushings because of the large numbers of bushings present on any electricity network. For example a power utility that with installed generation capacity of 44,281MW, typically generates 246,676 GWh each year, consumes 4,114GWh and transmits 242,562 GWh, ultimately generating revenue from sales of 216 274 GWh. Transmission energy losses may be 2.5 %, distribution energy losses 6.8 % and with average losses of 8.8%. If a utility manages a good energy efficiency program, it may result in demand savings, of 171.5MW and internal savings of Internal energy efficiency, 10.4 GWh. By focusing on bushings rated at 145kV alone, the same utility with 1120 substations at this voltage, each with 2 transformers can realistically expect to reduce losses by 1.758 MW equivalent to 15GWh.
How energy efficiency of bushings impacts on families who need electricity
By choosing not to use energy efficient bushings, transformer owners with limited generation capacity are choosing to exclude households from their electricity networks. Table 1 based on World Energy Council data lists number of households that consume the energy wasted by 145kV bushings on 1120 transformers is the same as that required by 1568 households in the USA or Canada in a year, or 4732 households in South Africa in a year or 9679 households in China.
Table 1. Household consumption information relative to bushings
|Excluded household/ transformer installed set of bushings|
How much do bushings cost in generation capacity
Implementing a small scale generation project of between 1MW and 10MW takes at least 18 months in countries where the regulatory approval process is efficient and project management is effective. Frank (2014) in Table 1 shows that the annualised cost of generation capacity of 1.7MW starts at $475,000 per year if wind energy is installed, $617,000 for solar, $497,000 for hydro-electric plant, up to $1.1 million per year for nuclear power generation.
Table 1. Capacity Cost per MW per Year: New No-Carbon Electricity Plants
|“Overnight” Capital Cost per KW (1)||$2,213||$3,873||$2,936||$5,530|
|Years for Construction (2)||1.5||1.5||5.0||5.0|
|Cost of Capital during Construction (3)||$138||$242||$551||$1,037|
|Total Capital Cost||$2,351||$4,115||$3,487||$6,567|
|Annualized Capital Cost per Year per MW||$230,645||$326,737||$268,713||$521,412|
|Fixed O & M per Year per MW (1)||$39,550||$24,690||$14,130||$93,280|
|Total Annual Capacity Cost per MW||$270,195||$351,427||$282,843||$614,692|
Energy Information Administration (April 2013a) Table 1, p.6
International Energy Agency 2011, Executive Summary
Weighted Average Cost of Capital = 7.5%
Transformer owners and manufacturers need to consider the impact of bushings on overall ability to deliver electricity to customers. If a set of bushings on a transformer are consuming enough power to connect sixteen families to the grid, then clearly it is time replace those bushings with energy efficient alternatives. In addition, network owners must take into account how increasingly stringent environmental regulation of carbon dioxide, mercury, sulfur dioxide and nitrous oxide emissions, waste water disposal, and disposal will have on the cost of operations now and into the future.
Frank Jr, C. R. (2014). The net benefits of low and no-carbon electricity technologies. The Brookings Institution, Working Paper, 73.
Future discussion about bushings
Our next blog will discuss bushings and greenhouse gas emissions