Canadian Electrical Industry News Week

March 9 2016

Short circuits or faults can and do occur on electric power and distribution systems. When a fault occurs on the load side of a transformer, the fault current will pass through the transformer. As components on these systems, transformers need to be able to withstand these fault currents.

Fault currents flowing through transformers are significantly higher than the rated currents of the transformers. In a worst case scenario, the current would be as high as the current that would flow if system voltage was applied to the primary terminals while the secondary terminals are shorted — limited by the transformer impedance only. These currents produce both mechanical and thermal stresses in the transformers.

Photo credit: Hammond Power Solutions

Forces resulting from the currents passing through the transformer act on the conductors. The forces are a function of the peak asymmetrical current (the highest peak value of any cycle of the current), which is usually at its highest during the first half cycle of the fault. The duration of the fault is not normally a concern for mechanical withstand because the peak value of each cycle of the current reduces as the fault persists. The transformer manufacturer needs to ensure these forces do not damage the transformer.

The thermal stress is caused by the high current causing heating in the transformer. Both the RMS symmetrical current magnitude and duration of the fault contribute to the heating of the transformer. The transformer manufacturer needs to ensure the components of the transformer do not become hot enough to be damaged.

General purpose dry type transformers are typically designed to withstand the mechanical and thermal stresses caused by a short circuit occurring on the secondary terminals of the transformer with rated voltage applied to the primary terminals for a maximum of 2 seconds, provided the current does not exceed 25 times rated current. The fault current magnitude is a function of the transformer impedance. The table below shows the fault current for selected impedances and applies to both line currents and phase currents.

 

Transformer Impedance  Fault Current (times rated)
4.0% 25.0
5.0% 20.0
6.0% 16.7
7.0% 14.3
8.0% 12.5

 

The maximum of 25 times rated current is listed so that transformers with an impedance below 4% need only be able to withstand 25 times rated current, although the fault current could be higher than this. It does not mean that all transformers are able to handle a fault current up to 25 times rated current. With rated voltage applied to the primary a transformer impedance above 4% will not allow 25 times rated current to flow.

Many specifications indicate a fault level at the primary terminals of the transformer. Some customers will ask for a transformer to be braced for the primary fault level. A general purpose transformer is suitable to be connected to a system with the specified fault level, but the transformer impedance will limit the fault current through it to well below the available fault level. As an example, the customer requests a 2500 kVA transformer, 13.8 kV delta to 480Y/277 V, 5.75% impedance to be braced for 750 MVA fault level at 13.8 kV. In this case, the available fault current at the primary terminals is 31.4 kA. For a fault on the secondary side of the transformer, the transformer impedance will limit the fault current that flows in the primary to 1.8 kA in the lines and 1.1 kA in the coils — significantly lower than the available fault level. There is no need for the transformer primary conductors to be sized and braced to handle a 31.4 kA fault current.

Some operating conditions need special attention. Some customers specify the transformer to operate continuously with load at higher than rated voltage. If a fault occurs when the transformer is operating at higher than rated voltage, the resulting fault current would be higher than a typical transformer is designed for. This will increase both the forces in the transformer and the heating of the transformer. Some customers specify a fault duration longer than 2 seconds without specifying a higher voltage. This does not affect the forces but does increase the heating in the transformer. In these cases, a special design may be required.

One case in particular requires special attention: transformers directly connected to a generator. When a generator is supplying a load and the load is suddenly disconnected, the output voltage of the generator rises significantly for a short time until the excitation system decreases the voltage. If a fault occurs on the secondary of a transformer at this time, the fault current can be significantly higher than a typical transformer is designed for. Some applications may not have any overcurrent protection between the generator and the transformer primary winding, resulting in an increased duration. In such cases, it is recommended that IEEE C57.116 IEEE Guide for Transformers Directly Connected to Generators be reviewed to determine the short circuit withstand requirement for the transformer.

General purpose transformers have short circuit withstand capabilities that are sufficient for many applications. The transformer manufacturer needs to be informed of cases where a fault could occur on the secondary of the transformer when the transformer is supplied above rated voltage or the fault duration is longer than two seconds to ensure the transformer is suitably designed to withstand the possible secondary faults.


This document was first published as a white paper by Hammond Power Solutions, the largest manufacturer of dry-type transformers in North America. Hammond Power Solutions engineers and manufactures a wider range of custom transformers that are exported globally in electrical equipment and systems. The firm supports solid industries such as oil and gas, mining, steel, waste and water treatment, and wind power-generation.

 

 

Changing Scene

  • Prev
This month, IDEAL is challenging competitors to draw an Electrical Power One-Line Diagram ...
EngWorks Inc. and the Alberta Electrical Alliance have announced a strategic partnership as of May ...
David Collie, ESA’s President & CEO, signs the new Leadership Accord, proudly committed to ...
Electro-Federation Canada (EFC) represents electrical and automation manufacturers, distributors ...
Demand for electric vehicles in Canada keeps increasing; 68% of Canadians will consider ...
ESA is warning on potential electrical hazards associated with the replacement of metallic water ...
The Canadian Apprenticeship Forum (CAF-FCA) has released its latest labour market information ...
The Ontario government is introducing new measures to help tradespeople get their certification ...
MP Scott Duvall has introduced an amendment to the Income Tax Act regarding travel expenses for ...
George Brown College has partnered with Hilti (Canada) Corporation to help women build rewarding ...


 

ABB RoboticsABB Robotics is driving automation in the construction industry with new robotic automation solutions to address key challenges, including the need for more affordable and environmentally friendly housing and to reduce the environmental impact of construction, amidst a labor and skills shortage.

Robotic automation offers huge potential to enhance productivity, efficiency and manufacturing flexibility throughout the construction industry, including automating the fabrication of modular homes and building components off-site, robotic welding and material handling on building sites and robot 3D printing of houses and customized structures. 



Read More


 

Canadian Electrical Contractor Discussion Group: Can You Count the Deficiencies?

EIN CECD 400Have you ever been called to fix the work of a 'handyman'?

"Was supposedly done by a"certified ' electrician....told the homeowner that he got a $266 permit....no record at TSBC. Can you count the deficiencies?"

"There is a second panel change in the triplex also.......even more deficiencies. Think the guy was a glorified handyman. Ones not obvious: 240 BB heat hooked up 120....drier on 2p20....range on 2p50....water heater fed with 2c14 Bx on 2p15."

Go HERE to join the discussion

 


 

Smart GridHarnessing Canada’s immense clean energy resources requires transformational investments to modernize our electricity grid. The Government of Canada is investing in renewable energy and upgrading the electricity grid to make clean, affordable electricity options more accessible in communities across Canada.

The Honourable Seamus O’Regan Jr., Minister of Natural Resources, today launched a $964-million program to support smart renewable energy and grid modernization projects that will lower emissions by investing in clean energy technologies, like wind, solar, storage, hydro, geothermal and tidal.

Read More

 


 



Trilliant Partners with the City of CowansvilleThe City of Cowansville in south-central Quebec is the largest city in the Brome-Missisquoi region, with more than 15,000 residents. Despite being a smaller-sized city, it is known as an economic and industrial hub.

It also has a strong focus on innovation and efficiency — as demonstrated by decisions such as the one it made in 2017 to use beet juice to help combat icy winter roads, allowing the City to reduce the amount of salt it was using, thereby saving money and decreasing the impact on the environment. 

 

 

Read More


 

Keith SonesBy Keith Sones

The writing was on the wall.  The closures would happen. But a lot of people were upset, and I was one of them. 

In the early 2000s, my family and I were living in a mainly rural (at least by city dweller standards) valley in south central British Columbia.  The West Kootenay region is known for its diverse outdoor recreation activities and as a great place to raise a family.  It has a proud industrial history, evidenced through the longstanding pulp mill, a massive lead zinc smelter a few miles away and several hydroelectric dams, all of it within spitting distance of the mighty Columbia River. 

Read More


 

Product News

  • Prev
Klein Tools introduces the new Magnetic Wire Puller, to help professionals quickly and easily fish ...
Siemens new 3VA molded case circuit breakers offer safe, efficient and variable application options ...
Hubbell’s illuminated plugs and connectors are the latest addition to the already broad line of ...
The ABV is a specification high bay that provides high performance and reliability. Available with ...
The Vive PowPak phase select dimming module is a radio frequency (RF) control that operates phase ...
6 functions in one pair of pliers. Multifunctional pliers for the electrical installation; to grip ...
With the ABB StarTeck® selector web app you can match cables with Teck fittings quickly and easily. ...
WPS Gen 4 wall pack series is a classic and familiar design integrated with modern LED technology ...
These new controllers offer indoor or outdoor ON/OFF, photocell, dimming, scene and color tuning ...
Eaton’s broad selection of Wi-Fi smart devices offer reliability with unbeatable ease of setup. ...

 

Lumenquad New VersionsLumenpulse has announced the release of two additional smaller sizes of the Lumenquad, a rectilinear projector for both outdoor and indoor environments. Developed for architectural applications such as lighting landscapes, highlighting details, pathways and monuments, the Lumenquad Small and Medium are compact, low-wattage, high-performance projectors, complementing the two existing products in the family.

The Lumenquad Small and Medium are the latest additions to a family of sleek, elegant, high-performance projectors that has already been validated with honours, including recognition in the PIA Awards in 2019, together with a Lux Awards for Exterior Luminaire of the Year in 2019. 

Read More


 

 

Wiha Lineman's Pliers and CrimpersWiha Insulated SoftFinish® Cushion Grip Pliers and Cutters are the standard for premium quality featuring ergonomic cushion grip handles for comfort and control, dual durometer construction for long-lasting durability, and handles directly molded to the tool steel for a permanent bond.

The grips feature a slip guard handle design for added protection at the front-end and raised rear-finger steps for easy opening at the back-end. Wiha Insulated SoftFinish® Cushion Grip Pliers and Cutters consist of premium quality tool steel for strength and durability and induction hardened cutting edges and jaws for superior sharpness and longevity. 

Read More


 

 

eLumigen Poultry Lamps - 2000K, 3000K & 5000KIdeal for rough service applications, the A19 & PAR Series are engineered for high efficiency, vibration resistance, shatter-resistance, elevated heat environments, and wet locations. These dimmable LED Lamps help reduce energy costs, labor costs, and the headaches of frequent lamp changes in tough applications.

eLumigen employs a unique 21-point validation process that goes above and beyond industry standards. Our lamps have been tested to survive levels of vibration exceeding 20G forces. Our unique temperature foldback design improves both safety and thermal management of our lamps. 

Read More


 

Peers & Profiles

  • Prev
Bryan Smith started his now 20-year career at the ground floor, so to speak, as a draftsperson and ...
From small construction to sophisticated industrial projects, House of Electrical Supplies has been ...
Kyle Manfredi is the owner of ARK Electrical alongside his wife, Shannon. Operating out of ...
Like most major events over the last year, the COVID-19 pandemic put serious restrictions on the ...
This past December Jennifer Green was honoured with Canada’s Most Powerful Women Top 100 Award for ...
“It was quite surprising,” said Stephanie Smith of being named EHRC’s Leader of the Year. ...
As an advanced networked lighting controls company serving the industrial and large commercial ...
Trilliant, an international provider of utility solutions for advanced metering and smart grid ...
For more than a century, ABB has been investing in Canadian technologies and products to support ...
Mackenzie Gillan, a bright young lady from Baysville, Ontario, tells us about how she learned ...


House of Electrical SuppliesFrom small construction to sophisticated industrial projects, House of Electrical Supplies has been servicing clients in the industrial, OEM, entertainment, and construction markets across the Greater Toronto Area for just over 40 years. The company has earned a reputation for providing a high-quality customer experience.

As per President Austin Brennan, their experienced and knowledgeable team can be depended upon in any situation to deliver quick and efficient service. On top of their product solutions — ranging from electrical, automation, safety, lighting and portable power distribution — 

Read More


 

Copper $US Dollar price per pound

Kerrwil Publications Great Place to Work. Certified December 2019 - December 2020

538 Elizabeth Street, Midland,Ontario, Canada L4R2A3 +1 705 527 7666
©2021 All rights reserved

Use of this Site constitutes acceptance of our Privacy Policy (effective 1.1.2016)
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of Kerrwil