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Innovations in Power Efficiency: The Design of Air Cooled 3

Phase Transformers

Joint Electrical Institutions Sydney - Engineers Australia, IEEE, IET

DATE & TIME

Thursday, 10 September, 2015

5:30 pm for 6:00 pm start

VENUE

Engineers Australia Harricks Auditorium

Ground Floor, 8 Thomas Street, Chatswood NSW 2067

COST

EA, IET, IEEE Members –

Complimentary

Students – Complimentary

Non-members - $30

CPD

Eligible for 1.5 Continuing Professional Development

hours. RSVP

HOSTED BY

Joint Electrical Institutions Sydney

Presentation by Michael Larkin - Managing Director of Tortech Pty Ltd and Tortech Lighting Pty Ltd

The design of 3 phase transformers has been standard for some years. However, with the introduction of new magnetic material and the ever increasing demand for power efficiency, we are constantly developing new designs to meet these efficiency requirements.

Recently our team at Tortech has researched IP56 3 phase transformer design for the NSW State Railway using special stainless steel enclosures. We have successfully overcome the problem of high temperature failures by using air cooled transformers. The solution is in using thermodynamic principles incorporated in with the Electrical transformer design.

In addition, our Solar Isolation Transformer Design incorporates the perfect solution for minimising the core losses, and thereby improves the efficiency and temperature characteristics of the enclosed transformer. This has enabled the Solar Inverters to operate more efficiently and provide substantial cost savings to the customer.

The talk will review some of Tortech’s R & D research areas including: 1) Calculation of temperature rise of enclosed 3 phase air cooled

transformers 2) Use of different core steel characteristics based on application 3) Design of IP56 stainless steel enclosures for 3 phase

transformers

4) The solution for the problem of “in rush” current for railway applications

5) The use of aluminium windings in air cooled transformers

This talk will review the innovation in winding techniques and cooling calculations that have been developed recently for the major industry applications in Mining, Railway, Transport and Solar Power. The talk will be stimulating and interesting to both the experienced engineers and those new to the workplace.

1. 1975-1984: Power Transformer Designer at Tyree

Westinghouse at Moore Bank, NSW

Specialised in Current and Instrument Transformer

Design, including high voltage 500 KV CT, 500 KV

CVT, Line traps and magnetic voltage transformers.

2. 1985-1987: Power Transformer Designer at Ferguson

Transformers at Moore Bank, NSW

Specialised in three phase transformers and control

gear for HID equipment, including lighting control

design for Western Australia Cricket ground and

MCG.

3. 1987-Present: Established two companies: Tortech Pty Ltd

and Tortech Lighting Pty Ltd at Greenacre, NSW.

We Quote, Design, Manufacture, Test and organise

approvals for transformers, lighting, Inverters,

Inductors, etc.

We import and export both in Australia and overseas

to countries such as Indonesia, Malaysia, Brazil,

China, New Zealand

3

• Calculation of the temperature rise of air cooled

Transformers

• The use of a variety of core and conductor

material

• The design of transformers in IP23 Indoor & IP55

Outdoor enclosures

• Design challenges for Railway & PV centralised

MV Transformer applications

• Resin encapsulated F1 fire retardant class

transformers

4

To expose engineers to new design techniques using

alternative materials

• What are the main parameters of any

transformer quotation?

Design / Price / Availability / Application

• How do we get the best for our client?

• “Build with the End in mind”

Rationale

To improve the competitiveness and efficiency of the

transformers and to meet customer requirements in a

competitive global market. 5

Let’s explore the 4 main considerations for 3 Phase transformers:

1. The design of a conventional 3 phase transformer

• The use of Non-Grain stacked cores

• Design parameters – Non-grain steel has low remanence flux

density

• Applications e.g NSW Railways, QLD Railways, PV Panels for

Solar Power

• Underlying principles and design parameters – especially for

Railway to limit in rush current to less than 10 times the rated

current/turns on current.

• Winding techniques to modify the self inductance and

resistance of the coils

• Enclosures – IP23 or IP55 – environment

• Example: Table of G.O.S.S, Non-G.O.S.S and Amophorous

Core’s

Non-Grain Stacked Core 6

G.O.S.S Unicore Non-G.O.S.S Core Amorphous Core

Design

• Choice of material

Non-G.O.S.S Core G.O.S.S Unicore Amorphous Core

Low Remanence Flux density High Remanence Flux density Moderate Remanence Flux density

Cheapest in Cost Reasonably Expensive Expensive

High loss: Watts/Kg Low loss: Watts/Kg Very Low loss: Watts/Kg

Suitable for Rail applications which

typically require very low inrush

current (8-12x rated current)

Suitable for Solar PV installations which

require high efficiency and outdoor

applications which require low loss

*G.O.S.S=Grain Oriented Silicon Steel 7

Non-G.O.S.S G.O.S.S Amorphous

Saturation

Flux Density

1.5 Tesla 1.8 Tesla

1.5 Tesla

Remanence 1 Tesla 1.7 Tesla <0.5 Tesla

Core Loss

(50Hz)

2 W/Kg 1.1 W/Kg <0.2W/Kg

8

OPTION (A) Aluminium Windings and Sheet

Advantages Disadvantages

• Extremely Cheap • Higher Loss than Copper

• Not readily Available

OPTION (D) Aluminium Rectangular Conductor


• Extremely Cheap • Higher Loss than Copper


OPTION (C) Copper Sheet


• Low Loss • Highly Expensive


OPTION (B) Copper Rectangular Conductor


• Low Loss

• Readily Available

• Highly Expensive

9

When Analysing a design with a customer we look for:

1)

2)

3)

• Do you require off load Tap changer switches on the transformer?

• Do you require a screen and why do you require a screen?

Working Environment

Ambient Temp.

Outdoor Indoor

IP22 IP23 IP55 IP67 Is it 30˚C Is it 50˚C

What is the type of protection used?

D-Curve Breaker

C-Curve Breaker

Installation

Lifting Lugs?

Bushings?

Access Points?

Cable Entry?

10

Specially designed core and coils have reduced induction

levels, resulting in a reduction in stray losses.

Electrostatic shield reduces transient noise in the system which

may affect sensitive computer loads.

Reduced core flux density prevents core from saturation and

overheating from voltage distortions caused by harmonic

currents.

High Grade, Non-aging, silicon steel with high magnetic

permeability provides core induction levels without saturation.

Neutral bus sized and configured to accommodate at least

200% of the rated currents compensates for increased neutral

currents found in non-linear loads, thus reducing heat.

This is caused by harmonics in the input supply current. 11

3-Phase’s

Air Ducts in

each phase

G.O.S.S Core

Flux Density at 1.55

Tesla,

Star IN–Delta OUT

12

Aluminium-Copper

Welding through Electrofusion

13

Sources: Michael, A.

Afflerbach 2005, Solar

Atmospheres

Manufacturing, Inc, IEEE,

Indianapolis, IN

14

∆TC = 𝑳𝒐𝒔𝒔

[ K𝒓A𝒓 + K𝒄A𝒄 ]

𝑳𝒐𝒔𝒔 = 𝑻𝒐𝒕𝒂𝒍 𝑳𝒐𝒔𝒔 𝒇𝒓𝒐𝒎 𝑺𝒖𝒓𝒇𝒂𝒄𝒆 𝑾

K𝒓 = 𝑪𝒐𝒆𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒕 (𝑾/˚𝑪 𝒊𝒏𝟐)

A𝒓 = 𝑹𝒂𝒅𝒊𝒂𝒕𝒊𝒐𝒏 𝑨𝒓𝒆𝒂 𝒊𝒏𝟐

A𝒄 = 𝑪𝒐𝒏𝒗𝒆𝒄𝒕𝒊𝒐𝒏 𝑨𝒓𝒆𝒂 𝒊𝒏𝟐

K𝒄 = 𝑪𝒐𝒆𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒕 (𝑾/˚𝑪 𝒊𝒏𝟐)

Electrical Equivalent Circuit

15

Sources: Calculation of the

temperature rise A thesis by Walter

Johnson June 1942 . PA State

College

Electrical Equivalent Circuit

16

Sources: Calculation of the

temperature rise A thesis by Walter


College



Atmospheres


Indianapolis, IN

Un-Ducted

Design

17



Atmospheres


Indianapolis, IN

End Ducted

Design

18



Atmospheres


Indianapolis, IN

Full Ducted

Design

19



Atmospheres


Indianapolis, IN 20

Overall Design

Core Loss: 785.65

Flux Density 1.55 Tesla

Temperature Rise: 70˚C

Half Duct-Half way through the HV

Half Duct-Half way through the LV

Full Duct

between LV and HV

Full Duct-Half way through the LV

21

1. No HV

Intermediate Duct

2. No LV Intermediate

Duct 3. No HV and LV

Intermediate Ducts

Increase in

Temperature

Rise to 105˚C

Increase in

Temperature

Rise to 175˚C

Temperature

Rise

Stays at 175˚C 22

Increase in

Conductor

Size

High in

Temperature Rise

159˚C

Having Removed all ducts with increased conductor size on

primary Winding

23

Half & Full Ducts:

Dog-Bones

Half Ducts

Full Ducts

How the ducts are Wound:

24

Natural Air Currents near Heated Plate

Heated Plate

Duct Width Restriction Factor

(Fr)

Over 1/2” 1.00

3/8” 0.75

1/4” 0.50 25

Reference: A thesis by Walter


College

To allow Air Flow, Notice the

bend in Bus bar

26

Final Product

27

Dry-Type

25 KVA Transformer:

28

Taps on

each Phase Resin Encapsulated Transformers:

Cross flow fans 29

Shiny Stainless

Steel Grade

304 Material

Inside wall

painted Matt

black

Top Sun

Shield

enclosing the

Transformer

Large Vents at

Bottom of the

enclosure

Large Vents at

Top of the

enclosure

To allow for

Air Flow

32

Electrostatic

Shield Earth

connections

33

Temperature

Rise 71˚C

34

35

IP55 Stainless Steel Enclosure

*EN = Enclosure

36

These are some of the questions you have to ask your customer:

• What duty cycle do you have? Is it 20%, 50% or 100% duty cycle

• Is the customer looking for a transformer that has a low loss or a high loss?

• Are they interested in a transformer that costs less but has a high operating costs?

• What K-Factor do you need?

• What is your required temperature rise

• What is your Ambient Temperature requirements

37

The Design of a three-Phase Dry type transformer is one of the most difficult designs to do as one must consider the inside and outside performance.

The communication with the client is essential as the engineer must investigate all parameters of the client’s requirements, helping him/her to understand the ramification of they’re requirements. So the end product will be appreciated by the client – Job Satisfaction is highly vital (for both the customer and the Designer).

We want to get the job right the first time around.

38

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