CM_APW_2015

Power 101Introduction to Transformers for Residential and Industrial Applications

ABB Automation & Power World: March 2-5, 2015

© ABBSlide 2May 3, 2023

Power 101Introduction to Distribution Transformers for Residential and Industrial Applications

Chris Morrow Power & Automation Leaders Program

ABB - Jefferson City, MO

Liquid Filled Distribution Transformers

Kevin Liu Product Manager – Dry-type transformers NAM

ABB - Bland, VA

Dry-type Distribution Transformers


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Introduction to Transformers for

Residential and Industrial Applications


Presentation Outline

Transformer Purpose What Does a Transformer Do? How Does it Work?

Electrical Design Characteristics Transformer Losses Efficiency & Impedance Example Design

Design Considerations and Flexibility Core Type Winding Material Winding Connections System Connection Transformer Configuration Tank Material

Product Requirement Considerations Cooling Methods Monitoring Devices Protection Devices

Application Considerations Functional Examples

Loss Evaluation








Loss Evaluation


What Does a Transformer Do?

Changes voltage level on a power system

Step up - increase voltage Step down - decrease voltage

Allows for long distance, high voltage power transmission

Generator step up transformers Power transmission transformers Distribution transformers

Distribution transformer:

The final voltage change to meet customer needs in the power network


11000 VOLTSGENERATED

POWER HOUSEVOLTAGE INCREASES

NETWORK FAULT

66000 VOLT TRANSMISSION

SUB-STATION FROMTRANSMISSION LINE

INDUSTRIAL CUSTOMER

1st VOLTAGE REDUCTION(TRANSMISSIONSUBSTATION)

4000 VOLT DISTRIBUTION

2nd VOLT REDUCTION(DISTRIBUTIONSUBSTATION)

POWER CENTERINDUSTRIAL PLANT

22000 VOLTS LOW VOLTAGE TRANSMISSION

SUB-STATION FROMLOW VOLTAGE TRANSMISSION

Electrical Service From The Generator To The Customer

SUBWAY VAULT

COMMERCIALCUSTOMER

15

DISTRIBUTIONTRANSFORMER

RESIDENTIALCUSTOMER

120/240VOLTS

GenerationTransmission

Distribution


How Does it Work?

A transformer consists of two windings on the same iron core Primary & secondary (HV & LV)

Primary winding (1) receives AC power from external source

AC current in the primary winding produces varying magnetic field in the core

Varying magnetic field induces current and voltage in the secondary winding (2)


How Does it Work?

Flux, Φ

Flux, Φ

AC Current (amps) α Δ in Magnetic field (B) Faraday’s Law

HighVoltageLowVoltage

=TurnsHVTurnsLV

=𝐓𝐮𝐫𝐧𝐬𝐑𝐚𝐭𝐢𝐨








Loss Evaluation


Electrical Design Characteristics

Design Parameters:

Number of Phases (1 vs 3)

Power Rating (kVA)

High Voltage (V)

HV BIL (kV)

Low Voltage (V)

LV BIL (kV)

Frequency (Hz)

Temperature Rise (Deg C)

Design Optimization Features:

Transformer Losses

Efficiency

Impedance


Transformer No-Load and Load LossesIron and Copper Losses

No-load losses are caused by the alternating magnetization of the core (hysteresis losses) and by eddy-currents in the core – They occur as soon as a transformer is energized

Load losses are caused by the losses in the conductors (resistive and eddy current). They have a quadratic dependence on the load factor

DOE estimated average load of the utility distribution transformers is only 50%…

Canada: study* on weighted average load of LV dry-type distribution transformer : (office, manufacturing, health care, school, retail): 15.9%

Reduction of no-load loss has major focus

* Office of Energy Efficiency, Canada: “Metered load factors for LV, dry-type transformers in commercial, industrial and public buildings”, Nov. 2008

400 kVA BkBo distribution transformer

no-load loss

load loss

total loss

0500

1'0001'5002'000

2'5003'0003'5004'0004'500

0% 20% 40% 60% 80% 100%load

loss

(W)


Efficiency & Impedance

Efficiency Desired output / required input

Lower losses = higher efficiency (and vice versa)

Very high (typically greater than 98%)

Minimum standards set by DOE, CSA

Impedance Function of resistance and reactance of windings

Manipulated to control short circuit current, voltage regulation, load balance under parallel operation

Recommended tolerances provided by IEEE


Example Distribution Transformer Design:

Number of Phases: 3 - Phase Power Rating: 750 kVA High Voltage: 12470 V (Delta) Low Voltage: 480 / 277 V (Grounded Wye) Frequency: 60 Hz Temp. Rise (liquid): 65 Deg C Temp. Rise (dry): 150 Deg C

Efficiency: 99.32% Impedance: 5.76% Load Loss: 6786 W No Load Loss: 967 W

Ref: JC61384








Loss Evaluation


Design Considerations & Flexibility

Core Type Wound Core

Stacked Core

Winding Material Winding Connections

System Connection Transformer Configuration

Radial Feed

Loop Feed

Tank Material


Single Phase:

Jeff City units manufactured as Shell Form Core is unwound on short end, slid onto the coil, and rewound around coil

Core Type – Wound Core


Single Phase Shell Form

Can be wound as Lo-Hi-Lo (shown to the right) or Lo-Hi.

Lo-Hi-Lo typically has lower impedance and lower regulation than a similar Lo-Hi.



Three Phase Construction – Five Legged Wound Core

Same process as single phase with two extra cores to attach around the coils

Provides a return path for the magnetic flux – necessary for grounded wye connections



Core Type – Stacked CoreThree Phase Construction – Stacked & Wound Core Options

Only wound core option is five legged

Stacked core options provided as three or four legged

Core leg used as mandrel and coils are wound onto the core leg (WOCL)


Core Type – Stacked Core

Coils are installed over “E” (stacked core without top yoke)

Top yoke stacked after coils are wedged in place

Mechanical members are installed


ABB uses one core technology for all Dry Transformers

Stacked core Allows for simple installation of coils Automated cutting lines result in good

fabrication Assembly of limbs and yokes can be time-

consuming

Step-lap joints Good flux distribution at joints resulting in

lower no-load losses

Thin grain-oriented electrical steels Lower hysteresis and eddy losses Many pieces to handle during assembly

Single or multi-step cross-section profile Accepts round, oval, or rectangular coils Optimization of steel widths and stack

height needed to maximize filling of the core circle

Core Type – Stacked Core


Winding Material

Copper Tight size requirements

Salt spray environments

Tough efficiency requirements

Aluminum Light weight requirements

Typically less expensive


Winding Connections – Single Phase

Single Phase – 1 coil

Must bank / connect 3 single phase units to obtain alternate voltages

Common HV connection terminology:

Delta

Wye

Grounded Wye


Winding Connections – Single Phase

LV typically connected in 2-wire or 3-wire configuration

3-wire tapped at midpoint of windings for optional voltage

4-wire connection available


Winding Connections – Three Phase

Depends on system configuration

Number of service wires

Grounded vs. ungrounded sources

Impedance matching when banking

Desired phase shift


Delta – Grounded Wye

Delta – Delta

Grounded Wye – Grounded Wye

Wye – Delta

AVOID Grounded Wye – Delta

Subject to primary grounding duty

Dry-type units (Bland) grounded by customer

Liquid filled distribution units (Jeff City) grounded by manufacturer

Winding Connections – Three Phase

Phasor Diagrams


System Connection – Live vs. Dead Front Live Front:

Non-insulated

HV porcelain bushings

LV spades

For bus bar, close couple, etc.

Dead Front: Insulated

Molded epoxy / rubber

Bushing wells and inserts

For load-break elbow connection

http://www.h-jenterprises.com/catalog/index.php?category=746&submit=go


Configuration – Radial Feed

The last transformer before the end user One incoming HV line per phase, no outgoing HV lines “End of the line” i.e. electricity is not fed through


Configuration – Loop Feed

Continues the feed of power through the grid One incoming HV line per phase, one outgoing HV line per phase


System ConnectionDry-type transformers

Bus coordinated to close-coupled switchgear Cable In/Out


Tank Material

Mild Steel Less expensive

Ease of manufacturability

Stainless Steel Corrosion resistance

Non-magnetic

Strength, hardness, longevity

More expensive


Enclosure Construction

NEMA 1 (Indoor) Least expensive

Protection from small animals

NEMA 3R (Outdoor) Protection from rain and deflected splash from all

directions

Protection from snow

Dry-type Submersible (similar tank to liquid filled) Maintenance free

Arc-flash resistant

More expensive








Loss Evaluation


Product Requirement Considerations

Cooling Methods Insulating Fluid

Forced Cooling

Monitoring Devices Protection Devices

Fuses

Switches

Lightning Arresters


Insulating Fluid

Air = Dry type transformer

Oil = Liquid filled transformer

Factors to consider: Environment

Application

Loading profile

Temperature rise constraints

* Temp. rise does not affect HVAC requirements for indoor applications

*


Forced Cooling

Radiator banks Bolted/welded fins allow for enhanced

heat exchange with external environment

Greater surface area of fins = higher cooling effect

Decreases losses, increases efficiency

Fans Forces air through radiators to provide

additional cooling

Usually tripped by oil temp / winding temp alarm contacts at preset temperature thresholds

Only provided on substation type transformers


Dry-type Cooling

Fans / blowers Typically controlled with optional winding

temperature monitor

FA rating – up to 50% increase

Indirect hydro-cooling Non-ventilated enclosure (i.e. closed

cooling system)

Keeps transformer protected against contaminated environments

Rating increase up to 25%


Monitoring Devices

Various gauges monitor critical operational factors

Liquid level

Oil temperature

Winding temperature

Internal tank pressure

Optional alarm contacts to trip relays, external breakers, alert SCADA systems, etc.


Protection Devices Fuses

Protects system in the event of transformer winding failure

Can prevent line crews from re-energizing a faulted transformer

Single or double fusing schemes

Expulsion fuses with isolation links

Expulsion fuses with partial range current limiting fuses

Switches Allows isolation of incoming or outgoing lines

On/off switch provides control of transformer usage


Protection Devices

Arresters Protects transformer in case of high voltage

surge due to lightning strike, voltage inrush from system, etc.

Routes voltage surge to ground

Metal Oxide Varistor Elbow arresters (dead front)

Distribution Class arresters (live front)








Loss Evaluation


Application Considerations

Transformer Location Indoor vs. outdoor

Proximity to buildings / people

Accessible to public vs. enclosed in secure room

Main Customer Residential vs. commercial

Rural vs. urban environment

Utility service vs. industrial project

Loading Conditions Continuous vs. intermittent

System peak vs. transformer peak


11000 VOLTSGENERATED

POWER HOUSEVOLTAGE INCREASES

NETWORK FAULT

66000 VOLT TRANSMISSION

SUB-STATION FROMTRANSMISSION LINE

INDUSTRIAL CUSTOMER

1st VOLTAGE REDUCTION(TRANSMISSIONSUBSTATION)

4000 VOLT DISTRIBUTION

2nd VOLT REDUCTION(DISTRIBUTIONSUBSTATION)

POWER CENTERINDUSTRIAL PLANT

22000 VOLTS LOW VOLTAGE TRANSMISSION

SUB-STATION FROMLOW VOLTAGE TRANSMISSION

Electrical Service From The Generator To The Customer

SUBWAY VAULT

COMMERCIALCUSTOMER

15

DISTRIBUTIONTRANSFORMER

RESIDENTIALCUSTOMER

120/240VOLTS

GenerationTransmission

Distribution


Functional ExamplesDry-type Primary Substation Transformers

69kV Indoor transmission substation (above)

25MVA 69kV – 13.8kV

46kV Outdoor transmission substation (right)

4MVA 46kV – 4160V


Functional ExamplesDry-type Distribution Transformers

15kV Outdoor distribution substation

2500kVA

15kV – 480V

15kV Indoor distribution substation

3000kVA

15kV – 480V

15kV Subway type submersible network

500kVA

15kV – 480V


Functional ExamplesLiquid Filled Secondary Unit Substation Transformers

34.5kV Outdoor distribution substation 3000 KVA 34.5kV – 2400V


Functional ExamplesLiquid Filled Padmount Distribution Transformers

27.6kV Outdoor 3PH padmount transformer (top left)

500 KVA 27.6kV – 480V

12.47kV Outdoor 1PH padmount transformer (bottom right)

100 KVA 12.47kV – 240V


Functional ExamplesPolemount / Submersible Distribution Transformers

2400V Outdoor 1PH polemount transformer (top left)

50 KVA 2400V – 240V

24.94kV 1PH submersible / vault transformer (top right)

167 KVA 24.94kV – 600V

14.4kV 3PH submersible / vault transformer (bottom left)

1000 KVA 14.4kV – 480V



Protected industrial environment Data centers, Utility spot networks, rail, food & bev, office

buildings, hospitals

Environmental contamination Metals, power generation (e.g. coal fired), Offshore O&G, Utility

spot networks



Shock/vibration and cold climates

Offshore O&G, Mobile equipment (e.g. cranes, etc.), Pipelines (critical power and compressor stations)

Public distribution and power projects Utility networks, housing developments, commercial buildings,

high volume public power providers








Loss Evaluation


Loss Evaluation Cost of Losses = Cost of No Load Loss + Cost of Load Loss

Costs associated with: Power generation

Purchasing of power

Loading practice (system peak vs. transformer peak)

Average transformer life

Interest rate (cost of money)

All of these are used to calculate the A and B factors A factor – No Load Loss

B factor – Load Loss


Loss Evaluation Total Ownership Cost (TOC) = Initial Transformer Price + Cost of Losses TOC = Price + (A x No Load Loss) + (B x Load Loss)

Loss

Cos

t Cost ofLosses

TransformerCost


Questions?


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Contact information

If you have further questions , please refer to our contact information below:

Chris Morrow Kevin Liu

ABB - Jefferson City, MO ABB - Bland, VA

+1 (573) 659 6341 +1 (276) 688 1545

[email protected] [email protected]

mailto:[email protected]



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