transformer basics

1

TRANSFORMER BASICSFECA Clearwater FL June 11, 2009

Transformer Applications – FECA Agenda

08:30-10:00 Transformer Overview - Basic Construction - Lightning / LV Surges - Voltage Regulation / Flicker - Life Cycle Costing / DOE Efficiency Ruling

10:00-10:15 Break

10:15-12:15 Insulation Life (C57.91) + TAP Simulations - The “Meaning of Life”- the C57.91 Loading Guide

- Over Head – Residential + flicker - Padmount – Residential + fusing + Short Circuit

- Padmount 3Φ + harmonics - Vault 3Φ + vault restrictions - Substation/Power Transformers - Ratings/Cooling Modes – Settings - Contingency Modeling

1:00 – 2:45 Power Transformer Maintenance, Monitoring & DGA

2:45 – 3:00 Exams/Discussions/wrap-up

Revised June 2009 dad

June 11, 2009

Generation Step Up - GSU

Generation…

Transmission…

Substation…

Distribution - Outdoors

Distribution - Downtown

Distribution - Indoors

Transformer Function

• Converts electricity from high voltage and low current Converts electricity from high voltage and low current to low voltage and high current … to low voltage and high current … or … vice versaor … vice versa

• Electricity is better generated and used at low voltage, Electricity is better generated and used at low voltage, and better transported at high voltage…and better transported at high voltage…

• Transformers are the basic links of a T&D system…Transformers are the basic links of a T&D system…

• Electricity and Magnetism work together to produce Electricity and Magnetism work together to produce “transformer action”…“transformer action”…

• Thin Electrical Grade Steel provides an excellent path Thin Electrical Grade Steel provides an excellent path for magnetic flux…for magnetic flux…

Distribution – Wound Core

Basic Distribution Transformer Core Loop

Distribution – ‘Stacking a Core’

Wound Coil - Note “LV Crossovers” Shell Type … Note ‘Core Grounding’

Core and Coil (LV Side) Core and Coil (HV Side)

Distribution – Shell Type - Interlaced LV windings

Interlaced SPS Shell Type C&C Cross-section

core & coil

- excellent Short Circuit strength...

- natural impedance's typically 1.5-2.0% for SPS construction...

P SSS S P SSS S

Distribution – Non-Interlaced LV windings

Non-Interlaced SPS Shell Type C&C Cross-section

core & coil



P SS P SS

Distribution – Core Type

Core Type C&C Cross-section

P P P PS S S S

core & coil

- good dielectric strength...

- typically good on thermal performance...- natural impedance's typically 2.5-3.5%...

- MUST be interlaced...

Distribution - 3Φ 5 Legged Construction

3 Phase 5-Legged C&C Cross-section

3 Φ core & coil

P SPS P SPSSP S P

Power – Stacked Core Form

Stacked Core – Core Cutting

Power – Disk Windings

Disk Windings

Power Transformer – Disk Winding

Power – Disk Windings

Power Transformer – Clean Room

Power Transformer – 667MVA 1Φ

Power – Pan-Cake Windings

Pan-Cake Windings

Power – Shell Form Construction

Transformer Function

• Converts electricity from high current and low voltage Converts electricity from high current and low voltage to low current and high voltage … to low current and high voltage … or … vice versaor … vice versa

• Electricity is better generated at low voltage, and Electricity is better generated at low voltage, and better transported at high voltage…better transported at high voltage…

• Transformers are the basic links of a T&D system…Transformers are the basic links of a T&D system…

• Electricity and Magnetism work together to produce Electricity and Magnetism work together to produce “transformer action”…“transformer action”…

Transformers – Basic Equations

Ampere’s Law

Faraday’s Law of Induction

Gauss’s Law for Electricity

Gauss’s Law for Magnetism

Maxwell’s EquationsDifferential form - General Case

x H = J +

x E = -

· D = ρ

· β = 0

δD δt

δβ δt

∆

∆

∆

∆

H = Magnetic Field Strength J = current densityE = Electric Field β = Magnetic FieldD = Electric Displacement ρ = Charge Density

where,

Transformers – Electric and Magnetic Fields

When a wire is connected to an AC power source, current flows When a wire is connected to an AC power source, current flows through it and a magnetic field is created around the wire… through it and a magnetic field is created around the wire…

Transformer – Ratings

• Transformers are rated in Volt-Amperes @ a specified Maximum Average Winding Temperature Rise in degrees Centigrade.

For example, a 25 kVA 65 Deg C rise transformer is rated to transform 25,000 Volt Amperes from one voltage/current level to another voltage/current level WITHOUT exceeding an Average Winding Rise of 65 Deg C above the Ambient.

• Liquid Filled (Mineral Oil or Natural Esters) Distribution Transformers are rated in kVA at 65 Deg C. Typically 10-167 kVA 1Φ or 15-2500 kVA 3Φ.

• Power Transformers are usually specified in MVA (million volt amperes). Multiple ratings can be specified at either or both 55 and/or 65 Degree C Rise.

Power Transformers can have multiple ratings based on optional cooling systems such as Fans or Pumps. For example OA/FA/FA (or under the new EIC definitions ONAN/ONAF/ONAF) for the ratings based on ‘Natural Air/Oil Cooling/Forced Air Cooling/and a second stage of Fans’.

kVA/MVA is a ‘Thermal’ Statement!!!

Transformers – Turns Relationships

Vpri

Npri=

Vsec

Nsec

N = turns ratio = Npri

Nsec

Vpri = Vsec x N and Isec = Ipri x N

= volts per turn

Transformer - Turns/Volts/Current

N = 3240 108

= 30 : 1

Isec = 25,000 VA

240 V= 104.7 Amps

Ipri = 25,000 VA

7200 V= 3.47 Amps

120

120

2407200

25 kVA

3240 turns 108 turns

Transformer - Core Loss & Exciting Current

A

vw

Iex

NL Watts

Vrated

%Iex = Iex

Irated

x 100

Rated Voltage is put across the LV terminals with the PrimaryOpen... the No Load Loss and Exciting Current are measured...

Transformer - Core Losses

No Load Loss = Hysteresis Loss + Eddy Current Losses

Hysteresis Loss is caused by the energy used in lining upthe magnetic domains in the core...

Eddy Currents are circulating currents in the core due toinduction. The thicker the core lamination, the more EddyCurrent losses...

Hysteresis Loss is a functionof the area enclosed by theHysteresis Loop...

β

H= magnetic field intensity = mmf = Ampere Turns

flux density = kl/in2

Transformer – Winding Measurements

A

vw

Irated

LL Watts

VIZ

%IZ = VIZ

Vrated

x 100

Rated Current is put into the HV terminals with the LV Shorted... the Load Loss and Impedance Voltage (IZ) are measured...

low impedancebolted short...

Transformer – Winding Measurements

Load Loss = Ip2Rp + Is

2Rs + Stray Losses

Stray Losses = Eddy (skin effect) Losses + Circulating Current Losses + Non-current carrying parts being influenced by leakage flux

Load Losses produce heating within the windings and resistance losses increase with temperature...

In order to cool the windings, oil ducts are inserted within the windings to allow the oil to circulate and transfer the heat to the tank walls and cooling fins...

Transformer – Eddy Current Losses

“No-Mag” plates (304L) are used in larger kVA transformers to reduce Eddy Current Losses due to High Current Flow…

Transformers - Voltage Regulation

%IR = LL

kVA x 10 %IX = IZ2 IR2

pf = power factor q = 1 pf2

%Reg = pf x IR + q x IX +( pf x IX - q x IR)2

200x K

where, K = p.u. load

Transformers – Resistance & Reactance in Ohms

then, ISC AMPS = kV x 1000

Ztscalar

In addition to the TRANSFORMER, the LV Fault Current is also limited by the Impedances of the SYSTEM to/from the Transformer, the LV circuit to/from the Fault, and the impedance of the FAULT… complexity is added with Line-Line and/or Line to Neutral Faults and the connections (Y-Y or Y-D)... And of course the transformation base levels…

Ztvector = Rt + j Xt (vector form)

Ft = [ kV2 / kVA ] x 10

Rt = Ft x %IR = ohms resistance

Xt = Ft x %IX = ohms reactance

Ztscalar = √ Rt2 + Xt

2 (scalar form)

…which of course is “Ohms Law”

θtscalar = tan-1(Xt/Rt ) (scalar form)

Transformers - Efficiency

Efficiency =

% Eff = 100 x K x kVA / (kVA x K + (NL + LL x K2))

OR

where K = per unit Load…

Power OUT

Power IN

Transformers – Distribution Polarity

H1 H2 H1 H2

X3 X2 X1 X1 X2 X3ADDITIVE SUBTRACTIVE

> 200kVA

> 8,660kV

Transformer Polarity indicates the direction of current flow through the HV windings with respect to the direction of the current flow through the LV windings…

Polarity is either “ADDITIVE” or “SUBTRACTIVE”

40

Lightning Surges and Protection

Lightning – Stroke Density Map

Lightning – Stroke Current Magnitude

Lightning Stroke Current Magnitude

0

0.2

0.4

0.6

0.8

1

1.2

1 10 100 1000

Stroke Current (KA)

Prob

abili

ty <

Abc

issa

Lightning Stroke Current magnitude is a probability distribution.

Lightning - Transformer Failures

Lightning is the most common cause of Transformer Failures...

Wildlife is the most common cause of Transformer Outages...

Transformer Outages1995-1996

0.00%2.00%4.00%6.00%8.00%

10.00%12.00%14.00%16.00%

Anim

al

Def

ectiv

e Eq

uip

Ligh

tnin

g

Tree

Unk

now

n

Stor

m

Con

nect

or

Ove

rload

OH

Sec

UG

Sec

UG

PR

I

Hum

an E

rror

- Pub

Misc

Vehi

cle

Hum

an E

rror

- FPC

Dig

-In

Emer

g- C

ust

Con

st E

quip

Emer

g FP

C

R/W

Cause Code

Pct

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

Cum

ulat

ive

Pct

Lightning

Lightning acts as a current source which deposits a large charge of electrons on the power line. This charge appears as a current wave propagating along the power line.

The current wave has a very steep wave front, i.e., high di/dt. The power system is highly inductive. The voltage produced is V=L di/dt. This can result in voltages approaching 1 million volts.

Such voltages will fail the insulation system of transformers and other equipment.

Lightning – Arrester Discharge Voltage

Lightning Arresters act to limit the voltage between conductors. This is accomplished by transferring charge (current) between conductors. The arrester is modeled electrically as a non-linear resistor.

Voltage

Current

Typical MOV Arrester characteristics 10 kA = 30 kV

MOV Arrester

Linear Resis

torSilicon Carbide Arrester

Lightning – Arrester Lead Lengths

MOV Arrester

Voltage AcrossTransformer

#6 CopperLead Length +/- 6 feet

Arrester Voltage= + Lead Voltage

- The Lead Inductance of #6 Copper is typically 4 microhenerys per foot (uh/ft)...

- The di/dt for Florida Lightning averages 20 kA per microsecond...

- Lead Length voltage is V = L di/dt = 4 uh x 20 kA/usec = 8 kV per Foot.

Lead Length Voltage = 6 feet x 8 kV/ft = 48 kV

Transformer Voltage = 30 kV + 48 kV = 78 kVfor a 10 kA stroke with a 20 kA/usec rise time.

The Transformer BIL for 12470 GRDY/7200 is 95 kV...

The probability of a stroke > 10 kA is 95%...

kV

Current

30kV

Arrester – Lead Length Reduction

Reduction of lead length voltage is accomplished by use of either Tank Mountedor Internal Under Oil Arresters.

Tank mounted or under oil arresters cannot be used on wye-delta banks due tosingle phase switching over voltages. Under Oil arresters are used only onsingle bushing transformers.

MOV Arrester Voltage AcrossTransformer

= Arrester Voltage

48

Low Side / Secondary Surges

Lightning – Transformer Winding Failures

Lightning on the High Voltage winding can produce 2 failuremodes

- Layer to Ground (anywhere in the winding)

- Layer to Layer at the H1 end of winding

Lightning on the Low Voltage winding can produce layer-to-layerfailures at either end of the High voltage winding or layer-to-groundin the Low Voltage winding.

Lightning – Poletype Winding Failures

TRANSFORMER FAILURE CAUSESPOLE TYPE (167 UNITS)

HVPROB43%

LEAD2%

LVPOS17%

LVPROB19%

NONE4%

SEC10%OVRLOAD

5%

Lightning – Padmount Winding Failures

TRANSFORMER FAILURE CAUSESPAD-MOUNTED (84 UNITS)

LEAD1%

LVPOS18%

LVPROB36%

NONE11%

OVRLOAD1%

SEC21%

HVPROB12%

Low Side Surges

• 5% of Stroke Currents Exceed 85 kA

• 50% Exceed 35 kA

• 35-50% of Surges enter on the LV side

• The Average LV Surge is 1500 amps/transformer/year?

• The Majority do not exceed 5000 amps?

Distribution – Core Type

Core Type C&C Cross-section

P P P PS S S S

core & coil

- good dielectric strength...

- typically good on thermal performance...- natural impedance's typically 2.5-3.5%...

- MUST be interlaced...

Distribution – Non-Interlaced LV windings

Non-Interlaced SPS Shell Type C&C Cross-section

core & coil



P SS P SS

Distribution – Shell Type - Interlaced LV windings

Interlaced SPS Shell Type C&C Cross-section

core & coil



P SSS S P SSS S

Lightning – ‘Anonymous’ Winding Failures

H2

H1

HVLV LV

“The Anonymous Failure Mode”


P SS P SS

During the 1960’s, the Transformer Manufacturers switched from Conductor wound Copper LV windings to Aluminum Sheet wound construction… COST $$$

Driven by COST, the practice of NON-INTERLACED Construction found favor with those Manufacturers who could make this change…

During the 1970’s, the installed failure rate of distribution transformers began to rise dramatically!!!

Teardown analysis began to show a special failure signature which became known as “The Anonymous Failure”… this is a “turn-turn” or “layer-layer” dielectric failure near the grounded end of a single bushing transformer…

And this seemed to be associated with the Non-Interlaced Shell Type Construction…


H2

H1

HVLV LV

• Layer to Layer failures near the grounded end of the HV winding is a “signature” of a low side surge occurrence...

“The Anonymous Failure Mode”


• The majority of LV surges probably enter the Transformer through the LV ground connections... either due to Primary Arrester operation or from the ground following direct or nearby strokes...

E = Ldidt = the voltage developed across

the ground leads...

Arrester


LV LV

HV

• Surge currents flowing through the LV windings of a Non-Interlaced LV winding produce a high magnetic field across the primary coil...


kV

H2 H1

• The rapidly changing magnetic field induces a very high voltage in the primary winding...

290 kV winding voltageto ground...

10 kVA 95kV BIL

• The lightning arrester connected across H1 to H2 does not see any voltage...

HV winding layers


kV

H2 H1

10 kVA 95kV BIL

HV winding layers

Layer to Layer Voltage

Peak 80 kV

• The high layer to layer stress in the HV winding will cause coil failure near either end of the coil... but usually at or near the grounded end of the winding...

Lightning – Low Side Surges

LV

HV

• Surge currents flowing through the LV windings of an Interlaced LV winding cancel and produce a weak magnetic field across the primary coil...

LV LV LV


kV

H2 H1

290 kV winding voltageto ground...

HV winding layers

Non-Interlaced

Interlaced3 kV to ground...

• Interlacing the LV winding balances the winding and significantly reduces the stress due to LV Surges...


kV

H2 H1

10 kVA 95kV BIL

HV winding layers

Layer to Layer Voltage

Peak 80 kVNon-Interlaced

InterlacedPeak 1 kV

• Interlacing the LV winding balances the winding and significantly reduces the stress due to LV Surges...


• Non-Interlaced LV windings are the major cause of Distribution Transformer (DT) Lightning Failures...

• Small kVA’s are MORE susceptible because of more turns...

• Primary Arresters DO NOT Protect the HV against LV Surges...

• Interlacing or LV Arresters reduces DT Failure Rate...

interlaced types non-interlaced types

0.5 %

1.0 %

FailureRate

Lightning - Summary

• The proper application and choice of Arresters can reduce the failure rate significantly… especially in the Southeastern USA…

• Arrester Lead length can be very important…

• About 50% of lightning surges come from the low side… on the smaller kVA transformers, Interlaced windings and/or LV Arresters can reduce winding failures…

68

Starting Transformers and Motors

Motor Starting Issues

• The current required to start equipment such as Electric Motors or Transformers requires a starting current, typically known as ‘Inrush’ or ‘locked rotor current’…

• For fusing, the typical ‘inrush’ rule is to keep the fuse melt beyond 8-12 times rated current at 0.1 second (about 6 cycles)…

• The short term voltage drop or ‘Flicker’ is a function of the required ‘Locked Rotor’ current required to start the equipment… a number of papers and information is available to the user on this issue…

• In addition to the impact on the local low voltage circuits, starting equipment such as large motors can cause voltage quality issues on the primary circuits of the distribution feeders… which can affect associated equipment…

• Some electronic systems may be sensitive to these changes!

Transformers – Resistance & Reactance in Ohms

then, ISC AMPS = kV x 1000

Ztscalar

In addition to the TRANSFORMER, the LV Fault Current is also limited by the Impedances of the SYSTEM to/from the Transformer, the LV circuit to/from the Fault, and the impedance of the FAULT… complexity is added with Line-Line and/or Line to Neutral Faults and the connections (Y-Y or Y-D)... And of course the transformation base levels…

Ztvector = Rt + j Xt (vector form)

Ft = [ kV2 / kVA ] x 10

Rt = Ft x %IR = ohms resistance

Xt = Ft x %IX = ohms reactance

Ztscalar = √ Rt2 + Xt

2 (scalar form)

…which of course is “Ohms Law”

θtscalar = tan-1(Xt/Rt ) (scalar form)

Motor Start – calculations

The voltage drop across the transformer:

%T = [1-Zm/sqrt((Rm+Rt)^2 + (Xm+Xt)^2))] x100 where, Zm is the motor impedance is calculated as, Zm = (line-line voltage rating of the motor) / LRA LRA = locked rotor amps PF = motor starting power factor Rm = Zm x PF ohms Xm = sqrt( 1-PF^2) ohms To translate the %Impedance ( %IZ ) into Real and Reactive components, we use the transformer impedance factor, Ft. Ft = [ [(Secondary voltage in kV)^2] / kVA rating of Transformer ] x 10 Rt = Ft x %IR ohms Xt = Ft x %IX ohms %IR and %IX are calculated from the Load Loss watts (LL) and Impedance (%IZ) of the specific transformer. %IR = LL / (kVA x 10) %IX = sqrt[ %IZ^2 - %IR^2 ] The voltage drop across the secondary conductor is:

%C = [ [ Rc x LRA x PF ] + [ Xc x LRA x sqrt(1-PF^2) ] ] x 100 / LV where LV is the line-line secondary voltage, typically 240 volts and,

Rc = conductor resistance in ohms per 100 feet x [ 2 x length /100 ] Xc = conductor reactance in ohms per 100 feet x [ 2 x length /100 ] The conductor length is multiplied by 2 as the current must have a return path. If the return path conductor is not the same size and characteristics as the line conductor the calculation must be adjusted accordingly.

Flicker

Flicker is typically the voltage drop caused by the Locked Rotor Current required to start a air-conditioner compressor motor.

The duration of this current for residential air conditioners varies from4 to 20 cycles. A voltage drop occurs in each component of the system,i.e., Transformer and Conductors, based on the magnitude of the currentand the impedance of the components.

The most common occurrence is during the startup of residential air conditioners. Customers see this as a dimming of the lights or, underextreme conditions, as a shrinking of the TV picture.

Customer sensitivity varies based on individual perception, themagnitude and duration of the voltage dip, and the type oflight source.

Flicker – Motor Starting Current 15-20 cycles

RAYSAC

Measured : 02/14/97 11:47:57

Channel A (V) Channel A (I) Sec.0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

VoltsY1

-400

-300

-200

-100

0

100

200

300

400Amps

Y2

-300

-200

-100

0

100

200

300

Motor Start – Single Phase

Capacitor Start motors utilize a capacitor in series with thestart winding to provide phase shift in the current throughthe start winding. This phase shift causes an angular displacement in the magnetic fields between the Run and Start windings resulting in a torque on the rotor.

Rotor

Start Winding

Run Winding

Run Winding

Start Winding

The larger the Capacitor - the larger the phase shift - the larger the starting torque - the shorter the starting cycle

Motor Start – Permanent Split Capacitor Motor

Run Capacitor

Start Run

Line

The Start winding and Run Capacitor remain energized at all times

Motor Start – Conventional 3 wire Hard Start

Potential Relay

Run Capacitor

Start Capacitor

Start Run

Line

The Potential Relay removes capacitor with StartWinding back E.M.F.

Residential Air Conditioners

Residential Air Conditioners use one of two types of Motors

- Permanent Split Capacitor

- Capacitor Start / Capacitor Run

Residential Air Conditioners use one of two types of Compressors

- Reciprocating (Piston)

- Scroll (new High Efficency units)

Motor Sizing rules are Different for Different Compressors

Motor Start Flicker – Field Test Data

AC Starting Characteristics

0.0

50.0

100.0

150.0

200.0

250.0

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

Tons

LRA

RECIP Test DataRecip RegressionScroll Test DAtaScroll Regression

Motor Start Flicker – Kickstart TO-5

Motor Start Flicker – Kickstart TO-5

Potential Relay

Run Capacitor

Start Capacitor

Start Run

Line

The Potential Relay removes capacitor with Startand Run Winding back E.M.F.

Flicker – Kickstart Motor Starting Current 4-6 cycles

RAYG4KS

Measured : 02/25/97 16:39:47

Channel A (V) Channel A (I) Sec.0.00 0.05 0.10 0.15 0.20 0.25

VoltsY1

-400

-300

-200

-100

0

100

200

300

400Amps

Y2

-400

-300

-200

-100

0

100

200

300

400

Compressor/Motor Start Flicker – Summary

• Compressor Flicker is a momentary (5-30 cycle) voltage drop caused by Motor Start… such as a Residential Air Conditioner…

• Compressor Flicker is ‘as perceived by the user’… Not everyone can notice it… once seen, the mind can ‘tune-in’ to it…

• Flicker is a function of the required ‘Locked Rotor’ Starting Amperes… the High Efficiency ‘Scroll Type’ Compressors require Higher Starting Amps… thus going to Higher Efficiencies can cause other issues!

• Adding extra Capacitive Reactance will not reduce the magnitue of the required starting current, but can reduce the amount of time required to get the compressor started… thus reducing the ‘perception of Flicker’…

83

Transformer Costs and Efficiencies

Quantifying Transformer Costs

• Capital Vs. Expense Dollars

• Financial Math Relationships

• Cost of Losses – the A and B Factors

• Band of Equivalence

• DOE Efficiency Rules

Capital Dollars

The purchase cost of a transformer is amortized over theexpected life. This is done by applying a Fixed ChargeRate (FCR) to the purchase price...

Price x FCR = Annualize Fixed Cost

The result is an annual cost which is uniform for the life ofthe unit...

FCR (%) = Fixed Charge Rate - The cost of carrying a capital investment made up of:- The weighted cost of capital (stocks, bonds)- Depreciation on the investment- Taxes (Income, Ad valorem, Gross Receipts)- Insurance

Expense Dollars

Expense costs such as Cost of Losses or future Change-Out are levelized to an annual form with the Capital Recovery Factor which considers only the cost of money and time…

Change Out Cost x CRF = Annualize Change Out Cost

The result is an annual cost which is uniform for the life ofthe unit...

CRF (%) = A/P = i(1+i)n /((1+i)n-1)

Note: In ANNUAL form Expense and Capital are equal!

Basic Financial Math

Annuity

Present Value

FutureValue

Compound Interest Factor F/P = (1+i)n

Capital Recovery FactorA/P = i(1+i)n /((1+i)n-1)

Present Value FactorP/F = 1/(1+i)n

Present Worth FactorP/A = ((1+i)n-1)/i(1+i)n

Compound Amount FactorF/A = (1+i)n-1/i

Sinking Fund FactorA/F = i/((1+i)n-1)

Moving Money (Value) through Time

Cost of Transformer Losses

The cost to operate a Transformer over it’s life is affectedby the Cost to Supply the capacity, or Demand (SC $/kW-yr),and the Cost incurred to supply the Energy (EC $/kW-Hour).

The No Load losses are continuous as long as the transformeris connected to the system, typically 8760 hours/year.

The Load Losses vary with transformer load and are affected by the annual load factor and the timing of the system peak.

AOC = Price x FCR + A x NL + B x LL

The Annual cost of ownership (AOC) is:

NOTE: draft C57.12.33 Loss Evaluation methodology currently under development by the IEEE…

The ‘A’ Factor

A = $ per No Load (excitation) Loss Watt

A =

where,

SC = Avoided Cost of System Capacity ($/kW-yr) - - The levelized avoided (incremental) cost of generation, transmission, and primary distribution capacity required to supply the next kW of load to the distribution transformer coincident with the peak load.

SC + 8760 x EC

1000 $/watt

EC = Avoided Cost of Energy ($/kWh-yr) - - The levelized avoided (incremental) cost for supplying the next kWh, which may be produced by the utility’s generating units or purchased from an energy supplier.

The ‘B’ Factor

B = $ per Load (winding) Loss Watt

B =

where,

( SC x RF + 8760 x LsF x EC) x PL2

1000 $/watt

PL = Equivalent Annual Peak Load “ON THE TRANSFORMER”

RF = Peak Loss Responsibility Factor - Defines the relationship between thetransformer peak load and the transformer load at the time of system peak load.

LsF = Loss Factor - A ratio of the annual average load losses to the peak value of load losses on the transformer. LsF = [Σ(K2

n*tn)/t]/K2peak

NOTE: An empirical relationship for loss factor for RESIDENTIAL transformers is the Propst/Ganger relationship: LsF = 0.15 (Load Factor) + 0.85 (Load Factor)2

Evaluation Forms

The Transformer Evaluation Equation may be written as: Total Owning Cost (TOC) = F x Price + A x NL + B x LL Where the factor F is a multiplier against the Price and is used toexpress the owning cost equation in three forms: Type description F form . - EFC Equivalent First Cost 1.0 Capital form - PW Present Worth FCR/CRF Expense form - AC Annual FCR Annuity form

Band of Equivalence

• The BOE was described by the Shincovich and Stephens (EEI 1981)as a way to address the uncertainty of the future estimates on factorssuch as Energy Costs, Loading, etc… 1% was suggested!

• “Uncertainty” of course can result in HIGHER or LOWER future costs!

• However, this idea has been expanded as a tool to force lower first pricesat the expense of future costs… 3-10% BOE is not uncommon! • BOE reduces the actual value of the Loss Evaluation Factors… Typically, a 3% BOE effectively reduces the A&B Factors by ½ or more!

Variances would be better addressed with tools such as Crystal Ball… or the Economics Variance module in TAP…

A & B Variance

LCC – Mild Steel Tank vs. Stainless

95

DOE Transformer Efficiencies – 2010 Rule

Energy Policy and Conservation Act

The Energy Policy and Conservation Act (EPCA) of 1975 established an energy conservation program for major household appliances. The National Energy Conservation Policy Act of 1978 amended EPCA to add Part C of Title III, which established an energy conservation program for certain industrial equipment. The Energy Policy Act of 1992 amended EPCA to add certain commercial equipment, including distribution transformers.

The Department of Energy, Office of Energy Efficiency and Renewable Energy, Building Technologies Program conducts the program that develops equipment energy conservation standards and has overall responsibility for rulemaking activities for distribution transformers in fulfillment of the law.

http://www.eere.energy.gov/buildings/appliance_standards/


Distribution Transformers The first step in developing energy conservation standards was the Secretarial determination in 1997 that, "Based on its analysis of the information now available, the Department has determined that energy conservation standards for transformers appear to be technologically feasible and economically justified, and are likely to result in significant savings" 62 FR 54809 (October 22, 1997). The Department of Energy (DOE) conducted two rulemakings for Distribution Transformers:

• an energy conservation standard• a test procedure



• In response, NEMA developed the TP-1 Minimum EfficiencyGuidelines in the early 1990’s… note: basically a 3 year payback!

• In August 2006, the DOE published the Notice of Proposed Rulemaking with a recommendation for to the Trial Standard Level 2 (TSL-2)…

• Mixed responses… some opposed mostly based on increased cost and material availability… some saying it doesn’t go far enough…


Trial Standard Levels

Efficiency = Power OUT / Power IN

%E = 100 x kVA x 0.5 / [ kVA x 0.5 + ((NL + LL x 0.9 x 0.52)/1000)]

Where NL and LL are in watts…

Note: 0.9 = Load Loss Temp correction from 85 to 55 deg C…

KVA NEMA TP1 TSL-2 TSL-3 TSL-410.0 98.40% 98.40% 98.43% 98.46%15.0 98.60% 98.56% 98.59% 98.62%25.0 98.70% 98.73% 98.76% 98.79%37.5 98.80% 98.85% 98.99% 99.14%50.0 98.40% 98.90% 99.04% 99.19%75.0 99.00% 99.04% 99.18% 99.33%

100.0 99.00% 99.10% 99.24% 99.39%167.0 99.10% 99.21% 99.35% 99.50%

75.0 98.70% 98.91% 99.09% 99.27%112.5 98.80% 99.01% 99.19% 99.37%150.0 98.90% 99.08% 99.26% 99.44%225.0 99.00% 99.17% 99.35% 99.53%300.0 99.00% 99.23% 99.41% 99.59%500.0 99.10% 99.32% 99.50% 99.68%750.0 99.20% 99.24% 99.42% 99.60%

1000.0 99.20% 99.29% 99.47% 99.65%1500.0 99.30% 99.36% 99.42% 99.48%2000.0 99.40% 99.40% 99.46% 99.50%2500.0 99.40% 99.44% 99.50% 99.55%

•TSL-1 = NemaTP1•TSL-2 = 1/3 between TP1 and TSL-4•TSL-3 = 2/3 between TP1 and TSL-4•TSL-4 = minimum Life Cycle Cost•TSL-5 = max Energy Savings with no change in LCC•TSL-6 = max Energy Savings

Final Rule – October 12, 2007

“Effective January 1, 2010, Liquid Filled Distribution Transformers manufactured for sale in the United States MUST meet or exceed the following Efficiency levels…”

Efficiency = Power OUT / Power IN @ 50% Load

%Eff = 100 x kVA x 0.5 / [ kVA x 0.5 + ((NL + LL x 0.9 x 0.52)/1000)] where NL and LL are in watts…

Note: 0.9 = Load Loss Temp correction from 85 to 55 deg C…

DOE Final Rule

• Similar rules are in place for Medium Voltage Dry type Transformers…

• The DOE rule resolves the issue between Single and Three Phase designs by using the same Efficiency Value for the Single Phase design for the equivalent 3 Phase kVA… For example, the required efficiency value for a 3Φ 150 kVA transformer is the same as a 50 kVA 1Φ unit…. (3 x 50 = 150 kVA)…

• Pre-Existing Distributor Stock, Re-manufactured units, and Transformers intended for Mining Operations are excluded from the rule…

• For Liquid Filled Transformers, the relationships to the Trial Standard Levels are…

• 1Φ 10-167 kVA slightly above TSL-4• 1Φ 250-833 kVA between TSL2 and TSL3

• 3Φ 45-300 kVA TSL-2• 3Φ 500 kVA between NEMA TP-1 & TSL-2• 3Φ 750 kVA slightly greater than TSL-3• 3Φ 1000-2500 kVA TSL-3

For the final rule, DOE set average A & B values of A=3.85 and B=1.16 $/watt 1Φ and B=1.93 $/watt 3Φ

DOE Projected Benefits

Energy Saved Quads = 1.77 2.39 3.15 3.63 6.9 9.77

TSL-1 TSL-2 TSL-3 TSL-4 TSL-5 TSL-6

CO2 (Mt) reductions = 123.1 167.3 218.5 252.7 483.1 679.5

NOX (kt) reductions = 34.1 46.4 60.9 71 134.9 188

Hg (t) reductions = 3 3.7 4.3 4.9 6.4 6.5

NOTE: The QUAD is used by the U.S. Department of Energy in discussing world and national energy budgets. One Quad = 1015 BTU. The global primary energy production in 2004 was 446 quads…

Conclusion

Q/A?Don A. Duckett, P.E.Technical Sales EngineerHD Supply Utilities

(407) [email protected]

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