7/31/2019 C2Luze09

1/25

Distribution Transformer

Size Optimization byForecasting Customer

Electricity Load

Jarrod Luze

Black Hills Power

Rapid City, South Dakota

7/31/2019 C2Luze09

2/25

Introduction

Electric utilities face common challengesdetermining transformer sizes.

Study consists of 960 three phase pad-mounted transformers.

Research and categorization of existingtransformers

Ideal vs. actual benefit/cost analysis

Forecasting future customer power demand

7/31/2019 C2Luze09

3/25

Study of Existing Transformers in Service

Compared kVA name-plate rating to peakdemand of customer

R+_ signifies that a transformer isundersized and would ideally require alarger transformer for the load.

R-_ signifies the transformer is under-loaded, and a smaller transformer wouldsuffice.

7/31/2019 C2Luze09

4/25

Study of Existing Transformers in Service

Out of 960, 605 were oversized-63%

Over 10% at least 3 sizes too big

150 kVA, 300 kVA and 500 kVA are the leastaccurately sized

Very few transformers over-loaded

Overall results of study show an overlyconservative sizing method

7/31/2019 C2Luze09

5/25

Existing Transformers in Service

E xisting T ransformers in S ervice

Transformer Classification

0%

20%

40%

60%

80%

100%

kV A kVA kVA kV A kV A kVA kV A kV A kVA kVA kV A

75 112 150 225 300 500 750 1000 1500 2000 2500

Transformer S ize (kVA)

3-PhasePadmounts

R -5

R -4

R -3

R -2

R -1

R

R +1

7/31/2019 C2Luze09

6/25

Study of Existing Transformers in Service

7/31/2019 C2Luze09

7/25

Financial Analysis

Capital expense of the equipment

Operating cost = No-load power loss

Wholesale electricity rate of $0.04/kWH

was used

7/31/2019 C2Luze09

8/25

Financial Analysis Capital

Estimated by using the price of the mostrecently purchased transformer of thatsize

Sums entire purchase price* of the 960transformers (total capital expense)*Purchase price includes installation costs

Theoretical estimated purchase cost vs.actual estimated purchase cost

7/31/2019 C2Luze09

9/25

Financial Analysis

7/31/2019 C2Luze09

10/25

Financial Analysis Operating

No-load power loss (Watts)

Not considered: Full-load loss, repairs and maintenance

Conservative estimate

PF of 0.95 used, if unable to gatherfrom database

7/31/2019 C2Luze09

11/25

Financial Analysis

No-Load Power Loss (O&M)

7/31/2019 C2Luze09

12/25

Financial Analysis - Overall

Assuming sizing methods and results areconsistent for all BHP transformers

Three-phase, pad-mount share of the transformerpurchase cost is roughly 26% of the $2.5 million annual

transformer purchase cost budget

At 17%, $425,000 annual benefit

7/31/2019 C2Luze09

13/25

Research Application

Increase efficiency from the sizingstatistics

Possibilities

Review current transformer placement,and change-out existing units based oneconomic feasibility.

Develop more accurate transformersizing method

7/31/2019 C2Luze09

14/25

Forecasting Customer Electricity

Loads Many factors

Size of structure to be powered

General purpose of structure

Structural components

Machines and Appliances to be installed

Location

Personnel capacity of building orstructure

7/31/2019 C2Luze09

15/25

Customer Categories

This study includes

Retail Stores

Business offices Apartments (gas heated, electric heat)

Many others to be considered, time-

constraints limit this study

7/31/2019 C2Luze09

16/25

Data Collection and Calculation

Cooperation of Customers

Tax Equalization office supplied squarefootage information

Averages based on Peak kVA demands

Power factor assumed 0.95 if Unavailablein database

Calculations of W/sf, mA/sf Consistent values, low standard of deviation in

data

7/31/2019 C2Luze09

17/25

Results Business Offices

Averaged 5.76 watts per square foot

Highest: 7.09 Lowest: 4.52W/sqft

Averaged 34% of Main Switch

Ampacity Mainly fluorescent lighting

Gas heated

7/31/2019 C2Luze09

18/25

Business Offices

7/31/2019 C2Luze09

19/25

Results - Retail Stores

Averaged 4.98 W/sqft

High: 8.13 / Low: 2.86

Averaged 46% of Main SwitchAmpacity

Mostly Fluorescent Lighting, some

spot lighting

7/31/2019 C2Luze09

20/25

Retail Stores

7/31/2019 C2Luze09

21/25

Results - Apartments

Gas Heated, summer peaking, 94.7% occ.

Averaged 1.42 W/sqft, 1.5 W/sqft @ 100%

High: 2.09 / Low: 0.82

Electric Heat, winter peaking, 81.5% occ.

Averaged 3.53 W/sqft, 4.3 W/sqft @ 100%

High: 4.14 / Low: 2.71

7/31/2019 C2Luze09

22/25

Apartment Buildings

7/31/2019 C2Luze09

23/25

Applications

Gives utility representatives statisticswhen discussing options with customers &contractors.

Presents evidence & factual history to helpdecide on transformer size.

Provides foundation and structure forfurther research of future demand andtransformer sizing.

7/31/2019 C2Luze09

24/25

Summary

Sizing analysis shows significant costavoidance capabilities: 17% $425,000

O&M savings (NLL only) of 31%

Customer demand indicators may

help utility reps with transformersizing, and provide a basis toadvance research

7/31/2019 C2Luze09

25/25

Questions?