Electricity + Control February 2018

TRANSFORMERS + SUBSTATIONS

Liquid

Cast

Dry

Total losses (kW)

6,76

12,18

12,25

KWH billing rate x

R0,55

R0,55

R0,55

Annual hours x

8760

8760

8760

Annual cost of energy due to Losses @ 50% load: =

R32 569,68

R58,683,24

R59 020,50

Excess annual energy costs

R26 113,56

R26 450,82

Base

10-Yr* excess energy costs:

R261 135,60

R264 508,20

Base

*Simple costs, assumes no interest rate or escalat- ing energy costs

3 Feature: Liquid filled transformers have a small- er footprint. Materials and Resources Benefit: Smaller equip- ment reduces building size demand. Constants: Assume Industrial space rental at R55,00 per square metre Typical cost per square metre

Additional cost of transformer losses – air-conditioning energy consumption Energy consumption by the transformer is not the only energy factor. Transformer losses are dissipated as heat, which must be removed from a controlled tem- perature environment by air conditioning. Illustrat- ed below are calculations to convert transformer losses into increased air conditioning energy con- sumption.

Liquid (FR3)

Dry Differ- ential

KVA

R55,00 per m 2

Depth: m 1,402 1,676 Width: m 1,402 2,438 m 2 1,966 4,088 Depth: m 1,585 1,676 Width: m 1,463 2,438 m 2 2,319 4,088 Depth: m 1,920 1,676 Width: m 1,341 2,438 m 2 2,575 4,088

750 kVA

Constants 1 kW = 3 415 BTU/Hr

2,12

m 2

R116,70 per m 2

1 Ton Air Conditioning = 12 000 BTU/Hour 1 Ton Air Conditioning = 1,7 kW power use

1 000 kVA

1,77

m 2

R97,29

per m 2

Liquid

Cast

Dry

Total Losses (kW)

6,76

12,18

12,25

1 500 kVA

BTU/HR/KW x

3 415

3 415

3 415

1,51

m 2

R83,19 per m 2

BTU/HR =

23 085

41 595

41 834

BTU/HR per ton A/C ÷

12 000

12 000

12 000

A smaller building also has the benefit of requiring less lighting and ventilation. 4 Feature: Liquid filled transformers have superi- or operating life, maintainability, and repairability. Materials and Resources Benefit: Less waste/ disposal/replacement/labour.

A/C (tons) =

1,92

3,47

3,49

kW power usage per ton A/C x

1,7

1,7

1,7

kW

=

3,27

5,89

5,93

Annual hours of operation(h) x

8 760

8 760

8 760

Annual energy usage (kWh) =

28 649

51 619

51 916

kWH billing rate x

R0,55

R0,55

R0,55

Annual cooling costs =

R15 756,95

R28 390,45

R28 553,80

Operating life: Typical dry-type lifespan: 15 - 25 years Typical liquid-filled lifespan: 25 - 35 years

Excess annual cooling costs

base

R12 633,50

R12 796,85

10-Yr excess energy costs

base

R126 335,00

R127 968,50

2 Feature: Liquid filled transformers have a lower operating sound level. Indoor environmental quality benefit: Less noise pollution. Decibels is a logarithmic function, and sound pres- sure doubles for every three decibel increase. Research shows that decibel levels over 60 can reduce a person's attention span. A study by the American Society of Interior Designers showed that office productivity would increase if workspaces were less noisy [2] [3].

The retirement age of transformers removed from service for a variety of reasons ranges from 14 to 35 years; the average is 25 years. However, the average life of liquid- immersed transformers that remain in service is 30 years or more [1]. Because liquid-filled transformers last longer than dry-type, they save on material, labour to replace, and oper- ational impact due to outage to replace.

Maintainability Recommended annual maintenance for a typical

34 Electricity + Control

FEBRUARY 2018