I.17 ELECTRICAL EQUIPMENT HEAT DISSIPATION

1.0 Purpose

This Standard establishes the procedures for determining heat losses from electrical equipment. It summarizes several manufacturer losses for standard electrical equipment where these are available.

The total heat loss for each major type of electrical equipment shall be calculated in accordance with this Standard.

Heat loss values presented in this standard are conservative estimates based upon contractor information and engineering judgment. These heat loss values are intended to be used for air conditioning and heating load calculation; computations of actual energy losses (dollars per kilowatt) shall not be made using these values.

2.0 Scope

This Standard provides estimated heat loss values for major electrical equipment used in both fossil-fuel and nuclear power plants. The heat loss values presented herein are applicable during normal full load operation only; heat loss values during shutdown or accident conditions (e.g.: LOCA in a nuclear plant) may be significantly different due to the following reasons:

a) space heaters may be energized when breakers are open,

b) most essential loads will be energized,

c) most normal plant lighting may be de-energized, and

d) certain items such as diesel generator switchgear, tie breakers, and emergency motor driven pumps, only operate during shutdown or accident conditions.

The heat loss of these emergency items when they are de-energized must be considered for normal plant operation (e.g. space heater power must be considered as the normal heat loss) and the heat loss of the equipment which operates during shutdown or accident conditions must be considered for operation during emergency conditions.

When large motor control centers or switchgear are located in areas where environmental conditions must be accurately controlled (such as in safety related areas of nuclear plants), it will be advantageous to identify those circuit breakers and motor starters which do not continuously carry current (e.g. motor starters

for motor operated valves). For such items, the normal operation heat loss values given in this Standard will not apply, but the engineer must determine if a space heater, control power transformer, or indicating lights will be continuously energized and if so include their heat loss.

3.0 Methodology

3.1 Medium Voltage Switchgear

Heat loss values are given in TBL.17A. All heat loss values are in watts per cubicle at full load. Heat loss values listed in TBL. 17A shall be replaced by contractor data for each project, if such contractor data is available at the time heat losses are computed.

Space heater values shall be added to the cubicle heat losses, if the space heaters remain energized at all times. If space heaters are thermostatically controlled, the space heater value shall be added for compartments only if the circuit breaker in that compartment is normally open (such as in the case of a tie breaker). Auxiliary compartment heat losses include relays and instruments, for a compartment without a circuit breaker. These losses are not to be added to cubicle heat losses unless a given cubicle combines both a breaker and a fully equipped auxiliary compartment.

Heat losses from internal buswork and power cable connections are included in the heat loss values given in TABLE 1.

Total heat loss from any given switchgear line-up shall be computed by adding the heat loss values (from TABLE 1) for each cubicle.

3.2 Unit Substations

3.2.1 Unit Substation Transformers

Heat loss values are given in TABLE 17B for dry-type transformers with a temperature rise of 150°C over a 30°C ambient, and for liquid filled type transformers with a temperature rise not to exceed 60°C over a 30°C ambient. The heat loss values given in TBL 17B are independent of transformer independence.

3.2.2 Unit Substation Components – High Voltage

Heat losses for the incoming line breaker of unit substations shall be obtained from TABLE 1, if a power breaker is used. If an air interrupter switch is used, then use the power circuit breaker values given in TABLE

17A. If an air filled terminal chamber is used rather than a power circuit breaker, 50% of the values given in TABLE 17A shall be used.

3.2.3 Unit Substation Components –Low Voltage

Heat loss values are given in TABLE 17C for the low voltage distribution equipment. Space heater values listed in TABLE 17C shall be replaced by contractor data for each project, if such contractor data is available at the time heat losses are computed.

Space heater values shall be added to the vertical stack heat losses, if the space heaters remain energized at all times. If space heaters are thermostatically controlled, the space heater value shall be added for compartments only if the circuit breaker in that compartment is normally open (such as in the case of a tie breaker). If the circuit breaker is normally open, the heat loss of that breaker shall not be included in the total for the unit substation. Auxiliary compartment heat losses include relays and instruments, without circuit breaker.

Heat losses from internal buswork and power cable connections are listed in TABLE 17C under the heading “Buss Losses, per Vertical Stack”. These values shall be added to the heat losses for each circuit breaker, etc., to obtain the total for the unit substation.

If fusible switches are included in the unit substation, heat loss values shall be obtained from TABLE 17D.

3.3 Motor Control Centers

Heat loss values are given in TABLE 17D for motor control centers. Heat loss values listed in TABLE D shall be replaced by contractor data for each project, if such contractor data is available at the time heat losses are computed. Space heater values shall be added to the vertical stack heat losses, if the space heaters remain energized at all times. If space heaters are thermostatically controlled, the heater value shall not be added.

Heat loss values for combination starters include the control power transformer, a magnetic contractor, and either a fused switch or molded case circuit breaker. Heat loss values for individual molded case circuit breakers also apply to fused switches used as feeder devices.

3.4 Power and Lighting Transformers and Panelboards

Refer to TABLE D for heat losses of power and lighting transformers and panelboards.

3.5 Station Batteries

For HVAC design purposes, heat loss from station batteries need not be considered. During normal operation, the station battery is maintained on float charge, with the normal dc load supplied from the battery chargers. Station batteries generate a small amount of heat when being charged, and while on float charge, this heat is insignificant. When a battery is discharged, it experiences a temperature drop and actually absorbs a small amount of heat from the environment.

3.6 Battery Chargers

Heat loss from battery chargers shall be computed using Equation 1 which calculates the power lost within the battery charger, as the “inefficient percent” of the normal load on the charger. (Normal load is the float charge requirement plus the steady state dc load). The diversification factor accounts for the fact that the battery charger only operates at rated capacity when the battery must be completely recharged. The diversification factor shall be computed using Equation 2, which determines the percent of the ampere rating of the battery charger being normal used for the float charge current and the steady state dc load. The multiplier of 1.25 provides a safety factor for the actual ampere load carried by each battery charger during normal operation. Efficiency shall be assumed as 0.11 amperes for lead-antimony batteries and 0.011 amperes for lead-calcium batteries, float current (1F ) is defined as the current drawn by the battery for each 100 ampere-hours of its total rating.

Equation 1

Heat loss from battery charger (watts) = ampere rating of battery charger x voltage rating of battery charger x diversification factor x percent inefficiency/100.

Equation 2

Diversification factor = 1.25 [ ]where LA = Steady state DC load amps

IF = Current drawn by battery for each 100 amp-hoursAHB = Amp-hour rating of batteryBC = Number of battery chargersABC = Amp-rating of each battery charger

See Example 1 at the end of the text for sample calculation.

IF x AHB

LA + 100 amp-hrBC x ABC

3.7 Uninterruptible Power Supplies (UPS)

Uninterruptible power supplies consist of a dc-ac inverter, regulated bypass ac power supply, load transfer switch, and all accessory equipment and devices necessary to furnish uninterruptible power. Heat loss from uninterruptible power supplies shall be computed as the percent inefficiency of the kilowatt rating of the UPS, refer to Equation 3 following and Example 2 at the end of the text.

Equation 3

Heat loss, (watts) = kVA rating x 1000 x power factor x percent inefficiency/100.

3.8 DC Switchgear

Heat loss values for dc switchgear shall be obtained in accordance with 3.2.3 and TABLE 17C (assume same heat losses as for unit substation components.)

3.9 Computers

Heat loss values shall be obtained from the computer contractor, since strict environmental conditions are required for proper computer operation.

When heat loss estimates must be computed prior to receipt of contractor information, heat loss values shall be computed as 250 watts per linear foot, for full height, single unit depth (approximately 24 inches deep) computer cabinets. Calculations shall be revised, if required, when contractor heat loss values are obtained.

3.10 Control Boards and Relay Cabinets

If contractor information is not available, heat loss values shall be computed at 30 watts per square foot of the total panel front surface area.

A better estimate can be made if the kVA of power required by the unit is known. In that case, heat loss can be estimated as 80 percent of the kVA input to the unit.

A more accurate estimate can be made if the front view of the unit is available. In this case heat loss totals shall be computed on the basis of 10 watts per indicting light, 2 watts per control switch, and 25 watts per relay or meter.

3.11 Motors

Heat loss from motors shall be computed in accordance with Equation 4, when motor efficiency is known. See also Example 3 at the end of the text.

If the efficiency is unknown, an efficiency of 90 percent can be assumed. Heat loss values for motors of 90 percent efficiency are given in TABLE 17E.

Equation 4

Heat loss (watts) = Horsepower x 746 (watts/horsepower) x percent inefficiency/100.

3.12 Lighting

Heat loss from lighting shall be computed as the sum of the lighting load, in watts, for the area in question. The lighting load in watts can be obtained from the lighting panel schedules.

If the heat loss is to be computed by the sum of ratings (watts) of individual luminaires, the following factors shall be used to account for heat loss from bassasts:

Incandescent: Heat loss = lamp watts x 1.0Fluorescent: Heat loss = lamp watts x 1.2High Intensity Discharge: Heat loss = lamp watts x 1.4

3.13 Cable Tray (Power Cables Only)

Heat loss for cable trays containing power cables shall be estimated in accordance with the information below. These estimates are based on a mixture of single conductor power cables. Tray fill has been assumed as 40 percent of the cross sectional area of the usable depth (for a 4 inch nominal tray depth). Each cable has been assumed to carry a load equal to its derated cable capacity divided by 1.25. A 60 percent diversity factor has been applied, to account for the fact that not all the cables are continuously loaded.

Tray Widthinch

Heat Losswatts/foot

600V 5KV 15KV12182430

23354758

26395365

26425568

3.14 Isolated Phase Bus System

The isolated phase bus duct which connects the main generator to the step-up transformer has definite heat losses. The bus duct is either forced-cooled or self-cooled, and in either case, specific losses are provided by the contractor for the purpose of loss evaluation. These contractor’s stated losses shall be used as the heat loss for the isolated phase bus duct, as well as any isolated phase potential transformer equipment which is purchased with the bus duct.

3.15 Neutral Grounding Equipment

Neutral grounding transformers and associated resistors normally do not carry current. Therefore, there will be no heat loss from this equipment during normal operation.

3.16 Generator Circuit Breaker or Load Break Switch

When such a circuit breaker or switch is mounted indoors, specific losses will be provided by the contractor. The contractor’s stated losses shall be used as the heat loss for this equipment.

3.17 Generator and Exciter

The turbine-generator manufacturer will provide specific losses for the generator and the exciter. These manufacturer’s stated losses shall be used as the heat loss values.

3.18 Medium Voltage Bus Duct

Non-segregated phase bus, commonly used as a feeder between unit auxiliary transformers and medium voltage switchgear, will generate some heat due to the I2R losses of the conductors carrying load. This heat loss, however, will be very small compared to losses from other equipment located in the areas being traversed by the bus duct and need not be considered. Heat losses from other electrical equipment and from mechanical equipment will generally be much greater than any calculated losses from non-segregated phase bus. Also, the quantity of non-segregated phase bus is in general very small when compared to the amount of cable tray, lighting, and other heat-generating apparatus.

Losses from non-segregated phase bus shall only considered if the bus passes through an area which has strict environmental requirements, such as an air-conditioned area of a nuclear plant. Good design practice, however, usually precludes medium voltage bus duct from traversing such areas.

4. Examples

Example No. 1

Determine the heat loss from a battery charger rated 400 amperes at 125 volts. There are four (4) battery chargers connected to a dc bus which floats an 1800 ampere-hour battery (lead-calcium type) and supplies a steady state dc load of 240 amperes. Battery charger efficiency is assumed to be 85 percent.

Solution:

From Eq 2

Diversification factor = 1.25 [ ] = 0.188

From Eq 1

Heat loss = 400 amps x 125 volts x 0.188 x (1.00-0.85) = 1410 watts

Example No. 2

Compute the heat loss from a 25 kVA uninterruptible power supply. Power factor is 0.9; overall efficiency is 80 percent.

Solution:

From Eq 3

Heat loss = 25 kVA x 1000 x 0.9 x (1.00-0.80) = 4500 watts

Example No. 3

Compute the heat loss of a 2000 HP motor which is 94 percent efficient.

Solution:

From Eq 4

Heat loss = 2000 x 746 x (1.00-.94) = 89,500 watts

240 amps + (0.011 amps x 1800 amp-hr) 100 amp-hr

4 x 400 amps

HEAT DISSIPATIONS OF ELECTRICAL EQUIPMENT

A. Transformers: (see Table I.17B for additional information)

1. Dry Type, 600 volts and under: 30 through 500 kVA; over 600 volts: 750 through 1000 kVA.

a) Approximate % Total Loss (from Square D)

80° Temp Rise 115° Temp Rise 150° Temp Rise kVA Range2.58% 2.98% 4.20% 30-752.10% 2.30% 3.50% 112.5-2251.45% 1.64% 2.30% 300-5001.13% 1.32% 1.55% 750-1000

2. Oil Filled

a) Approximate Total Loss in Watts

5/8.33 KV 25 KV Class 35 KV Class KVA Range5800 Watts 6300 Watts 6880 Watts 500 KVA7500 8750 9400 7509900 10500 11500 100014600 15400 16300 150018500 19400 19900 200022500 23900 24700 2500

* Westinghouse, Catalog 47-121 Page 4, Plazatron Network

B. Motor control centers approximately 200 watt loss per vertical section.C. Cable: I2 Load x R (per foot, per conductor, per phase)D. Bus: I2 Load x R (per foot)E. The following Tables I.17A through I.17E list heat dissipation for various

electrical equipment. Values are based on fully loaded conditions.

TABLE 17A

MEDIUM VOLTAGE SWITCHGEAR

Heat Loss, Watts per Cubicle

Current Amps

5kV 7.2kV 13.8kV1200A Breaker

2000A Breaker

3000A Breaker

1200A Breaker

2000A Breaker

3000A Breaker

1200A Breaker

2000A Breaker

3000A Breaker

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

94

213

378

590

850

-

-

-

-

-

-

-

-

-

48

108

192

300

432

588

768

972

1200

-

-

-

-

-

36

80

142

222

320

436

569

720

889

1075

1280

1502

1742

2000

111

250

444

694

1000

-

-

-

-

-

-

-

-

-

54

122

216

338

486

662

864

1094

1350

-

-

-

-

-

40

90

160

250

360

490

640

810

1000

1210

1440

1690

1960

2250

117

263

467

729

1050

-

-

-

-

-

-

-

-

-

60

135

240

375

540

735

960

1215

1500

-

-

-

-

-

44

100

178

278

400

544

711

900

1111

1344

1600

1878

2178

2500

5kV 7.2kV 13.8kVSpace Heater, per Cubicle

Auxiliary Compartment

250

300

400

400

500

500

TABLE 17B

UNIT SUBSTATION TRANSFROMERS (DRY TYPE)4160V – 480V, 6900V – 480V, 13800V – 480V

TRANSFORMER SIZEKVA

HEAT LOSSAT FULL LOAD

WATTS

300

500

750

1000

1500

2000

2500

6,000

10,000

15,000

20,000

25,000

35,000

40,000

UNIT SUBSTATION TRANSFROMERS (LIQUID FILLED TYPE)4160V – 480V, 6900V – 480V, 13800V – 480V

TRANSFORMER SIZEKVA

HEAT LOSSAT FULL LOAD

WATTS

500

750

1000

1500

2000

2500

7,660

9,950

12,630

17,440

22,470

26,300

TABLE 17C

UNIT SUBSTATION COMPONENTS

CIRCUIT BREAKERS, 600 VOLTS OR BELOW

HEAT LOSS, WATTS

Current Amps

Circuit Breaker Frame Size225A 600A 1600A 2000A 3000A 4000A

70

90

100

125

150

175

200

225

250

300

350

400

500

600

800

1000

1200

1600

2000

2500

3000

4000

39

64

79

123

177

241

316

400

-

-

-

-

-

-

-

-

-

-

-

-

-

-

*

*

*

*

50

68

89

113

138

200

272

355

555

800

-

-

-

-

-

-

-

-

*

*

*

*

*

*

*

*

*

32

43

56

88

127

225

352

506

900

-

-

-

-

*

*

*

*

*

*

*

*

*

56

76

100

156

225

400

625

900

1600

2500

-

-

-

*

*

*

*

*

*

*

*

*

36

49

64

100

144

256

400

576

1024

1600

2500

3600

-

*

*

*

*

*

*

*

*

*

*

*

40

63

90

160

250

360

640

1000

1562

2250

4000

* Use lowest value in column

ITEM HEAT LOSS, WATTS

Space Heater, per Vertical Stack 400Auxiliary Compartment 400Bus, per Vertical Stack 300

TABLE 17D

MOTOR CONTROL CENTERS

ITEM HEAT LOSS, WATTSCombination Starter NEMA Size 1 NEMA Size 2 NEMA Size 3 NEMA Size 4 NEMA Size 5

Molded Case Circuit Breaker (or Fused-Switch) Current, Amps 15 – 30 40 – 50 60 – 70 100 – 125 150 – 225 250 – 300 400 – 500 600 – 800

Auxiliary Relay Compartment

Bus, per Vertical Stack

Space Heater, per Vertical Stack

Power and Lighting Transformers 3 Phase, 480 – 280/120 Volt 9 kVA 15 kVA 30 kVA 75 kVA 112 kVA

Incoming Line Reactor Ampere Rating 600 700 800 1000 1200

Power and Lighting Panelboards Number of Single Pole Circuits 12 24 36 42

6090140190350

41620284060100200

100

80

200

300500140032205400

2503505007001000

150300450525

TABLE 17E

MOTORS (90 percent efficient)

HORSEPOWER HEAT LOSS, WATTS HORSEPOWER HEAT LOSS, WATTS

1/3

½

1

5

7 ½

10

15

20

25

30

40

50

60

75

100

25

37

75

373

560

746

1119

1492

1865

2238

2984

3730

4476

5595

7460

125

150

200

300

400

500

600

700

800

900

1000

2000

3000

4000

5000

9325

11190

14920

22380

29840

37300

44760

52220

59680

67140

74600

149200

223800

298400

373000