DG Sizing of Generator

March 12, 2018 | Author: pokiri | Category: Electric Generator, Resistor, Quantity, Electrical Equipment, Mechanical Engineering

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Description

ELECTRICAL DESIGN PROCEDURES

BATTERY SIZING CALCULATIONS

DTP-E-GEN-1006-00

ROLTA INDIA LIMITED

EDS ELECTRICAL DESIGN PROCEDURES DG Sizing Calculations Calculations DTP-E-GEN-1006-00 Revision History Revision Level

Revision Date

Revision Description

This Document and all contained herein are proprietary of ROLTA INDIA LIMITED and is subjected to confidentiality restrictions

between ROTLA INDIA LIMITED and the Recipient. Copyright Reserved.

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Page 1 of 21

ELECTRICAL DESIGN PROCEDURES

BATTERY SIZING CALCULATIONS

Subject

DTP-E-GEN-1006-00

Page no

8. EMPIRICAL FACTORS USED IN SIZING FOR MOTOR LOADS.................................................7 9. LOAD ANALYSIS...........................................................................................................................9 12 REQUIRED CALCULATION INPUTS:.......................................................................................15 13 REQUIRED CALCULATION OUTPUTS:...................................................................................15

1. Purpose & Scope DG sets are used under the following conditions: 1. As a primary source of power a. Supplying isolated loads in the rural areas b. Supplying essential loads in power / industrial / chemical plants. 2. As a backup to the main or grid supply a. DG set operating in parallel with the grid b. DG set sunning in isolation from grid supply for meeting the deficit or for some critical loads. © Copyright 2008. Rolta India Limited. All Rights Reserved.

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ELECTRICAL DESIGN PROCEDURES

BATTERY SIZING CALCULATIONS

DTP-E-GEN-1006-00

This design guide for Diesel – Generator Set (DG SET) covers the following aspects. • Standard DG ratings and voltage levels • Sizing of DG set • Parallel operation with the grid Neutral earthing

2. Applicability This procedure is applicable to all projects. 3. References ASME B15.1

Safety Standard for Mechanical Power Transmission Apparatus

ASME B31.1

Power Piping Code

IEEE 80

Guide for Safety in Substation Grounding

IEEE 112

Standard Test Procedure for Polyphase Induction Motors and Generators

IEEE 115

Test Procedure for Synchronous Machines

IEEE 43

Recommended Practice for Testing Insulation Resistance of Rotating Machinery

IEEE 1050

Guide for Instrumentation and Control Equipment Grounding in Generating Stations

NEMA 250

Enclosures for Electrical Equipment (1000 Volts Maximum)

NEMA AB 1

Molded Case Circuit Breakers and Molded Case Switches

NEMA ICS-1

Industrial Controls and Systems

NEMA ICS-2

Industrial Control Devices, Controllers, and Assemblies

NEMA ICS-6

Enclosures for Industrial Controls and Systems

NEMA MG1

Motors and Generators (Including Rev. 1 and 2)

NEMA MG2

Safety Standard for Construction and Guide for Selection, Installation, and Use of Electric Motors and Generators

4.0 DG Set Ratings & Voltages :

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ELECTRICAL DESIGN PROCEDURES

BATTERY SIZING CALCULATIONS

DTP-E-GEN-1006-00

DG sets upto 1000 KVA are rated for 415V and those above 1000 KVA are rated for 3.3 / 6.6 / 11 KV as per the requirement of primary distribution voltage in the plant. Some of the typical ratings available in India are as follows : 415V : 10 / 25 / 50 / 75 / 100 / 125 / 150 / 200 / 250 / 300 / 400 / 500 / 650 / 750 /

800 / 1000 KVA

3.3/6.6/11 KV : 1460 / 2200 / 3000 / 5000 / 6500 / 8000 / 12000 KVA 5.0 Diesel Engine Speeds :

Diesel engine speed is normally classified into following three categories : 1. High Speed (above 750 RPM) 2. Medium Speed (above 300 RPM and upto 750 RPM) 3. Low Speed (upto 300 RPM) When DG sets are used for continuous duty i.e. more than 6000 hours per year, it is recommended that engine of either low speed or medium speed are selected for getting high service life. DG sets used for emergency purpose can be of high speed type. The above considerations are true only for the conventional loads like pump / fan motors, heaters, lighting etc. However sizing of DG for feeding non-conventional loads like Arc Furnace and Rolling Mills is very complex and not considered here. 6. DEFINATIONS: 1.1.1

System Performance The power generating system shall conform to the following performance requirements:

1.1.1.1

Rating Engine continuous horsepower shall be sufficient to deliver full rated generator set kW/kVA when operated at rated rpm and equipped with all engine-mounted auxiliary loads.

1.1.1.2

Start Time and Load Acceptance Upon receiving a start signal, the standby diesel generator shall be capable of starting automatically without local attendance, reaching synchronous speed and rated voltage and frequency within 10 sec and be ready to accept load to its rated capacity under at normal operating temperature, in accordance with NFPA 110. The unit shall be capable of three consecutive starts without recharging. The standby diesel generator set shall be capable of either manual or automatic start and, in either case, check synchronization, automatically synchronize and close to either a live or dead bus.

1.1.1.3

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ELECTRICAL DESIGN PROCEDURES 1.1.1.4

BATTERY SIZING CALCULATIONS

DTP-E-GEN-1006-00

Voltage regulation Generator terminal voltage shall be maintained at rated voltage ±0.5% for any steady state load between no load and full load.

1.1.1.5

No load operation It is required that the standby diesel generator be capable of operating at full speed, no load, for one hour.

1.1.1.6

Transient Operation When loaded in accordance with the above requirements, the transient voltage drop shall be limited such that the generator voltage is not less than 80 percent of nominal voltage, and frequency is not less than 95 percent of nominal. In addition, the voltage at the generator shall recover to within 90 percent of nominal voltage and the frequency to 98 percent of nominal within 2 sec after load application. During recovery from transients caused by load application, or resulting from 100 percent load rejection, the speed of the generator set shall not exceed nominal speed plus 75 percent of the difference between nominal speed and the overspeed trip set point or 115 percent of nominal, whichever is lower.

1.1.1.7

Load Banks Properly sized three-phase load bank, including associated switching equipment, shall be provided for use during periodic exercising of the diesel generator.

7. GENERATOR LOADING: Type of Electrical Load Loads vary according to applications and it is useful to examine and classify their characteristics as follows: Passive Loads Include heating, lighting and domestic type loads. Easily evaluated. Usually expressed in kW on assumption of unity P.F. In sizing generating sets passive loads are usually treated as constant at the specified kW. Cage Induction Motors The most common type of industrial load characterized by a high initial starting kVA at low P.F. and a fairly high peak kW during run-up. Motor output usually expressed in kW so that:-

F.L. input kW

=

Rated kW output Per Unit F.L. efficiency

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ELECTRICAL DESIGN PROCEDURES and F.L. kVA

input =

BATTERY SIZING CALCULATIONS

DTP-E-GEN-1006-00

F.L. input kW

F.L. power factor If the motor output is expressed in HP:-

F.L. input kW

=

0.746 X Rated HP Output Per Unit F.L. efficiency

Columns (1) to (6) of Fig. 1 list typical full load performance figures for induction motors from 1.1 to 1000kW output. The method used for starting squirrel cage motors is most important. The simplest method id D.O.L. (direct-on-line) starting at full voltage and a typical motor would drawn an initial starting kVA of about 6.5 times the full load value, and a possible peak input kW during run-up of about 3.25 times full load value. A motor supplied from a generating set and started in this way would probably produce serious transient voltage dip problems and might, under some conditions, require an oversize engine to power the run-up. To reduce the demand on the supply during starting, cage motors frequently use different forms of reduced voltage starting, the two most common being start-delta and auto-transformer starting. Both the initial kVA and the peak kW are substantially reduced but the motor develops reduced torque, which prolongs the run up time. Columns (7) to (12) of Fig. 1 show initial start kVA and peak input kW for typical cage. motors with three methods of starting, D.O.L., auto-transformer with 75% tap and start-delta. Slip ring Induction Motors Used where high starting torque is required with a moderate starting current. Starting involves full voltage applied to stator and series rotor resistance which is progressively cut out during run up. Starting kVA is typically between 1.25 and 2.0 times rated input and starting power factor is high, typically 0.9 so that generating set sizing considerations usually centre on engine power rather than transient voltage dip. Columns (13) to (18) of Fig.1 show the kVA and kW input to slip ring motors during starting for three starter settings 1.25, 1.5 and 2.0 times full load input. Rated load input is as for cage. motors and can be taken from columns (1) to (6).

Rectifier and Similar Non-Linear Loads Rectifier and thyristor type loads draw a current which is high in harmonics and when the supply is obtained from a generating set the consequence distortion of the alternator voltage wave may be sufficient to affect the operation of other equipment running from the same supply. Generator temperature and © Copyright 2008. Rolta India Limited. All Rights Reserved.

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ELECTRICAL DESIGN PROCEDURES

BATTERY SIZING CALCULATIONS

DTP-E-GEN-1006-00

voltage control instability may also occur. Because of this, generators supplying non-linear loads should be generously rated so that the kVA rating should be at least twice the full load kVA input to the rectifier or thyristor.

Regenerative Loads Cranes and hoists sometimes use electrical regeneration as a means of braking. The effect of returning power to a generating set is to reduce the engine power requirement and produce an increase in speed. Small levels of regeneration will be absorbed in the losses of the set but if it becomes appreciable, the speed may rise to an unacceptable extent since the governor can have no effect in limiting the speed under such conditions. To guard against this the net regenerated power should not exceed 20% to 25% of the generating set kW rating, the lower figure for sets above 200 kW, the larger figure for small sets of say 20 kW rating. If this cannot be achieved then a ballast load should be connected across the generator (activated by a reverse power relay) intermittently rated but capable of absorbing the maximum regenerated kW’s.

Capacitive Loads Although not normally a factor in sizing generating sets, mention should be made of the effect of capacitive loads on generating sets. Such loads may result in an overall leading power factor condition which tends to self excite the generator and in extreme cases may lead to excess terminal voltage which the AVR cannot control. Special consideration must therefore be given to such cases.

8. EMPIRICAL FACTORS USED IN SIZING FOR MOTOR LOADS 8.1“K” FACTOR In the absence of Vendor Data the starting kVA for an induction motor may be estimated by the application of the “K” factor to the full load kVA as shown in Fig.1. Thus:a. Initial starting kVA – F.L. kVA x K For cage motors K will depend on the design of the motor and the method of starting. For D.O.L. starting, K may vary between 5.0 and 7.5 a typical average value being 6.5 which may be used in the absence of an actual figure. If reduced voltage starting is used then the K value will be reduced as the square of the voltage so that:b.K for reduced voltage start = K for D.O.L. x V2 c. (where V is the reduced start voltage in P.U. of normal volts). Thus for typical cage motors:-

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ELECTRICAL DESIGN PROCEDURES

BATTERY SIZING CALCULATIONS

Starting Method

Applied Voltage

K Factor

D.O.L.

1.0

6.5

Start-delta

0.58

2.2

Auto-transformer (60% tap)

0.60

2.3

Auto-transformer (75% tap)

0.75

3.6

DTP-E-GEN-1006-00

For slip ring motors the starting kVA is restricted by the external starter resistance in the rotor are usually determined by the starting torque requirements of the load. a. A typical valve would lie between 1.25 and 2.0, but the Motor Vendor must advise.

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ELECTRICAL DESIGN PROCEDURES Effective peak kW

BATTERY SIZING CALCULATIONS =

Start kVA x E

=

FLkVA x K x E

DTP-E-GEN-1006-00

a. The value given to E will depend on the application and particularly the motor load inertia. For squirrel cage motors the maximum value will be 0.5 and other values can be found with the aid of Fig.2. For slip ring motors maximum kW occurs at the instance of starting and to allow for the high starting power factor a value of 0.9 should be assigned to E for this class of machine. The same value can be used for squirrel cage motors using special “soft start” techniques. where the run of characteristics obtained from thyristor controls is not unlike that of a slip ring motor. 9.

Maximum Starting kVA This is the highest value in line reference 6 and is the highest suddenly applied kVA increment which the alternator will experience. It must therefore be used to determine the alternator size in relation to transient voltage dip limits.

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ELECTRICAL DESIGN PROCEDURES

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DTP-E-GEN-1006-00

After analysing the load as described above it is worth checking to see whether a different sequence of applying the load elements would be beneficial. Clearly it cannot affect the final kW but it could result in a lower maximum total peak kW which frequently determines engine size.

10. Sizing the Set The Engine The engine must meet two requirements. First it must be able to supply all the connected load elements operating at their individual ratings for the required duration. Thus the “final kW” in Figure 3 must not exceed the rating of the set, continuous or standby as appropriate. The second requirement is that the engine must be able to develop sufficient power to meet the “maximum total peak kW” also evaluated in Fig.8. If this is only slightly higher than the plant rating determined above then it may make use of any engine short term reserve power which may be available (such as the ten percent overload capacity for continuously rated sets). In many cases however, it will be substantially greater in which case it will become the deciding factor in choosing the engine. The special, but not uncommon, case of a generating set powering only a single large motor often results in an engine peak power requirement out of all proportion to its continuous power rating. Since no other loads are involved effective economy can sometimes be made using the frequency tied start method in which the load motor and the generating set are run up together. The generating set controls for this, although not complicated are not standard and would only be justified for the larger sets where the special engineering costs could be absorbed. The Generator

The generator must have a continuous (or standby if appropriate) rating comparable with the “final kW” figure used in engine sizing. The load power factor is almost always taken to be 0.8 PF lagging but very occasionally a different operating power factor may be specified and this must be taken into account when choosing the generator. A further requirement is that the generator must be able to handle the largest step kVA load without excessive voltage dip which, in the absence of a prescribed figure should be taken as about 25 percent with 30 percent as an absolute maximum. The three factors which determine transient voltage dip are:a. Alternator reactance b.Load impedance c. Load power factor Considering a simple circuit comprising a generator represented by a voltage source and inductive reactance (generator transient reactance) in series with the load impedance. The simple generator is assumed to develop 1.0 Pu. volts at the terminals before the load switch is closed. On closing the switch a current flows, limited by the load impedance and the generator reactance in series so that part of the original 1.0 Pu volts is now dropped across the generator reactance leaving a reduced voltage at the machine terminals.

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ELECTRICAL DESIGN PROCEDURES Let:

BATTERY SIZING CALCULATIONS

E

=

Generated emf (= 1.0 Pu)

VT

=

Voltage at machine terminals

X

=

Pu transient reactance of generator

ZL

=

Pu. load impedance comprising in series

XL

RL

=

Generator kVA x SIN (COS–1 ∅)

XL

DTP-E-GEN-1006-00

=

Generator kVA x COS ∅ Step kVA load

Total impedance

circuit

Z = ZL + X (added vectorially) = RL + j (XL + X) = √R2L + (XL + X)2.Pu Circuit prior to connecting transient load I = E = 1.Pu ZZ Generator terminal voltage on connecting transient load, VT = IZL.Pu

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ELECTRICAL DESIGN PROCEDURES Transient Dip,

BATTERY SIZING CALCULATIONS

DTP-E-GEN-1006-00

Voltage

= E – VT = 1 – VT.Pu The accurate estimate of running load of DG set can be made considering individual motor rating , efficiency and power factor. KVA =

P * LF PF * η * DF

Where, KVA =

Minimum DG capacity

P

=

Connected KW on DG

DF

=

Diversity Factor (>=1.0).

=

Sum of Individual Max. Demands

Max. Demand on Power Station

The diversity factor is always greater than 1. If it is not available the same can be assumed as 1.

LF

=

Load Factor (0.6 to 0.9) Maximum real power consumed

=

maximum real power that would be consumed

11.0 Performance of Generating Sets Between the required maintenance intervals and under the site ambient conditions. Generating set power outputs are defined in the Codes by one of the following: Continuous Power This is the power that a generating set is capable of delivering © Copyright 2008. Rolta India Limited. All Rights Reserved.

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DTP-E-GEN-1006-00

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ELECTRICAL DESIGN PROCEDURES

BATTERY SIZING CALCULATIONS

DTP-E-GEN-1006-00

remains within the new steady state speed band. For G1 governing 8 seconds maximum for the load changes defined for transient speed variation limits.

Influence of Alternator Reactance on Transient Performance Transient reactance of generators is effective whenever load changes occur. On applying a sudden load it behaves as a series reactance, absorbing some of the generated voltage and © Copyright 2008. Rolta India Limited. All Rights Reserved.

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ELECTRICAL DESIGN PROCEDURES

BATTERY SIZING CALCULATIONS

DTP-E-GEN-1006-00

causing the temporary voltage dip at the alternator terminals. Transient reactance is usually expressed in per unit terms (although sometimes percentage) related to the rated load impedance. Thus a 0.25 Pu (or 25 percent) transient reactance would be numerically equal to a quarter of the impedance of the rated load circuit. Since transient reactance is purely reactive whereas the load impedance usually comprises both resistance and reactance it follows that the effect of transient reactance on voltage dip will depend on the load power factor and zero power factor lagging will produce the greatest transient voltage dip for a given load current. 12

REQUIRED CALCULATION INPUTS:

The following is a summary of the required inputs to the calculation to satisfy this procedure:a. Generator Bus Design Loading kW and KVAR (Motor) kW and KVAR (Non Motor) b.Profile for Load Changes c. Permitted limits for voltage and frequency under steady state and transient conditions.

13

REQUIRED CALCULATION OUTPUTS:

Size of engine and generator required to meet all possible combination of load conditions while remaining within the voltage and frequency limits.

FIG.1 – PERFORMANCE OF TYPICAL INDUCTION MOTORS

Maximum Input during starting and Run-up Rated

Typical

Cage Motors

Slip Ring Motors

Output

(E = 0.5)

(E = 0.9)

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ELECTRICAL DESIGN PROCEDURES

kW

Appro x HP

P.F .

P.U. Eff

BATTERY SIZING CALCULATIONS Inpu t

Inpu t

kVA

kW

D.O.L. K = 6.5

DTP-E-GEN-1006-00

Auto Transfor

StartDelta

K = 3.6

K = 2.2

K = 1.25

K = 1.5

kVA

kW

kVA

kW

kVA

kW

kVA

kW

kVA

kW

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13)

(14)

(15)

(16)

1.1

1.5

0.8 1

0.75

1.81

1.47

11.8

5.88

6.52

3.26

3.98

1.99

2.26

2.04

2.72

2.44

3

4

0.8 3

0.81

4.46

3.70

30

15

16.1

8.03

9.81

4.91

5.58

5.02

6.69

6.02

7.5

10

0.8 3

0.85

10.6

8.82

68.9

34.5

38.2

19.1

23.3

11.7

13.2

11.9

15.9

14.3

15

20

0.8 2

0.885

20.7

16.9

135

67.3

74.5

37.3

45.5

22.8

25.9

23.3

31.1

27.9

30

40

0.8 2

0.905

40.4

33.1

263

131

145

72.7

88.9

44.4

50.5

45.5

60.6

54.5

50

67

0.8 3

0.925

65.1

54.1

423

212

234

117

143

71.6

81.4

73.2

97.6

87.9

80

107

0.8 5

0.935

101

85.6

656

328

364

182

222

111

126

114

151

136

100

134

0.8 5

0.94

125

106

812

406

450

225

275

137

156

141

187

169

125

167

0.8 5

0.942

156

133

1014

507

562

281

343

172

195

175

234

211

150

200

0.8 6

0.945

185

159

1202

601

666

333

407

203

231

208

277

250

170

228

0.8 6

0.945

209

180

1358

679

752

376

460

230

261

235

313

282

200

268

0.8 6

0.945

246

212

1599

800

886

443

541

271

307

277

369

332

250

335

0.8 6

0.945

308

265

2002

1001

1109

554

678

339

385

346

462

416

300

400

0.8 5

0.945

373

317

2424

1212

1343

671

821

410

466

420

559

504

400

536

0.8 5

0.945

498

423

3237

1618

1793

896

1096

548

622

560

747

672

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ELECTRICAL DESIGN PROCEDURES

BATTERY SIZING CALCULATIONS

DTP-E-GEN-1006-00

500

670

0.8 4

0.945

630

529

4095

2047

2268

1134

1386

693

787

709

945

850

600

804

0.8 4

0.945

756

635

4914

2457

2722

1361

1663

832

945

850

1134

1021

800

1070

0.8 3

0.945

1020

847

6630

3315

3672

1836

2244

1122

1275

1147

1530

1377

1000

1340

0.8 2

0.945

1290

1058

8385

4192

4644

2322

2838

1419

1612

1451

1935

1741

.50

(a)

.45 (b)

.40

(c) .35

10

20

50

100

200

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500

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ELECTRICAL DESIGN PROCEDURES

BATTERY SIZING CALCULATIONS

Rated kW

DTP-E-GEN-1006-00

Input kW

Input kVA

K

50

50

-

A

Lighting and Heating

B

SR Motor – Crusher – 2 x FLC Start

250

265

308

2.0

C

SC Motor – Unloaded Compressor – Auto transf. 75% Top

200

212`

246

3.6

D

SC Motor – Pump – DOL Start

7.5

8.8

10.6

6.5

E

SC Motor – Fan – Y-∆ Start

15

16.9

20.7

2.2

F

SC Motor – Fan – DOL Start )

3.0

3.7

4.5

6.5

)

) Started together

G H

A

B

C

D

(1)

0

50

315

527

F.L. kW

(2)

50

265

212

F.L. kVA

(3)

50

308

Start K Factor

(4)

-

Element

Start E Factor

(5)

Start kVA Eff Peak kW

E

F

8.8

16.9

3.7

246

10.6

20.7

4.5

2.0

3.6

6.5

2.2

6.5

-

0.9

0.38

0.45

0.45

0.4 5

(6) = (3) x (4)

50

616

886

69

46

29

(7) = (5) x (6)

50

554

336

31

20

13

Total Effective Peak kW

(8) = (1) + (7)

50

604

651

591

Final kW

(9) = (1) + (2)

50

315

52.7

556

Initial kW

Applied

Max value of Total Eff. Peak kW (max value of line ref 8)

651

Max value of Final kW (max value of line ref 9)

556

Sizing Recommendation Cummins KTA 3891

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G

H

ELECTRICAL DESIGN PROCEDURES

BATTERY SIZING CALCULATIONS

Max value of Start kVA (max value of line ref 6)

886

DTP-E-GEN-1006-00

577 kW Cont/635 kW O/L with V/H2 AVR functions to handle 651 kW peak.

Rating Class

Cont

K1

°C ambient

30°C

M.ASL

1000

K2

952

Service HZ

Alt temp rise

100°C (F)

K3

1.0

Equiv. kVA

529

Max % V.Dip

Alt Equiv cont kW

14.

1.0

Alt Wdg type

A

.

Service Volts

380 50

Max

start

982

L Low Reactance Alternator Frame E7B Cont kW = 620 Start kVA for 20% dip = 1023

Transient

20

NEUTRAL EARTHING :

DG sets upto 500 KVA solidly earth system is recommended. The earthing is provided so as to minimise the damage to stator winding in the event of an earth fault. If DG is envisaged to operate in parallel with the grid, it is recommended to provide solidly earth system irrespective of KVA rating. In case of isolated operation of DG set, for rating above 500 KVA, resistance earthing is considered for limiting the earth fault current to maximum full load current of the DG set. DG sets of 3.3 / 6.6 / 11 KV are always provided with resistance grounded system. The earth fault current is limited to maximum full load current of the DG set. The value of neutral resistor is given by R = VL √3 * IL Where, VL = Line to Line RMS voltage in Volts IL = Rated Current in Amps © Copyright 2008. Rolta India Limited. All Rights Reserved.

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T S G S

ELECTRICAL DESIGN PROCEDURES R

BATTERY SIZING CALCULATIONS

DTP-E-GEN-1006-00

= Resistor value in Ohms

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ELECTRICAL DESIGN PROCEDURES

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