Diesel Generator Sizing- REV0

DIESEL GENERATOR SIZING

CONTENTS

1.

Introduction

2.

Reference Document

3.

Diesel Sizing

4.

Generator Sizing

5.

Motor Starting Study

App. 1:

Generator Efficiency

App. 2:

Ambient Temperature Derating Factor

App. 3:

Generator Starting Capability

1.

INTRODUCTION

The purpose of this document is to illustrate the Diesel Generator sizing method and its results. The diesel generator set under consideration, will provide emergency power to essential board's loads in the case of loss of power. 2.

REFERENCE DOCUMENTS

3.

DIESEL SIZING

According to “Electrical Load List”, total required active power of diesel generator is equal to 120 kW. Considering 20% spare capacity D/G set load will be equal to:

Pde = 1.2 ×120= 144 kW Which will be used for prime mover power estimation. According to attached load list, total reactive power requirement is equal to

Qde = 87.1kVAR and

S de = 149kVA By adding 20% spare capacity:

S de = 1.2 ×149 = 179kVA Which will be used for generator sizing. For calculation of mechanical shaft power electrical demand shall be divided by generator efficiency. Generator efficiency according to attached typical efficiency curves [Appendix 1] is about 93.7% (at =80% of rated kVA), so:

Pdm = Pde / 0.937 = 154kW 5 kW cooling fan power requirement (a typical value) shall be added to this power:

Pd = 154 + 5 = 159kW To estimate required diesel power, derating factor for site condition shall be foreseen. Typical derating factor for ambient temperature is 1.5% per each 5°C over 40°C. So derating factor for 51.8°C (rounded up to 55°C) maximum ambient temperature will be: dt=15/5 x 1.5= 4.5% (95.5%). For altitudes below 1000m no de rating factor shall be required.

da=1 For Humidity no derating factor is recommended by manufacturers.

P( net ) =

Pd 159 = = 166kW d a ⋅ d t 0.955

Diesel engine with prime power more than 166 kW at ISO standard condition (25°C, 100m a.s.l. and 60% relative humidity) shall be selected.

4.

GENERATOR SIZING

Generator shall have a power rating greater than 179 kVA at site condition. To consider effect of working in 51.8°C, a typical derating factor equal to 0.9 according to Appendix 2 is considered. So the rated generator apparent power shall be about 200 kVA at 40°C.

5.

MOTOR STARTING STUDY

Motor starting capability of diesel generator system shall be studied according to attached transient voltage curves of a sample generator. The largest motor in the present system is Fire Fighting Jockey Pump Motor. Rated starting kVA of this motor= 257 A × 690 = 177 kVA According to a sample manufacturer transient curves, voltage variation during starting of largest motor are as described below: For MX (PMG Excited) type AVR and 400V system: 11% For MX (Self Excited) type AVR and 400V system: 13.5% Considering that 20% variation in voltage during starting is acceptable, the selected diesel generator will be suitable for starting duty especially with PMG Excitation. It should be considered that the voltage setter of AVR will normally be at 1.05 Un (420V), so the resulting voltage drop during motor starting at generator busbar with reference to nominal voltage (400V) is 6% with PMG exciter and 8.5% with Self Excitation scheme.

APPENDIX 1 GENERATOR EFFICIENCY

APPENDIX 2 AMBIENT TEMPERATURE DERATING FACTOR

APPENDIX 3 GENERATOR STARTING CAPABILITY