DESIGN, INSTALLATION AND TESTING OF RELIABLE LOW VOLTAGE EMERGENCY DIESEL GENERATOR SYSTEMS
Copyright Material PCIC Europe Paper No. IS-01 PCIC Europe
Karla da Costa Ribeiro
AkzoNobel EOS
PO Box 9300, 6800 SB Arnhem
The Netherlands
Willem Aartse
AkzoNobel EOS
PO Box 9300, 6800 SB Arnhem
The Netherlands
Abstract - This paper deals with the design, installation and testing principles of emergency diesel generator systems with the focus on reliability. A functional block diagram of a typical emergency diesel generator system is presented and explained throughout this paper. Basic principles to be included in the Basis of Design of such installations are also discussed in order to give the design engineer the correct starting points for proper system design.
Index Terms - emergency generator systems, basis of design, reliability, design for simplicity, onshore installations.
- INTRODUCTION
Within a chemical industrial site emergency situations may arise when a failure of the normal power supply occurs (unplanned power outages). When an unplanned power outage occurs, some of the electrical power consumers within the plant, such as emergency lighting, process control and supervisory equipment and vital pumps need to remain running to safeguard the process safety and/or to safeguard asset integrity. For this reason, these important electrical power consumers must be connected to an emergency electrical power installation which will automatically take over the functions of the failed electrical power supply. A common practice within industrial facilities is to use a low voltage synchronous generator driven by a diesel engine as the source of emergency electrical power. This paper presents a proposal for design, installation and functional testing of low voltage emergency diesel generator systems with the focus on aspects that can make a difference to the reliability. Maintenance aspects are also of great importance but these are not covered by this paper because the specific maintenance of the various parts of the system should always be carried out according to the recommendations of the relevant equipment suppliers.
The term “systems” is used throughout this paper because such installations comprise not only the emergency generator set (synchronous generator, diesel engine, associated control system, exhaust, batteries, etc.), but also control systems responsible for initiating the emergency operation and the switching on and off of power switches, supervision system, switchgear installation, auxiliary electrical power supply, power and control cables, etc. The design principles presented in this paper are based on the demands and recommendations of international standards with the additional focus on “Design for Simplicity”. The basic principle of a reliable design is to keep it simple. Complicated design increases the risk of failures and unreliable operation.
Firstly, a Basis of Design (BoD) must be made, discussed with the electrical, process and safety engineers involved in the project and with the customer/asset owner, documented, and acted upon. This makes the initial design phase a multidisciplinary task. One of the main aspects of the Basis of Design as approached in this paper is the reliability level of the electrical installation. The required reliability level is determined by using a risk matrix. When the required reliability level is determined and documented in the Basis of Design report, the design engineer then has a foundation on which the design, installation, test and maintenance of the system must be built. The design process and functional test philosophy which are presented in this paper, although applicable for general installations, are specifically described for applications within onshore chemical plants.
- EMERGENCY GENERATOR SYSTEM BLOCK DIAGRAM
Fig. 1 depicts a typical emergency generator system installation showing the main functional blocks.
IV-J
consumers
Fig. 1 Block diagram of a typical emergency diesel generator system
The division of the installation in functional blocks is important in order to have a simple overview of the whole system and in order to understand how the failure rates associated with each block/subsystem can influence the reliability of the total system. This is especially valid whenever reliability calculations on the system are performed. In Fig. 1, every functional block is numbered with a reference to the chapter where it is more fully described.
Before the aspects concerning each functional block are discussed, the Basis of Design of the emergency generator system will be presented.
- BASIS OF DESIGN OF THE EMERGENCY GENERATOR SYSTEM
The basic requirements of the emergency generator system must be documented in a form of a “Basis of a Design” report. The BoD report is the guidance document which is used during the detailed design to produce other documents such as technical specifications, procedures for operating and testing the system, etc. Furthermore, after installation of the system, the BoD serves as an input document for “Management of Change” procedures so that changes, if required, do not cause the system to deviate from its basic design starting points. The BoD must contain the following information as a minimum:
- Reliability
- Required reliability level
While determining the required reliability level of the emergency generator system, it is necessary to assess the risks associated with the emergency electrical power consumers being in a non-operational state. A single or a group of emergency electrical power consumers being in a non-operation state is considered to be a hazard scenario. Risk acceptance criteria associated with hazard sc
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DESIGN, INSTALLATION AND TESTING OF RELIABLE LOW VOLTAGE EMERGENCY DIESEL GENERATOR SYSTEMS
I INTRODUCTION
Within a chemical industrial site emergency situations may arise when a failure of the normal power supply occurs (unplanned power outages). When an unplanned power outage occurs, some of the electrical power consumers within the plant, such as emergency lighting, process control and supervisory equipment and vital pumps need to remain running to safeguard the process safety and/or to safeguard asset integrity. For this reason, these important electrical power consumers must be connected to an emergency electrical power installation which will automatically take over the functions of the failed electrical power supply. A common practice within industrial facilities is to use a low voltage synchronous generator driven by a diesel engine as the source of emergency electrical power. This paper presents a proposal for design, installation and functional testing of low voltage emergency diesel generator systems with the focus on aspects that can make a difference to the reliability. Maintenance aspects are also of great importance but these are not covered by this paper because the specific maintenance of the various parts of the system should always be carried out according to the recommendations of the relevant equipment suppliers.
The term “systems” is used throughout this paper because such installations comprise not only the emergency generator set (synchronous generator, diesel engine, associated control system, exhaust, batteries, etc.), but also control systems responsible for initiating the emergency operation and the switching on and off of power switches, supervision system, switchgear installation, auxiliary electrical power supply, power and control cables, etc. The design principles presented in this paper are based on the demands and recommendations of international standards with the additional focus on “Design for Simplicity”. The basic principle of a reliable design is to keep it simple. Complicated design increases the risk of failures and unreliable operation.
Firstly, a Basis of Design (BoD) must be made, discussed with the electrical, process and safety engineers involved in the project and with the customer/asset owner, documented, and acted upon. This makes the initial design phase a multidisciplinary task. One of the main aspects of the Basis of Design as approached in this paper is the reliability level of the electrical installation. The required reliability level is determined by using a risk matrix. When the required reliability level is determined and documented in the Basis of Design report, the design engineer then has a foundation on which the design, installation, test and maintenance of the system must be built. The design process and functional test philosophy which are presented in this paper, although applicable for general installations, are specifically described for applications within onshore chemical plants.
II BASIS OF DESIGN OF THE EMERGENCY GENERATOR SYSTEM
The basic requirements of the emergency generator system must be documented in a form of a “Basis of a Design” report. The BoD report is the guidance document which is used during the detailed design to produce other documents such as technical specifications, procedures for operating and testing the system, etc. Furthermore, after installation of the system, the BoD serves as an input document for “Management of Change” procedures so that changes, if required, do not cause the system to deviate from its basic design starting points. The BoD must contain the following information as a minimum:
A. Reliability
1) Required reliability level
While determining the required reliability level of the emergency generator system, it is necessary to assess the risks associated with the emergency electrical power consumers being in a non-operational state. A single or a group of emergency electrical power consumers being in a non-operation state is considered to be a hazard scenario. Risk acceptance criteria associated with hazard scenarios are defined according to a combination of consequence (severity) and likelihood (frequency) scale as shown in Equation (1) below.
Risk = Severity x Frequency (1)
Risks associated with hazard scenarios can be assessed in a qualitative way by using a risk matrix. An example of a risk matrix is presented in Fig. 2 in which the following code is applicable.
1. 2, 3, 4 or 5: Risk is acceptable; no further risk reduction is required.
2. 6: Action required unless risk ALARP (as low as reasonably practical); reduce the risk by a factor of 10 by using systems, procedures, training, audits, or hardware.
3. 7: Action required at first opportunity; reduce risk by a factor of 100 by introducing more control systems (hardware, software).
4. 8,9 10 or 11: Unacceptable, Immediate action required; a risk reduction of at least 1.000 is required; check if the frequency/probability of the scenario fits with the severity, consider using a more qualitative assessment.
The severity levels must be aligned with KPIrsquo;s (Key Performance Indicators) of the company where the emergency generator system will be installed. In the Fig.2, the severity level S1 is the least severe rating and the severity level S5 is the highest. During the severity rating classification, the consequences of the hazard scenario are usually evaluated by taking into account at least six aspects: (1) peoples safety, (2) health, (3) environment, (4) asset integrity, (5) companys reputation and (6) security.
For the frequency rating (harm probability) the matrix has six different levels. Each level increases the frequency by a factor of 10, ranging from F1 (low frequency, less than once per 10.000 years) to F6 (high frequency, more than once per year). To evaluate the total risk, the severity and frequency are then mu
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