Regulatory Guide 1.9: Difference between revisions

From kanterella
Jump to navigation Jump to search
(StriderTol Bot change)
(StriderTol Bot change)
 
Line 1: Line 1:
{{Adams
{{Adams
| number = ML12305A253
| number = ML012410194
| issue date = 12/31/1979
| issue date = 11/30/1978
| title = Selection, Design, and Qualification of Diesel-Generator Units Used as Standby (Onsite) Electric Power Systems at Nuclear Power Plants
| title = Selection of Diesel Generator Set Capacity for Standby Power Supplies
| author name =  
| author name =  
| author affiliation = NRC/OSD, NRC/RES
| author affiliation = NRC/RES
| addressee name =  
| addressee name =  
| addressee affiliation =  
| addressee affiliation =  
Line 10: Line 10:
| license number =  
| license number =  
| contact person =  
| contact person =  
| document report number = RG-1.009, Rev 2
| document report number = RG-1.009
| document type = Regulatory Guide
| document type = Regulatory Guide
| page count = 4
| page count = 3
}}
}}
{{#Wiki_filter:U.S. NUCLEAR REGULATORY COMMISSION
{{#Wiki_filter:"-
Revision 2 December 1979 REGULATORY G IDE
38/10/71 SAFETY GUIDE 9 SELECTION OF DIESEL GENERATOR SET CAPACITY FOR
* '
STANDBY POWER SUPPLIES
OFFICE OF STANDARDS DEVELOPMENT
A. Introduction large increases in current drawn from the die sel generator resulting from the startup of General Design Criterion 17 requires that induction motors can result in substantial volt the onsite (standby) power supply for a nuclear age reductions. The lower voltage could pre power plant be of sufficient capacity and capa- vent a motor from starting or cause a running bility to assure that (1) specified acceptable motor to coast down. Other loads also might be fuel design limits and design conditions of the lost if their contactors drop out. Recovery reactor coolant pressure boundary are not ex- from the transient caused by starting large ceeded as a result of anticipated operational motors or from the loss of a large load could occurrences and (2) the core is cooled and con- cause diesel engine overspeed which, if exces tainment integrity and other vital functions sive, might result in a trip of the machine.
REGULATORY GUIDE 1.9 SELECTION, DESIGN, AND QUALIFICATION OF DIESEL-GENERATOR UNITS USED AS
STANDBY (ONSITE) ELECTRIC POWER SYSTEMS AT NUCLEAR POWER PLANTS


==A. INTRODUCTION==
are maintained in the event of postulated acci- These same consequences also can result from dents. Diesel generator sets have been widely the cumulative effect of a sequence of more used as the power source for the standby power moderate transients if the system is not per supplies. This safety guide describes an accept- mitted to recover sufficiently between succes able basis for the selection of diesel generator mire tecover suent e.
General Design Criterion 17, "Electric Power Systems,"
of Appendix A, "General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50, "Domestic Licensing of Produc- tion and Utilization Facilities," includes a requirement that the onsite electric power system have sufficient capacity and capability to ensure that (1) specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded as a result of anticipated operational occurrences and (2) the core is cooled and con- tainment integrity and other vital functions are maintained in the event of postulated accidents.


Criterion III, "Design Control," of Appendix B, "Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants," to 10 CFR Part 50 includes a require- ment that measures be provided for verifying or checking the adequacy of design by design reviews, by the use of alternative or simplified calculational methods, or by the performance of a suitable testing program.
W sets of sufficient capacity and margin to imple- sive steps in a loading sequence.


Diesel-generator units have been widely used as the power source for the onsite electric power systems. This regulatory guide describes a method acceptable to the NRC
ments Genel su ignt Cap ity mrgin t7 rGenerally it has been industry practice to ment General Design Criterion 17.
staff for complying with the Commission's requirements that diesel-generator units intended for use as onsite power sources in nuclear power plants be selected with sufficient capacity and be qualified for this service. The Advisory Committee on Reactor Safeguards has been consulted concerning this guide and has concurred in the regulatory position.


==B. DISCUSSION==
specify a maximum voltage reduction of 15 B. Discussion percent when starting large motors from large capacity power systems and a 25 to 30 percent A diesel generator set selected for use as a voltage reduction when starting these motors standby power supply should have the capabil- from limited capacity power sources such as ity to (1) start and accelerate a number of, diesel generator sets. Large induction motors large motor loads in rapid succession, and be supplied with nominal voltage can achieve able to sustain the loss of any such load, and rated speed in less than 5 seconds when pow
A diesel-generator unit selected for use in an onsite electric power system should have the capability to (1) start and accelerate a number of large motor loads in rapid succession and be able to sustain the loss of all or any part of such loads and maintain voltage and frequency within acceptable limits and (2) supply power continuously to the Lines indicate substantive changes from Revision 1.
(2) supply continuously the sum of the loads ered from adequately sized diesel generator sets needed to be powered at any one time. This which are capable of restoring the voltage to guide provides an acceptable way of assuring
90 percent of nominal in about 1 second.


equipment needed to maintain the plant in a safe condition if an extended loss of offsite power occurs.
these objectives are met. The considerations Protection of the diesel generator set from involved in the need for the diesel generator to excessive overspeed, which can result from a start and achieve rated conditions in a short loss of load, is afforded by the provision of a period of time are evaluated on an individual diesel generator set trip, usually set at 115 per case basis.


IEEE Std 387-1977, "IEEE Standard Criteria for Diesel- Generator Units Applied as Standby Power Supplies for Nu- clear Power Generating Stations," 1 delineates principal design criteria and qualification testing requirements that, if followed, will help ensure that selected diesel-generator units meet their performance and reliability requirements.
cent of nominal speed.


IEEE Std 387-1977 was developed by Working Group 4.2C
A knowledge of the characteristics of each A problem arises in assessing whether the load is essential in establishing the bases for goal of continuously supplying the sum of the the selection of a diesel generator set that is needed loads is achieved with sufficient capacity able to accelerate large loads in rapid succes- and margin, because of the various interpreta sion. The majority of the emergency loads are tions of load ratings quoted by diesel generator large induction motors. This type of motor suppliers. The load ratings represent the loads draws, at full voltage, a starting current five at which the set can operate continuously with to ten times its rated load current. The sudden, a high availability, if various specified mainte
of the Nuclear Power Engineering Committee (NPEC) of the Institute of Electrical and Electronics Engineers, Inc.
9.1


(IEEE), approved by NPEC, and subsequently approved by the IEEE Standards Board on September 9, 197
nance programs are followed.


===6. IEEE Std===
The nominal rating, used as a datum for the overload rat ings, has been termed variously the "continu ous," "guaranteed," or "long term" rating. The definition used throughout this guide for "con tinuous rating" is "that load for which the sup plier guarantees continuous operation at a high availability (expected to be about 95%) with an annual maintenance interval". The over load ratings are similarly defined except that the specified maintenance intervals are shorter.
387-1977 is supplementary to IEEE Std 308-1974, "IEEE
Standard Criteria for Class 1E Power Systems and Nuclear Power Generating Stations,"l and specifically amplifies paragraph 5.2.4, "Standby Power Supplies," of that docu- ment with respect to the application of diesel-generator units. IEEE Std 308-1974 is endorsed, with certain excep- tions, by Regulatory Guide 1.32, "Criteria for Safety-Related Electric Power Systems for Nuclear Power Plants."
A knowledge of the characteristics of each load is essential in establishing the bases for the selection of a diesel-generator unit that is able to accept large loads in rapid succession. The majority of the emergency loads are large induction motors. This type of motor draws, at full voltage, a starting current five to eight times its rated load I
current. The sudden large increases in current drawn from the diesel generator resulting from the startup of induction- motors can result in substantial voltage reductions. The lower voltage could prevent a motor from starting, i.e.,
accelerating its load to rated speed in the required time, or cause a running motor to coast down or stall. Other loads might be lost if their contactors drop out. Recovery from the transient caused by starting large motors or from the loss of a large load could cause diesel engine overspeed which, if excessive, might result in a trip of the engine.


tCopies may be obtained from the Institute of Electrical and Electronics Engineers, Inc., United Engineering Center, 345 East
For example, the following are the load ratings of a typical diesel generator set:
47th Street, New York, New York 10017.
Ratings Continuous 2500 kW
Overload
2850 kW
2950 kW
3050 kW
Maintenance Interval Annual (8760 hr)
2000 hr
7 day
30 min If the power output is increased into the over load ratings, wearout is accelerated and the maintenance interval needed to assure high reliability is reduced. This discussion assumes that the diesel generator set is utilized solely as a standby power supply and that it does not serve a secondary function such as power gen eration for peak demand periods of a transmis sion network. The secondary functions, since they would affect wearout and availability of the diesel generator set, will be evaluated on an individual case basis. If found acceptable, the total amount of operation between mainte nance intervals will be limited by the technical specifications. This guide covers diesel gen erator sets used solely as a standby power sup ply which is the design most widely adopted.


USNRC REGULATORY GUIDES
The tabulation illustrates the sensitivity of the deterioration rate to increases in load above the continuous rating. For example, if the design basis loading were that corresponding to the 2000-hour rating, an error of only 8 per cent in estimating the loads could result in operation at the 30-minute rating. Although operation at the 30-minute rating would not be expected to stall the engine, such operation could lead to the danger of early failure.
Regulatory Guides are issued to describe and make available to the public methods acceptable to the NRC staff of implementing specific parts of the Commission's regulations, to delineate tech- niques used by the staff in evaluating specific problems or postu- lated accidents, or to provide guidance to applicants. Regulatory Guides are not substitutes for regulations, and compliance with them is not required. Methods and solutions different from those set out in the guides will be acceptable if they provide a basis for the findings requisite to the issuance or continuance of a permit or license by the Commission.


Comments and suggestions for improvements in these guides are encouraged at all times, and guides will be revised, as appropriate, to accommodate comments and to reflect new information or experience. This guide was revised as a result of substantive com- ments received from the public and additional staff review.
The uncertainties inherent in estimates of safety loads at the construction permit stage of design are of such magnitude that it is pru dent to provide a substantial margin in the selection of the diesel generator set load capa bility. This margin can be provided by esti- mating the loads conservatively and by select ing the continuous rating of the diesel genera tor set so that it exceeds the sum of the loads needed at any one time. A more accurate esti mate of safety loads is possible during the operating license stage of review due to the completion of the detailed designs and the availability of preoperational test data. This permits the consideration of a somewhat less conservative approach, such as operation with safety loads within the 2000 hour overload rating of the diesel generator set. A conserva tive estimate of safety loads based on design or measurements taken during preoperational testing of engineered safety features does not, however, represent with certainty the actual loads experienced under accident conditions.


Comments should be sent to the Secretary of the Commission, U.S. Nuclear Regulatory Commission, Washington, D.C. 20555, Attention: Docketing and Service Branch.
Therefore, an adequate margin is still essential.


The guides are issued in the following ten broad divisions:
C. Regulatory Position
1. At a time when the characteristics of loads are not accurately known, such as during the construction permit stage of design, each diesel generator set on a standby (onsite) power supply should be selected to have a continuous load rating equal to or greater than the sum of the conservatively estimated loads needed to be powered at any one time. In the absence of fully substan tiated performance characteristics for mechanical equipment such as pumps, the electric motor drive ratings should be calculated using conservative esti mates of these characteristics. (For example, pump run-out conditions and motor efficiencies of 90% or less.)
2. At the operating license stage of re view, the predicted loads should not exceed the smaller of the 2000-hour rating, or 90 percent of the 30-minute rating of the set.


====i. Power Reactors ====
3. During preoperational testing, the pre dicted loads should be verified by tests.


===6. Products===
4. Each diesel generator set should be ca pable of starting and accelerating to rated speed, in the required sequence, all the needed engineered safety fea ture and emergency shutdown loads. At no time during the loading sequence should the frequency and voltage de-
2. Research and Test Reactors
9.2


===7. Transportation===
crease to less than 95 percent of nomi nal and 75 percent of nominal, respec tively. During recovery from transients caused by step load increases or result ing from the disconnection of the larg est single load, the speed of the diesel generator set should not exceed 75 per cent of the difference between nominal speed and the overspeed trip set point or 115 percent of nominal, whichever is lower. Voltage should be restored to within 10 percent of nominal and fre quency should be restored to within 2 percent of nominal in less than 40 per cent of each load sequence time inter val.
3. Fuels and Materials Facilities


===8. Occupational Health===
5. The suitability of each diesel generator set of the standby power supply should be confirmed by prototype qualification test data and preoperational tests.
4. Environmental and Siting
9. Antitrust and Financial Review
5. Materials and Plant Protection 1


===0. General===
9.3
.Copies of issued guides may be purchased at the current Government Printing Office price. A subscription service for future guides in spe- cific divisions is available through the Government Printing Office.
/}}
 
Information on the subscription service and current GPO prices may be obtained by writing the U.S. Nuclear Regulatory Commission, Washington, D.C. 20555, Attention: Publications Sales Manager.
 
These same consequences can also result from the cumu- lative.effect of a sequence of more moderate transients if, the system is not permitted to recover sufficiently between successive steps in a loading sequence.
 
Generally it has been industry practice to specify a maximum voltage reduction of 10 to 15 percent when starting large motors from large-capacity power systems and a voltage reduction of 20 to 30 percent when starting these motors from limited-capacity power sources such as diesel- generator units. Large induction motors can achieve rated speed in less than 5 seconds when powered from adequately sized diesel-generator units that are capable of restoring the voltage to 90 percent of nominal in about 1 second.
 
Protection of the diesel-generator unit from excessive overspeed, which can result from a loss of load, is afforded by the immediate operation of a diesel-generator unit trip, usually set at 115 percent of nominal speed. In addition, the generator differential trip must operate immediately in order to prevent substantial damage to the generator. There are other protective trips provided to protect the diesel- generator units from possible damage or degradation.
 
However, these trips could interfere with the successful functioning of the unit when it is most needed, i.e., during accident conditions. Experience has shown that there have been numerous occasions when these trips have needlessly shut down diesel-generator units because of spurious operation of a trip circuit. Consequently, it is important that measures be taken to ensure that spurious actuation of these other protective trips does not prevent the diesel- generator unit from performing its function.
 
The uncertainties inherent in estimates of safety loads at the construction permit stage of design are sometimes of such magnitude that it is prudent to provide a substantial margin in selecting the load capabilities of the diesel-generator unit.
 
This margin can be provided by estimating the loads conser- vatively and selecting the continuous rating of the diesel- generator unit so that it exceeds the sum of the loads needed at any one time. A more accurate estimate of safety loads is possible during the operating license stage of review because detailed designs have been completed and preoperational test data are available. This permits the consideration of a somewhat less conservative approach, such as operation with safety loads within the short-time rating of the diesel- generator unit.
 
==C. REGULATORY POSITION==
Conformance with the requirements of IEEE Std 387-1977,
"IEEE Standard Criteria for Diesel-Generator Units Applied as Standby Power Supplies for Nuclear Power Generating Stations," dated June 17, 1977, is acceptable for meeting the requirements of the principal design criteria and qualifica- tion testing of diesel-generator units used as onsite electric power systems for nuclear power plants subject to the following:
1. When the characteristics of loads are not accurately known, such as during the construction permit stage of design, each diesel-generator unit of an onsite power supply system should be selected to have a continuous load rating (as defined in Section 3.7.1 of IEEE Std 387-1977) equal to or greater than the sum of the conservatively estimated loads needed to be powered by that unit at any one time.
 
In the absence of fully substantiated performance character- istics for mechanical equipment such as pumps, the electric motor drive ratings should be calculated using conservative estimates of these characteristics, e.g., pump runout condi- tions and motor efficiencies of 90 percent or less and power factors of 85 percent or less.
 
2. At the operating license stage of review, the predicted loads should not exceed the short-time rating (as defined in Section 3.7.2 of IEEE Std 387-1977) of the diesel-generator unit.
 
3. In Section 5.1.1, "General," of IEEE Std 387-1977, the I
requirements of IEEE Std 308-1974 should be used subject to the regulatory position of Regulatory Guide 1.32.
 
4. Section 5.1.2, "Mechanical and Electrical Capabilities,"
of IEEE Std 387-1977 pertains, in part, to the starting and load-accepting capabilities of the diesel-generator unit. In conjunction with Section 5.1.2, each diesel-generator unit should be capable of starting and accelerating to rated speed, in the required sequence, all the needed engineered safety feature and emergency shutdown loads. The diesel- generator unit design should be such that at no time during the loading sequence should the frequency and voltage decrease to less than 95 percent of nominal and 75 percent of nominal, respectively. (A larger decrease in voltage and frequency may be justified for a diesel-generator unit that carries only one large connected load.) Frequency should be restored to within 2 percent of nominal, and voltage should be restored to within 10 percent of nominal within
60 percent of each load-sequence time interval. (A greater percentage of the time interval may be used if it can be justified by analysis. However, the load-sequence time interval should include sufficient margin to account for the accuracy and repeatability of the load-sequence timer.)
During recovery from transients caused by step load increases or resulting from the disconnection of the largest single load, the speed of the diesel-generator unit should not exceed the nominal speed plus 75 percent of the difference between nominal speed and the overspeed trip setpoint or 115 percent of nominal, whichever is lower. Further, the transient following the complete loss of load should not cause the speed of the unit to attain the overspeed trip setpoint.
 
5. In Section 5.4, "Qualification," of IEEE Std 387-1977, the qualification testing requirements of IEEE Std 323-1974,
"IEEE Standard for Qualifying Class IE Equipment for Nuclear Power Generating Stations,"'
should be used subject to the regulatory position of Regulatory Guide 1.89,
"Qualification of Class IE Equipment for Nuclear Power Plants."
6. Section 5.5, "Design and Application Considerations,"
of IEEE Std 387-1977 pertains to design features for con- I
sideration in diesel-generator unit design. In conjunction with Section 5.5, diesel-generator units should be designed
1.9-2
 
to be testable during operation of the nuclear power plant as well as while the plant is shut down, The design should include provisions so that the testing of the units will simulate the parameters of operation (outlined in Regula- tory Guide 1.108, "Periodic Testing of Diesel-Generator Units Used as Onsite Electric Power Systems at Nuclear Power Plants") that would be expected if actual demand were to be placed on the system.
 
Testability should be considered in the selection and location of instrumentation sensors and critical components (e.g.,
governor, starting system components), and the overall design should include status indication and alarm features. Instrumentation sensors should be readily accessible and, where practicable, designed so that their inspection and calibration can be verified in place.
 
7. Section 5.6.2.2, "Automatic Control," of IEEE Std
387-1977 pertains to automatic startup requirements and their relationship to other operating modes. In conjunction with Section5.6.2.2, engine-overspeed and generator-differ- ential trips may be implemented by a single-channel trip. All other diesel-generator protective trips should be handled in one of two ways: Either, (1) a trip should be implemented with two or more independent measurements for each trip parameter with coincident logic provisions for trip actuation, or (2) a trip may be bypassed under accident conditions, provided the operator has sufficient time to react appro- priately to an abnormal diesel-generator unit condition. The design of the bypass circuitry should satisfy the requirements of IEEE Std 279-1971 at the diesel-generator system level and should include the capability for (1) testing the status and operability of the bypass circuits, (2) alarming in the control room abnormal values of all bypass parameters, and
(3) manually resetting of the trip bypass function. (Capability for automatic reset is not acceptable.)
8. Section 5.6.3.1, "Surveillance Systems," of IEEE Std
387-1977 pertains to status indication of diesel-generator unit conditions. In conjunction with Section 5.6.3.1, in order to facilitate trouble diagnosis, the surveillance system should indicate which of the diesel-generator protective trips is activated first.
 
9. In Section 6.3, "Type Qualification Testing Procedures and Methods," of IEEE Std 387-1977, the requirements of IEEE Std 344-1975, "Recommended Practices for Seismic Qualification of Class 1E Equipment for Nuclear Power Generating Stations," for seismic analysis or seismic testing by equipment manufacturers should be used subject to the regulatory position of Regulatory Guide 1.100, "Seismic Qualification of Electric Equipment for Nuclear Power Plants."
10. The option indicated by "may" in Section 6.3.2(5)(c)
of IEEE Std 387-1977 should be treated as a requirement.
 
11. Section 6.5, "Site Acceptance Testing," and Section 6.6,
"Periodic Testing," of IEEE Std 387-1977 should be supple- mented by Regulatory Guide 1.108.
 
12. Section 4, "Reference Standards," of IEEE Std 387-1977 lists additional applicable IEEE standards. The specific appli- cability or acceptability of these referenced standards has been or will be covered separately in other regulatory guides, where appropriate.
 
13. Section 6.3.2,
"Start and Load Acceptance Qualifi- cation," pertains to test requirements for diesel-generator unit qualification.
 
In conjunction with Section 6.3.2, fewer successful start-and-load tests and allowed failures than that specified-300 valid tests with no more than 3 failures-may be justified for a diesel-generator unit that carries only one large connected load tested under actual conditions, provided an equivalent reliability/confidence level is demonstrated.
 
14. In Section 6.3.1, "Load Capability Qualification," of IEEE Std 387-1977, the order of sequence of load tests described in parts (1) and (2) should be as follows: Load equal to the continuous rating should be applied for the time required to reach engine temperature equilibrium, at which time, the rated short-time load should be applied for a period of 2 hours. Immediately following the 2-hour short-time load test, load equal to the continuous rating should be applied for 22 hours. ,
 
==D. IMPLEMENTATION==
Except in those cases in which the applicant proposes an acceptable alternative method for complying with specified portions of the Commission's regulations, the method de- scribed herein will be used in the evaluation of applications for construction permits docketed after December 1979.
 
1.9-3
 
UNITED STATES
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D. C. 20555 OFFICIAL BUSINESS
PENALTY FOR PRIVATE USE, $300
if9'406002001
1 SN
US NRC REGION
I
OFFICE OF INSPECTION
& ENFORCE
R J BORES
631 PARK AVENUE
RE G. I
N I
KING OF PRUSSIA
PA
19406 POSTAGE AND FEES PAID
US.
 
NUCLEAR REGULATORY
COMMISSION
(}}


{{RG-Nav}}
{{RG-Nav}}

Latest revision as of 01:50, 17 January 2025

Selection of Diesel Generator Set Capacity for Standby Power Supplies
ML012410194
Person / Time
Issue date: 11/30/1978
From:
Office of Nuclear Regulatory Research
To:
References
RG-1.009
Download: ML012410194 (3)
v • d • e


"-

38/10/71 SAFETY GUIDE 9 SELECTION OF DIESEL GENERATOR SET CAPACITY FOR

STANDBY POWER SUPPLIES

A. Introduction large increases in current drawn from the die sel generator resulting from the startup of General Design Criterion 17 requires that induction motors can result in substantial volt the onsite (standby) power supply for a nuclear age reductions. The lower voltage could pre power plant be of sufficient capacity and capa- vent a motor from starting or cause a running bility to assure that (1) specified acceptable motor to coast down. Other loads also might be fuel design limits and design conditions of the lost if their contactors drop out. Recovery reactor coolant pressure boundary are not ex- from the transient caused by starting large ceeded as a result of anticipated operational motors or from the loss of a large load could occurrences and (2) the core is cooled and con- cause diesel engine overspeed which, if exces tainment integrity and other vital functions sive, might result in a trip of the machine.

are maintained in the event of postulated acci- These same consequences also can result from dents. Diesel generator sets have been widely the cumulative effect of a sequence of more used as the power source for the standby power moderate transients if the system is not per supplies. This safety guide describes an accept- mitted to recover sufficiently between succes able basis for the selection of diesel generator mire tecover suent e.

W sets of sufficient capacity and margin to imple- sive steps in a loading sequence.

ments Genel su ignt Cap ity mrgin t7 rGenerally it has been industry practice to ment General Design Criterion 17.

specify a maximum voltage reduction of 15 B. Discussion percent when starting large motors from large capacity power systems and a 25 to 30 percent A diesel generator set selected for use as a voltage reduction when starting these motors standby power supply should have the capabil- from limited capacity power sources such as ity to (1) start and accelerate a number of, diesel generator sets. Large induction motors large motor loads in rapid succession, and be supplied with nominal voltage can achieve able to sustain the loss of any such load, and rated speed in less than 5 seconds when pow

(2) supply continuously the sum of the loads ered from adequately sized diesel generator sets needed to be powered at any one time. This which are capable of restoring the voltage to guide provides an acceptable way of assuring

90 percent of nominal in about 1 second.

these objectives are met. The considerations Protection of the diesel generator set from involved in the need for the diesel generator to excessive overspeed, which can result from a start and achieve rated conditions in a short loss of load, is afforded by the provision of a period of time are evaluated on an individual diesel generator set trip, usually set at 115 per case basis.

cent of nominal speed.

A knowledge of the characteristics of each A problem arises in assessing whether the load is essential in establishing the bases for goal of continuously supplying the sum of the the selection of a diesel generator set that is needed loads is achieved with sufficient capacity able to accelerate large loads in rapid succes- and margin, because of the various interpreta sion. The majority of the emergency loads are tions of load ratings quoted by diesel generator large induction motors. This type of motor suppliers. The load ratings represent the loads draws, at full voltage, a starting current five at which the set can operate continuously with to ten times its rated load current. The sudden, a high availability, if various specified mainte

9.1

nance programs are followed.

The nominal rating, used as a datum for the overload rat ings, has been termed variously the "continu ous," "guaranteed," or "long term" rating. The definition used throughout this guide for "con tinuous rating" is "that load for which the sup plier guarantees continuous operation at a high availability (expected to be about 95%) with an annual maintenance interval". The over load ratings are similarly defined except that the specified maintenance intervals are shorter.

For example, the following are the load ratings of a typical diesel generator set:

Ratings Continuous 2500 kW

Overload

2850 kW

2950 kW

3050 kW

Maintenance Interval Annual (8760 hr)

2000 hr

7 day

30 min If the power output is increased into the over load ratings, wearout is accelerated and the maintenance interval needed to assure high reliability is reduced. This discussion assumes that the diesel generator set is utilized solely as a standby power supply and that it does not serve a secondary function such as power gen eration for peak demand periods of a transmis sion network. The secondary functions, since they would affect wearout and availability of the diesel generator set, will be evaluated on an individual case basis. If found acceptable, the total amount of operation between mainte nance intervals will be limited by the technical specifications. This guide covers diesel gen erator sets used solely as a standby power sup ply which is the design most widely adopted.

The tabulation illustrates the sensitivity of the deterioration rate to increases in load above the continuous rating. For example, if the design basis loading were that corresponding to the 2000-hour rating, an error of only 8 per cent in estimating the loads could result in operation at the 30-minute rating. Although operation at the 30-minute rating would not be expected to stall the engine, such operation could lead to the danger of early failure.

The uncertainties inherent in estimates of safety loads at the construction permit stage of design are of such magnitude that it is pru dent to provide a substantial margin in the selection of the diesel generator set load capa bility. This margin can be provided by esti- mating the loads conservatively and by select ing the continuous rating of the diesel genera tor set so that it exceeds the sum of the loads needed at any one time. A more accurate esti mate of safety loads is possible during the operating license stage of review due to the completion of the detailed designs and the availability of preoperational test data. This permits the consideration of a somewhat less conservative approach, such as operation with safety loads within the 2000 hour0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> overload rating of the diesel generator set. A conserva tive estimate of safety loads based on design or measurements taken during preoperational testing of engineered safety features does not, however, represent with certainty the actual loads experienced under accident conditions.

Therefore, an adequate margin is still essential.

C. Regulatory Position

1. At a time when the characteristics of loads are not accurately known, such as during the construction permit stage of design, each diesel generator set on a standby (onsite) power supply should be selected to have a continuous load rating equal to or greater than the sum of the conservatively estimated loads needed to be powered at any one time. In the absence of fully substan tiated performance characteristics for mechanical equipment such as pumps, the electric motor drive ratings should be calculated using conservative esti mates of these characteristics. (For example, pump run-out conditions and motor efficiencies of 90% or less.)

2. At the operating license stage of re view, the predicted loads should not exceed the smaller of the 2000-hour rating, or 90 percent of the 30-minute rating of the set.

3. During preoperational testing, the pre dicted loads should be verified by tests.

4. Each diesel generator set should be ca pable of starting and accelerating to rated speed, in the required sequence, all the needed engineered safety fea ture and emergency shutdown loads. At no time during the loading sequence should the frequency and voltage de-

9.2

crease to less than 95 percent of nomi nal and 75 percent of nominal, respec tively. During recovery from transients caused by step load increases or result ing from the disconnection of the larg est single load, the speed of the diesel generator set should not exceed 75 per cent of the difference between nominal speed and the overspeed trip set point or 115 percent of nominal, whichever is lower. Voltage should be restored to within 10 percent of nominal and fre quency should be restored to within 2 percent of nominal in less than 40 per cent of each load sequence time inter val.

5. The suitability of each diesel generator set of the standby power supply should be confirmed by prototype qualification test data and preoperational tests.

9.3

/


Retrieved from "https://kanterella.com/w/index.php?title=Regulatory_Guide_1.9&oldid=5445662"