MIL-STD-705C.pdf

MIL-STD-705C

24 April 1989

SUPERSEDING

MIL-STD-705B

26 June 1972

MILITARY STANDARD

GENERATOR SETS, ENGINE DRIVEN

METHODS OF TESTS AND INSTRUCTIONS

AMSC N/A FSC 6115

DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.

DEPATMENT OF DEFENSE

Washington, DC 20301

Generator Sets, Engine-Driven, Methods of Tests and Instructions

1. This Military Standard is approved for use by all Departments and Agencies of the Department of Defense.

2. Beneficial comments (recmmendations, additions, deletions) and any pertinent data which may be of use in improving this document should be addressed to: USA Belvoir Research, Development, and Engineering Center, ATTN: STRBE–TSE, Fort Belvoir, VA 22060-5606 by using the self-addressed Standardization Document Improvement Propsal (DD Form 1426) appearing at the end of this document or by letter.

Beneficial comments (recommendations, additions, deletions) and any pertinent data which may be of use in improving this document should be addressed to: USA Belvoir Research, Development, and Engineering Center, ATTN: STRBE–TSE, Fort Belvoir, VA 22060-5606 by using the self-addressed Standardization Document Improvement Proposal (DD Form 1426) appearing at the end of this document or by letter.

ii

FORWARD

This standard is intended to explain, establish and standardize specific methods for measurements associated with the evaluation of electric generators, generator sets and related components. The intended use of this standard is to determine compliance with characteristics represented by procurement documents. In no case is failure criteria establish within this document. The specific methods are included herein, while the terminology, instrumentation, general methods of measurement, and informative electrical technology are presented in MIL-HDBK-705, Generator Sets, Electrical Measurements and Instrumentation.

This standard is closely allied with MIL-HDBK-705 and references from one to the other are freely used, particularly from this document to the handbook.

Specification writers and equipment inspectors will find the need for both the standard and handbook when working on electric generator equipment. Due to the complexity of the specified requirements needed in procurement documents covering engine driven electric generators and other similar types of electric machinery, the proper use of this standard through referencing the applicable specific test method should greatly simplify the preparation of specifications and help to expedite the purchase and acceptance of the subject equipment. The procurement document requirements paragraph, included as the final paragraph of each test method, gives an indication of the data required to be included in the procurement documents.

iii

CONTENTS

1.

1.1 1.2 1.2.1 1.2.2 1.3 2.

3.

4.

5.

6.

MIL-STD-705C

Page Scope Coverage Numbering system Method numbers Decimal system Method of reference

REFERENCED DOCUMENTS

SPECIFIC TEST METHODS 300–THR0UGH

700-SERIES

ALPHABETICAL INDEX

NUMERICAL INDEX

NOT APPLICABLE

iv

1. SCOPE

1.1 Coverage. This standard covers five series of specific test methods for testing and determining the characteristics of electric generators, generator sets, and associatd equipment. This standard establishes methods of test for determining characteristics desired by the Military Departments to insure that enerators and generaelectric g tor sets comply with Military requirements. Except as indicated in the applicable procurment documents, the test methods now appearing in the various joint-service specifications for testing electric generators and electric generator sets will be superseded by this standard. This standard establishes uniform test methods for the Military services, uniform test equipment and facilities, and uniform procdures for setting up and conducting the various tests. These methods provide for conservation of manpower, materials, equipment, and facilities. This standard does not establish limiting values for the results of the tests nor does it specify the tests required for any specific electric generator or generator set.

1.2 Numbering system. The methods are designated by numbers assigned in accordance with the following system.

1.2.1 Method numbers. The methods included in this standard are numbered in the 300-, 400-, 500-, 600-, and 700-series. (The series are not significant except that the method number assigned is the same as that formerly used in the Uncoordinated document MIL-G-10228 which has been in general use as a reference document.)

1.2.2 Decimal System. The decimal system is used to list similar or associated methods in numerical sequence and to provide means for readily identifying main and subparagraphs for purpose of reference.

1.3 Method of reference. Methods of test contained in this standard shall be referenced, when applicable, in the individual procur ts by specifyingement documen this standard and the method number. Equipment specifications will give specific requirements for test and limiting values.

2. REFERENCED DOCUMENTS

2.1 Government documents.

2.1.1 Specifications, standards, and handbooks. The following specifcations, standards, and handbooks form a part of this standard to the extent specified herein. Unless otherwise specified, the issues of these documents shall be those listed in the issue of the Department of Defense Index of Specifications and Standards (DODISS) and supplement thereto, cited in the solicitation.

MIL-HDBK-705 - Generator Sets, Electrical, Measurements, and Instrumentation

(Copies of specifications, standards, handbooks, drawings, publications, and other Government documents required by contractors in connection with specific acquisition functions should be obtained from the contracting activity or as directed by the contracting officer.)

2.1.2 Other Government documents and pub1ications. The following Government document(s), and publication(s) form a part of this standard to the extent specified herein. Unless otherwise specified, the issues shall be those in effect on the date of the solicitation.

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

Standard Atmosphere Tables and Data

(Applications for copies should be addressed to the Superintendent of Documents, Government Printing Off ice, Washington, DC 20402.)

2.2 Other publications. The following document(s) fores a part of this standard to the extent specified herein. Unless otherwise specified, the issues ocuments which are DoD adopted shall be those listed in the issue of theof the d DODISS specified in the solicitation. Unless otherwise specified, the issues of documents not listed in the DODISS shall be the issue of the non-Government documents which are current on the date of the solicitation.

AMERICAN NATIONAL STANDARDS INSTITUTE (ANSI)

C50 - Rotating Electrical Machinery (Included as a general reference) 40 - Sound Level Meters

(Application for copies should be addressed to the American National Standards Institute, 1430 Broadway, New York, NY 10018.)

2.3 Textbooks. The following textbooks are listed for information and are not to be considered as a part of this standard:

Electrical Engineering Laboratory Experiments, Ricker and Tucker, 4th Ed., McGraw-Hill Book Co.

Electrical Measurement, Harris, 1st Ed., John Wiley and Sons.

Electrical Engineers’ Handbook, Pender and Del Mar, Vol. 1, 4th Ed., John Wiley and Sons.

Standard Handbook for Electrical Engineers, Fink and Carroll, 10th Ed. , McGraw-Hill Book Co.

Chamber’s Technical Dictionary, Tiveney and Hughes, Rev. Ed., The MacMillan Co.

(Non-Government standards and other publications are normally available from the organizations which prepare or which distribute the documents. These documents also may be available in or through libraries or other informational services.)

2.4 Order of precedence. In the event of a conflict between the text of this standard and the references cited herein, (except for associated detail Specifications, specification sheets or MS standards),the text of this specification shall take Precedence. Nothing in this standard, however, shall be applicable laws and regulations unless a specific exemption has been obtained.

Figure 301.1-I. Typical test record for insulation resistance.

METHOD 302.1b

HIGH POTENTIAL TEST

CAUTION: OBSERVE SAFETY REGULATIONS. The voltages used in this method are dangerous to human life. Contact with the leads or the windings under test may cause severe, and possibly fatal, shock. Arrange the high voltage leads so that they are not in a position to be accidentally touched. Keep clear of all energized parts. Always reduce the test voltage to zero and ground the winding under test before making any mechanical or electrical adjustments on the equipment. When grounding windings which have been tested, always connect the connection wire to ground first, and then to the winding. Never perform this test without at least one other person assisting. The generator frame shall be securely grounded to the building ground or earth ground.

302.1.1 General. The generator insulation materials must be capable of withstanding, without damage, voltages higher than rated for definite periods of time to preclude damage during transient loading and short circuit conditions.

This test should be performed after the equipment is completely assembled so that damage to the insulation which might have occurred during manufacture and assembly will be detected.

302.1.2 Apparatus. A variable alternating current, high voltage, current-limited power source shall be required.

302.1.3 Procedure.

302.1.3.1 Preparation for test.

c.

a.

b.

d.

e.

Adequately ground the high potential apparatus to a solid electrical ground in accordance with instructions accompanying the apparatus. Also, enerator set and all windings of theconnect the main frame of the g generator, not under test, to the same ground.

Unless rectifiers and semiconductors are specifically designed to withstand the specified test voltage they should be removed or disconnected from the circuit along with any radio suppression capacitors prior to conducting the tests.

Raise, or remove, brushes from commutator and slip rings, if applicable.

Isolate the generator power output windings, the generator field windings, and the exciter armature and field windings if a part of the set. This is accomplished by disconnecting the various windings from the associated control circuits or other connections. Static excitation systems feeding the field excitation from the ac generator shall be tested with all rectifiers and capacitors disconnectd, unless such rectifiers and capacitors are designed to withstand the specified test voltage.

Connect the high voltage lead from the test apparatus to the winding or circuit under test. All other windings and circuits must be securely connected to ground.

Method 302.1b

302.1.3.2 Test.

a. Turn on the test apparatus in accordance instructions, after making sure that the not be greater than 600 volts.

with the manufacturer’s initially aplied voltage will

b. The test voltage shall then be raised approximately uniformly to the required value. This increase shall be accomplished in not less than 10 seconds nor more than 30 seconds. Unless otherwise specified in the rocurement dP ocument, the maximum test voltage for power output windings shall be equal to 1,000 volts plus twice the highest rated voltage of the generator. The test voltage for field windings shall be equal to 10 times the exciter ceiling voltage but in no case less than 1,500 volts nor more than 3,500 volts. Record on the data sheet the maximum voltage reached during this method (see figure 302.1-I).

c. Apply the maximum voltage for 1 minute. Record the voltage applied, including any breakdown in insulation observed.

d. After 1 minute the voltage shall be reduced gradually to the voltage initially applied. This reduction shall not be accomplished in less than 5 seconds.

e. Turn off the test apparatus.

CAUTION: Ground the high voltage lead of charge remains on the windings which have

f. Remove the high voltage lead from the test apparatus to make sure that no been under test.

the winding and proceed with the tests of the remaining circuits to be tested. Make sure that all the circuits not under test are securely grounded.

g. After test is completed, reconnect all circuits to original configuration.

302.1.4 Results. Compare the results with the procument document requirements.

302.1.5 Procment document requirements. The following items must be specified in the individual procurement document:

a. Test value of applied voltages, if different than those specified in 302.1.3.2.

b. Windings to be tested, other than those specified in 302.1.3.

c. Definition of insulation breakdown.

Method 302.1b

METHOD 301.1c

INSULATION RESISTANCE TEST

CAUTION: OBSERVE SAFETY REGULATIONS. The voltages used in this method are dangerous to human life. Contact with the leads or the windings under test may cause severe, and possibly fatal, shock. Arrange the high voltage leads so that they are not in a position to be accidentally touched. Keep clear of all energized parts. Always reduce the test voltage to zero and ground the winding under test before making any mechanical or electrical adjustments on the equipment. When grounding windings which have been tested, always connect the connection wire to ground first, and then to the winding. Never perform this test without at least one other person assisting. The generator frame shall be securely grounded to the building ground or earth ground.

301.1.1 General. To assure that the current leakage is kept to a minimum, the insulation resistance must be as high as practicable.

301.1.2 Apparatus Instrumentation shall be as described and illustrated in MIL-HDBK-705, method 105.1, paragraph 105.1.5.2.

301.1.3 PROCEDURE.

301.1.3.1 Preparation for test.

a. Disconnect the circuit under test from all other circuits. Each circuit enerator pof each g resents an individual problem and no specific instructions can be given here.

b. Disconnect all radio suppression capacitors from the circuit to be tested.

c. In the case where several windings constitute a circuit, all leads of the circuit may be connected together and the resistance measured between this connection and ground.

d. Ground all circuits except the one being tested.

e. When testing a stator element, connect the ground lead from the test enerator frame (ground).apparatus to the g When testing elements that rotate, connect the test apparatus ground lead to the shaft.

f. Connect the other lead to the circuit under test.

301.1.3.2 Test.

a. Operate the test apparatus in accordance with the manufacturer’s instructions.

b. Record the insulation resistance after one minute of operation (see figure 301.1-1). Also record ambient temperature.

c. Turn off test apparatus. Ground the winding under test and the test lead before disconnecting apparatus leads or touching circuit under test.

d. Remove the leads to the circuit under test and repeat the procedure for all other circuits to be tested.

e. After all circuits are tested, reconnect all circuits to original configuration.

Method 301.1c

301.1.4 Results. Compare the results with the procurement document requirements.

301.1.5 specified

Procurement document requirements. The following items must be in the individual procurement document.

a. Minimum allowable insulation resistance.

b. Circuits to be subjected to this method.

Method 301.1c

Custodians:

Army - ME Navy - YD Air Force - 80

Review activities:

Army - CE, TE Navy - AS

User activities:

Preparinq activity:

Army - ME

Project No. 6115-0213

Army - AT, ER Navy - MC Air Force - 11

Figure 302.1-I. Typical test record for high potential test.

METHOD 401.1b

WINDING RESISTANCE TEST

401.1.1 General. Winding resistance measurements are commonly used to determine temperature rises; to compare winding resistance with design data; to compare production models against first article models; and to detect defective windings.

401.1.2 Apparatus. Instrumentation for measuring winding resistances shall be as described and illustrate in MIL-HDBK-705, method 105.1.

401.1.3 Procedure.

401.1.3.1 Preparation for test.

a. Isolate the winding whose resistance is to be measured by disconnecting one end from all other circuits.

b. Winding resistance measurments shall be made by one of the following approved methods: Wheatstone bridge; Kelvin bridge; drop-in potential; or comparison. These methods are described in MIL-HDBK-705, method 105.1.

c. Connect the measuring apparatus across the winding in accordance with the apparatus manufacturer’s instructions. If the drop-in potential or comparison methods are employed, measure the voltage only on the portion of the circuit to be included in the resistance measurements. Since these measurements are used in comparing one reading against another, care should be taken to measure the voltage at the same location during each measurement of like windings.

d. Cold resistance measurements shall be made with the generator set at approximately the surrounding ambient temperature; that is, the measurements shall be taken after the generator set has been inoperative for a sufficient time (approximately 12 hours) to bring the major generator mass temperature to within 3 °C of the ambient temperature.

401.1.3.2 Test. Operate the test apparatus in accordance with the applicable method selected and record the resistance value for the winding(s) under test (see figure 401.1-I). The resistance values shall as a minimum be recorded to four significant digits.

When this test method is used for temperature change determination, speed in taking the measurements is essential (see MIL-HDBK-705, method 110.1). The ambient temperature at which the resistance readings are taken shall also be recorded.

401.1.4 Results. The corrected (see MIL-HDBK-705, method 221.1) values determined by these measurements shall be compared with p t orrocurement documen design requirements, or shall be used in other computations.

Method 401.1b

401.1.5 Procurement document requirements. The following items must be specified in the individual procurement document:

a. The minimum and maximum allowable resistance values for each component tested, if applicable.

b. The standard temperature to which these measurements are to be corrected, if applicable.

Method 401.1b

Figure 401-1-I. Typical test record for winding resistance test.

METHOD 410.1b

OPEN CIRCUIT SATURATION CURVE TEST

410.1.1 General. The open circuit saturation curve is used by design engineers in conjunction with the short circuit and zero power factor saturation curves to determine certain performance characteristics of the generator under various load conditions. It is used also in comparison with data obtained from tests on production models as a check to ascertain that the quality of the iron or the length of the air gap in the production generators has not been changed from that of the first article model.

410.1.2 Apparatus. Instrumentation for measureing terminal voltage, generator speed, exciter field voltage and current (generator field voltage and current, if applicable) shall be as described and illustrated in MIL-HDBK-705. In addition, a prime mover having a steady state speed regulation not greater than ±1 percent of rated speed and a separate, variable dc source for excitation shall be required. A voltmeter having an accuracy of ±0.5 percent of the reading or better shall be required for measuring the terminal voltage.

410.1.3 Procedure.

410.1.3.1 Preparation for test.

a. Mechanically connect the generator to the prime mover and provide the external excitation supply to the generator. Observe correct polarity when connecting the dc supply to field windings.

b. Connect the instrumentation as illustrate in MIL-HDBK-705, method 205.1 for the applicable voltage connection.

410.1.3.2 Test.

a. Start and operate the prime mover such that the generator is operating at rated speed, open-circuited and zero excitation. Read and record all instrumentation.

b. Increase the applied voltage to the field to increase the field current in steps from zero upward to give approximately 20, 40, 60, 80, 90, 95, 100, 105, 110, 120, and 130 percent of rated generator voltage (unless otherwise specified in the procurment document). Read and record all instrumentation at each step. All readings must be taken with rising field current and without interuption (see figure 410.1-I).

NOTE: Should it become necessary to decrease the excitation, the field current must be reduced to zero and then increased to the desired value.

c. When performing this test on three phase machines, readings should be taken of the terminal voltage (line-to-line) of all three phase to check phase balance. These readings should be made under constant conditions of excitation and speed, and with the same voltmeter.

Method 410.1b

410.1.4 Results. A curve of generator terminal voltage (vertical axis) versus exciter field current (and generator field current, if applicable) (horizontal axis) shall be plotted. If the knee of the curve is not well defined, repeat

410.1.3.2 taking additional readings as needed to better establish this portion of the curve. This curve is defined as the open circuit saturation curve (figure 410.1-II). Compare the results with the procurement document requirments.

410.1.5 Procurement document requirements. The following items must be specified in the individual procurement document.

a. Voltage connection(s) and frequency(ies) at which this method is to be performed.

b. Maximum value of no load exciter field current, if applicable.

c. Maximum value of no load generator field current, if applicable.

Method 410.1b

Figure 410.1-I. Typical test record for open circuit saturation curve test.

Figure 410.1-II: Family of saturation curves

METHOD 411.1b

SYNCHRONOUS IMPEDANCE CURVE TEST

(SHORT—CIRCUIT SATURATION CURVE)

411.1.1 General. Synchronous impedance curves assist in determining the performance of an alternating current generator during periods of short circuit.

This information is needed to properly design protective devices and to assure designers that the air gap, coils and steel meet requirements.

411.1.2 Apparatus. Instrumentation for measuring line current, field voltage and current and generator speed shall be as described and illustrated in MIL-HDBK-705. In addition, a prime mover capable of driving the generator at rated speed with the short-circuit applied and having a speed regulation not greater than ±1 percent of rated speed and a separate dc source for excitation shall be required. Instruments for measuring the field and short circuit currents shall have an accuracy of ± 0.5 percent of reading or better.

411.1.3 Procedure.

411.1.3.1 Preparation for test.

a. Medically connect the generator to the prime mover and connect the external excitation supply to the generator.

b. Connect the instrumentation as illustrated in MIL-HDBK-705. method 205.1, for the applicable voltage connection.

c. Apply the short-circuit to the generator terminals through the ammeters.

NOTE: The short-circuit leads shall be as short as possible to reduce heating effects.

411.1.3.2 Test.

a. Start and operate the prime mover such that the generator is operating at rated speed, short-circuited and zero excitation. Read and record all instrumentation.

b. Increase the field current until 100 percent of rated current exists in each phase. Read and record the current in all three phases to check current balance. If the current is not balanced within ±1 percent of each other, or within the tolerance specified in the procure t, thement documen cause of the unbalance shall be located and corrected before proceeding with the test.

c. After the phase balance is determined to be satisfactorily within tolerance, increase the field excitation until 150 percent of rated current is present in each phase.

CAUTION: Do not maintain overload current long enough to cause generator overheating.

Method 411.1b

d. Record all instrument readings.

e. Reduce the field excitation in steps to obtain 125, 100, 75, 50 and 25 percent of armature current in each phase. Read and record instrument indications at each step. All readings shall be taken without interuption.

411.1.4 Results. A curve of generator armature short-circuit current (vertical axis) versus generator or exciter field current (horizontal axis) shall be plotted.

This curve is defined as the synchronous impedance , or short-circuit saturation curve (figure 411.1-II). Compare the results with the requirements of the procurement document.

411.1.5 Procurement document requirements. The following item must be specified in the individual procurement documen t:

a. The voltage connection(s) and speed(s) at which this method is to be performed.

b. The allowable current variation, if other than as specified herein.

Method 411.1b

Figure 411.1-I. Typical test record for synchronous impedance curve test.

Figure 411.1-II - Family of saturation curves.

METHOD 412.1b

ZERO POWER FACTOR SATURATION CURVE TEST

412.1.1 General. The zero power factor saturation curve is used by design engineers in injunction with the short-circuit and open-circuit saturation curves to determine certain performance characteristics of the generator under various load conditions. The family of generator saturation curves can be used to approximate the generator field current for any load condition.

412.1.2 Apparatus. Instrumentation for measuring load renditions and generator field voltage and current shall be as described and illustrated in MIL-HDBK-705. In addition, a prime mover capable of maintaining constant rated speed of the generator under all load conditions of this method within ±1 percent and a source of dc power for generator excitation shall be required. Instruments for measuring the field current and terminal voltage shall have an accuracy of ± 0.5 percent, of reading or better. The power factor inter used shall be capable of indicating power factor to 0.3 lagging.

412.1.3 Procedure.

412.1.3.1 Preparation for test.

a. Mechanically connect the prime mover to the generator and provide the external excitation supply to the generator.

b. Connect the load and field instrumentation in accordance with the applicable figure of MIL-HDBK-705, method 205.1, for the voltage connection and frequency specified in the procurement document.

412.1.3.2 Test.

a.

b.

d.

e.

f.

c.

Start and operate the prime mover such that the generator is operating at rated speed with zero excitation. Adjust the low power factor load to minimum reactance.

NOTE: During all portions of this method the power factor of the load shall not exceed 0.40 and shall not be less than 0.30. Load current on polyphase generators shall be balanced.

Increase the field current until the generator is supplying rated load current.

Record all instrument readings.

Increase the load slightly, then increase the field current until the generator is again supplying rated load current. Adjust the excitation of the generator to approximately 20 percent rated voltage while maintaining the load current constant at the rated value.

Record all instrument readings.

Repeat steps d and e above to obtain at least seven equally spaced steps of terminal voltage up to and including 130 percent of rated voltage (unless otherwise specified in the procurement document). All readings shall be taken without interruption.

Method 412. 1b

412.1.4 Results. A curve of terminal voltage (vertical axis) versus generator or exciter field current (horizontal axis) shall be plotted. This curve is defined as the zero-power-factor saturation curve (figure 412.1-II). Compare the results with the requirements of the procurement document.

412.1.5 Procurement document requirements. The following items must be specified in the individual procurement document:

a. The voltage connection(s) and speed(s) at which this method is to be performed.

b. The limiting terminal voltage, if other than as specified herein.

Method 412.1b

Figure 412.1-I. Typical test record for zero power factor saturation curve test.

Figure 412.1-II - Family of saturation curves.

METHOD 413.1b

RATED LOAD CURRRENT SATURATION CURVE TEST

413.1.1 General. The rated load current saturation curve is used by design engineers as an aid in determining the field current requirements of the generator. The family of generator saturation curves can be used to approximate the generator field current for any load condition.

413.1.2 Apparatus. Instrumentation for measuring load conditions and field voltage and current shall be as described and illustrated in MIL-HDBK-705. In addition, a separate, variable dc source for generator excitation and a prime mover capable of maintaining the generator speed within ±1 percent of rated speed under all load conditions of this method shall be required. Instruments for measuring the terminal voltage and field current shall have an accuracy of ±0.5 percent of reading or better.

413.1.3 Procedure.

413.1.3.1 Preparation for test.

a. Mechanically connect the generator to the prime mover and provide the external excitation supply to the generator.

b. Connect the load and instrumentation to the generator in accordance with the applicable figure of MIL-HDBK-705, method 205.1, for the voltage connection and frequency specified in the procurement document.

413.1.3.2 Test - ac generators.

a. Start the prime mover and operate the generator at rated frequency, approximately 50 percent of rated voltage, rated load current and rated power factor (0.8 lagging if not otherwise specified).

NOTE: The load current of polyphase generators shall be balanced.

c.

b. After the conditions of step a above have been reached, record all instrument readings.

Reduce the field current to zero using the adjusment on the dc source.

d. Increase the field current in steps from zero upward while adjusting the load for rated generator output current and rated power factor to vary the terminal voltage to approximately 70, 80, 90, 95, 100, 105, 110, 120, and 130 percent of rated voltage (unless otherwise specified in the procurement document). All readings must be taken with a rising field current. Should it become necessary to decrease the excitation, the field current must be reduced to zero and then increased to the desired value.

Then increase the field current to obtain the desired output voltage. Read and record all instrument readings at each step. All readings shall be taken without interruption. Take sufficient additional steps to clearly define the curve (figure 413.l-I).

Method 413.1b

413.1.3.3 Test - dc generators.

a.

b.

c.

d.

Start the prime mover and operate the generator set at rated speed, approximately 20 percent of rated voltage and rated load current.

After the renditions of step a above have been reached, record all instrument readings.

Reduce the field current to zero using the rheostat on the separate dc source.

Increase the field current in steps to obtain 20, 40, 60, 80, 90, 95, 100, 105, 110, 120, and 130 percent of generator rated voltage (unless otherwise specified in the procurement document) while adjusting the load for rated generator output current. All readings must be taken with a rising field current. Should it become necessary to decrease the excitation, the field current must be reduced to zero and then increased to the desired value. Read and record all instrument readings at each step. All readings shall be taken without interruption.

413.1.4 Results. Plot a curve of terminal voltage versus generator or exciter field current (figure 413.1-II) from the data obtained. Compare the results with the procurement document requirements.

413.1.5 Procurement document requirements. The following items must be specified in the individual procurement document:

a. The voltage connection(s) and frequency(ies) at which this method is to be performed.

b. The maximum allowable generator or exciter field current.

c. The maximum terminal voltage, if other than as specified herein.

Method 413.1b

Figure 413.1-I. Typical test record for rated load current saturation curve test.

Figure 413.1-II - Family of saturation curves.

METHOD 414.1c

ROTAING EXCITER SATURATION CURVE TEST

(CONSTANT RESISTIVE LOAD)

414.1.1 General. The saturation curve for a rotating exciter aids the design engineer in determining the suitability of a particular exciter for use with a particular generator.

414.1.2 Apparatus. Instrumentation for measuring exciter output voltage, exciter field current and exciter speed shall be as described and illustrated in MIL-HDBK-705. In addition a prime mover capable of driving the exciter at rated speed with a speed regulation not greater than ±1 percent of rated speed, a separate variable dc source for excitation and a resistive load equivalent to the generator field resistance at 75 °C shall be required. Instruments for measuring the dc terminal voltage and exciter field current shall have an accuracy of ±0.5 percent of reading or better.

414.1.3 Procedure.

414.1.3.1 Preparation for test.

a. Connect the instrumentation in accordance with the applicable figure of MIL-HDBK-705, method 205.1.

b. Connect the resistive load to the output of the exciter. (Slip rings may be necessary if the generator is not so equipped.)

NOTE: In order to obtain zero exciter field current, it may be necessary to open the exciter field circuit. To prevent high voltage hazard to personnel, the exciter field current should be reduced to the minimum possible value before opening the field.

414.1.3.2 Test.

a. On exciters with brushes, check that the brush settings are positional in accordance with the manufacturer’s recommendation.

b. Start and operate the prime mover such that the exciter is operating at its rated speed. Adjust the exciter field current to obtain nominal exciter voltage. Operate the exciter under these conditions for a 30 minute period. Read and record all instrumentation initially and every 10 minutes thereafter.

c. Reduce the exciter field current to zero. Read and record all instrumentation (see figure 414.1-1).

d. Increase the exciter current in steps to obtain exciter terminal voltages of approximately 20, 40, 60, 80, 90, 95, 100, 105, 110, 120, and 130 percent of nominal exciter voltage. Read and record all instrumentation at each step. All readings shall be taken without interruption.

Method 414.1c

414.1.4 Results. Plot a curve of exciter terminal voltage versus exciter field current (figure 414.1-II), using the data obtained above. This curve shall be known as “the loaded exciter saturation curve”. Compare this curve with the requirements of the applicable generator or the procurement document.

414.1.5 Procurement document requirements. The following items must be specified in the individual procurement document:

a. The nominal exciter voltage.

b. Exciter rated speed.

c. Exciter ceiling voltage, if applicable.

d. Generator field resistance or current value.

Method 414.1c

Figure 414.1-I. Typical test record for rotating exciter saturation curve test.

FIGURE 414.1-II. SAMPLE LOADED EXCITER

SATURATION CURVE.

METHOD 415.0b

SUMMATION OF LOSSES TEST

415.0.1 General. The internal generator losses are inversely related to the efficiency. The efficiency of agenerator determines the capacity of the prime mover necessary for proper operation. The summation of losses test allows design engineers to investigate the problem of increasing the efficiency of a generator.

415.0.2 Apparatus. Instrumentation for measuring load conditions, field voltage and current, set temperatures and prime mover output power shall be as described and illustrate in MIL-HDBK-705. In addition, a prime mover (dynamotor or dc motor) shall be required. If a dc motor is used, a curve of power output (in kW) against input current at a constant input voltage shall be furnished (see figures 415.0-I and 415.0-V). If a calibrated dc rotor is used as the prime mover, a constant voltage power supply corresponding to the motor calibration curve shall be used. The dc motor, if used, shall have a horsepower rating of not less than 25 percent nor more than 50 percent of the generator kilowatt rating. A separate variable source of dc power for generator excitation shall be provided. A direct reading torque meter (connected between the prime mover and generator) may be utilized for calculating actual generator input power. Electrical instrumentation used for the following tests shall have an accuracy of ±0.5 percent of reading or better.

415.0.3 Procedure.

415.0.3.1 Preparation for test.

a. Mechanically connect the generator assembly, including its cooling fan to the prime mover and provide the external excitation supply to the generator.

b. Connect the load and field instrumentation in accordance with the applicable figure of MIL-HDBK-705, method 205.1, for the voltage connection and frequency specified in the procurement document.

c. As applicable, connect the instrumentation necessary to measure the output power of the prime mover. The instrumentation requirements of a dynamotor shall be connected in accordance with the manufacturer’s instructions; the instrumentation for a calibrated dc motor shall be connected to measure the motor input voltage and current and the field voltage and current similar to that shown in MIL-HDBK-705, method 205.1, figure 205.1.XLI and figure

205.1.XLII.

415.0.3.2 Test.

415.0.3.2.1 Bearinq friction and windage loss.

a. Raise the brushes, if applicable, so that they do not touch the slip rings or the commutator.

b. The friction and windage loss is the power input to the machine being tested, with zero excitation.

Method 415.0b

c. Start and operate the prime mover at rated generator speed until the bearing(s) reach constant temperature so the bearing friction becomes stable.

d. Record the data necessary to complete the output power of the prime mover (motor input power or dynamometer constant and scale reading).

e. Complete the prime mover output power in kW. This value represents the bearing friction and windage loss of the generator.

415.0.3.2.2 Brush friction loss.

a. Adjust the brush pressure on all generator brushes to the pressure recommended on the set or in the technical manual.

b. Start and operate the prime mover at rated generator speed until the bearing(s) reach constant temperature so that bearing friction becomes stable.

c. Record the data necessary to complete the output power of the prime mover (motor input power or dynamometer constant and scale reading).

d. Compute the prime mover output power in kW and subtract the prime mover output power found in 415.0.3.2.1e. This difference represents the brush friction loss.

415.0.3.2.3 Brush contact loss.

a.

b.

c.

d.

e.

f.

g.

Adjust the brush pressure on all generator brushes to the pressure recommended on the set or in the technical manual.

Start and operate the prime mover at rated generator speed until the bearing(s) reach constant temperature so that bearing friction becomes stable. For dc generators, apply a short circuit to the output terminals and adjust the excitation to obtain rated load current. For ac generators adjust the field current to its value at rated load.

With a low-range voltmeter (range of approximately 3 volts), read and record the voltage between the brush bracket holder and at least four equally spaced points along the commutator brush span (see figure

415.0-IX).

Repeat steps b and c above for all other load conditions specified in the procurement document.

For each load condition average the four voltage readings found for that load condition.

Compute the brush contact loss by multiplying twice the average voltage found in step e above by the load current under which the average was found.

For the summation of losses the brush contact loss shall be taken as the loss found with the generator operating at rated load multiplied by the number of pairs of brushes on the on the commutator or slip rings.

415.0.3.2.4 Open-circuit core loss (ac generator only).

a. Start and operate the prime mover at rated generator speed, without generator excitation, until the bearing(s) reach constant temperature and friction becomes stable. (Two-hour operation will be sufficient with no more than a 3 0C change in the average ambient temperature).

b.

c.

d.

e.

MIL-STD-705C

Using the external excitation supply raise the terminal voltage from zero to give approximately 20, 40, 60, 80, 90, 100, 105, 110, 120, and 130 percent of rated voltage.

Simultaneously read and record the generator field current and voltage, the generator terminal voltage and the data necessary to compute the output power of the prime mover for each step, including the zero step.

All readings shall be taken with a rising field current. Should it be necessary to reduce the excitation current it must be reduced to zero and then returned to the desired value (see figure 415.0-VI).

From the prime mover output power at each step subtract the bearing friction and windage loss and, if applicable, the brush friction loss to obtain the open circuit core loss for each field current value.

Plot a curve of generator open-circuit core loss versus terminal voltage (see figure 415.0-II). The value of open-circuit core loss at rated voltage shall be used in this summation of losses.

415.0.3.2.5 Open-circuit core loss (dc generators only).

a.

b.

c.

d.

e.

f.

g.

h.

Start and operate the prime mover at rated generator speed, without generator excitation, until the bearing(s) reach constant temperature and friction become stable. (Two-hour operation will be sufficient with not more than a 3 °C change in the average ambient temperature).

Using the external excitation supply, raise the terminal voltage from zero to its rated value.

Simultaneously read and record the field voltage and current, the generator terminal voltage and the prime mover output power in kW (see figure 415.0-VII).

Calculate the internal generator voltages corresponding to 25, 50, 75, and 100 percent of rated load by adding the armature circuit (armature, brushes, commutating field, and series field) voltage drops due to resistance at each of the above load renditions to the rated terminal voltage.

Using the external excitation supply raise the terminal voltage to obtain each of the values calculated in step d above.

Simultaneously read and record the generator field voltage and current, the generator terminal voltage and the prime mover output power in kW at each step.

From the prime mover output at each step subtract the bearing friction and windage loss and, if applicable, the brush friction loss to obtain the open circuit core loss for each terminal voltage step.

Plot a curve of generator open-circuit core loss versus generator terminal voltage (see figure 415.0-III). The value of open-circuit core loss which corresponds to the calculated internal voltage at rated load shall be used in this summation of losses.

415.0.3.2.6 Armature I2R Loss.

a. The armature I2R loss is defined as the product of the square of the armature current under any specified load and the resistance of the armature winding as measured in accordance with MIL-HDBK-705, method 105.1, corrected to 25 °C plus the stabilized temperature rise of the armature winding under the same load condition. The following formula for copper windings shall be used to determine the armature resistance:

Rc = Ro(234.5 + Tr)

234.5 + To

Where:

is the corrected resistance.

is the measured resistance.

is the temperature rise in Celsius degrees(C°).

is the temperature of the winding at the time Ro is measured in degrees Celsius(°C).

b. The armature I2R loss shall be calculated for rated load current in the armature winding(s) and used in this summation of losses. For a 3-phase machine the loss is the summation of the losses of the individual phase windings.

c. To determine the stabilized armature winding temperature rise perform method 680.1, Temperature Rise Test (Generator Only).

415.0.3.2.7 Field I2R loss.

a.

b.

c.

The field I2R loss is defined as the product of the square of the field current under any specified load rendition and the resistance of the field as measured in accordance with MIL-HDBK-705, method 105.1, corrected to 25 °C plus the stabilized temperature rise of the field winding under the same load condition. Use the formula given in 415.0.3.2.6a above to determine the corrected field resistance.

The field I2R loss shall be calculated for rated load field current in the field winding and used in the summation.

To determine the Stabilized field winding temperature rise perform method 680.1, Temperature Rise Test (Generator Only).

415.0.3.2.8 Stray load loss.

a. Short circuit the generator through the load current transformers (or shunt). A wye connected geenerator shall be shorted line-to-neutral (all phases) while a delta connected generator shall be shorted line-to-line (all phases).

b. Start and operate the prime mover at rated generator speed. Adjust the external excitation supply for approximately 125 percent of rated current (If the phase currents of a mlti-phase machine are not approximately balanced, shut down the prime mover and the excitation supply and correct the trouble before proceeding). This test shall be performed with decreasing field current. (During this test, should the field current accidentally be increased , it shall be returned to the value which will cause approximately 125 percent of rated generator current, then reduced to the desired value.)

c. Decrease the excitation to obtain approximately 100, 75, 50, and 25 percent of rated current in the short-circuit ammeters. At each of these steps, including the 125 percent step, read and record the generator output current, the speed of the generator and the prime mover output power in kW (figure 415.0-VIII).

d. From the recorded values of prime mover output power subtract the bearing friction and windage loss, the brush friction loss, brush contact loss, and the armature I2R loss (which must be calculated for each current step-see 415.0.3.2.6), to obtain the stray load loss.

e. Plot a curve of stray load loss versus armature current (figure

415.0-IV).

f. The value of stray load loss at the armature current corresponding to rated armature current shall be used in the summation of losses.

415.0.3.2.9 Exciter loss. Connect a “dummy” load consisting of a resistor equal to the field resistance of the generator as defined in 415.0.3.2.7.

415.0.3.2.9.1 Rotating exciter directly coupled to the generator

a. Start and operate the prime mover at rated generator speed, without generator excitation and with slip ring or commutator brushes raised.

Adjust the exciter output voltage and current to the values required to excite the generator at rated load at rated voltage and rated speed.

b. Read and record the prime mover output power in kW, and the output current and voltage of the exciter.

c. From the prime mover output power subtracted the field I2R loss and the bearing friction and windage loss. This value is the exciter loss in kilowatts.

415.0.3.2.9.2 Rotating exciter separately driven.

a. Mechanically connect the exciter to a calibrated motor dynamotor (prime mover).

b. Start and operate the prime mover at the exciter’s rated speed. Adjust the exciter output voltage and current to the values required to excite the genentor at rated load at rated voltage and rated speed.

c. Read and record the prime mover output power in kW and the output voltage and current of the exciter.

d. From the prime mover output power subtract the field I2R loss to obtain the exciter loss in kilowatts.

415.0.3.2.9.3 Static exciter.

a. Connect the load instrumentation in accordance with the applicable figure of MIL-HDBK-705, method 205.1, for the exciter input power.

b. Using a variable resistor in series with the voltage sensing lines (variable auto transform for ac generators) adjust the input voltage to vary the excitation voltage and current. Adjust the exciter output voltage and current to the values required to excite the generator at rated load at rated voltage rated speed.

c. Record all instrument readings.

d. From the kilowattmeter reading of the input power to the exciter, subtract the field I2R loss to obtain the exciter loss in kilowatts.

415.0.4 Results.

a. Total the following power losses:

1.

2.

3.

4.

5.

6.

7.

8.

Bearing friction and windage loss at rated speed.

Brush friction loss at rated speed, if applicable.

Brush contact loss at rated speed, if applicable.

Open-circuit core loss at rated voltage.

Armature I2R loss at rated current.

Field I2R loss at rated load.

Stray load loss at rated load.

Exciter loss at rated load, if applicable.

b. Substitute the above calculated total in the following formula to determine the efficiency of the generator.

Generator efficiency (in percent) = Rated kW output x 100 Rated kW output + total losses in kw

c. Compare the generator efficiency found in step b above with the requirements of the procurement document.

415.0.5 Procurement document requirements. The following items must be specified in the individual procurement document:

a. The voltage connection and frequency at which this method is to be performed.

b. The minimum allowable generator efficiency.

c. Load renditions at which brush contact loss is to be performed.

FIGURE 415.0-I TYPICAL PRIME MOVER CALIBRATION CURVE.

FIGURE 415.0-II TYPICAL OPEN-CIRCUIT CORE LOSS

CURVE FOR A-C GENERATOR

FIGURE 415.0-III TYPICAL OPEN CIRCUIT CORE LOSS CURVE FOR

D-C GENERATOR

FIGURE 415.0-IV TYPICAL STRAY LOAD LOSS CURVE.

Figure 415.0-V. Portion of a typical test record for summation of losses test.

Figure 415.0-VI: Portion of a typical test record for summation of losses test.

Figure 415.0-VII. Portion of a typical test record for summation of losses test.

Figure 415.0-VIII. Portion of a typical test record for summation of losses test.

FIGURE 415.0-IX. Method of determining brush contact loss.

METHOD 415.1c

GENERATOR POWER INPUT TEST

415.1.1 General. The power required to drive the generator at rated load is important in determining the size of the prime mover and expected operating costs.

415.1.2 Apparatus. Instrumentation for measuring load conditions, field voltage and current, ambient temperature and prime mover output power shall be as described and illustrated in MIL-HDBK-705.