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MI L - S TD - 202 - 301 M E TH O D 301 DI E L E CT RI C W I T HS T A NDI N G V O L T A G E 1. SCOPE 1. 1 P urpose . T he die l ec t r i c w i t hs t and i ng v ol t age t e s t ( a l s o c al l e d hi gh - po t ent i al …

MIL-STD-202-301

CONTENTS

PARAGRAPH PAGE

FOREWORD…………………………………………………………. ii

1. SCOPE 1

1.1 Purpose………………………………………….……..…………. 1

1.2 Precautions…………….……………………….……..…………. 1

1.3 Factors affecting use…………….…………….……..…………. 1

2. APPLICABLE DOCUMENTS 1

3. DEFINTIONS 1

4. GENERAL REQUIREMENTS 1

4.1 Apparatus……………….…….…………………….….........……. 1

4.1.1 High voltage source.…….…………….………….….........……. 1

4.1.2 Voltage measuring device……………………….….………….. 2

4.1.3 Leakage current measuring device………….….……….…….. 2

4.1.4 Fault indicator.….……….……………………………………….. 2

4.2. Procedure…………….………………………..….….………….. 2

4.2.1 Preparation..……………..…………………..……..……………. 2

4.2.2 Test voltage…….…………………………………….………….. 2

4.2.3 Points of application…………………………..……..……….…. 2

4.2.4 Rate of application……..……………………..……..……….…. 2

4.2.5 Duration of application………………………..……..……….…. 2

4.2.6 Examination and measurement of specimen……..……….…. 2

5. DETAILED REQUIREMENTS 3

5.1 Summary…………………………………………..…..…………. 3

6. NOTES 3

6.1 Supersession data………………………………………………. 3

iii

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MIL-STD-202-301

METHOD 301

DIELECTRIC WITHSTANDING VOLTAGE

1. SCOPE

1.1 Purpose. The dielectric withstanding voltage test (also called high-potential, over potential, voltage-

breakdown, or dielectric-strength test) consists of the application of a voltage higher than rated voltage for a specific

time between mutually insulated portions of a component part or between insulated portions and ground. This is

used to prove that the component part can operate safely at its rated voltage and withstand momentary

overpotentials due to switching, surges, and other similar phenomena. Although this test is often called a voltage

breakdown or dielectric-strength test, it is not intended that this test cause insulation breakdown or that it be used for

detecting corona, rather, it serves to determine whether insulating materials and spacing in the component part are

adequate. When a component part is faulty in these respects, application of the test voltage will result in either

disruptive discharge or deterioration. Disruptive discharge is evidenced by flashover (surface discharge), sparkover

(air discharge), or breakdown (puncture discharge). Deterioration due to excessive leakage currents may change

electrical parameters or physical characteristics.

1.2 Precautions. The dielectric withstanding voltage test should be used with caution particularly in inplant quality

conformance testing, as even an overpotential less than the breakdown voltage may injure the insulation and thereby

reduce its safety factor. Therefore, repeated application of the test voltage on the same specimen is not

recommended. In cases when subsequent application of the test potential is specified in the test routine, it is

recommended that the succeeding tests be made at reduced potential. When either alternating-current (ac) or direct-

current (dc) test voltages are used, care should be taken to be certain that the test voltage is free of recurring

transients or high peaks. Direct potentials are considered less damaging than alternating potentials which are

equivalent in ability to detect flaws in design and construction. However, the latter are usually specified because high

alternating potentials are more readily obtainable. Suitable precautions must be taken to protect test personnel and

apparatus because of the high potentials used.

1.3 Factors affecting use. Dielectric behavior of gases, oils, and solids is affected in various degrees by many

factors, such as atmospheric temperature, moisture, and pressure; condition and form of electrodes; frequency,

waveform, rate of application, and duration of test voltage; geometry of the specimen; position of the specimen

(particularly oil-filled components); mechanical stresses; and previous test history. Unless these factors are properly

selected as required by the type of dielectric, or suitable correction factors can be applied, comparison of the results

of individual dielectric withstanding voltage tests may be extremely difficult.

2. APPLICABLE DOCUMENTS

This section not applicable to this standard.

3. DEFINTIONS

This section not applicable to this standard.

4. GENERAL REQUIREMENTS

4.1. Apparatus.

4.1.1 High voltage source. The nature of the potential (ac or dc) shall be as specified. When an alternating

potential is specified, the test voltage provided by the high voltage source shall be nominally 60 hertz in frequency

and shall approximate, as closely as possible, a true sine wave in form. Other commercial power frequencies may be

used for inplant quality conformance testing, when specified. All alternating potentials shall be expressed as root-

mean-square values, unless otherwise specified. The kilovolt-ampere rating and impedance of the source shall be

such as to permit operation at all testing loads without serious distortion of the waveform and without serious change

in voltage for any setting. When the test specimen demands substantial test source power capacity, the regulation of

the source shall be specified. When a minimum kilovoltampere rating is required, it shall be specified. When a direct

potential is specified, the ripple content shall not exceed 5 percent rms of the test potential. When required, a

suitable current-limiting device shall be used to limit current surges to the value specified.

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MIL-STD-202-301

4.1.2 Voltage measuring device. A voltmeter shall be used to measure the applied voltage to an accuracy of at

least 5 percent, unless otherwise specified. When a transformer is used as a high voltage source of alternating

potential, a voltmeter connected across the primary side or across a tertiary winding may be used provided it is

previously determined that the actual voltage across the test specimen will be within the allowable tolerance under

any normal load condition.

4.1.3 Leakage current measuring device. When any leakage current requirement is specified, a suitable method

shall be used to measure the leakage current to an accuracy of at least 5 percent of the specified requirement.

4.1.4 Fault indicator. Suitable means shall be provided to indicate the occurrence of disruptive discharge and

leakage current in case it is not visually evident in the specimen. The voltage measuring device of 4.1.2, the leakage

current measuring device of 4.1.3, or an appropriate indicator light or an overload protective device may be used for

this purpose.

4.2. Procedure

4.2.1 Preparation. When special preparations or conditions such as special test fixtures, reconnections,

grounding, isolation, or immersion in water are required, they shall be specified.

4.2.2 Test voltage. Specimens shall be subjected to a test voltage of the magnitude and nature (ac or dc)

specified.

4.2.3 Points of application. The test voltage shall be applied between mutually insulated portions of the specimen

or between insulated portions and ground as specified. The method of connection of the test voltage to the specimen

should be specified only when it is a significant factor.

4.2.4 Rate of application. The test voltage shall be raised from zero to the specified value as uniformly as

possible, at a rate of approximately 500 volts (rms or dc) per second, unless otherwise specified. At the option of the

manufacturer, the test voltage may be applied instantaneously during inplant quality conformance testing.

4.2.5 Duration of application. Unless otherwise specified, the test voltage shall be maintained at the specified

value for a period of 60 seconds for qualification testing. For inplant quality conformance testing, when specified,

reduced time with a possible correlated higher test voltage may be used. Specimens with movable parts shall be

tested as specified, in a manner to assure that repeated stresses are not applied to the same dielectric. Upon

completion of the test, the test voltage shall be gradually reduced to avoid surges. At the option of the manufacturer,

the test voltage may be removed instantaneously during inplant quality conformance testing.

4.2.6 Examination and measurement of specimen. During the dielectric withstanding voltage test, the fault

indicator shall be monitored for evidence of disruptive discharge and leakage current. Following this, the specimen

shall be examined and measurements shall be performed to determine the effect of the dielectric withstanding

voltage test on specific operating characteristics, when specified.

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