Surge Test Voltages and Standards

This page describes the three main standards used for surge test voltages. To learn more about how the iTIG is used for surge comparison tests, see Surge Test Summary and Surge Test Methods.

Electrom surge testers meet the requirements of these three main standards that are used for surge test voltages:

  1. ANSI/EASA AR100-2015
  2. IEEE 522-2004
  3. IEC 60034-15 Edition 3.0 2009

Note that the standards presented here are recommendations only. Any voltage can be agreed upon between the parties involved (such as the device maintainer and device owner). If there are any concerns, the voltage should be reviewed by those involved.

For a summary containing tables, graphs, and recommendations, see Summary and Recommendations.

Surge Test Voltage Standard Recommendations Followed by Electrom

ANSI/EASA AR100-2020

ANSI/EASA AR100-2020 is the ANSI/EASA Recommended Practice for Repair or Rotating Electrical Apparatus [1]. For random wound and form wound coils and motors, ANSI/EASA uses this formula:


where E is the RMS rated line-to-line voltage of the motor.

This ANSI/EASA formula is the most commonly used test voltage formula for windings, stators, assembled motors, and generators of all kinds. The standard does not distinguish between new and used machines, and is used for both random wound and form wound stators and assembled machines.

See Insulation Resistance Test Methods for details.

[1]AR100, E. A. S. A. “Recommended Practice for The Repair of Rotating Electrical Apparatus, St.” Lois, MO: Electrical Apparatus Service Association, inc (2020).

IEC 60034-15 Edition 3.0, 2009

Impulse voltage withstand levels of form-wound stator coils for rotating AC machines.

This standard applies to sample tests of form coils, typically of at least two form coils, “carried out on coils in new condition which adequately represent the configuration of the finished item to be used in the machine for the purpose of evaluating the manufacturing procedures and processes incorporated in the insulation system.” Note that these coils are not yet installed in a stator.

IEC Surge Test Voltage Formula for Sample Form Coils Before Installation in the Stator
Lightning Withstand peak voltage: UP = 4 UN + 5 kV UN = Rated L-L RMS voltage
Peak rated impulse voltage: U’P = 0.65 UP Rise time T1 = 0.2 ± 0.1μs up to 35kV
Surge test impulse voltage: U’P = 0.65 (4 UN +5) kV Reduced to 40-80% installed in stator before connections

Front rise time T1 is defined as 1.67 times the interval between the instants when the impulse is 30 % and 90 % of the peak value.

For inverter fed machines (power systems using VFD, ASD etc.) the test voltage may be increased. This is to ensure that the motor insulation is good for the peak of VFD-associated switching transients. The standard states that the overshoot factor at the motor terminals can be as high as 1.7 for a 3-level inverter. For more information on this subject see Inverter (VFD/VSD/ASD) generated PD.

The standard states that “the test coils shall have completed their manufacturing process, including corona protection layer and stress grading if used, and shall be either embedded in earthed slots or fitted with the slot portion wrapped in earthed conducting tape or foil. The number of sample coils shall be at least two.”

The standard further says: “Routine tests may be performed on coils after insertion in the stator core but before processing and making the connections.”
In this condition, a reduced surge test voltage should be used, typically 40% to 80% of the surge test impulse voltage U′P. The test voltage depends on the insulation technology used, and should be agreed to between the manufacturer and user.

Uncured and “Green” Form Coils

The test voltage is reduced to 40% to 80% of the formula, depending on the insulation materials and technology.

The standard says that coils may be tested at one or more of the following steps:

  1. Prior to insertion in the stator

  2. After coil installation, wedging and bracing, but before any connections are made. Each coil should be tested.

  3. After series connections are made, but before insulation them and before making connections between phase groups.

  4. After connecting into phase groups, but before connecting phase groups to each other. This can be done before or after insulating the series connections.

  5. After all connections are made and insulated. Maintenance tests are normally made in this condition.

IEEE 522-2004

IEEE 522-2004 is the IEEE Guide for Testing Turn Insulation of Form-Wound Stator Coils for Alternating-Current Electric Machines [2]. This IEEE guide applies to:

  • Individual stator coils after manufacture.

  • Coils in completely wound stators of original manufacture.

  • Coils and windings for rewinds of used machinery.

  • Windings of machines in service to determine their suitability for further service (preventive maintenance testing).

The table below shows the IEEE Surge Test Voltage Formula for Form Coils and Form Wound Machines.

IEEE Surge Test Voltage Formula for Form Coils and Form Wound Machines
Rated line-line RMS Voltage VL  
V1= 1 per unit (1p.u.): V1= √2/3VL
V1 = 0.8165VL
At a theoretical rise time of
Tr = 0 seconds
Surge test voltage V2: V2=3.5 V1
V2=3.5 x 0.8165 VL
V2=2.86 VL
Rise Time Tr=0.1-0.2μs
Voltage reduced to 40-80% for uncured coils
Voltage reduced to 75% for used machines

In the standard, V₂ is called the momentary withstand capability across a coil. This is the voltage a new coil should be able to handle, and therefore the value against which the coil should be surge tested. Unless there are defects, new coils can handle much higher surge voltages.

The standard defines a withstand envelope (surge test voltage profile) that changes with the rise time of tr for the surge pulse. As the rise time increases, the peak surge test voltage should increase per the withstand envelope. V₁ should be multiplied by a higher factor of f to get to the test voltage of V₂. See the Standard profile in the graph below. This is the voltage used for coils in machines where high-magnitude, fast-rising surges or switching transients occur frequently or continuously.

The Alternate profile in the graph can be used for coils not likely to experience high-magnitude fast-rising surges. The factor in the formula would typically be f = 2.

Voltage Withstand Envelope image V_2=f x V_1

IEEE suggests a rise time of:


and a factor of:


for turn-to-turn surge tests.

The rise time is dependent on impedance properties of the load being tested. It is defined as the time it takes for the voltage to rise from 10% to 90% of the peak surge test voltage. Neither the users nor manufacturers of surge testers can control the rise time of a surge test pulse. Therefore, in practice, surge tests have been done with rise times longer than 0.2 µs in high impedance loads. This has been done with excellent results for a very long time using f = 3.5, as well as using the ANSI/EASA surge test formula.

[2] “IEEE Guide for Testing Turn Insulation of Form-Wound Stator Coils for Alternating-Current Electric Machines,” in IEEE Std 522-2004 (Revision of IEEE Std 522-1992) , vol., no., pp.1-28, 9 Aug. 2004, doi: 10.1109/IEEESTD.2004.94591.

Maintenance Test and Diagnostic Tests of Used Machines

IEEE 522 recommends testing at 75% of the formula when testing used machines.

Summary and Recommendations of Voltages to Use

The following graphs and tables show the differences between the recommendations in the standards.

Electrom Instruments Recommendations for Surge Tests of Machines

For Used Machines

Use the ANSI/EASA formula. The low surge test voltage for IEEE at lower operating voltages will result in fewer weaknesses being found, especially for inverter driven motors.

All the standards mention that the surge test formulas do not take inverter drive spikes into account, and that a higher surge test voltage may be considered for inverter applications.

Industrial users will sometimes de-rate surge test voltages down to the line to line RMS rated voltage for machines that are in operation, especially for those considered to be ‘dirty’. A test voltage lower than the peak operating voltage equal to RMS x 1.41 Volts, will not cover the whole operating voltage range of the motor. Although a de-rated surge test voltage can be prudent at times, it will not provide information about problems to come unless it is higher than the peak operating voltage.

For New Machines

Use the ANSI/EASA formula for machines with operating voltage of 1,000V or less.
Use either standard for higher voltages. The higher IEEE voltages for machines operating above 1,000V are still far below what the machine should be able to handle.

Keep in mind that Surge and Hipot tests should not be done if the insulation resistance megohm measurement does not support it. Click here for more information.

Surge Test Voltages (V) for Maintenance of Used Machines
RMS Line-to-Line Voltage 460 575 1,000 2,300 3,300 4,160 6,600 11,000 12,000 13,800
ANSI/EASA AR100-2015: Random and form wound machines: V=2*E+1000 1,920 2,150 3,000 5,600 7,600 9,320 14,200 23,000 25,000 28,600
IEEE 522-2004: Form coil wound machines: V=2.86*E*75%=2.15E 986 1,232 2,143 4,930 7,073 8,916 14,146 23,576 25,720 29,578

Surge Tests of Form Coils

The options for testing form coils are many, and the standards address the subject differently.

IEC differentiates between sample coils that are surge tested before installation in the stator (bench test), and coils installed in the stator but not connected yet. The bench test of sample coils embedded in earthed slots or fitted with the slot portion wrapped in earthed conducting tape or foil, is at a much higher voltage than tests done on coils installed in a stator. IEC does not address testing of installed coils that are connected, or completed machines.

Sample testing and testing of all coils after manufacture should not be compared. They are two different types of tests. Once the coils are installed in the stator, the surge test voltages for the two standards are more similar. Installed in the stator, many users will also apply the ANSI/EASA formula which is in the same range as the IEEE and IEC formulas.

Electrom Instruments Recommendations for Surge Tests of Form Coils

The user should agree with the manufacturer of the form coils what surge test voltages to use.

There are many different insulation materials and technologies, and each may require different test voltages at different stages of production of a machine.

IEEE does not discuss bench testing of sample coils, but covers bench tests of all coils after manufacture, surge tests of coils at different stages of machine production, and tests of complete machines.

Surge Test Voltages (V) for New Form Coils
RMS Line-to-Line Voltage 460 575 1,000 2,300 3,300 4,160 6,600 11,000 12,000 13,800
IEEE 522-2004, New fully cured coils: V = 2.86*E 1,315 1,643 2,858 6,573 9,431 11,888 18,861 31,435 34,293 39,437
IEEE 522, Unimpregnated coils: 60-80%, 70% used here 920 1,150 2,000 4,601 6,601 8,322 13,203 22,005 24,005 27,606
IEEE 522, Uncured resin rich coils: 40-60%, 50% used here 657 822 1,429 3,286 4,715 5,944 9,431 15,718 17,146 19,718
IEC 60034-15-2009, New sample coils not installed in stator: V = 0.65(4E+5000) 4,446 4,745 5,850 9,230 11,830 14,066 20,410 31,850 34,450 39,130
IEC 60034-15, New coils installed in stator before processing/connections: 40-80%, 60% used here 2,668 2,847 3,510 5,538 7,098 8,440 12,246 19,110 20,670 23,478