Surge Test Overview

Why surge tests are critical

Surge tests are critical because they are the only test that finds turn-to-turn insulation weaknesses. These weaknesses start at voltages above the operating voltage of the motor and are precursors to serious failures and shutdown of a motor. Surge tests are also used to find hard shorts and a number of other mistakes in windings and coils.

Good Surge Test, surge test waves

Three nearly identical waves from a 3-phase motor.

Most winding failures, including shorts to ground, start with weak turn-to-turn insulation. Once the weakness causes turn-to-turn arcs, an electrical closed loop is created. Due to transformer action, current starts flowing in the loop. This current is dissipated as heat and creates a hotspot. More turns short out due to the hotspot and subsequently more heat is created. Eventually the winding shorts to ground.

Surge tests are also known as surge comparison tests because the result from a coil or phase is compared to the result from another coil or phase. Coils are designed to be identical so the surge test results should be nearly identical.  When windings or phases are not identical or there is nothing to compare to, operators use the pulse-to-pulse surge test.

What can be tested by a surge tester?

Any type of coil is testable – from tiny sensors, antennas, and actuating coils in relays or solenoids, to the biggest electric motors and generators. The surge test is a load dependent test so operators must consider test voltage standards.

What typical failures can and cannot be detected with a surge test?

Weaknesses and Faults Found With Surge Test

Which issues are only found with a surge test?

A surge test is the only test that finds weak turn-to-turn insulation. This is due to higher voltages used in a surge test. Low voltage tests do not stress the insulation and consequently dielectric weaknesses are not found.

A surge test is the only test that finds weak coil-to-coil and phase-to-phase insulation.  A hipot test is sometimes used if coils and phases are hipot tested individually against the other coils and phases but doing so is not practical.

Lastly, some connection mistakes are only found with a surge test. An inductance test is sometimes used but only when the resistance is correct.

Why Industrial Users Need a Surge and PD Tester

Surge Test Uses

For a summary of what surge tests are used for and more information on how they are conducted, see Surge Test Summary.