[FAQ] What is Partial Discharge, Method a, Method b1, and Method b2 tests?

Please note that all definitions and references are based on the latest standard IEC 60747-17

The robustness and reliability of isolators and their isolation barrier are assessed using a series of tests. These tests are conducted using one of three test methods. The exact voltages and time intervals used for each method vary according to the parameter that is being tested and the level of isolation claimed by the device.

Each method is composed of two parts, an isolation test and a partial discharge test:

• Isolation test – verifies the ability of the isolator to withstand the given isolation voltage.
• Partial Discharge (PD) test – verifies there is no degradation of the insulation through controlled localized electrical discharges.

Partial Discharge:

This test is conducted as a subset of the method a and b testing below. The purpose of a partial discharge test is to verify the insulation between input and output of the coupler by measuring the partial discharge level on the output of the coupler.

Method a:

Method a is a destructive test used during the type test, also known as the qualification test, which is conducted by the certifying body. Method a is also used during sample testing, which occurs every 3 months and is completed by the component manufacturer and reviewed by the certifying body. This method first applies an initial test voltage to simulate a transient overvoltage followed by the partial discharge test.

Procedure:

1. Voltage begins well below the expected inception and is slowly increased to the specified initial test voltage V_pd(ini)a
2. Voltage remains at V_pd(ini)a for a time interval of t_ini
3. Voltage is reduced to the specified partial discharge voltage V_pd(m)
4. Voltage remains at V_pd(m) for a time interval of t_m
5. The maximum value measured during the time interval t_m is recorded as the partial discharge magnitude q_PD

The specified voltages and time intervals used for TI isolators can be found under the “Test Conditions” column in the Insulation Characteristics table in the device datasheet.

Method b1: (routine tests = production test)

Method b1 is used during routine tests, also known as production tests, which occur during manufacturing of the devices. Method b1 testing is similar to method a, but a higher voltage is applied during the isolation test and the entire procedure occurs over a shorter time duration.

Procedure:

1. Voltage begins well below the expected inception and is slowly increased to the specified initial test voltage V_pd(ini)b
2. Voltage remains at V_pd(ini)b for a time interval of t_ini,b
3. Voltage is reduced to the specified partial discharge voltage V_pd(m)
4. Voltage remains at V_pd(m) for a time interval of t_m
5. The maximum value measured during the time interval t_m is recorded as the partial discharge magnitude q_PD

The specified voltages and time intervals used for TI isolators can be found under the “Test Conditions” column in the Insulation Characteristics table in the device datasheet.

Method b2:

Method b2 is similar to method b1 and can be used as an alternative to method b1 during routine tests. Both isolation and partial discharge tests occur, but instead of occurring sequentially like in method a and method b1, the two tests are combined.

Procedure:

1. Voltage of V_pd(ini,b) is applied and maintained for a time period of t_st
2. Voltage remains at V_pd(ini,b) for a time period of t_st
3. The maximum value measured during the time interval t_m (a subset of t_st), is recorded as the partial discharge magnitude q_PD

The specified voltages and time intervals used for TI isolators can be found under the “Test Conditions” column in the Insulation Characteristics table in the device datasheet.