Model M3K
Testing and Maintaining Power Semiconductors for System Reliability
Power Semiconductors are a family of devices used in all types of industries mainly for AC/DC conversion and motor speed control.
A variety of different packages and configurations are available, e.g stud mounted, press pack (hockey puck), single and dual thyristor/diode modules, and transistor modules.
When a Power Semiconductor fails, expensive loss of production is the immediate result.
In most cases, un-scheduled down-time, i.e. loss of production, due to faulty or marginal components, can be avoided by testing the Power Semiconductors regularly during scheduled outages or service days.
It is imperative that only instruments specifically designed for testing Power Semiconductors are used. Meggers and hi-potters should under no circumstances be used, since these kind of instruments can easily damage the components
Ohm meters are ONLY reliable to detect a short, since they do not have enough voltage to properly energize the silicon wafer in a Power Semiconductor
WHY POWER SEMICONDUCTORS FAIL
A Power Semiconductor could fail, or degrade, for a number of different reasons, mechanical or electrical.
Some failures can easily be prevented with proper service, maintenance, and handling. Others are impossible to prevent, since they are inherent with the system where they are installed.
COMMON REASONS FOR FAILURES
ELECTRICAL
- Transients on the electrical power feed.
- Faulty, or wrong, replacement component installed.
- Surface leakage due to dirty components.
- Low resistance/short in device controlled by the component.
MECHANICAL
- Mishandling of component.
- Shipping damage.
- Improper installation.
Figure 2: Typical Power Semiconductor Components
Fig.1: Power Semiconductor Tester - Model M3300
MINIMIZING FAILURES IN
POWER SEMICONDUCTORS
TEST COMPONENTS BEFORE INSTALLATION
Make sure that the replacement component is functional, before being installed.
CLEAN POWER SUPPLY
Try to keep the power supply as noise free as possible, i.e. free from transients (spikes), and harmonics. In some cases an isolation transformer is the only way to get a clean supply.
KEEP COMPONENTS CLEAN
Dirt and moisture on the components could cause surface leakage.
FOLLOW INSTALLATION SPECIFICATIONS
Make sure that press pack components are torqued in accordance to specifications.
HANDLE COMPONENTS WITH CARE
Power Semiconductors may look rugged, but they could easily be mechanically damaged if dropped.
