DWH Technical Topic: Surge suppression

By Clarence Klassen, P. Eng.

Have you checked your grounding? You will hear this first question when calling tech support with an intermittent drive or controller problem. This question serves two purposes. 1) Perhaps the grounding is bad. 2) It provides time to look for the real answer.

The problem may be with surges introduced by other equipment. A pneumatic or hydraulic solenoid may be switched or a contactor or starter picked up. A simple surge suppressor on each solenoid and other coils may solve your intermittent problem. This applies only to coils switched with dry contacts, not solid-state PLC outputs.

Putting a suppressor across all coils switched with dry contacts is easily done and inexpensive. Many of these suppressors look like shotgun shells with two outgoing leads.

The worst case of EMI interference in my career happened in a paper mill whenever a vacuum-pump motor was started using old vacuum contacts in a high-voltage circuit breaker. The interference was so bad, dozens of thyristors in drives over three paper machines would fail. Once we knew where the problem was coming from, it was easy to fix.

Over the past year working in a paper mill, I have inquired about the cause of damaging surges. Some reasons were improper switching sequences, applying power-factor-correcting capacitors, and vehicles crashing into sub-stations.