Flipping the switch: monitoring electrical equipment

The Natref petrol refinery, a jointly owned venture between Sasol and Total, has been at the cutting edge of refining technology ever since its inception nearly half a century ago. Because the local market for heavy fuel oil is limited, Natref is designed to get the most out of crude oil. By optimising its use of the bottoms upgrading refining process, Natref can produce 70% more white product than coastal refineries, which rely on heavy fuel oil.

Across the 17 substations situated on site at Natref, automatically operated circuit breakers are used to protect electrical circuits from damage in the event of a short circuit or system overload. They do this by interrupting current flow if a fault is detected. Unlike a fuse, which can only be used once before being replaced, circuit breakers are reset to resume normal operation. However, they have a finite operating life and can only be reset a certain number of times before being replaced.

Monitoring the operation of circuit breakers at the substations has been a long-standing problem for maintenance engineers since they traditionally had no way of knowing if one went off and had automatically reset. Existing on-site alarms only showed the current state of the circuit breakers so, if they had been reset, they would present as normal. This meant that engineers were unaware of underlying issues at the substations because all circuit breakers were showing as normal when inspected, and incidents went undetected.

Being unable to detect and record faults in the system led to increased maintenance costs because engineers weren’t aware of issues until they were serious enough to cause system failure and unplanned down-time. To overcome these problems, the plant managers at Natref engaged Omniflex to provide a way of monitoring and recording circuit breaker activity.

Monitoring the switches

Omniflex’s solution implemented alarm annunciators that monitored circuit breaker operations and sequence of events logging that recorded events at the substations to better than 1 millisecond. The data is timestamped and recorded on a built-in SD card to produce an electronic data repository for auditing purposes. The biggest benefit is narrowing down the root cause of the trip by recording the sequence of events down to 1 milli-second resolution, improving fault finding performance.

From each monitored switch, the signal is split so it goes to the annunciator and the sequence of events recorder in parallel. The contact from the circuit breaker is monitored, open or close, and the annunciator traps the momentary alarm caused by the circuit breaker tripping and maps it to the alarm status. This enables engineers to see if there has been an incident, even if the circuit breaker has automatically reset in the meantime. The event stream is captured on the SD card ensuring the momentary trip and its actual sequence in time is recorded.

Each substation has a GPS time synchronisation module which updates and synchronises time across the entire system so time in one substation is the same in the next, allowing useful comparisons to be made across the plant on a unified time-base.

By adopting this technology at its substations, plant managers at Natref can reduce maintenance down-time, implement a predictive maintenance programme, replacing circuit breakers as they reach the end of their service life and minimising unplanned downtime. Furthermore, by tracking all circuit breaker trips, problem areas in the system can now be identified by looking at repeated circuit breaker trips that would have previously gone unnoticed or undocumented. Omniflex is a specified technology partner of the Natref refinery for providing this Alarm and Sequence of Events technology.