INDUSTRY FOCUS Oil & Gas
Monitoring mission-critical equipment at a petrol refi nery
Ian Loudon, international sales and marketing manager at Omniflex, discusses how alarm annunciators and sequence of events recording came to the aid of plant operational managers at the Natref refinery
T
he Natref petrol refi nery, located in the industrial region of Sasolburg, is one of South Africa’s oldest inland refi neries, commissioned in 1971. It is jointly owned between Sasol and Total, and has been at the cutting edge of refi ning technology since its inception. 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 refi ning process, Natref can produce 70% more white product than coastal refi neries, which rely on heavy fuel oil. Across the 17 substations situated on site
at Natref, automatically-operated circuit breakers are used to protect electrical equipment from damage in the event of a short circuit or system overload. They do this by interrupting current fl ow 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 fi nite 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. Historically, engineers at the refi nery have had diffi culties monitoring the operations of circuit breakers at the refi nery’s substations, leading to increased maintenance costs and unplanned downtime. 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 downtime. To overcome these problems,
28 February 2021 | Automation
Natref’s substations at the refinery
the plant managers at Natref engaged Omnifl ex to provide a way of monitoring and recording circuit-breaker activity.
Monitoring the switches Omnifl ex’s solution implemented alarm annunciators that monitored circuit- breaker operations and sequence of events logging that recorded events at the substations to better than 1ms. The data is time-stamped and recorded on a built-in SD card, to produce an electronic data repository for auditing purposes. The biggest benefi t is narrowing down the root cause of the trip by recording the sequence of events down to 1ms resolution, improving fault fi nding performance. From each monitored switch, the signal is split so it goes to the annunciator and the sequence of events recorder in parallel.
Omniflex control cabinet with circuit breakers
The contact from the circuit breaker is monitored, open or closed, 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.
Each substation has a GPS time
synchronisation module that updates and synchronises time across the entire system, allowing useful comparisons to be made across the plant.
By adopting this technology at its substations, plant managers at Natref can reduce maintenance downtime, implement a predictive maintenance programme, replacing circuit breakers as they reach the end of their service life, and minimise unplanned downtime. Furthermore, by tracking all circuit breaker trips, problem areas in the system can now be identifi ed by looking at repeated circuit breaker trips that would have previously gone unnoticed or undocumented.
CONTACT:
Omniflex Limited
www.omniflex.com
automationmagazine.co.uk
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