The hidden Creators of unreliable power plants
By Tom Finucane
There is an abundance of articles on how to install, upgrade or modernize a power plant control system. These generally focus on the core DCS or control system infrastructure and often gloss over the importance of upgrading the plant ecosystem. In other words, we fix the brain but ignore the nervous system and the limbs! Wiring, sensors and actuators are often subjected to harsh working environments resulting in degradation over time which can lead to failure. This blind spot leaves most plants vulnerable to the unexpected, resulting in lowering equipment reliability.
In addition to improved reliability and availability, modern field devices are designed with digital plants and the Internet of Things (IoT) in mind. As such, a prudent owner or operator that performs a detailed plant assessment developing a framework to best utilize existing field device infrastructure, may improve plant reliability and availability and in some cases yield untapped performance benefits.
Breaking this down there are three areas of focus:
1. Actuators, motors & switchgear
2. Sensors & other instruments
3. Wiring, cable trays and busway
Actuators, motors & switchgear:
Many plants are filled with “dumb” actuators or in cases where plants have smart devices, they are likely underutilized. Why? Whether it’s building, maintaining or upgrading existing plant equipment, most owners or EPC contractors simply do not pay enough attention to the integration of field devices into the plant control system. In many cases, they are just not scoping to that level of detail as they concentrate on major items such as the rotating equipment, boiler and associated auxiliaries. Further, during a new build, control system vendors are typically unaware of field instrumentation choice at the hardware design phase, when control system features are locked down. By the time the plant SME’s (Subject Matter Experts) get engaged, it is too late as the design, cost and schedule is already established. This unintended oversight may introduce an element of unreliability to existing plant operations that likely will become more acute as plants age over time.
Typically, plant operations are blind to the condition of field devices which can be overcome by using proven technologies such as HART and Foundation Fieldbus (FFB). Such technologies allow most devices to provide a health report when interrogated by a handheld system or preferably through an Asset Management System (AMS) that is integrated with the plant control system or DCS. These reports are invaluable to the maintenance team as potential failures can be anticipated.
This paradigm is not confined to traditional actuators, for electrical equipment there has been a proliferation of modern Intelligent Electrical Devices (IED’s) which seamlessly interface with low and medium voltage motor control centers (MCC’s) and plant switchgear. These powerful devices can provide a wealth of useful data on the performance and characteristics of electric motors, which not only helps with motor condition but also provides useful insights into the driven equipment, e.g. you can tell a lot about the condition of a pump if you can see how the driving motor is behaving. The devices also allow the maintenance department to assess the suitability of motor or switchgear protection settings based on actual operating data.
Sensors & other instruments:
Unlike actuators most sensors delivered today have an inherent capability of being deployed with a smart technology such as HART (or when specified, FFB). Unfortunately, in many cases this capability is often not leveraged by the control system OEM and the sensor is simply connected as a standard analog input (4-20 mA device). This is easily corrected by replacing the IO card with one that is HART cable or by adding in HART multiplexers in the circuit. For less critical signals a “wireless HART” infrastructure and can be deployed and is especially useful in larger plants where most signals are converted to 4-20 mA at the source to save on wiring costs.
These smarter instruments provide valuable insights to calibration and maintenance needs as well as sensor condition and degradation over time. They also provide the data stream that is associated with connectivity to Digital Plant implementations which will be the subject of a further blog.
Wiring, cable trays and busways:
Wire insulation degrades over time, especially if exposed to sunlight, heat, water or mechanical vibration. Additionally, damage due to vermin is common. Minimizing the number of terminations in a circuit is critical as each wire termination introduces a potential failure point and increases the risk of loss of field loop; and data integrity. For analog signals, particular care is required for grounding and shielding systems as once their integrity is breached it can lead to a multitude of signal issues. A thorough audit of plant wiring can reveal hidden issues, for instance many redundant sensors take the same wiring route back to the control system and in some cases may be within the same multicore cable. Replacement and maintenance can be time consuming and costly if the original installation and subsequent maintenance actions are not performed with prudent industry practices in mind.
As plants age, the cost of replacing cables can be excessive. To solve this, many projects are embracing fieldbus technologies or highly distributed remote I/O modules reducing the burden of field run cable. For Greenfield projects, this can drastically reduce installation costs as the majority of multicore I&C cables are replaced by either a fieldbus run or an optical fiber cable. In Brownfield upgrades, many users simply opt to abandon older cable in place and deploy the new technology and sensors.
There are multiple benefits to partnering with expertise to better leverage and maintain the plant ecosystem, including using smart technologies embedded into field devices. Such an approach can transcend the plant’s maintenance practices from reactive to proactive. If coupled with a well-designed and implemented digital strategy, plant personnel will be well positioned to better understand potential incipient failure modes prior to field device failure, therefore supporting improved operations based on better operational insights. A well-engineered digital strategy will ensure to avoid the “tyranny of alarms” where operators and maintenance personnel are simply bombarded with information without the context to know what is important and what is not. The importance of well implemented alarm management strategy as part of a digital deployment cannot be understated.