Time is Everything to Power System Reliability
When electricity is out, flashlights come to life. It would be one thing if electrical systems were as simple as flashlights, but of course they’re not…and they serve many more purposes than just illumination.
Despite technologies in electrical infrastructures that prevent unplanned outages, systems still go dark unexpectedly sometimes. Utilities, industry, rate payers – no one wants power interrupted. Beyond the inconvenience, there could be dangerous and expensive consequences.
Our daily lives depend on electricity; it’s the lifeblood of our modern existence. The health and reliability of its vast infrastructures is of the essence. Even a slight issue in any of the countless interdependent processes hosted across fleets of system assets could be enough to cause a blackout.
Things are fine until they aren’t. Avoiding unplanned outages means knowing the condition of generating machinery, transformers, and conducting equipment, and intervening as quickly as possible to protect them from electrical damage. Condition monitoring and protection and control (P&C) systems help owner-operators get ahead of issues concerning the reliability of their critical assets and go a long way in protecting those investments as well.
Syncing up
Devices that form condition monitoring and P&C systems are nodes in network topologies that connect electrical infrastructures to control centers. These utility and industrial operational technology (OT) systems, along with SCADA, EMS, and others, require a common time reference. Ensuring various devices and multiple networks remain precisely synchronized is extremely important and no small engineering feat.
Network engineers and OT communications specialists factor latency (source-to-destination time of signals in a network), jitter (the timing variations of latency), and drift (the degradation of time accuracy) into the networks they architect. The manufacture and locations of network devices – IEDs, MUs, RTUs, HMIs, to name a few – influence the selection of mediums (fiber or copper cable, wireless, power line carrier, microwave, satellite) to design into communication schemes.
Communication mediums have their strengths and weaknesses. System architects weigh physical (cost, durability, connectivity) and virtual (bandwidth, format, transfer rate) considerations in coming up with workable network infrastructure designs. The fruits of their labor are communication systems of myriad devices that operate in sync to monitor, measure, protect, and control electrical systems.
A matter of time
P&C stands out among electrical infrastructure OT systems for its role in interrupting power flow. Relays are the backbone of P&C, standing ready to initiate circuit breaker “open” operations upon detecting electrical faults sensed via signals from PT/VTs and CTs. Reclosers do the opposite, causing breakers to close in quick succession after each relay trip until a “lockout” suspends the breaker contacts in the open position if a fault cannot clear on its own which then requires manual intervention. Automatic relay, recloser, and circuit breaker operations happen in a fraction of a second, causing that brief flicker that might happen during a storm…and maybe just before the power goes out.
But storms aren’t the only causes of power interruptions. P&C relays, like so many other OT devices, have settings that conform them to the parameters their applications call for. But unlike other OT devices, relays can require lots of settings, particularly modern IED relays that can carry out multiple communications automatically as fault detection and breaker control occurs.
Relay schemes work in concert with communication schemes in time-coordinated sequences among local and remote devices. Whether current and voltage signals are sent hundreds of miles over fiber optic cables, or a high frequency signal is sent over a power line itself, coordination (timing) between the protective relays is imperative. If the latency on the fiber optic cable is too high, the time difference between the current and voltage data being sent and received can look like a line fault to the relays interpreting the data. The time it takes the transceiver at either end of a power line to receive the high-frequency signal needs to be accounted for and settings applied correctly to ensure proper coordination for the protection at either end of a line.
If for some reason a relay or a breaker fails – or a communication channel – a backup scheme kicks in. If the timing of either scheme is off, primary or backup, fault levels could persist long enough for catastrophic consequences to ensue while devices meant to prevent calamity stand idly by despite having correct settings.
The emergence of digital protection further highlights the importance of time and complicates the efforts of network engineers and OT communication specialists. Redundancy is a key aspect of power systems and that doesn’t change as P&C moves into the digital realm. Digital protection systems, such as those using IEC-61850, require redundant, parallel networks essentially doubling the network demands and all requiring microsecond accuracy or better. As more data gets put onto the networks that protect the power system, timing and high accuracy synchronization will only become more crucial.
The time is now
Lately, the business of electricity seems to be moving as fast as electricity itself. Modernization and expansion are the talk of the power industry. The advent of OT device technologies capable of operating at microsecond – even nanosecond – speed is changing electrical infrastructures that system coordination and stability depend on.
Electric power and industrial entities are evolving quickly, replacing OT devices they have used for years with upgrades that measure and respond to electrical signal propagations at much higher speed. Beyond faster communications and tripping, the advanced OT devices coming online improve sequence-of-event data capture with time stamping that has greater resolution for more precise event analyses and investigations.
Numerous standards relevant to the time domain spell out requirements that devices and systems must meet for reliable performance. Owner-operators and vendors alike have stakes in OT devices working as they should. With more on the line than ever and no room for error, being on time is critical.
Additional Information:
- Special thanks to Blake Harris and Peter Newell from Doble Engineering for their technical expertise and textual contributions.
- Originally published in the The Relay™ Newsletter. Subscribe on LinkedIn.
