Valiant Communication introduces its Grid Automation and Grid Islanding solution.

The application of this solution and to identify the trouble-spots and isolate the Power Utility from the national grid in the event of an impending failure. The additional objective of the solution is also to create islands within Power Utility’s micro-grid, by isolating any area or zone that is threatening to destabilize Power Utility’s power distribution network from within.

While the conventionally regarded “over-load” and “under-frequency” conditions are not the only ones that can threaten the stability of any national power grid, the bigger threat, in today’s scenario, arises from cyber-attacks and hostile intrusions that could be initiated by an enemy country or a bad actor that is seeking to cripple any nation’s infrastructure. Therefore, it becomes imperative that counter-defense measures are put into place so that if any such eventuality arises, it can be effectively contained by “isolation” and “islanding”.

In the event of an impending “National Grid Failure”, the power generation within a state or a specific region needs to be isolated and islanded so it can continue to generate and supply power to its consumers and ensure that all its downstream feeders and consumers remain in healthy condition. The primary purpose of the solution in achieving the given objective, which would be to identify and isolate in a phased manner, the problem points that inter-connect Power Utility’s power infrastructure to the national grid.

Commenting on the solution, Mr. Inder Mohan Sood, CEO s “Under normal operating conditions, the national power grid of any country must operate and exist as a cohesive, monolithic organism in which the power generation and power consumption are evenly matched, and the entire national grid is operating at a single frequency. In the event a particular state, or a zone starts to draw excessive power and over-load the grid for any reason, it can destabilize the national grid. Similarly, in the event a particular power producer, within the state, begins to generate and off-load excessive power into the grid it can also threaten the stability of the grid. Such an example is especially true in the case of renewable energy producers who can start to feed excess power into the grid, periodically, whenever their renewable power generation assets attain their peak power production.

Monitoring and maintaining grid stability: The “wrong way” and the “right way”:

The “Wrong Way”: Using the under-frequency and over-frequency feature of the protection relays is the “wrong way” to monitor and maintain the stability of the unified power grid. Protection relays are primarily designed to function independently and intended to shield the areas or zones against faults that are directly connected to, controlled, and supervised by them. Whenever a fault occurs in its vicinity and whenever the user set under-current / over-current and under-frequency / over frequency thresholds of any protection relay are exceeded, the protection relay shall trip the local circuit breakers that are connected to it. The protection relay is primarily designed to protect against local and territorial faults, and the reach and the function of the protection relay is limited to and does not go beyond the immediate zone that it is installed to monitor and protect. This renders it unsuitable for applications that are designed to monitor and protect a monolithic power grid at the national, the state, or even at the regional level.

The “Right Way”: The right way to monitor and protect the stability of national grid, a state, or even a region (i.e. a micro-grid) within that national power grid, would be to take a holistic and a comprehensive view of the total area that is required to be monitored and protected against anomalies, such as voltage and frequency deviations (including leading and lagging phase angle variations), and initiate suitable remedial measures that can encompass and be triggered from a central location to trip multiple breakers across a very wide-area. Such a solution would need to be installed at various vantage points within the micro-grid, as well as at points at it the periphery of the micro-grid - wherever the micro-grid connects to the national power grid.

An effective solution to monitor and manage the grid-stability can only be implemented by using PMUs (Synchrophasors compliant to IEEE C37.118 protocol) and PDCs that can be cohesively integrated with Digital Teleprotection (Protection Signaling Equipment [PSE] / DTPC) units and installed at various vantage points within the core of the micro-grid; as well as at the periphery of that micro-grid where it connects to the national power grid; or at points where the renewable power producers connect to that micro-grid from within”.

Valiant Communications provides such a unique solution and is working with Electricity Boards and relevant authorities to implement these cutting-edge technologies in the Power Sector, globally.

The phasor data, collected from all such point shall be transmitted to the actionable PDCs installed at the load-dispatch centers within the microgrid which shall log and analyze the received data and isolate or island the problem points that are threatening to destabilize protected zones.

The island may also be formed in two more scenarios with an intent to limit and contain any cascading failure, if the frequency is continuing to fall below the prescribed threshold:

1. When the grid frequency falls below 48Hz (or whatever number is determined by the power distribution authority).
2. When the ROCOF (df/dt) value indicates that the grid frequency is expected to fall below 48Hz, giving a few extra milliseconds to complete the tripping action.

The island's perimeter shall dynamically expand and shrink based on the generation capacity within the island and its load. In the event the island is formed when frequency dips below 48Hz, the island shall continue to operate in a stable condition.

The islanding and dynamic perimeter features of the scheme shall require a high-speed communication network to transfer the measured frequency, load, and generation readings from the remote sites to a central site. The communication network between the sites shall also carry protection signaling that will be used to initiate the decoupling action in the event of a grid failure and change the blocked / operative modes of the sites.

The central site shall be used to host the NMS and the visual displays to report critical information of the current state of the grid and the island. Control and configuration capabilities of the island and administration of control elements shall be through the NMS at the central site.

It is important to maintain the stability of the independent island when it is operating as a sole entity. When the island is in effect, the frequency of grid within the island is tied to the load and generation within the island. The frequency of the island is a function of the load and power generation. To monitor the frequency within the active perimeter, all installed PMUs at various bus forks shall measure and stream this information to the central site. This information will be used to actively shrink or grow the perimeter up to the island's maximum allowed outer perimeter.

This decoupling action shall isolate the island from the rest of the national grid. The loads forming the island shall continue to draw the power from the locally generated power within the island. The central site shall continue to monitor load and frequency data from all sites. Till the time the national grid does not recover, local load and local frequency of all sites of the island will be monitored to control the perimeter of the island. Once the national grid recovers and the grid frequency is in the acceptable range, the central site shall clear the alarm and notify the Digital Teleprotection (Protection Signaling Equipment [PSE] / DTPC) stack. The Teleprotection stack shall issue a clear command over the IP/MPLS network to the remote sites in operative mode and again connect these loads to the national grid.

The islanding scheme shall support 3 conditions on which the grid islanding procedure shall be invoked.

1. Under-frequency – When the grid frequency falls below 48Hz, the island shall be formed.
2. Rate of Change of Frequency (ROCOF) – When the ROCOF values being read and various point in the electrical system cross a set ROCOF threshold. The breach of such a threshold indicates that the drop or rise in the frequency is rapid and drifting. The rate of change of frequency is such that it shall dip below 48 and can be predicted by the current trend being reflected in the ROCOF values.
3. Manual – The grid operator wants to test the island or invoke the grind islanding procedure manually.

Using ROCOF as a tool to predict and preempt a frequency fallout and any such imbalance in the grid gives the grid operator the time to respond and take action. It also gives an automated system like the one being proposed in this report to take corrective action well in advance to prevent grid failure and damage to generation equipment.

Underfrequency relays (UFR) are a less accurate tool to detect under and over-frequency conditions in the grid. There are several steps that need to be taken in parallel and in synchronization with each other across a large grid island for the islanding operation to be successful. Accurately detecting when an island needs to be formed is the first step of island formation. Detecting a drift in the frequency of the grid based on a single point based on data from a single under-frequency relay is shall not be a reliable method. Local faults in the grid such as transient loads, line faults and sudden localized load variations may cause the frequency reported by the UFR to breach the parameters that have been set to initiate the islanding process.

Use of UFRs to gather as well as isolate the island from the rest of the grid does not keep the entire grid in view when taking critical islanding actions. For the Islanding solution to be reliable and cohesive, any decision that needs to be taken to add or remove any load and to isolate or reconnect certain regions of the grid should ideally be based on data collected from multiple sources within the island and the grid. This ensures reliability of data and makes the solution resilient to localized faults and occurrences.

Moreover, an islanding solution based solely on UFRs to report the data may not be able to act and report changes in the grid frequency at a rate that is required to make the islanding schema effective. Typically, a UFR takes between 0.5 to 3 seconds to read and report data which exceeds the time required for catastrophic events to bring down the grid. A similar solution based on data reported by PMUs shall be able to act received frequency reading readings at a higher rate and take automated decisions much faster to improve stability of the grid and the island. Such a solution shall also be able to modify the perimeter of the island dynamically based on data being collected from multiples sources including load and generation data. The input of more data points shall allow such a solution to more reliably and dynamically manage the island which is not possible to implement using UFRs.

Copyright: Valiant Communication Limited

About Valiant Communications: Valiant Communications is a manufacturer and exporter of a wide range of communications, transmission, protection, synchronization and cyber security products. It is an approved manufacturer to various major power utilities across the globe, with track record of successful installations of its communications, transmission, protection, synchronization solutions in more than 5000+ power sub-stations worldwide including at 765kV, 440kV, 400kV, 384kV, 220kV, 132kV, 110kV, 66kV and 33kV power sub-stations.