| Internet-Draft | energy grids | June 2022 |
| Makhijani | Expires 26 December 2022 | [Page] |
This document describes communications specific scenarios emerging from the advances in the energy grid applications. These scenarios are derived to highlight that their behavior differs from the traditional best-effort networks and inter-networking paradigms, thereby leading to new requirements. Traditional energy grids have been a one way power distribution system, managed centrally. However, new sources of power generation and provisioning for efficient use of energy, requires two-way communication and coordination between different power generating and consuming entities in the power grid networks.¶
This note is to be removed before publishing as an RFC.¶
The latest revision of this draft can be found at https://kiranmak.github.io/draft-km-energygrid/draft-kmak-intarea-energygrid.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-kmak-intarea-energygrid/.¶
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The traditional power grids are a single-source centralized power distribution network. Power grid infrastructure involves a large power plant generator and from there on that power to be distributed over large geographical areas using transmission lines to the utility customer.¶
Essentially, the energy grid network is a large scale control system which is evolving with a goal of efficiently utilizing every unit of power generated.¶
The demand for energy will continue to grow; at the same time, it is difficult to expand resources in the energy grids and the transmission lines. There is always a possibility that when the demand for the energy goes very high, the power station will have to operate at full capacity or will re-distribute energy load from one customer-side substation to the other. Such power surges are not always predictable, therefore, the consumption must be done dynamically on-demand with the help of automated controls and tools.¶
Secondly, the energy grid infrastructure continues to evolve to connect new sources of energy into the grid. This also requires finer granularity of control to switch power-sources at the right time and without disruption based on pricing and on-demand parameters. Such type of actions should not have adverse effect on the stability of the networks.¶
Electrical grids and substations present difficult operating conditions for plant operators due to the hazards related to high voltages and current faults occur, requiring for safety of operations.¶
With the above mentioned challenges, this document provides role of communication systems to support automation and remote operation scenarios in the electric power grids.¶
This document also provides a background of the power-grid architecture to add more context to the discussions on scenarios requiring closer integration with the communication technologies.¶
are used in the power grids to detect defects and abnormal conditions in lines or apparatus to initiate appropriate control circuit action.¶
are microprocessor-based devices in the power systems that transmit and receive data or control external device such as microprocessor-based voltage regulators, protection relays, circuit breaker controllers, etc. that can communicate with other devices in the network.¶
Distributed energy resources are small, modular, energy generation and storage technologies that provide electric capacity or energy closer to the customer site. Typically producing less than 10 megawatts (MW) of power. DER systems may be either connected to the local electric power grid or be stand-alone applications Examples of DER technologies include wind turbines, photovoltaics (PV), fuel cells, microturbines, etc. [FED-ENERGY-MGMT]. DER involves power electronic interfaces, communications and control devices for efficient operation of multiple components of power management.¶
is used to convert voltage and current readings from potential and current transformers, respectively, into digital data and publish them as Sampled measured values.¶
The centralized power grid systems is a combination of devices and controllers operating at power generation, transmission, distribution substations and customer premises.¶
residential
cutomer
/\
| |
transmission +--+
/\ distribution |
/T\ +--+ |
+----+ +---+ | | |-------+
| |------| |----|-----+--+
| |------| | +--+
+----+ +---+---^------┤ ├-------+
bulk /T\ +--+ |
power /│\ sub- |
generation station /\
/ \
| |
+--+
industrial
customer
The entire grid relies on traditional operational technology (OT) functions and communications. It requires SCADA or similar setup to monitor and control the voltage and power in each substation associated with the transmission, distribution and customer sites . Several of these functions are identical focusing on the protection and distribution of electric current flowing through.¶
Time synchronization [SYNC] is an important aspect of power grids since accurate timing is used to detect when and where malfunctions or disruption in power distribution occurred. Time synchronized electric signals guarantee that current flowing through lines is in phase (ref and use case??)¶
TODO: Add more on limitations.¶
Communications in electric power systems are at two levels. >1. Intra-substation communications: To facilitate connectivity and control functions relating to substation automation. >2. Inter-substation communications: To facilitate connectivity for phase synchronization, load (re-)distribution and topology related functions.¶
The reference design used below in Figure 2 is based on IEC 61850 process bus. It is part of the T1-1 substation automation reference case study [RT-MSGS].¶
control and enterprise applications
.-. .-. .-.
( ) ( ) ( )
'-' '-' '-'
| | |
|----------LAN--or--WAN--layer------------|
|-------------------.-.-------------------|
( ) Firewall
'-'
+-------------------+ '-----'
|Interconnecting NE |----( SCADA )
+--:------:-------:-+ '-----'
/------| : |-----\
/ : \
===== : ===:= : ====*
+-| |---| : +-| |-+ : +----| |---|
| ===== | : | ===== | : | =/=== |
| | | : | | : | / |
+-+ +-+ +-+ :+-+ +-+ :+-+ +-+ +-+ _|
+-+ +-+ +-+ :+-+ IEDs+-+ :+-+ +-+ +-+
│ │ | : | │ : │ | |
:--------------:─-----------:------------:
:--------------:------------:------------:
(protection & safety equipment - voltage, current
transformers, circuit breaker, over-current protection)
The communication requirements are documented in IEC 61850: Part 5 standard and an overview of the communication architecture and messages are described in the [IEC-SPEC] paper.¶
Note: since this requires purchase of the copy of the standard, reference to this document is not added. Instead [IEC-SPEC] and [RT-MSGS] provide indirect references with sufficient context.¶
Power grid systems use different types of messages [RT-MSGS] as below.¶
One of the concerns with the Ethernet based payloads on process and station bus is that the Ethernet is a broadcast medium and without appropriate address validation (or lack of it) substation may be susceptible to flooding attacks. See [SMV-ATTACKS] for more vulnerabilities in SMV and GOOSE protocols.¶
+------+ +---+
|SCADA | MMS |RTU|
| |--------->| |
+------+ +---+
|
|Station Bus (MMS TCP/IP)
--+-------+---+-------+
+<=========>| |
| GOOSE +--+ +-+-+
+---+ | | | | (IEDs)
| | +-++ +-+-+
+-+-+ | |
| | |
---+--+----+---+-------+---
| | Process Bus (SV)
| -- |
.---+ .|. .-. |
( MU) (MU ) (MU --+
'-' '-' '-'
All the protocols use Ethernet addresses for lower layer interface (MUs) and IP addresses for IEDs and above.¶
see table below.¶
Note: This section should be moved.¶
Within the IETF technologies, some work on smart-grid is being done. [RFC6272] provides guidance for smart-grids to use existing IETF protocols.¶
Forwarding IPv6 packets over PLC interfaces is described in [I-D.ietf-6lo-plc]. It only relates to advanced metering infrastructure and disucsses how IPv6 packets are transported over constrained PLC networks, such as ITU-T G.9903, IEEE 1901.1 and IEEE 1901.2.¶
There are additional functions and characteristics necessary as well such as those related to latency guarantees, resiliency and reliability.¶
This section describes a broad view of the use cases requiring different perspective related to the communication in power-grid systems.¶
Smart grids are specifically defined as technologies that rely on connectivity to leverage and digital technologies to perform different power distribution functions.¶
We cover 3 scenarios:¶
Distributed energy resources (DERs) enable mechanisms to store locally generated energy for example from wind, solar, micro-turbines etc. They are smaller, cleaner and cheaper sources of energy as compared to bulk power generation.¶
The DER mechanisms require precise control and monitoring procedures.¶
IEEE-1547-2018 describes connection and inter-operability interface between bulk power utility and a DER. It is a technology agnostic specification, however, mandates a communication interface to exchange operations, capabilities and requirements between EPS and DER.¶
TODO: add examples.¶
Connecting different types of DERs to the grids leads to a large-scale single deplyoment requiring explicit resource co-ordination.¶
TODO:¶
The Substation automation system is responsible for control, monitoring and safety of transmission equipment in substations. It uses well-known industry control technologies like SCADA system and process bus to carry out sampled measurements of various operational parameters such as voltage, current, etc. It also sends command to several types of switchgear equipment such as transformers, voltage equipment, and circuit breakers over communication network.¶
Substation automation system uses process buses to control and monitor switchgear equipment to read voltage and frequency values.¶
The core functions of substations are:¶
The messages mentioned above are critical to the operations of the grid. They require guarantee of in-time and ordered deliveries and high reliability.¶
Messages for substation communication have been identified based on their criticality in IEC 61850. The messages types are mapped according to their communication performance requirements shown in Table 1 along with their types. The network is hybrid, it transmits critical and real-time messsages directly over the link layer. For example, type1, 1A are time-critical and are carried over the Ethernet directly. The 'type 2' are medium speed message (type 2) and several others are non-critical (source: [RT-MSGS]).¶
| Message Type | Example Application | Time Constraint |
|---|---|---|
| 1A--Fast messages, trip | Circuit breaker commands and states (GOOSE) |
<=3 ms |
| 1B--Fast messages, other | same as above | <=20 ms |
| 2--Medium speed messages |
RMS values calculated from type 4 messages |
<=100 ms |
| 3--Low speed messages | Alarms, non-electrical configurations | <=500 ms |
| 4--Raw data messages | Digital representation electrical measurement (SV) |
<=3 ms |
| 5--File transfer functions |
Files of data for recording settings |
<=1000 ms |
| 6--Time synchronization messages | synchronization | none |
In the current design, potential limitations that prevent complete automation of substations maybe observed as:¶
To summarize, automation requires leveraging IT-grade software and services. Then allowing those services to directly control and monitor the substations.¶
Smart-grids are a network of all the components in production and consumption of powers. It is necessary to interconnect different sources of energy, have a system level view of where peak-demand or consumption is changing, where faults are occurring and how energy can be used efficiently overall.¶
This requires finer granularity of monitoring, control, and data acquisition of the electricity network which will extend down to the distribution pole-top transformer. It can also extend to individual customers, either through the substation communication network, by means of a separate feeder communication network (chapter 22, [POWER-SUBS]).¶
- Metering - Wide area monitoring (using synchrophasors) -- use of time synchronization for phase matching in distribution network. - Power conditioning - Electricity storage¶
TODO¶
This document has no IANA actions.¶
TODO acknowledge.¶