A centralized protection and control system using a well proven transmission class protection relay

Chee-Pinp Teoh and Graeme Lloyd, GE Grid Solutions, UK, Rich Hunt, GE Grid Solutions, USA, and Gerardo Rebollar, GE Grid Solutions, France

Centralized Protection Solution Today

Centralized Protection Solution Today
There are many permutations of how centralized protection and control can be implemented. Proof of concept CPC devices have been based on industrial computers, due to the needs of software development, and not the true requirements of substation protection device.
Industrial computers are commonly used in utility substations to run more software-based applications such as SCADA services, control functions, HMIs, DER management, wide area fault detection and isolation, and microgrid integration and control. However, protection functions require a real time consistent and deterministic 10 ms-40 ms operating time.
The challenge to implementing protection functions in an industrial computer is to have a real-time operating system to run protection applications. The concern is in part due to technical considerations about running real-time and non-real-time operating systems in the same device for 24 hours a day, 365 days a year for a 20-year service life.
Also, the CPC system needs to protect a high number of bays, for example 24 bays for a typical size substation. This will require the computer to process large numbers of SV, including filtering, re-sampling, and handling missing samples deterministically. The conventional relay relies on Field Programmable Gate Arrays (FPGA) to manage values data, but FPGAs are not typically available in a standard industrial computer.
It is also important to remember that centralized protection devices will be installed in substations and must meet all the expected requirements in substations.
The device must pass all the environmental tests specified in IEEE 1613 and IEC 61850-3, including electromagnetic interference, surge immunity, and fast transients. For a CPC to be a successful solution, a utility must have confidence in the computing platform, both the hardware and the software or firmware.

Centralized Protection Solution with Proven Transmission Relay
A realistic approach to CPC is to base the design on well proven transmission class relay.  Once relays become optimized for process bus, the only limitation to the number of protection zones is the number of SV streams, and the capabilities of the processor to handle the data and the functionality.
Busbar protection relays are coming on to the market that accept up to 24 SV data streams, so the complete protection of small substations in a single relaying platform is possible.
A good concept to further prove CPC is to start with protection of a complete distribution substation. This involves a limited number of protection functions to use, lower risk in case of performance issues, and easier integration into the power system.
The CPC device therefore uses protection algorithms already developed for the relay platform, simply implementing more instances of these proven functions.

Proven protection algorithms for feeder, bus, and transformer protection:  By utilizing the spare processing power in an existing transmission-class protective relay hardware, this is relatively simple concept to develop off of existing hardware platforms. Because it is based on an existing relay platform with a proven operating history in substations, this solution offers a more secure, mature, and stable solution.

Proven hardware platform: A transmission class protection relay is a custom hardware specifically designed and type tested to the highest requirement of the harsh substation environment. The relay has comprehensive device health diagnostic tests at startup and continuously during run-time, preventing any failure to cause malfunction to the grid system. A transmission class protection relay also has a full portfolio of hardware options such as redundant power supply, conformal coating to protect the printed circuit boards, inter-substation C37.94 direct fiber communication, RTDs option, contact Inputs/Outputs option.
The hardware cost for a transmission class protection relay is comparable to an industrial computer. However, the relay platform is designed to operate in the harsh environment of a utility substation for more than 20 years, with a proven history of reliability. This far exceeds the shorter design life of an industrial computer.

A robust cyber security implementation:  The relay platform is already implementing cyber security that meets utility requirements. As the platform is upgraded for new requirements and capabilities, this is automatically done for the CPC as well. The relay platform meets NERC CIP, NIST, ISO, provides remote authentication, authentication without passwords, RBAC, syslog, encryption.

Support for multiple SCADA protocols (IEC 61850 and legacy protocols): The transmission class relay supports the most popular industry standard protocols enabling easy, direct integration into monitoring and SCADA systems such as IEC 61850 Ed. 1 and Ed. 2 Station Bus, IEC 61850-9-2LE / IEC 61869 Process Bus, and IEC 61850-90-5 PMU over GOOSE. Also, legacy protocols such as DNP 3.0 (serial & TCP/IP), Ethernet Global Data (EGD), IEC 60870-5-103 and IEC 60870-5-104, Modbus RTU, Modbus TCP/IP

Numerous communications ports to support separate connections to station bus, process bus, and engineering networks simultaneously: A transmission class relay is designed to support different communication network architectures, including SCADA/station bus, independent engineering access port, and process bus networks. This includes enough ports for each network to support industry standard communications redundancy methods such as PRP (parallel redundancy protocol) and HSR (high-availability seamless redundancy). For small distribution substations, it is convenient to have up to 8 process bus ports to allow simple point-to-point communications, without a network or switch, as in Figure 3.

Wide area monitoring and control:  Using a transmission class protection relay as a CPC automatically brings in other transmission features such as synchrophasors. The device can act as a phasor measurement unit (PMU), streaming data as per IEEE C37.118 or using R-GOOSE and R-SV as defined in IEC 91850-90-5. This means the CPC can easily integrate into wide area monitoring and protection and control schemes, as well as provide inter-substation signaling.

Scalable solution:  The number of bays in the substation is getting higher. The CPC solution must be scalable, down to small few bays substation and up to many bays in huge substations. A CPC is only as scalable as the number of SV streams the device can subscribe to. Once this limit is reached, multiple CPC devices are required. For example, for a smaller substation with 20 bays, a single CPC unit box will do; whereas for a larger substation of 40 bays, two CPC units could provide adequate protection.
Figure 4a illustrates two CPC units connected to the process bus network, but they only subscribe to data from the PIUs associated with a specific part of the bus. Figure 4b shows the same concept using an HSR ring for the process bus communications.

Let?s start with organization in protection testing