The Energy Independence and Security Act of 2007 (EISA 2007, USA)
data acquisition, measurement, control, protection, metering and monitoring, etc.; meanwhile it supports advanced functions such as real-time automatic control, intelligent regulation, analytical decision-making online, collaborative interaction.
Adopting advanced, reliable, integrated, low-carbon, and environmental-friendly intelligent devices, smart substations are based on the overall station information digitalization, communication platform networking, and information-sharing standardization.
The first full digital substation in France
The smart substation includes two main parts
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Most of them have no or small changes on the structure of the existing primary equipment (e.g., the installation of sensors).
Connected with the primary equipment using cables, the CBM IED uploads the status information of the primary equipment through GOOSE to control it in a real-time way. Meanwhile, connected with the secondary equipment via optical fibers, the CBM IED receives downlink control commands from the secondary equipment.
Forms of intelligent primary equipment
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(1) Keeping the actuators (such as spring clamps, hydraulic valves, a disconnector motor, an earthing switch motor, and a spring motor) and their electromechanical control loops unchanged, the CBM IED and the online monitoring unit are installed in the circuit breaker control cabinet, according to the partition of interval.
(2) Keeping the actuator and its electromechanical control loop unchanged, the CBM IED with online monitoring function is installed in the circuit breaker control cabinet dispersedly, according to the partition of interval.
(3) Keeping the actuator unchanged, the CBM IED performs electromechanical control and drives a circuit breaker tripping/closing coil, motors of isolator, a hydraulic pump, and a spring directly. Moreover, the CBM IED also has the online monitoring function, which is called “intelligent agencies”.
The potential failure can be found early, and the power supply reliability can be improved.
The online monitoring can monitor and judge the running power equipment continuously to provide the necessary judgment basis for the state maintenance of the power equipment.
- Online monitoring for transformer partial discharge.
- Online monitoring for transformer on-load tap-changer.
- Online monitoring for transformer bushing insulation.
- Online monitoring for transformer oil temperature, winding temperature, and load.
- Online monitoring for transformer micro-water in oil.
- Transformer oil’s gas chromatography monitoring.
(1) Partial discharge. The insulation performance of GIS is an important condition to ensure its safe operation.
(2) Monitoring of SF6 gas. Used for insulation and arc extinguishing, the performance of SF6 gas will be an important parameter of GIS. Hence, it is necessary to monitor pressure, leakage, and micro-water content of SF6 gas.
(3) Monitoring of mechanical characteristics of a circuit breaker. Monitoring for currents of closing and tripping coils: a compensated Holzer current transformer is used to monitor the current waveforms of the closing and tripping coils online.
Excellent insulating property
For electronic transformers, signals from the primary side are transmitted to the secondary side using optical fiber, whose insulating structure is simple, and cost grows slowly with the increase of voltage level.
Free of magnetic saturation and ferroresonance
Iron coils are no longer used in electronic transformers, thus they are free of magnetic saturation and ferroresonance, which results in the desirable transient response and stability, ensuring the reliability of the system.
Antielectromagnetic interference
For electronic transformers, optical fiber connects the two sides, which ensures the electrical isolation between them. Therefore, there are no risks of short or open circuits. Furthermore, since magnetic coupling does not exist, the transformer has antielectromagnetic interference.
Wide scope of transient response and high measuring accuracy
Their rated current can range from dozens of amperes to thousands of amperes. The overcurrent can be up to tens of thousands of amperes.
Wide range of frequency response
Adapted to electric power measurement and the digitization, computerization, automation, and intelligentization of protection
In practical engineering application, electronic transformers are classified into two types:
active electronic transformers and
passive electronic transformers.
They include optical current transformers (OCTs), optical voltage transformers (OVTs), electronic current transformers (ECTs) using air core coil or lowpower iron core coil, and electronic voltage transformers (EVTs), respectively. To date, ECTs and OCTs have been applied in the field with the realization of temperature stability and craft consistency.
The station level contains the common equipment for the substation – the HMI, communications interfaces, etc. – while the bay level is more circuit specific and the equipment for each circuit (such as the protection relays and local control units) reside here.
The primary equipment (such as instrument transformers and disconnectors and circuit breakers) is within the process level.
While the connections between levels have traditionally been copper wiring, the application of substation communication buses led to a reduction of cabling. IEC 61850 now enables devices from different manufacturers to be connected to the same communication bus and share information in a truly interoperable way. Not only can devices from different manufacturers be applied, but status signals can be shared between devices, meaning that multiple connections of plant status signals, etc. are no longer necessary – once the signal is configured for one device, it can be shared to others connected to the network in the substation. However, all these interoperability and interchangeability features require a standard configuration specification.
Protocols in substations
Tripping signals too can be issued via GOOSE (generic object-oriented system events) message over the network rather than conventional wiring, and a truly digital substation has become a possibility and reality. Figure shows some of the standards used in substations prior to the release of IEC 61850 and the comparable IEC 61850 parts. Note that while the substation bus and process bus are shown as being separate networks, they could in practice both be part of one single network.
Integrated information platform and advanced applications
The information integration platform provides standardized information access interfaces for intelligent applications and remote systems by collecting the whole substation supervisory control and data acquisition (SCADA) data, protecting information data, recording data, metering data, and online monitoring data. The platform solves the problems of too many station control systems and interfaces, poor data sharing and applying synthetically.
Based on the information integration platform, there are advanced functions, such as:
One-touch sequence control
Source-end maintenance
Intelligent alarm and fault comprehensive analysis
Smart ticketing
Optimization control of intelligent load
Station and Process Bus Architecture
Full advantage of all the features available in the new communication standard can be taken if both
the station and process bus are used.
Figure shows the functional hierarchy of such a system. IEC 61850 communication-based distributed applications involve several different devices connected to a substation LAN.
MUs will process the sensor inputs, generate the sampled values for the threephase and neutral currents and voltages, format a communication message, and multicast it on the substation LAN so that it can be received and used by all the IEDs that need it to perform their functions.
Another device, the IO unit (IOU) will process the status inputs, generate status data, format a communication message, and multicast it on the substation LAN using GOOSE messages.
All multifunctional IEDs will receive the sampled value messages as well as the binary status messages. The ones that have subscribed to these data then process the data, make a decision, and operate by sending another GOOSE message to trip the breaker or perform any other required action.
Simplified communication architecture of the complete implementation of IEC 61850
The number of switches for both the process and substation busses can be more than one depending on the size of the substation and the requirements for reliability, availability, and maintainability.
An illustration of how the substation design changes when the full implementation of IEC 61850 takes place
All copper cables used for analog and binary signals exchange between devices are replaced by communication messages over fiber. If the DC circuits between the substation battery and the IEDs or breakers are put aside, the “copper-less” substation is a fact.
The smart substation protection system adopts the hierarchical construction idea, synthesizes the panoramic data information of power grid, constructs the hierarchical protection control systems consisting of the time dimension, space dimension, and functional dimension.
The hierarchical protection control system is composed of
the local protection for the protected object,
the station area protection control for the substation, and
the wide-area protection control for the multiple substations in the area, which improves the existing relay protection performance, safety, and stability control levels and strengthens the first line of defense and the cooperation between the second and third line. It is helpful for building a more stringent security system of power grid.
In the local protection for a single object to be protected, the independent information of the protected object is used for judging and the fault is cutoff reliably and rapidly. The station area protection control for the substation is used for a wide protection system, and the instruction is sent through the station area protection.
The local level, station level, and wide-level multi-level protection control cooperate with each other to achieve the full range of power protection control coverage.
The system of hierarchical protection control
In the time dimension, the local protection of the various types of primary protection has no time delay (20–30ms). With the sub-delay, the backup protection achieves mutual cooperation. In order to meet the selectivity and reliability, the speed of the protection is sacrificed (0.8–1.2s).
Station-level and wide-area protection can utilize the comprehensive information to speed up local backup protection (0.3–0.5 s). The protection and stability control of each level cooperates with each other to enhance the relay protection performance and stability control level.
Throughout the developed world, the electric utility sector is beginning a fundamental transformation of its infrastructure to overcome the present challenges faced by the sector. These transformations are aiming to make the grid “smarter” and the resulting outcome is referred to as a “smart grid”. Advances in technology over the years and the introduction of microprocessor-based monitoring, control, protection, and data acquisition devices have made a marked improvement in the operation and maintenance of the transmission and distribution network. It allows substations in a smart grid to move beyond basic protection and traditional automation schemes to bring complexity around distributed functional and communication architectures, more advanced local analytics, and data management.
Thus, digital (or smart) substations are the cornerstone and significant support of strong smart grids, which bring a number of new technologies and promote a new generation of energy revolution.
