Integration SCADA Systems into Smart Grid.

AbstractNomenclatureIntroduction

Body

How SCADA Works

A SCADA system for a power distribution application is a typically a PC-based software package. Data is collected from the electrical distribution system, with most of the data originating at substations. Depending on its size and complexity, a substation will have a varying number of controllers and operator interface points.

In a typical configuration, a substation is controlled and monitored in real time by a Programmable Logic Controller (PLC) and by certain specialized devices such as circuit breakers and power monitors. Data from the PLC and the devices is then transmitted to a PC-based SCADA node located at the substation.

One or more PCs are located at various centralized control and monitoring points. The links between the substation PCs and the central station PCs are generally Ethernet-based and are implemented via the Internet, an intranet and/or some version of cloud computing.

In addition to data collection, SCADA systems typically allow commands to be issued from central control and monitoring points to substations. If desired and as circumstances allow, these commands can enable full remote control.

Supervisory Control and Data Acquisition (SCADA) systems are basically Process Control Systems (PCS) that are used for monitoring, gathering, and analyzing real-time environmental data from a simple office building or a complex nuclear power plant. PCSs are designed to automate electronic systems based on a predetermined set of conditions, such as traffic control or power grid management. Some PCSs consist of one or more remote terminal units (RTUs) and/or Programmable Logic Controllers (PLC) connected to any number of actuators and sensors, which relay data to a master data collective device for analysis. Gervasi (2010) described SCADA systems with the following components: Looking at the overall structure of a SCADA system, there are four distinct levels within SCADA, these being:

i. Field instrumentation,

For application of Electrical Power Systems the following measurements are required:

Electrical Measurement Sensors

Basic Parameters Measured

Voltage Current Time

Derived parameters

True power and RMS values – averaged over cycle Apparent power, power factor and VAR* Accumulated energy (watt-hours) Minimum and peak (e.g. voltage sag) Harmonics, sub-harmonics and flicker

Phase and frequency

*Volts-Ampere Reactive (power)

Power measurements

True power (Ptrue) is average of P(t) = V(t)*I(t) over a cycle Metering (revenue) always uses true power Apparent power (Papr) = Vrms * Irms Greater than true power if load is partly reactive (e.g. motor) Power factor (cos θ ) = Ptrue/Papr Less than 1.00 for non-resistive loads Precision of 0.1% requires 14-bit a/d or better True power meter chips available (e.g. CS5463) Often three phase needed.

Discussion of Non-Electrical Smart Grid Sensors

Smart Building Concept HVAC Energy Conservation Substation/ Transmission

HVAC Sensors (Heating, Ventilation and Air Conditioning)

Temperature

Humidity Air Flow Air quality (gases: CO2, CO, VOC) Also Actuators (control of heating, ventilation, AC)

Air Quality Sensors for smart buildings

Main gases:

Carbon Dioxide (CO2)

CO2 buildup in rooms when people present – signal for increased ventilation

Volatile Organic Compounds (VOC) and Carbon monoxide (CO)

Potentially harmful gases (possibly toxic also)

Signal Conditioners

Requires both analog and digital

Multiple sensor technologies complicates design

Energy Conservation Sensors

Temperature

Illumination

Occupancy sensors

Wireless room controls (e.g. lighting)

Remote access (Smart grid, Internet)

DALI -- lighting

Digital Addressable Lighting Interface (DALI) was developed for remote lighting control (e.g. dimmers)

Rugged bus (64 devices, data & power on 2-wire bus)

Asynchronous, half-duplex, serial protocol at 1200 Baud

Requires controller (master) or gateway

More popular in Europe

DALI – for sensors

DALI extended to general purpose sensor bus (sensoris slave)

Advantage of power and data on same 2-wire bus

Higher data rate (9600 baud)

Allows mix of standard and sensor DALI format on bus

Allows TEDS and standard formats for sensors

Actuators als

PLCs and / or RTUs,

A remote terminal unit (RTU) is a microprocessor-controlled electronic device that interfaces objects in the physical world to a distributed control system or SCADA (supervisory control and data acquisition) system by transmitting telemetry data to a master system, and by using messages from the master supervisory system to control connected objects

iii. Communications networks and

iv. SCADA host software.

SensorsController

Applications of SCADA Systems

Distribution and Substation AutomationFault protection and managementAdvanced Metering infrastructureEnergy Management