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 Data Acquisition and Control (DAC) Function 

Table of Contents

Overview

Scope: The Data Acquisition and Control (DAC) function, used in transmission and distribution operations, comprises multiple types of mechanisms for data retrieval from field equipment and the issuing of control commands to power system equipment in the field, including among field devices, between field devices and systems located in substations, and between field devices and various systems (including, but not limited to, SCADA systems) located in DER and utility control centers and engineering/planning centers.

Objectives: The DAC function provides real-time data, statistical data, and other calculated and informational data from the power system to systems and applications that use the data. The DAC function also supports the issuing of control commands to power system equipment and the setting of parameters in IEDs and other field systems.

Rationale: Power system real-time data is source of most information required for power system operations. Control over the power system equipment can be achieved by issuing control commands and setting parameters.

The Data Acquisition and Control (DAC) function, used in transmission and distribution operations, comprises multiple types of mechanisms for data retrieval and issuing of control commands to power system equipment. These mechanisms are often used in conjunction with each other to provide the full range of DAC interactions. The DAC function, in turn, is used by other functions, such as Supervisory Control and Data Acquisition (SCADA) systems, Energy Management Systems (EMS), Protection Engineering systems, and Advanced Distribution Automation (ADA), as the means for their interactions with the power system equipment.

Direct Power Equipment Monitoring and Control

Narrative

Direct power equipment monitoring and control is performed by an Intelligent Electronic Device (IED), a Remote Terminal Unit (RTU), or other microprocessor-based controller, sometimes based on internally generated control commands and sometimes based on externally requested control commands. These controllers monitor sensors for data about the power system and their associated power equipment (the actual equipment connected to the power system). The communications links are often very short (a few meters) but can also entail multi-mile links. The communications media typically are copper wires or optical fibers, but can include power line carrier, radio-based media, and possibly other media. They either use internal applications or are instructed by other entities to issue control signals to associated power system equipment. For example:

·         A Load Tap Changer IED raises and lowers the transformer tap position according to pre-set algorithms, based on voltage levels sensed by Potential Transformers (PTs).

·         A circuit breaker IED issues an electro-mechanical or solid-state-based trip signal to a circuit breaker.

·         A DER IED controller senses status and measurements of a DER generator and its prime mover, and then issues start and stop signals.

Diagram

 

Steps for Direct Power Equipment Control by IEDs

An IED receives sensor data from a Potential Transformer (PT), or a circuit breaker IED issues a trip signal to a circuit breaker device.

 

#

Event

Name of Process/Activity

Description of
Process/Activity

Information Producer

Information
Receiver

Type of Info Exchanged

IntelliGrid Architecture Environment

1.1

Continuous or very frequent data retrieval

Monitor sensors

IED performs analog-to-digital and/or digital-to-digital conversions from sensor inputs, retrieving data from its associated power system equipment and from PT and CT sensors.

IED then performs basic engineering conversions on the raw data, processes the information, and determines if any subsequent actions are needed based on limit checking and other process results

Sensors

IED

Raw sensor data

Deterministic Rapid Response intra-substation environment

1.2

Processed data indicates further local action needed

Send control commands

IED issues control commands to power system equipment, based on the results of processing the input data from the field

IED

Other IEDs or power system equipment, such as circuit breakers, voltage regulators, capacitor bank switches, LTCs, reclosers, etc

Signal data

Deterministic Rapid Response intra-substation environment

 

Local IED Interactions

Narrative

Local interactions among Intelligent Electronic Devices (IEDs) are undertaken to respond to a relatively local situation. The communications media are typically LANs, point-to-point cables, and point-to-multi-point radio channels. Protection actions require very Deterministic Rapid Response communication channels, with response timeframes of 1 to 4 milliseconds. For example:

·         A protection IED issues a trip command over a Deterministic Rapid Response LAN to a circuit breaker IED within a substation, based on its detection of different power system measurements, such as low frequency, current overload, etc.

·         Multiple automated switch IEDs, using point-to-multi-point spread spectrum radio communications media, respond to a fault condition on a feeder segment by opening and closing switches to isolate the fault and restore power to unaffected feeder segments.

Diagram

 

Steps for Local Interactions Among IEDs

A protection IED issues a trip command over a Deterministic Rapid Response LAN to a circuit breaker IED within a substation, based on its detection of different power system measurements, such as low frequency, current overload, etc.

 

#

Event

Name of Process/Activity

Description of
Process/Activity

Information Producer

Information
Receiver

Type of Info Exchanged

IntelliGrid Architecture Environment

2.1

Continuous monitoring

Sensor monitoring

Each IED in the group monitors local power system equipment

Power system equipment

IEDs

Sensor data

Deterministic Rapid Response intra-substation environment

2.2

Fault in a feeder segment occurs

Fault detection

A fault occurs in a feeder segment. This fault is detected by one or more IEDs, including a protection IED in the substation.

Sensor or IED

IED

Fault sensor data

Deterministic Rapid Response intra-substation environment

2.3

Protection IED issues trip command

Trip command

The protection IED issues a trip command to the recloser IED. Using the mechanisms described in section 2.2.1, the recloser IED issues a trip command to its recloser.

Protection IED

Equipment

Trip command

Deterministic Rapid Response intra-substation environment

2.4

Recloser trips

Monitor response to command

The recloser trips and this information is received by automated switch IEDs on the affected feeder.

Sensor or IED

IED

Control response sensor data

Deterministic Rapid Response intra-substation environment

2.5

IED internal analysis results – multiple iterations

Local IED response to fault

IEDs near faulted feeder segment communicate and determine which switches should be opened and which closed. This occurs a number of times, depending upon the results of the IED actions, the results of the recloser actions, and the parameter settings in the IEDs. Each IED performs its actions via the 2.2.1 process.

One IED

Other IEDs

Digital electric data

Critical intra-substation environment

 

Computerized Field Systems Monitoring and Control of Field Equipment via IEDs

Narrative

Computerized field systems perform monitoring and control of field equipment via IEDs, such as a data concentrator or substation master or Automated Control and Data Acquisition (ACADA) (SCADA in a control center is considered in Section 1.4.5). These are generalized systems, as opposed to IEDs or controllers, and usually monitor and/or control more than one power system device. Data concentrators just pass data through them, acting primarily as communication nodes, although they may include a local database. Substation masters may include applications to perform some local interactions, or may help coordinate IED actions. ACADA systems may perform closed loop control (e.g. does not interact with the human operator before issuing a control command). The communications media can be LANs, copper wire, optical cables, microwave, radio, leased telephone lines, cellphones, and many other types. Data exchanges range from a few 10’s of milliseconds up to 1 second. Examples include:

·         Data concentrator in a substation monitors data from IEDs that are located on feeders connected to the substation. It passes some of this data to a SCADA system and passes control commands from the SCADA to the IEDs. It may collect sequence of events data and some statistical information in a database.

·         Substation master coordinates the protection settings of substation IEDs based on requests from the SCADA system for different response patterns. For instance, different protection trigger levels are set for recloser responses if a storm is pending, or if reconfiguration of a feeder impacts the expected fault current level, or if DER generation levels could cause fuses to blow unnecessarily.

·         Substation master provides information to automated switch IEDs on a feeder as to the actual configuration of a neighboring feeder. This information will permit the automated switch IEDs to take more appropriate action if a fault occurs.

·         Automatic Control and Data Acquisition (ACADA) performs Advanced Distribution Automation, by responding to field conditions reported by IEDs and issuing control commands for volt/var optimization, fault location, isolation, and restoration, multi-feeder reconfiguration, and other ADA functions.

Diagram

 

Steps for Computerized Field Systems Monitoring and Controlling via IEDs

Substation master coordinates the protection settings of substation IEDs based on requests from the SCADA system for different response patterns. For instance, different protection trigger levels are set for recloser responses if a storm is pending, or if reconfiguration of a feeder impacts the expected fault current level, or if DER generation levels could cause fuses to blow unnecessarily.

#

Event

Name of Process/Activity

Description of
Process/Activity

Information Producer

Information
Receiver

Type of Info Exchanged

IntelliGrid Architecture Environment

3.1

On-going monitoring of data by substation master

Data monitoring

Substation master receives digital data from IEDs within a substation and along adjacent feeders. This data can be transmitted periodically or upon significant change of an analog value or upon status change

Multiple IEDs

Substation master

Digital electric data

Critical intra-substation environment

3.2

Request by SCADA to change protection settings

Change settings

As requested by the control center SCADA system, the substation master determines the appropriate settings for protective relays and reclosers for a specific scenario (e.g. storm, changed feeder configuration)

Substation master

Protection and recloser IEDs

Settings

Critical Operations DAC

3.3

Power system event with IEDs responding

Sequence of events recording

A power system event occurs, to which the local IEDs respond. They then report their sequence of events to the substation master for inclusion with disturbance records.

IEDs

Substation master

IED SOE

Critical Operations DAC

3.4

Operator initiates trip of breaker

Select before operate (SBO) command

The substation master ensures that a control request from the control center is authorized, then passes the request to the circuit breaker IED for execution

Substation master

Circuit breaker IED

SBO control request

Critical Operations DAC

 

DER Management Systems Monitoring and Control of DER Devices

Narrative

DER management systems perform monitoring and control of a DER device, either at a customer site or within a substation or from a utility's distribution control center (see Figure 1‑1). The DER management system could be a DER owner’s SCADA system, a customer’s Building Automation System (BAS), an energy aggregator’s system, or a distribution operations SCADA system. Communications media can include virtually any type, so long as response times of a few seconds can be accommodated. Examples include:

·         Loss of power is detected at a customer site. The backup diesel generator starts up, the automatic transfer switch connecting the customer to the utility EPS opens, and the generator is connected to the customer’s local EPS (or just the critical equipment).

·         The owner of the DER device decides to reduce his load on the utility EPS by increasing generation. The DER operator implements this decision by setting new parameters in the DER management system. (These are manual actions by persons.) As an automated result, another generator is started by the DER management system, synchronized with the local EPS, and interconnected.

·         An energy aggregator sets groups of DER devices to cycle on and off over the next day, taking into account pollution limits, the real-time price of energy, and contractual arrangements with the owners of the DER devices.

·         While a DER device is interconnected with the utility EPS, a fault occurs on the feeder. The DER management system ensures that the DER device either trips off or the interconnection circuit breaker opens.

·         The DER management system collects sequence-of-events, performance data, and statistical information from DER devices in a substation.

Diagram

Figure DER Management Systems Monitoring and Control of DER Devices

Steps for DER Management System Monitoring and Control of DER Devices

The owner of the DER device decides to reduce his load on the utility EPS by increasing generation. The DER operator implements this decision by setting new parameters in the DER management system. (These are manual actions by persons.) As an automated result, another generator is started by the DER management system, synchronized with the local EPS, and interconnected.

 

#

Event

Name of Process/Activity

Description of
Process/Activity

Information Producer

Information
Receiver

Type of Info Exchanged

IntelliGrid Architecture Environment

4.1

DER owner decides to reduce load

Owner decision

DER owner contacts (calls, e-mails, alarms) DER Operator that additional energy from DER generation is needed.

DER owner

DER Operator

Call by person

Call – Outside Scope of IECSA

4.2

DER operator enters new parameters

Establish parameters

DER Operator sets new parameters for DER generation output in the DER management system.

DER Operator

DER Management system

DER data entry

User interface (Outside scope of IntelliGrid Architecture)

4.3

Start command

Start DER

DER management system issues start command to a DER unit.

DER management system

DER unit

DER start-up command

DER Monitoring and Control

4.4

DER Unit started

Synchronization

DER Unit starts and synchronizes with the Local EPS, and reports success and current operating measurements to DER management system

DER unit

DER management system

DER reporting

DER Monitoring and Control

4.5

On-going DER unit operations

Monitoring DER

DER unit reports current operating measurements to DER management system for operational information as well as historical and statistical information

DER unit

DER management system

DER historical and statistical records

DER Monitoring and Control

4.6

Environmental limit reached

Environmental limit

DER management system calculates that a diesel generator has reached its daily (assigned) limit of emissions, and issues a stop command

DER management system

DER unit

DER stop command

DER Monitoring and Control

4.7

DER unit stops

Stop DER

DER unit stops and shuts down. It reports back to the DER management system with its latest data

DER unit

DER management system

DER reporting

DER Monitoring and Control

4.8

DER unit reports received

DER reports

DER management system provides DER unit data to DER operator via a User Interface

DER management system

DER operator

User display

User interface (Outside scope of IntelliGrid Architecture)

 

SCADA Systems Monitoring and Control of Field Equipment and IEDs

Narrative

SCADA systems perform remote monitoring and control of field equipment and IEDs (see Error! Reference source not found.). The term “SCADA” is used here to imply any centralized system which retrieves data from remote sites and may issue control commands when authorized. These SCADA systems are typically located in a utility control center, but may include an engineering “SCADA” system which retrieves protection data or disturbance data, or a maintenance “SCADA” system which monitors the health of both power system and communications equipment.

SCADA system monitoring can use communication channels directly to IEDs, via Remote Terminal Units (RTUs), through a data concentrator, through a substation master, or through a DER management system. The communications media can include virtually any type, so long as response times of 1 second can be accommodated. Although typically seen as used only for real-time distribution operations, the data acquired by the SCADA system can be used by many different systems, applications, and personnel in the control center. This Use Case is limited to the monitoring and control function by SCADA systems; other Use Cases (e.g. ADA Use Case) describe their interactions with the SCADA systems.

SCADA system monitoring and control examples include:

·         Power system operations SCADA system receives real-time data from power system equipment via:

    RTUs

    IEDs inside substations

    IEDs along feeders

    Substation masters

    DER (or other generation) management systems

    Other control centers

    Manual entry

·         Power system operations SCADA system issues control commands to power system equipment in real-time via:

    RTUs

    IEDs inside substations

    IEDs along feeders

    Substation masters

    DER (or other generation) management systems

    Other control centers (if authorized)

·         Power system operations SCADA system receives metering information

·         Data management “SCADA” system receives power equipment configuration data from devices. It may have its own communication channels to the remote sites, or it may acquire this data through the distribution operations SCADA system

·         Engineering “SCADA” system receives sequence of events data, oscillographic data (special handling required), historical data, and statistical data. It may have its own communication channels to the remote sites, or it may acquire this data through the distribution operations SCADA system

·         Maintenance “SCADA” system receives data related to the health of power system equipment and communications equipment. It may have its own communication channels to the remote sites, or it may acquire this data through the distribution operations SCADA system.

·         Planning “SCADA” system receives data that can be used for statistical analysis of power system measurements: maximums, minimums, averages, trends, profiles, power quality metrics, etc, needed for short and long term planning.

Diagram

Steps for Monitoring and Control by SCADA System

Distribution operations SCADA system monitors and controls power system equipment via a multitude of mechanisms.

 

#

Event

Name of Process/Activity

Description of
Process/Activity

Information Producer

Information
Receiver

Type of Info Exchanged

IntelliGrid Architecture Environment

5.1

Establish an association between SCADA and RTU and/or IED

Establish association

Using an interactive process between an RTU or IED and a SCADA system, an association is established. This interactive process varies from protocol to protocol, but essentially entails setting up what data is available and what data is to be sent under what conditions. In some protocols, many of the steps are manual, while in others they are almost entirely automatic.

SCADA and RTU/IED

RTU/IED and SCADA

Association

Critical Operations DAC

5.2

Status change occurs in power equipment

Detect status change

A status change occurs in some power system equipment. This status change is “immediately” sent (usually within 1 second) to the SCADA system.  Depending upon the communication “services”, the status value can be sent periodically, or can use the “report-by-exception” service, which sends a status value only if it changes

IED which is sensing power system equipment

SCADA system

Status change

Critical Operations DAC

5.3

“Significant” change in a measurement value

Detect significant measurement change

A significant change occurs in a measured value. (Significant implies it exceeds some pre-established limit.) This changed value is sent according to pre-established protocol services: e.g. report-by-exception sends it immediately (within 1 to 2 seconds), while periodically sends it when the time period elapses.

The protocol also determines what information is included, such as timestamp, quality code, etc.

RTU which is sensing power system equipment

SCADA system

Measurement change

Critical Operations DAC

5.4

SCADA issues control command

Issue control command

Either an operator or an application issues a control command through the SCADA system to an RTU or IED. These control commands are typically immediately implemented by sending a signal to the power system equipment

SCADA

RTU or IED which initiates signals to power system equipment

Control command

Critical Operations DAC

5.5

SCADA sends parameter settings

Set parameters

Either an operator or an application sends a parameter setting through the SCADA system to an RTU or IED. These parameter settings may be stored for later use or may be used immediately to initiate a signal to the power system equipment, such as a raise or lower control command

SCADA

RTU or IED

Parameter setting

Critical Operations DAC

5.6

SCADA requests specific data

Request data

Either an operator or an application requests specific data to be sent to the SCADA system from an RTU or IED.

SCADA

RTU or IED

Request

Critical Operations DAC

5.7

Sequence of Events log

Transmit sequence of events records

An RTU or IED has collected Sequence of Events log and initiates its transmittal to the SCADA system

RTU or IED

SCADA

SCADA SOE

Critical Operations DAC

 

 

 

IntelliGrid Architecture
Copyright EPRI 2004