A Short Overview of Hydro-Québec’sDe-icing System Control Unit

Edited by Kathleen Davis, senior editorFrom a longer paper by Yves Brunet and Alain Blais, Hydro-Québec Équipement, and Yvon Dodier, Hydro-Québec TransÉnergie

Hydro-Quebec’s power system is exposed to severe weather conditions. For example, the utility experienced a severe storm in 1998 when more than 150 towers collapsed due to ice accumulation. To reduce the impact of such events, Hydro-Quebec is implementing a de-icing system at the Lévis Substation, which is one of the most critical substations in the utility’s T&D infrastructure.

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This de-icing system is based on an HVDC converter (250 MW, ±17.4 kV, 7200 A) that will be used to inject DC current into the overhead lines to melt the accumulated ice. A de-icing line circuit must be set up by closing or opening de-icing disconnect switches prior to injecting DC current.

The de-icing system can also be used as a Static VAR Compensator (SVC) (+250 Mvar, -125 Mvar), which will be its main use. The de-icing control unit (DCU) controls SVC and De-icer operation. It can be operated locally or remotely from the Regional Telecontrol Center.

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Because five power lines can be de-iced from Lévis, there exist many scenarios, and special automation was designed to control and overview the process.

The Steps Required

The lines are de-iced in three steps in the case of 735 kV lines and in one step in the case of 315 kV double circuit lines. (Figure 2 shows an example of a de-icing line circuit for line 7020.) In order to ensure the reliability of de-icing sequences and provide network security, a DCU will coordinate and supervise all the actions required for de-icing each line.

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The required power line is isolated from the rest of the AC network and configured in de-icing mode. Next, the DCU remotely controls the de-icing disconnect switches to set up a line de-icing circuit. Then, the DCU sends all the setpoint commands to the de-icing converter to slowly raise the DC current in the circuit up to the desired level of current. The DCU remotely opens the de-icing disconnect switches, and, finally, the DCU releases the power line back to the AC network.

The main requirements and constraints for the development of the DCU control system are:

  • De-icer equipment is installed in the existing substation. The lines to be de-iced must stay in normal operation during the entire period of DCU development and start-up.
  • De-icing line equipment pre-operational testing must be performed before the final installation of the SVC/de-icer.
  • The de-icer will be used on rare but critical occasions. Operators will be under heavy stress. The man-machine interface (MMI) must have a guided mode.
  • There are 13 line topologies for the five lines to be de-iced. Four lines have three de-icing circuit topologies and one has only one. There are between 40 and 90 actions per line to be performed to complete the de-icing process.
  • The DCU must directly operate equipment in remote substations. Because a communications failure is always possible, the DCU must offer the operator the possibility to manually confirm the equipment’s state in order to continue the de-icing sequence.
  • Flexible simulation sequences for line equipment and SVC/de-icer are required. These simulation sequences are used for control logic and MMI validation, pre-operational testing and operator training.

Figure 3 provides details on system architecture.

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  1. SVC/De-icer supplied as a turnkey system with controller, local maintenance MMI and DNP3 Interface with DCU.
  2. DCU with MMI, telecontrol unit (TU) and data acquisition and control unit (DACU). The DCU is dedicated to the de-icer and SVC operations.
  3. Existing Lévis Substation.
  4. Québec Regional Control Center. This center will remotely operate the SVC/De-icer.
  5. Eastern Data Processing Center. This center receives data from all the installations in the eastern part of the Province of Québec and dispatches data to the regional telecontrol centers.
  6. Remote substations.

       

      Examining the Sequential Function Chart (SFC)

      Hydro Québec uses its ALCID control system for the DCU, which is a proprietary system widely used at Hydro-Québec for substation control and automation. ALCID uses SFC as the programming language for automatic sequences. (SFC is a subset of Petri-net. The SFC used by Hydro Québec is based on the French C.03.190 standard with some extensions.)

      The main extension to the standard added by Hydro Québec is the hierarchical SFC reset command. This command activates the initial step of the SFC and deactivates all the other steps. This extension simplifies structured programming with SFC.

      For each one of the five lines to be de-iced, a sequence hierarchy was defined. The security management SFC is at the top of the hierarchy. The SFC sequences are regrouped into an SFC program.

      Each SFC program can be separately loaded into the data acquisition and control unit (DACU) without stopping the DACU. When a new version of an SFC program is loaded, other related SFC programs are reset by their security management SFC in accordance with the current context. (It is also the security management SFC—at level 0—that responds to loss of communications with the SVC/de-icer, DACU and/or the remote equipment depending on context.)

      In the event of a communications loss with remote substations during a circuit continuity validation or de-icing sequence, we (the SVC/De-icer?) wait until the end of the sequence and then reset all SFCs. (all the SFCs are reset only after the sequence ends). The SVC/De-icer will stop if there is a fault. It is not possible to start a new sequence until communications recovery has taken place.

      In the event of a communications loss with the SVC/De-icer, the SVC/De-icer will stop if the communications loss duration exceeds one minute. The circuit continuity validation or line de-icing sequence is reset after the SVC/De-icer stop timeout delay. Disconnect and release-line sequences can be executed. The master sequence will no longer authorize the selection of circuit continuity validation or line de-icing sequence.

      The master sequence starts when a line circuit is selected.

    • It gives sequence selection authorization depending on context.
    • It calls the sequence selected by the operator.
    • It indicates the sequence status (in progress, stopped, completed, success).
    • It resets the SFC sequence when the operator stops the sequence.

    Before or after a sequence, the operator can select another circuit within the same line. The master sequence will authorize sequence selection depending on the new context.

    All the sequences have the same general pattern. The sequence starts when it is called by the master sequence.

    • It executes the required actions one by one in a predefined order.
    • It confirms the required status after an action if the sequence is blocked and the operator manually confirms the required status.
    • It indicates the sequence status (waiting, suspended, blocked).
    • It is reset by the master sequence when the operator stops the sequence.
    • It indicates the end of the sequence to the master sequence and returns to initial step when the sequence call is reset.

    Simulation

    For process and I/O simulation, Hydro Quebec used the SPOC software from Cooper/Cybectec. A software utility program is available to generate the SPOC I/O configuration files from the DCU configuration files. Figure 4 presents the complete system simulation configuration used during the period of development of the sequential functions and during the factory acceptance testing in the laboratory. Al I/O points are simulated by SPOC simulators. Automatic sequences simulate the control behavior of the SVC/De-icer Control System, the switchgear apparatus (breakers, line switches, de-icing switches, etc.), the automatic control circuits and other signals connected to the DACU.

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    This complete system simulation has been useful for:

    • Testing the sequential functions developed in DACU-03D and DACU-04D.
    • Validating the system configuration and the MMI.
    • Simulating abnormal cases (loss of communications link, loss of DACU, etc.).
    • Demonstrating the behavior of the DCU as well as the MMI screens to operation technical staff.
    • Carrying out the official testing program for the DCU.

    At the beginning of the project, it was considered that the SVC/de-icer supplier should develop simulation scripts for the SVC/de-icer control interface. Unfortunately, this specification was not well-defined and the simulation scripts delivered were only useful for DNP3 and basic data acquisition and control function testing. Hydro-Quebec will have to develop its own simulation sequences for the SVC/de-icer control system interface.

    Benefits

    There are 158 SFC sequences for de-icer operations regrouped into 25 SFC programs and 48 SFC sequences for SVC operations regrouped into eight SFC programs. Given that each SFC program can be separately loaded into the DACU without stopping the DACU, maintenance people can modify only one SFC program at a time. Unmodified SFC programs do not need to be revalidated. Structured programming and simulation have allowed Hydro-Québec to speed-up the process of:

    • Client acceptance of DCU before delivery to Lévis Substation.
    • DCU commissioning.
    • Modifications and/or corrections of SFC sequences and/or DCU database with validation in laboratory before delivery to Lévis Substation.

    Current project status: SVC/de-icer commissioning will resume during fall 2008 and winter 2009.

    Yves Brunet and Alain Blais are with conception–automatismes, Hydro-Québec Équipement.

    Yvon Dodier is with automatismes de transport, Hydro-Québec TransÉnergie.

    This article is an adaptation of a longer paper given at DistribuTECH 2008. The longer paper can be sent by request. E-mail senior editor Kathleen Davis at kathleend@pennwell.com to receive a copy.

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The Clarion Energy Content Team is made up of editors from various publications, including POWERGRID International, Power Engineering, Renewable Energy World, Hydro Review, Smart Energy International, and Power Engineering International. Contact the content lead for this publication at Jennifer.Runyon@ClarionEvents.com.

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