Emergency & Restoration - Over-frequency protection module
1.Description of the use case
1.1 Name of use case
- Name of the use case:
- Emergency & Restoration - Over-frequency protection module
- Area Domain(s)/ Zone(s):
- Transmission / Operation
1.2 Version management
| Version No. | Date | Name of author(s) | Changes | Approval status |
|---|---|---|---|---|
| 1 | - | EMSS | ||
| 2 | - | EMSS | Actors updated |
1.3 Scope and objectives of use case
Transmission system operation during emergency and restoration
Obj. 1: Create a centralized system that would simulate the lack of limited sensitive frequency mode-overfrequency (LFSM-O) on generating units in the power system
1.4 Narrative of use case
The Emergency & Restoration - Over-frequency protection module (OFPM) is designed as a replacement for the missing or insufficient controllers on generating units in the power system which can operate in limited frequency sensitivity mode – over-frequency (LFSM-O).
In the CROSSBOW project, two conceptual solutions for over-frequency protection system were developed, as a replacement for the missing or insufficient LFSM-O controllers (as defined in EU Regulation 2016/631 – Network Code on requirements for grid connection of generators) on generators in Serbia and in the region of Southeast Europe. According to EU Regulation 2017/2196 (Network Code on Emergency and Restoration), such a system must properly disconnect the generators. The first solution implied that the over-frequency protection system calculates settings for each generator in a predetermined order provided by TSOs (which takes into account local congestions), starting with 50.2 Hz (and up to 52Hz). These calculations are performed every 5 – 15 min due to changes in production in real time. In the event of a critical frequency, the Over-frequency Protection (OFP) system sends a command for generator disconnection to selected generators. In the case of application at the regional level, this system takes care not to cause unacceptable flows on the interconnecting transmission lines when the generator is disconnected by the over-frequency protection. The second solution implies that the generators, based on real-time measurements and calculations based on the developed algorithm, are assigned one of the predefined levels of over-frequency protection in the frequency range 50.2 - 52 Hz. Local constraints are controlled by assigning different levels of OFP to the protection devices on generators in one power plant. The OFP algorithm fills the quotas for each level of the over-frequency protection so that the effect corresponds to the virtual activation of the LFSM-O on all generators in the system. This solution was simulated for both national and regional levels. Based on CROSSBOW results, the modified over-frequency protection system will be implemented within R2D2 project in the transmission system of the Serbian TSO. As not all generators are equipped to carry out above given technical solution for the Emergency & Restoration - Over-frequency protection module (OFPM), they will be divided into several groups as follows: 1. The first group of generators are generators that are equipped with LFSM-O and they do not participate in the OFPM. 2. The second group of generators will be assigned fixed over-frequency protection settings (where there are no technical possibilities for remote signal sending neither LFSM-O controllers are installed) – this is not the part of this use case 3. To the third group (where there are technical possibilities for sending signals remotely), the OFPM sends appropriate signals, which can be related to: a) Reduction of active power production on generators (group А) b) Disconnection of the generators from the transmission grid (group B) This type of over-frequency protection system will have the role of reducing the total production in the system as closely as possible when impermissibly high frequencies occur, as if each generator is equipped with an LSFM-O controller. In addition, this system will ensure that there are no local violations of the security criteria in the network. On the other hand, as it will be implemented at the national and not at the regional level, this OFPM will only be able to control to a lesser extent the change in active power flows on the interconnecting lines and the impacts on neighbouring systems (this can only be achieved if there is a regional implementation of the OPFM, which may be the subject of one of the future projects). Also, this system is not intended to control high frequencies in case of splitting the system into subsystems, as its main intention is to bring the Serbian TSO into compliance with the binding provisions of the EU network codes.
1.5 Key performance indicators (KPI)
| ID | Name | Description | Reference to mentioned use case objectives |
|---|---|---|---|
| 12 | % of the installed capacity of generators that are included in the OFPM at the national level | =100%·DataID2/DataID1; - DataID1 - Sum of the installed capacity of generators lacking LFSM-O controllers; - DataID2 - Sum of the installed capacity of generators that are included in the OFPM at the national level | Objective 1 |
1.6 Use case conditions
| Assumptions |
|---|
| Generators that cannot receive command signals have fixed over-frequency protection settings harmonized with the OFPM. Protection devices operate autonomously in case of over-frequency. SCADA AGC runs autonomously after calculated set-points are received from OFPM. SCADA system transfers disconnection signal generated by OFPM to appropriate circuit breakers in the connection facility of a generator. |
| Prerequisites |
|---|
| Generating units are capable of receiving a set point to reduce their active energy production, or generating units can be remotely - disconnected from the TSO control centre, or over-frequency protection of the generating units can be reset from the TSO control centre. |
1.7 Further information to the use case for classification/mapping
| Relation to other use cases |
|---|
| none |
- Level of depth:
- High level of detail.
- Prioritisation:
- Highest priority (5). The centralized over-frequency protection does not currently exist in the Serbian power system, and it is necessary for the application of NC ER requirements.
- Generic, regional or national relation:
- Generic and national.
- Nature of the use case:
- System functional requirements description.
- Further keywords for classification:
- Over-frequency protection, Emergency operation.
1.8 General remarks
2.Diagrams of use case
2.1 Diagrams of use case
| Diagram name | Diagram image |
|---|---|
| SGAM Business Layer |
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| SGAM communication layer |
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| SGAM component layer |
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| functional layer |
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| Information object mapping |
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| SGAM functional layer |
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| sequence |
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3. Technical details
3.1 Actors
| Actor name | Actor type | Actor description |
|---|---|---|
| Over Frequency Protection Module | Control system | OFPM is a part of the control system designed to reduce active power production when an over-frequency threshold is reached. |
3.2 References
4. Step by step analysis of use case
4.1 Over-frequency identification
- No.
- 1
- Primary actor
- OFPM
- Triggering event
- Regular repetition
- Pre-condition
- Frequency is monitored
- Postcondition
- Over-frequency is identified and OFPM is activated
4.1 Steps of Over-frequency identification
| Step No. | Event | Name of process/activity | Description of process/activity | Service | Information producer (actor) | Information receiver (actor) | Information exchanged (IDs) | Requirement, R-IDs | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Regular repetition | SCADA measurements download | Each 2-4 seconds SCADA systems sends to the OFPM frequency and generators active power measurements | Data download | SCADA | OFPM | 1, 2 | IRI_017, IRI_105, IRI_106 | ||||
| 2 | Over-frequency threshold is reached | Calculations of needed active power decrease and available downward reserve | OFPM calculates needed active power decrease and available downward reserve | Data processing | OFPM | OFPM | 0 | IRI_017, IRI_088, IRI_089, IRI_090, IRI_091, IRI_105, IRI_106, IRI_107, IRI_108 | ||||
| 3 | Calculations are completed | Triggering of active power generation decrease mechanism or generators disconnection mechanism | Based on comparison of needed active power decrease and available downward reserve OFPM triggers 1) active power generation decrease mechanism or 2) generators disconnection mechanism | Data processing | OFPM | OFPM | 0 | IRI_017, IRI_092, IRI_093, IRI_105, IRI_106, IRI_108 | ||||
4.2 Active power generation decrease (generators of group A)
- No.
- 2
- Primary actor
- OFPM
- Triggering event
- OFPM triggered active power generation decrease
- Pre-condition
- Generating units of group A follow regular generation schedule
- Postcondition
- Generating units of group A decrease their active power output according to the set-point sent by the OFPM
4.2 Steps of Active power generation decrease (generators of group A)
| Step No. | Event | Name of process/activity | Description of process/activity | Service | Information producer (actor) | Information receiver (actor) | Information exchanged (IDs) | Requirement, R-IDs | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | OFPM triggered active power generation decrease | Set-points calculation | OFPM calculates generators set-points | Data processing | OFPM | OFPM | 0 | IRI_017, IRI_094, IRI_095, IRI_096, IRI_097, IRI_098, IRI_099, IRI_105, IRI_106, IRI_108, IRI_109 | ||||
| 2 | Set-points are calculated | Set-points transfer | OFPM sends generators set-points to SCADA/AGC | Data transmission | OFPM | SCADA | 3 | IRI_017, IRI_100, IRI_105, IRI_106, IRI_108, IRI_109 | ||||
4.3 Generators disconnection
- No.
- 3
- Primary actor
- OFPM
- Triggering event
- OFPM triggered generators disconnection mechanism
- Pre-condition
- Generating units of group B follow regular generation schedule
- Postcondition
- Some generating units of group B are disconnected
4.3 Steps of Generators disconnection
| Step No. | Event | Name of process/activity | Description of process/activity | Service | Information producer (actor) | Information receiver (actor) | Information exchanged (IDs) | Requirement, R-IDs | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | OFPM triggered generators disconnection mechanism | Frequency disconnection calculations | OFPM calculates generators disconnection frequency | Data processing | OFPM | OFPM | 0 | IRI_017, IRI_101, IRI_102, IRI_103, IRI_105, IRI_106, IRI_108, IRI_110 | ||||
| 2 | Disconnection frequency are calculated | Generators disconnection | OFPM sends disconnection signal for selected generators (according to calculated disconnection frequencies within scenario 1) | Data transmission | OFPM | SCADA | 4 | IRI_017, IRI_104, IRI_105, IRI_106, IRI_108, IRI_110 | ||||
5 Information exchanged
5.1 Information exchanged
| Requirement, R-IDs | Information exchanged, ID | Name of information | Description of Information Exchanged |
|---|---|---|---|
| IRI_111 | 1 | Active power measurements | Active power measurements on generating units |
| IRI_111 | 2 | Frequency measurements | Measured frequency in the power system |
| IRI_100 | 3 | Active power set-points | Set-point for generators’ active power controllers (controller leads generator’s active power to the set-point value) |
| IRI_104 | 4 | Disconnection signals | Signal which triggers selected circuit breaker opening. |
6 Requirements
6.1 Functional requirements
- Category ID
- 1
- Category name for requirements
- Functional requirements
- Category description
- Functional requirements define what a product must do, what its features and functions are. Functional requirements of the system are captured by describing how the system should respond in each step of a scenario
| Requirement R-ID | Requirement name | Requirement description |
|---|---|---|
| IRI_088 | Frequency activation requirement | IRIS OFPM must be active if frequency exceeds 50.2 Hz |
| IRI_089 | Active power decrease calculation requirement | IRIS OFPM must calculate total needed decrease of active power generation in case of over-frequency Pdec [MW] as follows (for LFSM-O droop of 5%): Pdec = Ptotal· (40·f-2008) |
| IRI_090 | Downward reserve calculation requirement | For each generator available for active power decrease, IRIS OFPM must calculate: Pdw = P – Pmin. In addition, the sum of Pdw for all generators shall be calculated – SUM(Pdw). |
| IRI_091 | Recalculation period setting requirement | IRIS OFPM must recalculate total active power decrease, available downward reserves and generators base (set) points in time interval set by OFPM operator. |
| IRI_092 | Downward active power reserve threshold requirement | IRIS OFPM operator must be able to set available downward active power reserve threshold (Ptreshold) and frequency threshold (ftreshold). |
| IRI_093 | Priority OFP mechanism requirement | IRIS OFPM will firstly activate reduction of active power on generators if f > 50.2 Hz and secondly disconnection of the generators if the following condition is met: SUM(PHdw) + SUM(PTdw) + SUM(PWdw) < Pthreshold or f > f threshold |
| IRI_094 | Generation decrease priority requirement | IRIS OFPM will reduce generators active power according to the following priority: Hydro Power Plants, Thermal Power Plants, Wind Parks (according to the Serbian pilot site characteristics). |
| IRI_095 | Downward capacity calculation per generation type requirement | Based on IRI_090 requirement, IRIS OFPM must calculate SUM(PHdw), SUM(PTdw) and SUM(PWdw). In the event of an outage of a generator that is in this mechanism, SUM(PHdw) / SUM(PTdw) / SUM(PWdw) is reduced by the Pdw of this generator |
| IRI_096 | Base-point calculation requirement 1 | If Pdec+SUM(Pvar) <SUM(PHdw), for each hydro generator IRIS OFPM must calculate new base point Pb as follows: Pb=P–[Pdec+ SU(Pvar)]· Pdw/SUM(PHdw). Thermal and wind generators get a base point equal to their active power when OFPM is activated. |
| IRI_097 | Base-point calculation requirement 2 | If SUM(PHdw)<Pdec+SUM(Pvar)<SUM(PHdw)+SUMA(PTdw), for each thermal generator IRIS OFPM must calculate new base point Pb as follows: Pb=P–[PdecSUM(Pvar)–SUM(PHdw)]·Pdw/SUM(PTdw). All hydro generators get Pb equal to their technical minimum. |
| IRI_098 | Base-point calculation requirement 3 | SUM(PHdw)+SUM(PTdw)<Pdec+SUM(Pvar)<SUM(PHdw)+SUM(PTdw)+SUM(PWdw), for each wind generator IRIS OFPM must calculate new base point Pb = P – [Pdec- SUM(PHdw) - SUM(PTdw)] · Pdw / SUM(PWdw) |
| IRI_099 | Base-point calculation requirement 4 | If SUM(PHdw) + SUM(PTdw) + SUM(PWdw) < Pdec + SUM(Pvar), IRIS OFPM must calculate for all generators new base point Pb equal to their technical minimum. |
| IRI_100 | Base-point communication requirement | IRIS OFPM shall communicate generators base point signal through: 1) Thermal power plant and wind park gateway 2) TSO connection facility gateway and GRAS devices installed in hydro power plants |
| IRI_101 | Disconnection criteria requirement | All generators in IRIS OFPM disconnection mechanism, will be sorted in array according to local security criteria and additional criteria set by generator owners according to the following priority: Hydro Power Plants, Thermal Power Plants, Wind Parks. |
| IRI_102 | Disconnection frequency calculation requirement | IRIS OFPM must calculate disconnection frequency for all generators as follows: f disci [Hz] = (2008 + SUM(Pvar) + 0,5·Pi + SUM(P1→i-1)/40 |
| IRI_103 | Disconnection frequency recalculation period requirement | IRIS OFPM must recalculate disconnection frequency for all generators in time interval set by OFPM operator. |
| IRI_104 | Disconnection signal communication requirement | IRIS OFPM must communicate generators disconnection signal to circuit breaker of the generator’s connection line in TSO connection substation |
| IRI_105 | Obervability requirement | IRIS OFPM must provide to operator observability of generators participating in active power generation decrease mechanism and generators disconnection mechanism. |
| IRI_106 | OFP mechanism activation requirement | IRIS OFPM operator must be able to include/exclude generators for one or both mechanism (active power generation decrease mechanism / generators disconnection mechanism) before or during OFPM activation. |
| IRI_107 | Sound alarm requirement | When over-frequency higher than 50.2 Hz is detected, IRIS OFPM must generate sound alarm that can be cancelled by operator. |
| IRI_108 | Summary display requirment | When over-frequency is detected, OFPM must generate summary display presenting: 1) actual frequency 2) time relapsed from over-frequency detection 3) calculated total active power to be reduced 4) total reduced power after over-frequency detection |
| IRI_111 | OFPM – SCADA communication requirement | IRIS OFPM and SCADA must communicate through IPC (inter-process communication). |
6.2 non functional
- Category ID
- 2
- Category name for requirements
- non functional
- Category description
- Requirements that cannot be captured this way are non-functional requirements, such as business rules, the user interface and other requirements that are not suitable to be described within a scenario.
| Requirement R-ID | Requirement name | Requirement description |
|---|---|---|
| IRI_109 | Genaration decrease display requirement | When OFPM active power generation decrease mechanism is activated, OFPM must generate a display presenting all data given in comments section. |
| IRI_110 | Genaration disconnection display requirement | If OFPM generators disconnection mechanism is active, OFPM must generate a display presenting: Generators’ active power at the moment of over-frequency detection, identification if generator is disconnected by OFPM / Generators disconnection mechanism |
7 Common terms and definitions
7.1 Common terms and definitions
| Term | Definition |
|---|---|
8 Custom information
8.1 Refer to section
| Refers to section | Value | Key |
|---|---|---|
Publisher Organization
| Organization name | Organization Acronym | Country |
|---|---|---|
| EMS Service | EMSS | Serbia |
- Technologies for use cases:
- High level Use Case:
- HLUC 7: Enhance System Supervision and Control including Cyber Security
- Related Project:
- R2D2