EDS KV, GRID AND PRIMARY SYSTEM PROTECTION AND CONTROL SCHEMES

Transcription

1 Network(s): Summary: ENGINEERING DESIGN STANDARD EDS KV, GRID AND PRIMARY SYSTEM PROTECTION AND CONTROL SCHEMES EPN, LPN, SPN This engineering design standard describes the requirements for the protection and control of the grid and primary system including 132kV, 66kV, 33kV, 11kV and 6.6kV busbars, transformers and feeders. Author: John Moutafidis Approver: Paul Williams Date: 14/09/2017 This document forms part of the Company s Integrated Business System and its requirements are mandatory throughout UK Power Networks. Departure from these requirements may only be taken with the written approval of the Director of Asset Management. If you have any queries about this document please contact the author or owner of the current issue. Applicable To UK Power Networks External Asset Management G81 Website Capital Programme UK Power Networks Services Connections Contractors Health & Safety ICPs/IDNOs Legal Meter Operators Network Operations Procurement Strategy & Regulation Technical Training THIS IS AN UNCONTROLLED DOCUMENT, THE READER MUST CONFIRM ITS VALIDITY BEFORE USE

2 Revision Record Version 7.0 Review Date 14/09/2022 Date 02/08/2017 Author John Moutafidis Reason for update: Periodic review. What has changed: No material changes to document required. This standard will be superseded by a new suite of protect standard documents in the near future. Associated documents EDS B-F reviewed with no changes Version 6.0 Review Date 24/03/2017 Date 19/03/2014 Author Kevin Burt General document review and replacement AVC and new Low-Frequency scheme schematics added. Version 5.0 Review Date Date 13/04/2007 Author Steve Spencer Drawing index updated Version 4.0 Review Date Date 15/11/2006 Author Stephen Tucker Completely revised to describe the newly issued standard protection schemes. Version 3.0 Review Date Date 12/06/2006 Author Steve Spencer Progress update including first schematic drawings. UK Power Networks 2017 All rights reserved 2 of 17

3 Contents 1 Introduction Scope Glossary and Abbreviations Protection Philosophy Introduction Main and Back-up Protection kV Busbar/Switching Stations, 132/33kV (132/66kV) (132/20kV) (132/11/(11)kV) Transformers and 132kV Feeders Grid Substations Primary Substations Current and Voltage Transformers Inter-tripping Remote Control and Indication Auto-reclose SF 6 Circuit Breaker Inhibit Supervision General DC Trip Circuit Supervision DC Protection Supply Supervision Fault Throwing Switch (FTS) Supervision Measurements Feeder circuits: Transformer circuits HV: Transformer circuits LV: Automatic Voltage Control Philosophy Design Standards Review of Design Standards References National and International Standards Dependent Documents Appendix A - Rough-balance Busbar Protection Appendix B - Block Diagrams Appendix C - Schematic Diagrams Appendix D CT Schedule Appendix E UKPN internal Design Standards Issue & Change Request Notification.. 15 UK Power Networks 2017 All rights reserved 3 of 17

4 Appendix F UKPN internal Design Standards Issues Log Appendix G References for Micom P series relays used in UK Power Networks standard schemes UK Power Networks 2017 All rights reserved 4 of 17

5 1 Introduction This engineering design standard implements the new harmonised protection and control standards (including voltage control) applicable to the UK Power Networks licensed networks at 132(66)kV, 33kV and 11(6.6)kV (primary) voltage levels. The standards are applicable to all parts of UK Power Networks and external organisations where plant and equipment is intended to form part of the UK Power Networks licensed networks. They shall be applied to all protection and control design (including switchgear) except through agreement in the following circumstances: Extension of existing switchboards where the application of the new standards is not practicable; Modifications to existing protection and control schemes where the proposed changes are minimal and compliance with the revised standards will require extensive additional work. The general applications referred to in this document are shown below, but this list is not exhaustive and does not reflect all schemes that may be required: 132kV feeders; 132kV busbar; 132/33(66)kV and 132/11/11kV transformers; 33kV busbars; 33kV underground cable and overhead line feeders; 33kV overhead ring; 33/11(6.6)kV primary transformer; 33kV voltage transformer; 11(6.6)kV busbars; 11(6.6)kV underground cable and overhead line feeders with and without auto-reclose; Voltage control applicable to all voltage levels. This engineering design standard is divided into the following main sections: Protection philosophy; Automatic voltage control philosophy; Protection and control scheme diagrams. This engineering design standard should be read in conjunction with the relevant specifications for switchgear and relay panels, ancillary equipment and wiring. All protection and control devices utilised in the development of the harmonised schemes are ENA assessed, and UK Power Networks approved. For the 33kV and 11kV schemes, the schemes draw on specific products from the Alstom, Siemens, and Schneider range. To reflect this, a scheme has been prepared for each and further schemes will be developed in due course for the Siemens Siprotec range, plus others as they become approved for use on the UKPN network. The 132kV schemes are intentionally not device specific at this stage, although currently UK Power Networks approved relay types are Alstom, Reyrolle and Siemens (Siprotec) at this voltage level. As project specific schemes are prepared, these will be used as the basis for developing type specific standards. Future introduction of new devices shall be in accordance with UK Power Networks EDS Introduction of New Protection Relays, which is an internal UK Power Networks document. No new product shall be used without the sanction of the UKPN Technical Sourcing and Standards team, within Asset Management. UK Power Networks 2017 All rights reserved 5 of 17

6 2 Scope The protection schemes described in this document relate to the distribution network nominal voltage levels of 132kV, 66kV, 33kV, 22kV, 20kV, 11kV and 6.6kV (50Hz, 3-phase). The schemes are developed on the basis of the following network characteristics: The 132(66)kV network consists of underground cable or overhead line solidly and multiply earthed with a general fault level of 31.5kA for 3 seconds; The 33kV network generally consists of underground cable or overhead line parallel primary transformer feeders with resistance or reactance earthing and a maximum rated fault level of 25kA or 31.5kA for 3 seconds; The 22kV and 20kV networks are generally confined to the Central London area and are exclusively underground cable systems connected to resistor or reactance earthed systems. Fault levels are nominally 2kA (single transformer infeed). The 11(6.6)kV network consists of underground cable or overhead line radial feeders with either solid, resistance or arc suppression coil earthing and a maximum rated fault level of 20kA for 3 seconds 3 Glossary and Abbreviations Term UK Power Networks Definition UK Power Networks (Operations) Ltd consists of three electricity distribution networks: Eastern Power Networks plc (EPN). London Power Network plc (LPN). South Eastern Power Networks plc (SPN). UK Power Networks 2017 All rights reserved 6 of 17

7 4 Protection Philosophy 4.1 Introduction This section describes the protection philosophy adopted in the harmonised protection schemes and is applicable to the following: 132kV feeders and busbars. Grid substations (33kV busbars and 33kV feeders). Primary substations (33/11(6.6)kV transformer. 11(6.6)kV busbars and 11 (6.6)kV feeders. At the higher voltage levels (132kV and 33kV and intermediate voltages) high-speed main protection schemes (circulating current, differential, phase comparison) and inter-tripping are provided to ensure fast fault clearance for failure of major plant, busbars, cables and overhead line circuits. The choice of main protection is determined by the specific network configuration and prospective fault levels. For the 132kV schemes, the philosophy adopted is in accordance with the general principles of ENA TS The complex and different nature of the 132kV networks in the UK Power Networks EPN, LPN and SPN areas precludes the development of standard protection schemes for specific circuit types (e.g. transformer, two ended/three ended circuits etc.). Therefore, the scheme designs are based on a modular basis whereby the designer assesses the network to be protected and selects those elements to provide main protection, back-up protection, inter-tripping, delayed auto-reclose, trip relay reset etc. as required to ensure a safe, secure and reliable network with the appropriate level of fault detection and clearance. The individual scheme 'modules' shall be selected and integrated to produce the overall required scheme solution to suit the network in question. 4.2 Main and Back-up Protection kV Busbar/Switching Stations, 132/33kV (132/66kV) (132/20kV) (132/11/(11)kV) Transformers and 132kV Feeders Unless impracticable to do so, main protection is applied to all elements of the 132kV system (busbars, plant, circuits) such that all parts are protected by a fast operating protection scheme. This will require the overlapping of zones in the majority of cases. Where this is not possible, interlocked overcurrent/earth fault or equivalent schemes are provided. Inter-tripping and blocking schemes are provided between circuit ends, and dedicated backup protection schemes are installed to ensure fault clearance in the event of main protection failure Grid Substations For the purposes of this document, grid substation refers to the provision of protection on the 33kV busbars and outgoing 33kV feeders. Rough-balance schemes provide the 33kV busbar and back-up feeder (stuck circuit breaker) protection, although each 33kV feeder has dedicated main and back-up protection, which may be contained within a single device. A narrative on the philosophy of this scheme is included in Appendix A as it is a new concept in some areas. UK Power Networks 2017 All rights reserved 7 of 17

8 4.2.3 Primary Substations The system transformer is protected by the normal range of schemes (LV restricted earth fault (REF), Buchholz, standby earth fault etc.). In addition, balanced earth fault and HV overcurrent and earth fault are introduced at the transformer HV bushings location. Neutral voltage displacement (NVD) and directional overcurrent (DOC) are fitted as standard, although the latter is only required where two transformers run in parallel. As with the 33kV busbar schemes, rough-balance (see Appendix A) is introduced onto the 11kV busbars to provide busbar protection and back-up clearance of stuck 11kV CBs. The main protection schemes are normally supplemented by definite-time and/or inverse definite minimum time (IDMT) overcurrent and earth fault protection on circuit breakers, transformers and other plant where a back-up protection scheme is required. This may take the form of directional (polarised) schemes where this is required to ensure discriminative clearance for backfed faults. NVD may also be provided to provide detection of backfed earth faults where the source circuit breaker has tripped, thereby removing the earth reference and also to cater for the loss of inter-tripping paths. 4.3 Current and Voltage Transformers CT and VT requirements (ratio, class, rating etc.) are intentionally not shown on the individual schemes as this is dictated by the minimum specification required to meet the duties of the protection device, network with which it is associated and the physical space available in the switchgear. In general 1A protection devices are preferred and the associated general CT requirements are developed on this basis and shown in the schedule in Appendix D. 4.4 Inter-tripping The inter-tripping schemes for all voltages have been developed around the following principles: Where privately owned metallic pilots are available, a two-wire surge proof monitored dead pilot system is used. This shall be a monitored and equipped with local/scada send and receive non-volatile/sustained indications; The provision of inter-tripping where grid and primary substations share the same site and the primary transformer is local shall be provided using dc inter-tripping; The inter-tripping send and receive relays shall be high burden/high level AC immunity type and shall give local indication of operation (via hand reset flags) and remote alarm intertrip receive alarm to SCADA. The intertrip circuit shall be separately sub-fused and the intertrip send circuit shall be supervised to give an alarm on loss of supply; Where rented pilots are used, a VF based inter-tripping scheme is used; Where neither of these are available fault throwers or local circuit breakers, depending on the particular network requirement, are to be used. The use of fibre optic based inter-tripping and protection schemes has not been developed at this stage, but will be in due course and included into the suite of drawings. UK Power Networks 2017 All rights reserved 8 of 17

9 4.5 Remote Control and Indication The principles adopted in the development of the schemes are on the following basis: All circuit breakers are provided with remote control facilities via SCADA together with remote indications, alarms and analogues; Controls, alarms and indications are interfaced to SCADA via hard wired connections. Serial communications are not universally available at this stage and therefore are discounted, albeit the appropriate schemes will be developed in due course; A simplified SCADA reference/numbering system is adopted which allocates a unique letter prefix to individual functions, followed by a three digit number unique to the control, alarm, indication or analogue, but not voltage, e.g. Control W123, Alarm/Indication X123, and analogue XE123 (voltage); This referencing system will apply equally to voltage control schemes, and other ancillary equipment (battery chargers, disconnectors, mains failure etc.). The key changes from existing practices are as follows: There is no identification of the panel to which the reference relates as it only exists within that panel (wires are only ferruled on the plant side and all other wiring is colour coded); The voltage of the circuit is no longer identified as part of the reference; There is differentiation between alarm and indication references; Analogues are the only continuously variable indications; The new range of references is the same for all voltages and similar functions; Controls are a single character followed by up to three digits; Alarms and indications are a single character followed by up to three digits; Analogues are two characters followed by up to three digits. Two characters are required in this instance to differentiate from normal protection wiring. Modifications and extensions to existing plant will be carried out using an extension of the schemes already in use. The SCADA numbering system is described fully in UKPN engineering document EDS Auto-reclose Auto-reclose at 11kV and 33kV is provided by the use of the available functionality of modern protection devices. This includes sequence co-ordination where appropriate. At 132kV, the auto-reclose function is provided by the use of dedicated relays with the option of Check Sync where it is deemed necessary. 4.7 SF 6 Circuit Breaker Inhibit Switchgear, using SF 6 gas as the arc-extinguishing medium, is provided with a two-stage gas pressure alarm and blocking facilities. The first-stage alarm is initiated when the gas pressure starts to fall below its normal level. The second-stage gas alarm is initiated when the gas pressure falls to a low level where the insulation can no longer be relied on to meet its specified impulse levels. The following functionality is provided: Stage 1 - gas pressure falling local and remote alarm; Stage 2 - gas pressure low local and remote alarm and inhibits both the trip and close of the circuit breaker. UK Power Networks 2017 All rights reserved 9 of 17

10 4.8 Supervision General The integrity of dc circuits and supplies to the protection/inter-trip schemes; and circuit breaker control/fault thrower circuits is monitored by one or more of the following: Internal device functionality and watchdog outputs; External dedicated supervisory devices; Alarms will be generated as discrete or common text as appropriate to the functionality DC Trip Circuit Supervision The circuit breaker control circuits are provided with trip circuit supervision to fully monitor the tripping bus wires from the fuse through to the circuit breaker trip coil. This is achieved by looping the wiring into and out of the supply side and switched side of each circuit breaker trip coil energising contact and via a normally open and normally closed circuit breaker auxiliary contact to provide full trip circuit supervision in both the circuit breaker open and closed positions. Trip circuit supervision is provided within the numerical protection relays unless a latched trip contact is used in the trip path, in which case the numerical relay supervision function is not suitable as the supervision opto input will be shorted for longer than the trip circuit supervision delay time of 400mS when the trip contact is operated. It should be noted that the resistor values and wiring of the standard trip circuit supervision scheme for the MiCOM range of relays requires the trip circuit supervision opto input to be set to 48V operation in the relay settings file for correct operation of the relay from the 110V battery. All other opto inputs are be set to 110V operation. Where a latched trip contact is used an external hardwired H7 (ENA ER S15) scheme supervision relay with three elements is provided. Trip circuit supervision on bus section rough-balance schemes is provided by an external hardwired supervision relay irrespective of whether the trip contacts are latched or fleeting so that the trip circuit supervision is independent of either zone 1 or zone 2 protection. The trip circuit supervision function or relay provides a trip circuit fail alarm for the following: Failure of trip supply; Open circuit trip coil or circuit wiring; Failure of circuit breaker tripping mechanism DC Protection Supply Supervision All protection and alarm dc supplies shall be monitored such that the maximum amount of the circuit is supervised, using looped connections between devices as far as possible. This supervision shall take the form of a watchdog within a protection device, or a discrete supervision relay and the appropriate alarms initiated to SCADA Fault Throwing Switch (FTS) Supervision All fault throwing switch tripping circuits are provided with a supply supervision relay wired across the circuit to de-energise for any break in trip path wiring or loss of supply. The supervision relay raises a FTS fail alarm to SCADA together with a local indication. UK Power Networks 2017 All rights reserved 10 of 17

11 4.9 Measurements The following analogue measurements are provided for transformer and feeder circuit breakers using current and voltage measuring devices Feeder circuits: Single (Yellow) phase current to SCADA via a self-powered transducer with 0-10mA output; Single (Yellow) phase current local indication via a meter mounted on the protection panel front Transformer circuits HV: Single (Yellow) phase current to SCADA via a self-powered transducer with 0-10mA output Transformer circuits LV: Three phase current to SCADA via a self powered transducer with 0-10mA output; Three phase current local indication via a meter mounted on the protection panel front; Single phase voltage SCADA via a self powered transducer with 0-10mA output; Single phase voltage local indication via a meter mounted on the protection panel front; Watts to SCADA via a self powered transducer with 0-10mA output; VARs to SCADA via a self powered transducer with 0-10mA output. Transducers used in the standards are to be self-powered 0-10mA type suitable with maintained accuracy for output burdens of 0 to 1K. Voltage and current transducers shall be unidirectional. Watts and VARs transducers shall be bidirectional. Transducers shall be suitable for over-range up to 125% circuit rating. 5 Automatic Voltage Control Philosophy The latest tap change units supplied with grid and primary transformers across the three licensed areas are generally two types: ATL (mainly on primary transformers), and MR in tank units (mainly on grid transformers). In addition, there are various other legacy units in service but to reduce OPEX costs, maintenance free units are being introduced on all transformers (e.g. MR Vacutap unit). To cater for current and future arrangements, the Reyrolle SuperTapp device (the N+ product is under UKPN assessment) has been chosen as the basis for a harmonised automatic voltage control (AVC) scheme offering the advantage of being compatible with all installation types and of proven reliability. It also includes built in monitoring which is superior to other devices. Harmonised AVC schemes have been developed by Fundamentals from their experience with the three licensed areas. These will provide the correct voltage regulation at all voltages (11kV 132kV) across the networks without modification. The new schemes can operate entirely without intervention using the functionality of the relays as designed. However, full remote control is also selectable, allowing the tap positions to be remotely raised and lowered as required. The AVC schemes will be available in a single cabinet with one device for one transformer or a single cabinet with two devices for two transformers. The two cabinet designs can be combined, where necessary, for three and four transformers. The scheme drawings referred to above are shown in Appendix C. UK Power Networks 2017 All rights reserved 11 of 17

12 6 Design Standards A list of the available protection scheme block diagrams and detailed schematics can be found in Appendix B and Appendix C respectively. The schemes use a standard drawing number format, e.g. EDS , where the first part of the number indicates that the drawing is linked to this engineering design standard and the second part is a unique reference number that is linked to the voltage level, (i.e. EDS is 11(6.6kV), is 33kV (Inc. intermediate voltages from 11kV), is 132kV (Inc. intermediate voltages from 33kV). Pdf and dgn (read only) copies of the standard schemes are available internally within UK Power Networks from the Alfresco Engineering Library. Drawings which may be required by an ICP will be available via the UK Power Networks Website (G81). UK Power Networks internally generated project specific drawings shall be created through ProjectWise in accordance with EDP The master copies of the scheme standard drawings will be updated as necessary and new versions published internally on DMS and where necessary on the UK Power Networks website. 7 Review of Design Standards Revisions to the harmonised protection schemes referred to in this document may be instigated by the following events: Scheme errors or deficiencies identified through the design or commissioning process. Introduction of new relay technology or device types. Changes in network design strategy. Periodic review of the schemes to ensure they continue to meet the network requirements. The UK Power Networks internal mechanism for proposing changes shall be through submission to the Protection Forum using the internal Issue & Change Request Notification proforma in Appendix E This shall state the reason for requesting the revision and proposed change(s). This proforma shall also be used for proposing the addition of new standard schemes. On completion the form shall be submitted to the Substation Standards Manager. Appendix F contains the UK Power Networks internal proforma for the Issues Log, which shall be the mechanism for recording proposed changes to the standard schemes and the agreed actions. The Issues Log shall be administered by the Technical Sourcing and Standards Manager. Independent of any proposed revisions, the UK Power Networks Protection Forum shall review the harmonised schemes periodically on a 12-month basis and re-issue modified schemes as appropriate. Where changes to the harmonised schemes are necessary at short notice to correct a deficiency and in order to facilitate the commissioning of a circuit then this may proceed without reference to the Protection Forum provided the changes are notified as soon as possible after the event. UK Power Networks 2017 All rights reserved 12 of 17

13 8 References 8.1 National and International Standards ENA TS ENA ER S15 Standard circuit diagrams for equipment in 132kV substations. Standard schematic diagrams. 9 Dependent Documents The documents below are dependent on the content of this document and may be affected by any changes. EDS EDS Introduction of New Protection Relays (Internal document) SCADA Numbering System UK Power Networks 2017 All rights reserved 13 of 17

14 Appendix A - Rough-balance Busbar Protection The rough-balance scheme shall be driven from three phase CTs fitted on the LV side of the transformer incomer circuit and on the bus section which shall be connected in parallel into rough-balance zone protection relays fitted on the bus section panel. These relays shall have a fast acting highset definite time overcurrent element and IDMT overcurrent and earth fault elements. The relays shall be set to be stable under normal and through fault conditions and to operate for an in-zone busbar fault where the fault is fed from each side (incomer and bus section) to summate at the relay. Note that for correct operation of this scheme the feeder circuits must be connected in-zone i.e. between the incomer and bus section. A trip output from the rough-balance zone relay shall operate into the bus section trip coil and a trip repeat output fed into the protection relays for the incomer and all feeders connected on to the faulted busbar zone via a busbar zone trip buswire. On receipt of the busbar zone trip input the incomer and feeder relays will initiate a trip output to trip their respective circuit breakers. For a feeder fault both the feeder and bus zone protection may pickup. A means must therefore be provided to discriminate between a feeder and busbar fault so that the bus zone protection does not have to wait to give the feeder protection time to operate in instances where the fault is on the feeder. This is done by a block signal from the feeder protection start which holds off the high set definite time bus zone protection giving the feeder protection time to operate to clear the fault. If the fault is on the busbar the feeder protection will not pick up, no block is present and the bus zone protection can operate almost instantaneously. Where the feeder protection fails to clear a fault (e.g. circuit stuck breaker), the bus zone protection IDMT elements will operate to trip the bus section and set the bus zone trip output high. The feeder protection start must be set low on completion of the feeder protection operation to remove any block to the bus zone protection to allow for stuck breaker situations. Appendix B - Block Diagrams See EDS B & C Index to Protection and Control Scheme Drawings. This is a separate document filed alongside this engineering design standard on the Alfresco engineering library, and available on request from the UK Power Networks website. Appendix C - Schematic Diagrams See EDS B & C Index to Protection and Control Scheme Drawings. This is a separate document filed alongside this engineering design standard on the Alfresco engineering library, and available on request from the UK Power Networks website. Appendix D CT Schedule This appendix gives the minimum CT and VT requirements (ratio, class, rating etc) required by the respective schemes as the minimum specification required to meet the duties of the protection device, network with which it is associated and the physical space available in the switchgear. The schedule is in the form of a spreadsheet (UKPN EDS D) and filed with this engineering design standard. It is also available by request from the UK Power Networks website. UK Power Networks 2017 All rights reserved 14 of 17

15 Appendix E UKPN internal Design Standards Issue & Change Request Notification EDS kV, Grid, Primary System Protection and Control Design Standards Issue & Change Request Notification Raised by: Date: Completed form and associated documents/drawings to be submitted to the Substation Standards Manager. Design issues raised by ICPs external to UK Power Networks should be referred to the responsible UK Power networks designer, who will deal with any issues in accordance with this procedure. Drawing No Issue Raised Proposed Solution The form is available internally as a separate document (EDS E) and is filed with this engineering design standard. UK Power Networks 2017 All rights reserved 15 of 17

16 Appendix F UKPN internal Design Standards Issues Log EDS kV, Grid, Primary System Protection and Control Design Standards Issues Log Date Issue Ref No Issue raised Raised by Assigned Priority 1 Proposed Action Planned Completion Date Action Completed The schedule is available internally in the form of spreadsheet (EDS F) and filed with this engineering design standard. Design issues raised by ICPs external to UK Power Networks should be referred to the responsible UK Power Networks designer. 1 The assigned priority will be 1, 2 or 3 where: 1 = requires immediate action to remedy an error or deficiency in the scheme design that may potentially result in loss of supplies, risk to health, incorrect operation of the scheme, or impact on procurement of plant and equipment. 2 = whilst not affecting the safe operation of the scheme should be addressed as soon as possible to incorporate improvements that will deliver short term benefit. Issue to be raised at next design and commissioning forum. 3 = similar to 2 but issue considered to be part of annual review of schemes. UK Power Networks 2017 All rights reserved 16 of 17

17 Appendix G References for Micom P series relays used in UK Power Networks standard schemes EDS G Micom P Series Relay References is a separate document stored alongside this Engineering Design Standard on the Alfresco engineering library. It is also available on request from the UK Power Networks website. UK Power Networks 2017 All rights reserved 17 of 17