Single line diagrams (SLDs) and #circuit configurations are essential tools for understanding and planning high-voltage (HV) and medium-voltage (MV) #switchgear #installations. Here’s a brief overview:
Single-Line Diagrams (SLDs)
The initial step in planning a #switchgear installation is to create its single-line diagram. This diagram shows the scope of the installation, including the number of #busbars and #branches, as well as the related equipment.
The most common circuit configurations for high and medium-voltage switchgear installations are depicted as single-line diagrams in the following paragraphs.
Circuit Configurations
The configuration of circuits for high-voltage and medium-voltage switchgear installations is determined by operational needs. The decision to use single or #multiplebusbars primarily hinges on the system's mode of operation and the requirement for sectionalizing to prevent excessive breaking capacities.
Consideration is given to the necessity of isolating sections of the installations for cleaning, maintenance, and potential future expansions.
In creating a single-line diagram, it is necessary to consider numerous potential combinations of incoming and outgoing connections. The most frequent configurations are depicted in the subsequent #diagrams.
The Table of Contents:
1. Most Common Circuit Configurations
1.1 Single busbars
Ideal for smaller installations, a sectionalizer enables a station to be divided into two distinct sections, allowing these sections to be disconnected for #maintenance activities.
1.2 Double Busbars
Busbar sectionalizing is preferred for larger installations due to its #advantages: it allows for cleaning and maintenance without disrupting the power supply. It also enables separate #operation of #station sections from bus I and bus II, thereby increasing operational flexibility.
1.3 Double busbars in U Connection
A low-cost, space-efficient configuration is available for installations with #doublebusbars and #branches extending to both sides.
1.4 Composite double bus/bypass bus
This configuration can be tailored to meet operational needs. The station may be run using a double bus system or with a single #bus complemented by a #bypassbus.
1.5 Double busbars with draw-out circuit breaker
In medium-voltage stations, the use of draw-out #breakers minimizes downtime during switchgear maintenance, and additionally, the need for a #feeder #isolator is removed.
1.6 Two-breaker method with draw-out circuit-breakers
Draw-out #circuitbreakers lead to cost-effective medium-voltage stations as they eliminate the need for busbar and feeder isolators. During station operation, these breakers can be slotted into a cubicle designated for either bus I or bus II.
1.7 Double busbars with bypass busbar (US)
The bypass bus refers to an additional busbar that is connected through the bypass branch. The advantage of this setup is that it allows for each branch of the installation to be isolated for maintenance purposes without disrupting the #powersupply.
1.8 Triple (Multiple) Busbars
For critical installations that supply electrically independent networks, or when rapid sectionalizing is necessary to limit #shortcircuit #power in the event of a #fault, this configuration often includes a bypass bus.
2. Special Configurations Primarily Found Outside of Europe
2.1 Double busbars equipped with a shunt disconnector.
The shunt disconnector "U" is capable of disconnecting each branch without interrupting the supply. During shunt operations, the tie breaker serves as the branch circuit breaker.
2.2 Two-breaker method with fixed switchgear
The two-breaker method using fixed switchgear entails the duplication of circuit breakers, branch #disconnectors, and #instrumenttransformers within each branch. This #configuration permits the interchange and isolation of busbars, as well as the removal of a branch breaker for maintenance purposes at any time without disrupting service.
In each branch, the circuit breaker, branch disconnector, and instrument transformers are replicated. It is possible to interchange busbars and #isolate a single bus, allowing for the removal of a branch breaker for #maintenance at any time without disrupting the #operation.
2.3 1 ½ breaker method
For the same level of flexibility mentioned earlier, fewer circuit breakers are required. This allows for isolation without disrupting service. Since all breakers are typically closed, the supply remains continuous even if a busbar fails. The branches can be interconnected using the linking breaker V.
2.4 Cross-tie Method
Using the cross-tie disconnector "DT," the power from line A can be transferred to branch A1, circumventing the busbar. This makes the #busbars available for maintenance.
2.5 Ring Busbars
Each branch necessitates only a single circuit breaker, and each breaker can be isolated without disrupting the power supply to the outgoing feeders. The ring busbar configuration is frequently employed as the initial phase of the 1 ½ breaker setups.
3. Configurations for Load-Centre Substations
Where:
A and B – Main transformer station,
C – Load-centre substation with circuit breaker or switch disconnector.
Opting for switch-disconnectors over circuit-breakers can lead to certain operational limitations.
Switch-disconnectors are commonly employed in load-center #substations to manage #feeders for #overhead #lines, cables, or transformers. Their application is influenced by operational requirements and economic factors.
3.1 Branch Connections
3.1.1 Overhead-line and cable branches
An earthing switch, such as Earthing Switch 7, discharges capacitive charges and safeguards against atmospheric charges on the #overheadline.
Where:
Busbar disconnector,
Circuit-breaker,
3Switch-disconnector,
Overhead-line or cable branch,
Transformer branch,
Branch disconnector,
Earthing switch,
Surge arrester)
3.1.2 Branch with unit earthing
The necessity for stationary earthing switches 7 arises from the escalation in short-circuit #powers and, in systems with impedance earthing, the earth-fault currents.
Where:
Busbar disconnector,
Circuit-breaker,
Switch-disconnector,
Overhead-line or cable branch,
Transformer branch,
Branch disconnector,
Earthing switch,
Surge arrester
3.1.3 Transformer Branches
Feeder disconnectors are often unnecessary in transformer branches since the #transformer is disconnected on both the high-voltage (h.v.) and low-voltage (l.v.) sides. For maintenance purposes, the use of an earthing switch is advised.
Where:
Busbar disconnector,
Circuit-breaker,
Switch-disconnector,
Overhead-line or cable branch,
Transformer branch,
Branch disconnector,
Earthing switch,
Surge arrester
3.1.4 Double Branches
Double branches serving two parallel feeders are typically equipped with branch disconnectors 6. In load-center substations, the installation of switch-disconnectors 3 allows for the connection and disconnection, as well as the through-connection, of branches 4 and 5.
Where:
Busbar disconnector,
Circuit-breaker,
Switch-disconnector,
Overhead-line or cable branch,
Transformer branch,
Branch disconnector,
Earthing switch,
Surge arrester
3.2 Connections of Instrument Transformers
3.2.1 Normal branches
Instrument transformers are typically positioned beyond circuit breaker 2, with the voltage transformer 5 following the #currenttransformer 4. This arrangement is proper for synchronization purposes.
Certain operations necessitate the use of a voltage transformer situated beyond the branch disconnectors, either directly on the cable or on the overhead line.
Where:
Busbar disconnectors,
Branch circuit-breaker,
Bypass circuit-breaker,
Current transformers,
Voltage transformers,
Branch disconnector,
Bypass disconnectors,
Earthing switch
3.2.2 Station with bypass busbar (Instrument transformers within branch)
Instrument transformers stop functioning when the bypass is activated. The line protection for the branch needs to be ensured by the instrument transformers and #protection #relays of the bypass. This can only be achieved if the ratios of the transformers in all branches are roughly the same.
The bypass's #protectionrelays must be configured with the correct values. Additionally, maintaining the branch #transformers is more convenient and can be performed while the bypass is operational.
When capacitive voltage transformers, which serve as coupling #capacitors for a high-frequency telephone link, are utilized, the link becomes inoperative in bypass mode as well.
Where:
Busbar disconnectors,
Branch circuit-breaker,
Bypass circuit-breaker,
Current transformers,
Voltage transformers,
Branch disconnector,
Bypass disconnectors,
Earthing switch
3.2.3 Station with bypass busbar (Instrument transformers outside branch)
During a bypass operation, the branch protection relays remain operational, and so does the telephone link when capacitive #voltagetransformers are utilized. The only required action is to redirect the relay-tripping circuit to bypass circuit-breaker 3.
Maintaining transformers becomes more challenging because the branch needs to be out of service during the process.
Whether to place instrument transformers inside or outside the branch is determined by factors such as branch currents, protection relays, maintenance feasibility, and for #capacitivevoltage transformers, the high-frequency telephone connection.
Where:
Busbar disconnectors,
Branch circuit-breaker,
Bypass circuit-breaker,
Current transformers,
Voltage transformers,
Branch disconnector,
Bypass disconnectors,
Earthing switch
3.3 Busbar Coupling Connections
Practical experience indicates that complex coupling arrangements are often required to fulfil the essential criteria for supply security and the flexibility needed during transitions or disconnections.
The increased complexity is apparent in the configurations of medium-voltage and high-voltage installations.
Generally, dividing into two bays is necessary to house the equipment used for #tiebreaker branches.
3.3.1 Double busbars
Where:
A and B = Busbar sections,
LTr = Busbar sectioning disconnector
3.3.2 Triple busbars
Reference: | Switchgear Manual (11th-edition) by ABB |
Format: | |
Size: | 27.96 MB |
Pages | 885 |
Download: |
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