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network will energize the primary feeder through the network transformer. This can be very dangerous, because a fault will continue to be 'fed' from the secondary network side of transformer. Even without a fault, if the electric utility wants to perform maintenance on that primary cable, they must have a way to fully disconnect that primary cable, without worrying about the cable being energized by the secondary network through the network transformer. Thus, the network protector is designed to open its contacts if the relay senses backwards flowing current.
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97:. The secondary grid system improves continuity of service for customers, since multiple sources are available to supply the load; a fault with any one supply is automatically isolated by the network protector and does not interrupt service from the other sources. Secondary grids are often used in downtown areas of cities where there are many customers in a small area.
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secondary contacts. The controlling relay monitors voltage and current in the transformer, and opens or closes the contact mechanism through electrical signals. The relay uses a power/time curve so that small, short term reverse power flow (such as from elevator hoists) are ignored. Spot units will be 277/480 and the grid units will be 120/208.
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Network protectors typically have three settings, "automatic", "open", and "close". The top side is fed from multiple protectors and is always energized unless all units on a spot network are in the open position. Grid units will always be energized on the top side from the many other units tied into
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set of contacts and a controlling protection relay. The components are enclosed in a protective housing; some network protectors are installed on transformers below grade and must be in water-resistant enclosures. The mechanism contains electrical and mechanical parts to switch open and close the
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on the primary feeder, the substation circuit-breaker is meant to open, disconnecting the primary feeder from one side. The problem is that this primary cable is also connected to a network transformer, which is interconnected to other network transformers on its secondary side. The secondary
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Analysis of the system is required to ensure that the system can, indeed, supply enough current to fuse the cables, wherever the fault is. This method tends to work well at 120 volts, but it is less reliable at higher voltages. The danger in depending on the cable to 'burn clear' is that some
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Typically the network protector is set to close when the voltage difference and phase angle are such that the transformer will supply power to the secondary grid, and is set to open when the secondary grid would back-feed through the transformer and supply power to the primary circuit.
143:(like fuses) to melt and disconnect the secondary fault under the right conditions. In other cases, the utility lets cable 'burn clear', in which case the fault is allowed to remain fed until the cables fuse, then the fault is isolated.
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However, if there is a fault on the secondary grid, the network protector is not designed to open its contacts up. The secondary fault will continue to be fed from the primary side of the system. In some cases, networks are designed with
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conditions will not cause the cable to burn in this manner and instead, the entire section of cable can be damaged from excessive, long-term overloading, causing fires and damage to the secondary network.
127:. The network protector is installed to protect the stability and reliability of the secondary grid by preventing power flow away from the customers and into the primary feeders.
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Typically, network protectors are contained inside a submersible enclosure which is bolted to the throat of the network transformer and placed in underground vaults.
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the grid. A spot network is 2 or more transformers dedicated to a single customer. The grid feeds multiple customers. A network protector has a
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The network protector does not protect the (secondary) network cable from
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154:standard C57.12.44 covers network protectors.
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57:Learn how and when to remove this message
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886:Renewable energy commercialization
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176:Richards Manufacturing Company
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881:Renewable Energy Certificates
841:Cost of electricity by source
763:Arc-fault circuit interrupter
639:High-voltage shore connection
896:Spark/Dark/Quark/Bark spread
694:Transmission system operator
654:Mains electricity by country
231:Automatic generation control
960:Electric power distribution
921:List of electricity sectors
916:Electric energy consumption
634:High-voltage direct current
609:Electric power transmission
599:Electric power distribution
276:Energy return on investment
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891:Renewable Energy Payments
380:Fossil fuel power station
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674:Single-wire earth return
614:Electrical busbar system
271:Energy demand management
181:Eaton network protectors
83:distribution transformer
79:electricity distribution
805:Residual-current device
795:Power system protection
785:Generator interlock kit
29:Some of this article's
965:Electrical engineering
589:Distributed generation
261:Electric power quality
73:is a type of electric
861:Fossil fuel phase-out
629:Electricity retailing
624:Electrical substation
604:Electric power system
217:Electricity delivery
826:Availability factor
778:Sulfur hexafluoride
659:Overhead power line
559:Virtual power plant
534:Induction generator
487:Sustainable biofuel
296:Home energy storage
286:Grid energy storage
251:Droop speed control
700:Transmission tower
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34:may not be
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331:Repowering
170:References
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281:Grid code
241:Base load
101:Operation
85:from the
47:July 2014
939:Category
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514:AC power
224:Concepts
158:See also
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465:Thermal
460:Osmotic
455:Current
435:Biomass
425:Biofuel
407:Nuclear
364:Sources
450:Marine
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807:(GFI)
696:(TSO)
482:Solar
470:Tidal
445:Hydro
132:fault
573:and
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475:Wave
385:Coal
152:IEEE
93:and
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