A protection plan for distribution feeders

A Protection Plan for Distribution Feeders J . R . H A Y D E N

A S S O C I A T E MEMBER A I E E

J . E . M A R T I N

MEMBER AIEE

R . L . T I L S O N

ASSOCIATE MEMBER AIEE

l O O A M P E R E i d ^ R E C L O S E R S U S E D TO I S O L A T E B R A N C H L I N E S O V E R T H R E E M I L E S LONG S U P P L Y I Ν G T O T A L L O A D S T O 4 0 0 K W l φ O R 100 0 K W 3 φ.

185 Α Μ Ρ Ε Κ Ε 3 Φ R E C L O S E R S ( 2 0 0 A M P E A E G R O U N D T R I P P I N G ) U S E D T O I S O L A T E 3 φ B R A N C H L I N E S O V E R 2 0 0 * L O N G S U P R L Y I N G T O T A L L O A D S O F 1 0 0 0 T O 2 0 0 0 K W 3 φ .

1 1 5 / 1 3 . β S U B S T A T I

R V O N r-nwa-i

/ φ D I S T R I B U T O R

U S E D T O I S O L A T E A G R O U P O F A D J A C E N T Ιφ B R A N C H L I N E S . V

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Fig. 1 . One-l ine d iagram showing plan in action.

140 A M P E R E ίφ S E C T I O N A L I Z Ε R S U S E D TO I S O L A T E B R A N C H L I N E S 2 0 0 F E E T T O

' 3 M l L E S L O N G S U P P L Y I N G T O T A L L O A D S T O 4 0 0 KW ιφ O R 1000 Κ \ ν 3 φ A N D TO S E C T I O N A L | Z Ε B E H I N D R E C L O S E R S .

E X T R A H E A V Y D U T Y C U T O U T S U S E O T O I S O L A T E B R A N C H L I N E S L E S S T H A N 2 0 0 F E E T L O N G «

D I S T R I B U T I O N T R A N S F O R M E R S C O N V E N T I O N A L T Y P E W I T H C U T O U T S ) A N D A R R E S T E R S U S E D ON S T A T I O N TO S T A T I O N C I R C U I T S . J S E L F - P R O T E C T E D T Y P E U S E D O N > B R A N C H L I N E S B E H I N D R E C L O S E R S A N D S E C T I O N A L I Z E R S . J

1 1 5 / 1 3 . β K V S U B S T A T I O N

M ANY U T I L I T I E S are increasing distribution sys­tem primary circuit voltages as a means of supply­

ing continually growing loads in urban areas. However, the fundamental advantage of higher-voltage feeder de­sign, the ability to serve more load in larger areas, pre­vents the substation circuit breaker and its associated relays from providing adequate protection for the entire feeder. Automatic line-sectionalizing devices must be provided to restrict outages to a portion of a feeder area, thereby limiting the customers without service and reducing the area that must be patrolled to locate the fault.

Planning the protection for a feeder requires the consideration of many factors including system voltage, normal load currents, inrush currents, maximum and minimum fault currents, number of branches, lengths of line, types of load, and equipment to be protected. T o el iminate the need for the individual analysis of each feeder and proposed sectionalizing point, the Pub­lic Service Company of Colorado has developed a plan for installing automatic l ine sectionalizing devices on its 13.2-kv feeders in the metropoli tan Denver area. T h i s plan provides for the protection of the feeder main from each of its branch circuits by automatic reclosers, sectionalizers, or cutouts depending upon the load, ex­posure, and length of the branch. Only one size each of single-phase sectionalizers, single-phase reclosers, 3-phase reclosers, and fuse cutouts is used.

T h e Public Service Company of Colorado designs its

7.6/13.2-kv feeders for loads of 6,000 kw or 7,500 kva. T h e main circuits, which are of 4 / 0 copper or its alu­minum equivalent, can be tied through normally open field switches to adjacent feeders. Distribution in an area is served by laterals tapped to the main circuit. T h e s e laterals constitute most of the exposure to the feeder and are subject to the largest percentage of faults

Fig. 1 illustrates the protection of a feeder in accord­ance with the rules of the plan. Some of the benefits achieved through this plan are:

1. Engineering time is conserved. 2. Stocking is reduced as only one size of each device

is used. 3. Uniform and consistent protection is achieved. 4. Protecting all feeder laterals means only the feeder

main must be patrolled when a fault has locked out the station breaker.

5. One station feeder breaker relay setting co-ordi­nates with either of the reclosers or the sectionalizer.

6. One sectionalizer size co-ordinates with the station breaker and both of the reclosers.

7. Load areas can be switched from feeder to feeder or to other substations without co-ordination being lost.

Digest of paper 58-174, recommended by the AIEE Transmission and Distribution Committee and approved by the AIEE Technical Operations Department for presentation at the AIEE Winter General Meeting, New York, N. Y., Feb. 2-7, 1958. Published in AIEE Power Apparatus and Systems, Aug. 1958, pp. 486-94. J . R. Hayden, J . E, Martin, and R. L . Tilson are with the Public Service Company of Colorado, Denver, Colo.

1 0 0 0 Hayden, Martin, Tilson—Protection Plan for Feeders ELKCTRICAL ENGINEERING