EE 434 POWER SYSTEM PROTECTIONLECTURE 14: OPERATION PRINCIPLES 

Ernesto Vazquez‐Martinez, ECERF

Typical protective devicelocation

Distributionsubstation

R

F3 F2

F1

S

F4

Recloser Sectionalizer

FuseCutouts

Relays

Overcurrent relays

Overcurrent relaysInstantaneous overcurrent relay

i

,e+

‐

→∞

fr

F

Other structures

Instantaneous overcurrentrelay block and trip regions

Time‐delay overcurrent relay

Torque in the disc (TDR) 

Time‐delay overcurrent relay block and trip regions

Dynamic behavior of TDR

Overcurrent relaycharacteristics

CO‐8curves

Otherrelay

Digital time‐delay overcurrent relay 

IEEE C37.112 – 1996

IEC 225 ‐ 4

Typical protective devicelocation

Distributionsubstation

R

F3 F2

F1

S

F4

Recloser Sectionalizer

FuseCutouts

Relays

Fuses

Medium voltage distribution: Distribution transformers. Laterals:Overhead. Underground.

Functional characteristicsof fuses

Combine fault detection and current 

interruption.

Extremely inverse time current 

characteristic.

Single‐phase operation.

Require Replacement.

Distribution fuse cutouts

Fuse operation

Typical fuse time currentcharacteristic

Typical ratings (1)

Max. DesignVoltage

(kV)Type

Continuous Current

(A)

InterruptingCurrent

(Symm. kA)

5.2 Enclosed 50, 100 & 200 1.6 through 12.5

7.8 Enclosed 50, 100 1.4 through 8.0

7.8 Open Link 50 1.2

7.8/13.5 Open 100, 200 3.6 through 12.5

15.0 Open Link 50 1.2

Typical ratings (2)

Max. DesignVoltage

(kV)Type

Continuous Current

(A)

Interrupting Current

(Symm. kA)

15.0 Open 100, 200 2.8 through 10.0

15/26 Open 100, 200 2.8 through 5.6

18 Open Link 50 0.75

27 Open 100 1.1 through 8.0

38 Open 100 1.3 through 5.0

Selection of fuse nominal current

Above maximum load. Above transformer inrush current: 25X transformer nominal current for 0.01 sec. 10X transformer nominal current for 0.1 s.

Above motor starting current.

Typical protective devicelocation

Distributionsubstation

R

F3 F2

F1

S

F4

Recloser Sectionalizer

FuseCutouts

Relays

Functional characteristicsof recloser Combine fault detection, current interruption, and reclosing. Operation sequence includes three or four trips and two or three reclosures. Hydraulically or electronicallycontrolled.

Untanked single‐phasehydraulic recloser

UNIVERSAL, CLAMP‐TYPE TERMINALS accept copper or aluminum conductor in horizontal or vertical position

HEAD CASTING supports bushings and operating mechanism

HYDRAULIC MECHANISM counts operations to lockout and establishes dual time‐current characteristics; includes means for field‐changing of operating characteristics

MOVING CONTACTS provide double‐break interruption; are self‐cleaning

COVER‐CLAMPED BUSHINGS of wet‐process porcelain can be replaced in the field

SLEET HOOD protects manual operating handle, operations counter, and allows easy access with switch stick

MANUAL OPERATING HANDLE is easily operated by conventional switch stick; provides indication of lockout

SERIES‐TRIP SOLENOID trips recloser when current greater than minimum‐trip value flows.  Coils can be changed to convert to a different rating

Typical recloser operationsequence

Fast operations

Load current

Fault current

Time‐delayed operations

Reclosing intervals

Recloser lockout

Typical protective devicelocation

Distributionsubstation

R

F3 F2

F1

S

F4

Recloser Sectionalizer

FuseCutouts

Relays

Functional characteristicssectionalizer Lack fault‐ interrupting capability. Isolate faulted section. Combined with recloser or relayed breaker.

Count current‐interrupting operations. Hydraulically or electronically controlled. Fault closing capability. Load interrupting and closing capability.

Sectionalizer operation

EE 434 POWER SYSTEM PROTECTIONLECTURE 14: OPERATION PRINCIPLES 

Ernesto Vazquez‐Martinez, ECERF