Copyright © SEL 2016

Performance Comparison Between Mho Elements and Incremental Quantity-Based

Distance ElementsGabriel Benmouyal, Normann Fischer, and Brian Smyth

Schweitzer Engineering Laboratories, Inc.

• Present characteristics of incremental distance in impedance plane

• Compare performance of mho elements and incremental distance elements based on their characteristics

• Compare performance with series compensation• Discover issues with mutually coupled lines and

three‐terminal lines

Overview

Superposition Principle

L R

ZL1 = 17.47 (86°) ohmsZL0 = 62.47 (75.38°) ohms

ZR1 = 20 (78°) ohmsZR0 = 62.08 (71°) ohms

ZS1 = 10 (73°) ohmsZS0 = 33 (68.5°) ohms

VM

Relay

VN (θ°)

d

230 kV SystemCT Ratio: 240/1VT Ratio: 2,000/1All impedances in primary values

Single-Phase Faults Pure-Fault Sequence Network

EfA

ZR0

RF

ZS0

I0F

N0

d ZL0 (1– d ) ZL0

RF

I2F

N2

ZS1 ZR1

d ZL1(1– d ) ZL1

ZR1

d ZL1

RF

N1

ZS1

(1– d ) ZL1

∆ I1F

–

+ PF

PF

V V VI I I= + ∆= + ∆

( )A LDEf VM ZS1 d•ZL1 •I= − +

( )A PF LD

0 F

Ef VA d• ZL1• IVA d• ZL1• IA K • I0 3R • I1F= − =

−∆ + ∆ + + ∆

Incremental Distance Principle

( )A PF LD

0 F

Ef VA d• ZL1• IVA d• ZL1• IA K • I0 3R • I1F= − =

−∆ + ∆ + + ∆

( )AG PF PF

AG 0

Vf VA r • Z1L •IAVd VA r • Z1L • IA K • I0

= −

= −∆ + ∆ +

Variation of VfAG and VdAG (r = 80%)

Vf AVd A Vd A

Simple Delta Filter

–

• Delta filters provide ∆V and ∆I during a time interval equal to the delay τ following a fault

• Delta filters can be used either in frequency domain with phasors or in time domain (high‐ and ultra‐high‐speed applications)

• Output is zero in steady state• Limitations are cascading events, evolving faults, and

switch-on-to-fault situations

Delta Filters

Incremental Distance Three-Phase Fault Characteristics

A F

A

Ef VA d• ZL1• IA R • I1FVd VA r • ZL1• IA

= −∆ + ∆ + ∆

= −∆ + ∆

' A FA APP _NLD

' AA

Ef REf ZS1 d• ZL1 ZS1 ZIA C1

VdVd ZS1 r • Z1LIA

= = + + = +∆

= = +∆

Incremental Distance Three-Phase Fault Characteristics

( ) ( )APP _NLDZS1 r • Z1L ZS1 Z+ ≥ +

( )( )

( )

0

0

x real ZS1y imag ZS1R ZS1 r ZL1

= −

= −

= +

Three-Phase Fault Characteristics

–5

–4

–3

–2

–1

0

1

2

–4 –3 –2 –1 0 1 2 3

Imag

inar

y (Z

AP

P)_

(ohm

s)

Real (ZAPP)_(ohms)

ZS1

r • ZL1

Incremental Distance Center

Incremental DistanceMho PSVMMho PSV

ZAPPd = 0.1 puRF = 1.65 Ohms

~(–|2 ZS1 + r ZL1|)

( )

( )

APP _NLD F

F

Z d 0.1, R 1.6465

RVA d• ZL1 2.199 j0.147IA C1

= = =

= + = + Ω∆

Three-Phase Faults Resistance Coverage

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.5

1

1.5

2

2.5

3

3.5

4

Distance to Fault (pu)

Res

ista

nce

Cov

erag

e (s

econ

dary

ohm

s) Incremental DistanceMho PSVMMho PSV

RF RF RF

a

b

c

RFGV = 0

Three-Phase Fault With ZS1 Divided by 20

–2

–1.5

–1

–0.5

0

0.5

1

1.5

2

–2 –1.5 –1 –0.5 0 0.5 1 1.5 2

Imag

inar

y (Z

AP

P)_

(ohm

s)

Real (ZAPP)_(ohms)

Incremental Distance Center

Incremental Distance

r • ZL1

ZS1

Mho PSVMMho PSV

Three-Phase Fault Resistance Coverage With ZS1 Divided by 20

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Distance to Fault (pu)

Res

ista

nce

Cov

erag

e (s

econ

dary

ohm

s)

Incremental Distance

Mho PSVM

Mho PSV

Single-Phase Fault Characteristics

–5

–4

–3

–2

–1

0

1

2

–4 –3 –2 –1 0 1 2 3

Imag

inar

y (Z

AP

P)_

(ohm

s)

Real (ZAPP)_(ohms)

r • ZL1

KSLO • ZS1

Incremental Distance Center

ZAPPd = 0.5 puRF = 1.43 ohms

Incremental DistanceMho PSVMMho PSV

• Mho element characteristics in impedance plane always exist

• Incremental distance element characteristics in impedance plane are defined only if ∆V and ∆I are non-zero (they do not exist in steady state)

• In steady state, mho element asserts for overload condition (incremental distance element does not)

Distance Element Characteristics

Series Compensation

MOV / Capacitor Equivalent

–jXC

MOV

IC ICRCEQ –jXCEQ

ZCEQ

2 4 6 8 10 12 14 16–1

0

1

2

3

4

5

6

7

Current (secondary A)R

esis

tanc

e (o

hms)

2 4 6 8 10 12 14 16–20–18–16–14–12–10

–8–6–4–20

Current (secondary A)

Rea

ctan

ce (o

hms)

Voltage Inversion No MOV, d = 0, RF = 0

–100

–50

0

50

–50 0 50

Imag

inar

y (Z

AP

P) _

(ohm

s)Real (ZAPP)_(ohms)

ZAPP at d = 0

Incremental DistanceMho PSVMMho PSV

–76.4

– j19.6 ohms 0

25.4ohms – j19.6 ohms

>

>

EQ

EQ

ZC d• ZL1

ZS1 d• ZL1 ZC

>

+ >

Current InversionNo MOV, d = 0, RF = 0, ZS1 Divided by 2

EQZC ZS1 d• ZL1> +

– j19.6 ohms 12.7ohms>

Linearized Sequence Network for Three-Phase Fault

Apparent Impedances for Three-Phase Fault d = 0, r = 50%

Three-Phase Fault Resistance Coverage

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

5

10

15

20

25

30

35

Distance to Fault (pu)

Res

ista

nce

(ohm

s)

Incremental DistanceMho PSVMMho PSV

Impact of Element Reach Example of Remote Infeed

L R

ZU1 = 6 (78°) ohmsZU0 = 18.7 (71°) ohms

ZR1, ZR0ZS1, ZS0

VM

Relay

VN (θ°)

VP (α°)

ZL1, ZL0

d

Mho AB Loop Scalar Product for Three-Phase Fault Applied From d = 0 to 1 pu

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

–100,000

–50,000

0

50,000

100,000

150,000

200,000

Distance to Fault (pu)

Mho A

B S

calar Product (V

2)

SP Mho AB (PSVM)

Operate Threshold

VfAB and VdAB for Three-Phase Fault Applied From d = 0 to 1 pu

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

50

100

150

200

250

300

Distance to Fault (pu)

Voltage (secondary V

)

VfAB

VdAB

• Incremental distance characteristics do not exist in steady state

• Incremental distance elements have increased sensitivity, increased resistance coverage, and immunity to voltage or current inversion

• Incremental distance element reach is affected in same way as mho elements (series compensation, remote infeed or outfeed, and parallel lines)

Conclusion

• Limits of incremental distance elements are limits imposed by delta filters (window typically of 1 cycle)

• Optimal configuration consists of mho element that is parallel with incremental distance element (high- or ultra-high-speed element with slower conventional mho element backup)

• Single comparator was considered in the study

Conclusion

Questions?