RET 670

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ABB Power Technologies AB, 2007

Substation Automation and Protection Training

2008-05-23 1

Substation Automation and Protection Training

RET 670 Transformer Protection Restricted Earthfault

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Up to three instances available Low impedance type Can be used on all directly or low impedance earthed windings Up to 4 three-phase CT inputs REF1REFPDIF_87N

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ABB Power Technologies AB, 2007

I3P I3PW1CT1 I3PW1CT2 I3PW2CT1 I3PW2CT2

2008-05-23 2

Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Able to handle multiple circuit breaker applications as well as autotransformers in 1½ CB applications

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ABB Power Technologies AB, 2007

I3P I3PW1CT1 I3PW1CT2 I3PW2CT1 I3PW2CT2

2008-05-23 3

Substation Automation and Protection Training

I3P I3PW1CT1 I3PW1CT2 I3PW2CT1 I3PW2CT2

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Functionality Zero sequence differential protection with a percentage biased operate/restrain characteristic, plus an additional zero sequence current directional comparison criterion Requires no current magnitude or phase correction, even when OLTC present Insensitive to inrush and overexcitation currents Only danger is eventual CT saturation

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ABB Power Technologies AB, 2007

2nd harmonic restraint (reactor energizing)

2008-05-23 4

Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Functionality Three-section operate/restrain characteristic Settings: IdMin

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ABB Power Technologies AB, 2007

Dependent on the magnitude of the bias current, the corresponding zone (section) of the operate - bias characteristic is applied.

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Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Functionality Operate/restrain characteristic Differential current – vector sum of the fundamental frequency neutral current and the fundamental frequency residual current (calculated from the three line-side fundamental frequency phase currents) Idiff = IN + 3I0 For multiple circuit breaker applications, the two contributing residual currents are internally summed to produce the overall line-side residual current

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ABB Power Technologies AB, 2007

I3PW1 = I3PW1CT1 + I3PW1CT2

2008-05-23 6

Substation Automation and Protection Training

I3P I3PW1CT1 I3PW1CT2 I3PW2CT1 I3PW2CT2

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Functionality Operate/restrain characteristic Single circuit breaker applications – ordinary power trfrs

I3P I3PW1CT1 I3PW1CT2 I3PW2CT1 I3PW2CT2

curr(x) = MAX [I3PW1CT1]

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ABB Power Technologies AB, 2007

curr(z) = IN i.e. Ibias = MAX [curr(x); curr(z)]

2008-05-23 7

Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Functionality Operate/restrain characteristic Multiple circuit breaker applications-CTFactor A factor to allow a sensitive function also at multi-breaker arrangement where the rating in the bay is much higher than the rated current of the transformer winding. CTFactor = Irated pri_CT / Irated_W The CTFactor is generally chosen so that when 1pu primary current flows through the CT, this would contribute a 1pu component to the bias calculation – e.g. Irated pri_CT = 1000A Irated_W = 500A

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ABB Power Technologies AB, 2007

contribution to bias calculation = 1000 / (1000/500) = 500A Ibias (pu) = Ibias (pri A) / IBase, where IBase = Irated_W Without CTFactor, a 1pu CT primary current would contribute a 1000A component to the bias calculation (i.e. 2pu) 2008-05-23 8

Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Functionality Operate/restrain characteristic Multiple circuit breaker applications – ordinary power trfrs

I3P I3PW1CT1 I3PW1CT2 I3PW2CT1 I3PW2CT2

curr(a) = MAX [I3PW1CT1] / CTFactorPri1

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ABB Power Technologies AB, 2007

curr(b) = MAX [I3PW1CT2] / CTFactorPri2 curr(x) = MAX [I3PW1CT1 + I3PW1CT2] curr(z) = IN i.e. Ibias = MAX [curr(a); curr(b); curr(x); curr(z)] 2008-05-23 9

Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Functionality Operate/restrain characteristic Multiple circuit breaker applications

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ABB Power Technologies AB, 2007

Applying the CTFactor gives a gain in the sensitivity for internal faults (by reducing the contribution to the bias from the T-side CTs), but still ensures adequate biasing for through fault conditions

2008-05-23 10

Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Functionality Operate/restrain characteristic Single circuit breaker applications – autotransformers

I3P I3PW1CT1 I3PW1CT2 I3PW2CT1 I3PW2CT2

curr(x) = MAX [I3PW1CT1] curr(y) = MAX [I3PW2CT1]

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ABB Power Technologies AB, 2007

curr(z) = IN i.e. Ibias = MAX [curr(x); curr(y); curr(z)] Note: set IBase = highest winding rated current, normally Irated_MV 2008-05-23 11

Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Functionality Operate/restrain characteristic Multiple circuit breaker applications – autotransformers

©

ABB Power Technologies AB, 2007

I3P I3PW1CT1 I3PW1CT2 I3PW2CT1 I3PW2CT2

2008-05-23 12

Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Functionality Operate/restrain characteristic Multiple circuit breaker autotransformer applications curr(a) = MAX [I3PW1CT1] / CTFactorPri1 curr(b) = MAX [I3PW1CT2] / CTFactorPri2 curr(c) = MAX [I3PW2CT1] / CTFactorSec1 curr(d) = MAX [I3PW2CT2] / CTFactorSec2 curr(x) = MAX [I3PW1CT1 + I3PW1CT2] curr(y) = MAX [I3PW2CT1 + I3PW2CT2] curr(z) = IN

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ABB Power Technologies AB, 2007

i.e. Ibias = MAX [curr(a);…….curr(z)]

2008-05-23 13

Substation Automation and Protection Training

I3P I3PW1CT1 I3PW1CT2 I3PW2CT1 I3PW2CT2

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Directional criterion – external earth fault zone of protection

s o A (L1) u r B (L2) c C (L3) e Uzs

zs voltage is max. at the earth fault

I zs1

I a0=

a (L1)

I zs1

I b0=

b (L2)

I zs1

I c0=

c (L3)

3Io=3I zs1

IN = -3Izs1

IN

Current in the neutral (IN) serves as a directional reference because it has the same direction for both internal and external faults.

For external fault ROA

3I0 IN ROA

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ABB Power Technologies AB, 2007

Restrain for external fault

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Substation Automation and Protection Training

MTA

Currents 3Io and IN are theoretically 180o out of phase for any external earth fault.

Reference is neutral current

Operate for internal fault

Relay Operate Angle (ROA) Settable 60° to 90

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Directional criterion – internal earth fault power system contribution to fault current

s o u r c e

zone of protection

A (L1) B (L2) C (L3)

Izs2

Izs1

I

a= 0

a (L1)

Izs2

Izs1

I

b= 0

b (L2)

Izs2

Izs1

I

c= 0

c (L2)

Ifault

Uz s

3Io = -3Izs2

IN

IN = - 3Izs1 Return path for 3Izs2

Return path for 3Izs1

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ABB Power Technologies AB, 2007

ROA

For internal fault 3I0 IN

ROA

Restrain for external fault 2008-05-23 15

Substation Automation and Protection Training

MTA

Reference is neutral current

Operate for internal fault

Current in the neutral (IN) serves as a directional reference because it has the same direction for both internal and external faults.

The residual current 3I0 and the neutral current IN are theoretically equal in magnitude and 180 degrees currents 3Io and IN are approximately in phase for an internal earth fault.

Relay Operate Angle (ROA) Settable 60° to 90

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) 2nd harmonic analysis / blocking Required primarily to prevent unwanted operation on reactor energizing due to possible line-side CT saturation caused by a high dc component of long duration. The current through the neutral CT does not have the same dccomponent, or the same amplitude, and consequently the risk of saturation in this CT is much less The differential current that appears as a result of the saturation may be so high that it reaches the operate area of the characteristic

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ABB Power Technologies AB, 2007

If the ratio between 2nd harmonic and fundamental exceeds 60%, the function is blocked

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Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Overview of restricted earthfault protection function 3I0 < 3% of Ibase 3I0 > 3% of Ibase

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ABB Power Technologies AB, 2007

Directional check

IN > 50% of Idmin 2008-05-23 17

Substation Automation and Protection Training

A directional check is only executed if The magnitude of the line-side residual current (3I0) is at least 3% of IBase start has been registered from the operaterestrain characteristic

≥1

&

TRIP

&

START

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N) Function block

‘Analog’ quantity inputs

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ABB Power Technologies AB, 2007

‘Analog’ quantity outputs

2008-05-23 18

Substation Automation and Protection Training

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ABB Power Technologies AB, 2007

RET 670 – Restricted Earthfault Protection - Settings

2008-05-23 19

Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection - Settings Settings Settings group N1 Differential protection LowImpREF(PDIF,87N)

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ABB Power Technologies AB, 2007

Off; On

2008-05-23 20

Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N)

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ABB Power Technologies AB, 2007

Service values

2008-05-23 21

Substation Automation and Protection Training

RET 670 – Restricted Earthfault Protection Restricted earthfault protection (PDIF, 87N)

©

ABB Power Technologies AB, 2007

Service values

2008-05-23 22

Substation Automation and Protection Training

ABB Power Technologies AB, 2007

©

2008-05-23 23

Substation Automation and Protection Training