chp133 bbp ms

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Technology and SolutionsProtection and Substation Automation

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Topic:

Busbar Protection

Measurement System

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Busbar Protection – Measurement System

r Introductionr BBP Requirement r BBP Basicsr Special Condition for the BBP (≠ LP, TP, GP ….)r The “problem” on CT Saturationr High Impedance Measurement Principler Low Impedance Measurement Principle

q Example and Features of different Methods / Algorithmsq INX-2q INX-5q REB500q REB670

r Calculation examples: Differential & Restraining Current / Differential Voltage

r Open CT / Differential current Supervision r Additional Release / Tripping Criteriasr Intertripping

Objectives / Overview

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Introduction

q It is extremely important for Busbar Protection applications to have good security since an unwanted operation might have severe consequences

q The unwanted operation of the Busbar Protection will have the similar effect as simultaneous faults on all power system elements connected to the bus

q On the other hand, the BBP has to be dependable as well. Failure to operate or even slow operation in case of a busbar fault can have fatal consequences. Human injuries, power system blackout, transient instability or considerable damage to the surrounding substation equipment and the close- by generators are some of the possible outcomes

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Introduction

q A fault on a busbar in the network is relatively seldom: Statistically once in every 20 – 30 years per switchgear

q A fault on an overhead line in the network is statistically more than factor 100 higher

q The life time of busbar protection systems could be more than 30 – 40 years

q According to studies all costs to integrate a BBP system will be covered in case of ONE successful trip in it’s life time

q Remember: maloperating / unwanted operating as well as non operating BBP system can and have caused blackouts

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BBP RequirementsNumber the requirements depending on the importance

___ STABILITY in case of external faults (even with extreme CT saturation)

___ RELIABILITY (extensive selfsupervision)___ TRIPPING SPEED

___ easily EXTENDABLE

___ extensive SELFSUPERVISION

___ SIMPLE OPERATION (Maintenance & Commissioning)

___ low CT REQUIREMENTS

___ SELEKTIVITY (only the fault affected busbar is allowed to trip)

___ MALOPERATION extremely unacceptable

___ matching to all switchgear CONFIGURATIONS

___ integration of BREAKER FAILURE PROTECTION (additional protection & monitoring functions)

___ SENSITIVITY

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Who knows Mr. Kirchhoff ?

BBP Basics

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Kirchhoff’s 1st Law: Node Rule

I1 + I2 + I3 = Σ I = 0

The sum of all

currents must be zero

BBP Basics

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Kirchhoff’s 1st Law: Node Rule

I1 + I2 + I3 = Σ I

≠0

⇒ Fault on the busbar

⇒ Trip circuit breaker

If

BBP Basics

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Differential current measurement

Σ I = I1 + I2 + I3

If

Σ I > differential current setting

⇒Trip Busbar Protection

BBP Basics

the measurement (system) has to be phase segregated3 (4) measurement systems: R; S; T (& special: N)

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External Fault

BBP Basics

I1 I2

Σ I

⇒ No Differential Current

⇒ No Trip

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Internal Fault

BBP Basics

⇒ High Differential Current

⇒ TripI1 I2

Σ I

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External Fault – with DC component

BBP Basics

I1 I2

Σ I

⇒ No Differential Current

⇒ No Trip

A DC component will be super-imposed if the short circuit does not occur at the voltage peak

The DC component will decade with the network time constant τ = L / R

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Internal Fault – with DC component

BBP Basics

⇒ High Differential Current

⇒ Trip

I1 I2

Σ I

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Protection Zones

Special Condition for the BBP (≠ LP, TP, GP ….)B

usba

r

Busbar

Line

Tran

sfor

mer

Gen

erat

or -

Tran

sfor

mer

BBG

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All protection system (excl. BBP):The current in the current transformer (CT) due to a fault inside the protection zone is usually higher than the current in the CT due to a fault outside the protection zone. The reason for this is:

• In case on a feeder fault (near the busbar) the current in the feeders CT is equal to the sum of all feeder currents connected to the busbar.

• In case on a busbar fault the currents in the CTs are limited by the line or transformer reactance.

I external fault < I internal fault• Stability condition: on relatively low currents - CT saturation unlikely

• Tripping condition: on extremely high currents - CT saturation very likely

Special Condition for the BBP (≠ LP, TP, GP ….)

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Busbar protection system:The current in the current transformer (CT) due to a fault outside the protection zone is usually higher than the current in the CT due to a fault inside the protection zone. The reason for this is:

• In case on a feeder fault (near the busbar) the current in the feeders CT is equal to the sum of all feeder currents connected to the busbar.

• In case on a busbar fault the currents in the CTs are limited by the line or transformer reactance.

I external fault > I internal fault• Stability condition: on extremely high currents - CT saturation very likely

• Tripping condition: on relatively low currents - CT saturation unlikely

Special Condition for the BBP (≠ LP, TP, GP ….)

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External Fault

CT Saturation

I1 I2

Σ I

⇒ the CT saturation will produce a differential current which could result in a MALOPERATION

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External Fault – with DC component

CT Saturation

I1 I2

Σ I

The DC component will increase the saturation

⇒ the CT saturation will produce a differential current which could result in a MALOPERATION

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High Impedance Measurement Principle

q The only BBP system which can handle CT saturation without any other quantity than Idiff(Σ I ) is the High Impedance Protection System.

q The High Impedance Measurement Principle uses the physical behaviour of the CT saturation to prevent (mal-) operation in case of external fault with (high) CT saturation.

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CT2

feeder 1 feeder 2

RR

BB 1

CT1 U1 UR

RL1 RL2

UR > 0

U2 ImIm

Principle / Components

CT secondary reactance

Line resistance from CT to relay

High impedance (input)

I2I1Idiff = Σ I

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CT refresher course:

Im [A]

10’000

100

1’000

0.001 0.01 0.1 1

U [V

]

2Excitation or magnetizing current

Magnetizing Curve

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Im [A]

10’000

100

1’000

0.001 0.01 0.1 1

U [V

]

2Excitation or magnetizing current

Magnetizing Curve

Knee point voltage (when saturation starts)

Dynamical resistant:du/di = r <<<<<<

Dynamical resistant:du/di = r >>>>>>

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CT2

feeder 1 feeder 2

RR

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CT1 U1 UR

RL1 RL2

UR > 0

U2 ImIm

Internal Fault

Principle:

An internal fault will immediately result in a differential current and therefore a (high) voltage on the high impedance. The overvoltage relay which is measuring at the high impedance will pick up instantly.

The pick up voltage level must be set depending on the lowest possible fault current and the maximum load.

I2I1Idiff = Σ I

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CT2

feeder 1 feeder 2

RR

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CT1 U1 UR

RL1 RL2

UR > 0

U2 ImIm

Internal Fault

General setting rule:(since UR max = Uk)

RR = High Impedance (e.g. 2000Ω)UR = Voltage at the high impedanceUk = CT knee point voltage (e.g. 400V)N = CT ratio (e.g. 4000A/1A)Uset = overvoltage pick up setting

I2I1Idiff = Σ I

Å Uset ≤ 400V

Uset ≤ Uk

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feeder 1 feeder 2

RR

BB 1

CT1 U1 UR

RL1 RL2

UR > 0

U2 ImIm

External Fault (without CT saturation)

I2I1Idiff = Σ I

CT2

Principle:

An external fault (without CT saturation) will practically produce a very low differential current and therefore “no” voltage on the high impedance. The overvoltage relay which is measuring at the high impedance will not pick up.

RW

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feeder 1 feeder 2

RR

BB 1

CT1 U1 UR

RL1 RL2

UR > 0

U2 ImIm

External Fault (with CT saturation)

I2I1Idiff = Σ I

CT2

Principle:

In case of CT saturation the secondary reactance of the saturated CT will practically come to zero. Only the secondary resistant RCT(winding resistant) will result (du/di = r <<<<<<).

The High impedance will be bypassed by the relatively small sum of RW + 2RL2. Therefore the voltage UR will not reach the pick up level.

RCT

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CT2

feeder 1 feeder 2

RR

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CT1 U1 UR

RL1 RL2

UR > 0

U2 ImIm

Setting rules for stability: UR = Voltage at the high impedanceIkmax = maximum possible ext. fault current (e.g. 45kA)N = CT ratio (e.g. 4000A/1A)Uset = overvoltage pick up settingRCT = CT winding resistant (e.g. 6Ω)RL2 = lead resistant (e.g. 2Ω)2.5 = safety margin

I2I1Idiff = Σ I

Ç Uset ≥ 2.5 / 4000 * 45kA * (6Ω + 2 * 2Ω)≥ 281V

External Fault (with CT saturation)

Uset ≥ 2.5 / N * Ikmax * (RCT + 2 * RL2)

RCT


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RR = High Impedance (e.g. 2000Ω)Ikmin = minimum possible fault current (e.g. 1kA)N = CT ratio (e.g. 4000A/1A)Uset = overvoltage pick up settingIM = magnetising current at UK/2 (e.g. 0.3mA)x = number of CTs (e.g. 2)

Actual value of primary pick-up current


Requirements:Å Uset ≤ 400V Ç Uset ≥ 281V

Minimum pick up value for the detection of the minimum primary fault currentUset ≤ (Ikmin / N – x * IM) * RRUset ≤ (1000A / 4000 – 2 * 3mA) * 2KΩUset ≤ 488 V

Minimum primary fault current detection with actual setting of Uset = 300 V:Ikmin = N * (Uset / RR + x * IM)Ikmin = 2000 * (300V / 2000Ω + 2 * 3mA)Ikmin = 624 A

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If necessary,q an additional parallel resistor RP can be connected to change / adapt the sensitivityq an additional VDR can be connected to limit the voltage on the high impedance (to prevent damage)q an additional time delayed low stage overvoltage unit / function can be connected to detect open / missing CT inputs during load condition

Alternatives (1)

Alarm

BlockUR U>>

TripRP VDR U>

t

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There is also the possibility to insert a current instead of voltage measurement.Advantage: the Ikmin can be set directly in a current value: Ikmin = Iset * N

Alternatives (2)

Alarm

Block

UR RP VDR

I>> Trip

I>t

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q simple, sensitive and extremely stable measurement system – CT could theoretically be saturated / pre- magnetised 100%

q tripping time around one halfcycle

q easily extendable, if the correct CT is available!

q CT class TPS (old class X or BS) required – the TPS class defines

q the knee point voltage

q the magnetising current at half of the knee point voltage

q the winding resistance (at 75°C)

q inexpensive protection system – expensive CTs

q all CTs have to be the same type incl. ratio

q no other protection devices are allowed in the same CT circuit

q therefore no integration of CB Failure Protection etc. is possible

Features

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q in case multiple busbar configuration the current switching must be realised mechanically (risk of maloperation during switching; burned / damaged contacts / CTs !). A check zone and therefore a second CT core is strictly required (see following page)

q good testing facility of the measurement system but NOT of the current switching logic (which is the sensitive / week part)

q the principal is a mix of physical behaviour of the CT and numerical (or mechanical / analogue) current and voltage measurement – it is not possible to realize it 100% numerically (with a low impedance scheme)

q the possibility to record the CT currents is not given – therefore fault evaluation is not possible

The state of the art:Usually the High Impedance Protection Principle will only be installed in single busbar or 1 ½ CB configuration

Features

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Multiple Busbar with CT Switching and Check ZoneI

X X

X

II

+

I II

Checkzone

DiscriminatingZone

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Low Impedance Measurement Principle

Additional Quantity (s) to keep the Stability in case of External Fault with CT Saturation

q as described in the previous slides the quantity Idiff (Σ I ) is NOT sufficient in a Low Impedance Measurement System to guarantee Stability in case of External Fault with CT Saturation

q this additional quantity varies between the products and relay generations

q some examples of “clever” solutions are shown SIMPLIFIED in the following slides

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Low Impedance Measurement Principle – BBP Type INX-2– electronic relay generation

Idiff set < | ∑ I |differential current measurement

with instantaneous values

Phase Comparisonphase angle supervision = current

direction supervision with instantaneous values

& t

t = integration

time

TRIP CBs

Setting:- Maximum load < Ikmin < minimum short circuit currentto prevent false operation in case of shorted CT and to detect lowest possible fault current

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Typical INX-2 Feature:q centralised protection system, location in a centralised panel q automatic test cycle which supervises around 50 – 60 % of all HW components in the protection system and will block the system automatically in case of a HW faultq sometimes it is tricky to find faulty components since the fault indication of the automatic test is not very detailed and a lot of modules / electronic cards are availableq differential current and phase comparison (phase angle) measurement system which evaluates instantaneous current values. The system includes no special CT saturation detection facilityq low CT requirements: 2-3 ms of current signal must be available. This represents 5 times saturation on symmetrical fault currents (see following page)q tripping time around 12msq integration of CB failure and End fault Protection is possible q installation from around year 1968 – 1985q at present, the systems are still being extended (relatively seldom) q around 1200 systems are / were installed

Low Impedance Measurement Principle – BBP Type INX-2– electronic relay generation

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Low Impedance Measurement Principle


T-3

-2

-1

0

1

2

3

0 5 10 15 20 ms

A1

A2 A3

The areas are equal

t

A1 A2 A 3= = = •∫ i(t) dt10ms

Saturation at symmetrical current due to over-burdening or to high primary current

Ial = 1: current on which the CT starts to saturates

5 – times saturationmeans

5 – times Ial

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Ikmin < | ∑ I |differential current measurement

with instantaneous values

kset < |∑ I | / ∑ | I |stabilising / restraining measure-

ment with quantity Ires = ∑ | I | with instantaneous values

& t

t = integration

time

TRIP CBs

CT saturation detection

CT saturation detection with instantaneous values

Low Impedance Measurement Principle – BBP Type INX-5– static relay generation

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Low Impedance Measurement Principle – BBP Type INX-5D

iffer

entia

l cur

rent

I diff=

| ΣI |

Restraint current IRest = Σ | I |

internal

fault

no faultIkmin

k= 0,8

k= 1

0

Stabilised / Restraint Characteristic

Setting:- Maximum load < Ikmin < minimum short circuit currentto prevent false operation in case of shorted CT and to detect lowest possible fault current - K typically to 0.8

– static relay generation

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Low Impedance Measurement Principle – BBP Type INX-5

Internal Fault


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External Fault – without CT saturation


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External Fault – with CT saturation


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External Fault –

with CT saturation


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External Fault –

with CT saturation


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Depending on the saturation degree; the k – factor is reached for a longer or shorter time. Maloperation is still possible.


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Depending on the saturation degree; the k – factor is reached for a longer or shorter time. Maloperation is still possible.


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Electronic circuit to generate Blocking Signals”: e.g. Negative Blocking Signal


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The CT saturation detection will send blocking signals:

Positive CT saturation blocking signal will block the trip on negative differential current

Negative CT saturation blocking signal will block the trip on positive differential current

POS BLOCKING

SIGNAL (B+)

(B+)


Neg BLOCKING

SIGNAL (B+) (B-)

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(B+)

neg

I diff


neg

I diff

pos

I diffpos

I diff(B+)

(B-) (B-)

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& t

t = integration

time

TRIP CBsB-

Idiff pos

& t

B+

Idiff neg ≥1

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The Stability is maintained


(B+)

neg

I diffneg

I diff

pos

I diffpos

I diff(B+)

(B-) (B-)

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External Fault – with CT saturation & full DC offset

The Stability is maintained

(Idiff -)

(B+)(B+)(B+)(B+)

(Idiff -) (Idiff -) (Idiff -)

BLOCKING METHOD: tripping in case of external fault with CT saturation will be blocked till the next zero crossing is reached


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Internal Fault – with CT saturation & full DC offset

TRIP (no blocking)

(Idiff +)

(B+)(B+)(B+)

(Idiff +) (Idiff +)





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Typical INX-5 Feature:q centralised protection system, location in a centralised panel q automatic test cycle which supervises around 75 – 85 % of all HW components in the protection system and will block the system automatically in case of a HW faultq easy to find faulty components since the fault indication of the automatic test is very detailed and a small number of modules / electronic cards are availableq restrained differential current measurement characteristic which evaluates instantaneous current values. The system includes a CT saturation detection facility: BLOCKING METHOD. A blocking time which is too long delays the tripping command in case of evolving faults (fault evolves from external to internal)


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Typical INX-5 Feature:q low CT requirements: 2 ms of current signal must be available. This represents 5 times saturation on symmetrical fault currentsq tripping time around 12msq integration of CB failure and End fault Protection is possibleq installation from around year 1980 – 2003q at present, the systems are still being extended frequentlyq around 800 systems are / were installed


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Low Impedance Measurement Principle - BBP Type REB500– numerical relay generation

Ikmin < | ∑ I |differential current measurement with fundamental current values


ment with quantity Ires = ∑ | I | with fundamental current values & TRIP CBs


direction supervision with fundamental current values

Firs

t har

mon

ic (f

unda

men

tal)

filte

ring

by F

ourie

r filt

er

The REB500 BBP system will evaluate only the fundamental frequency current signal. This increases accuracy in the case of

relatively small, offset differential currents

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I1I1 I1

I1 I2

I2I2 I2

0 0t

I2

t

Primary current

Restrained differential current and phase comparison algorithms which evaluates “only” the fundamental wave of the current signal:

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I1I1 I1

I1 I2

I2I2 I2

0 0t

I1 I2

t

Secondarycurrent



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I1I1 I1

I1 I2

I2I2 I2

0 0t

I1 I2

t

Fundamentalfrequency component



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The result is a huge amplitude change (Δ a) and a big phase shift (Δ α) between the two current signals which could result in a maloperation in condition of extreme CT saturation

0 t

IΔ a

Δ α

Fundamentalfrequency component


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Result with extreme CT saturation

t ms

50 IN

I / In

Ires / In

Restrained differential current algorithm


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t ms

50 IN

I / In

t


k


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t ms

50 IN

I / In

t

Phase comparison algorithm

k

Phas

e sh

ift Δ

α


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Restrained differential current and phase comparison algorithms which evaluate the fundamental wave of the reconstructed current signal:

q The REB500 system will evaluate reconstructedfundamental current values (Fourier filtered values). The system will approximate the saturated current values to it’s origin

q This is realized with the from ABB patented so called “Maximum Prolongation Algorithm”. With this it can be obtained that the system is never blocked due to CT saturation: UNBLOCKING METHOD


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Maximum Prolongation Algorithm


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Restrained differential current and phase comparison algorithms which uses the “Maximum Prolongation Algorithm” followed by the fundamental wave filter (Fourier filter)

I1I1 I1

I1 I2

I2I2 I2

0 0t

I1 I2

t

Reconstructedcurrent signal

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The result is a relatively small amplitude change (Δ a) and more important a very small phase shift (Δ α) between the two current signals

0 t

IΔ a

Δ α

Fundamental frequency Component of the Maximum Prolongation signal

Restrained differential current and phase comparison algorithms which uses the “Maximum Prolongation Algorithm” followed by the fundamental wave filter (Fourier filter)

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Result using the “Maximum Prolongation Algorithm”with extreme CT saturation

t ms

50 IN

I / In

Ires / In


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t ms

50 IN

I / In

t


k


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t ms

50 IN

I / In

t

Phase comparison algorithm

k

Phas

e sh

ift Δ

α


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Conclusion:

By prolonging the maximum value, the signal is compensated such that the best possible approximation of the PHASE ANGLE and AMPLITUDE of the origin primary signal is achieved

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Ikmin < | ∑ I |differential current measurement with reconstructed fundamental

current values


ment with quantity Ires = ∑ | I | with reconstructed fundamental current

values& TRIP CBs


direction supervision with reconstructed fundamental current

values

Firs

t har

mon

ic (f

unda

men

tal)

filte

ring

by F

ourie

r filt

er

max

imum

pro

long

atio

n on

all

CT

Cur

rent

sig

nal

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Measurement Algorithm: Stabilized differential current

Restraint Current IRest

Differential currentIDiff

Intern

al Fau

lt

No FaultIkmin

k= 0,85

k= 1

0

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Measurement Algorithm: Phase comparison

Im

Re

Case 1: external fault ∆ϕ ≥ 74°

ϕ12 =139°

I2

I1

Im

Re

ϕ12 =40°

Case 2: internal fault ∆ϕ < 74°

I1

I2

I2I1

Tripping area

Pha

se d

iffer

ence

∆ϕ

No Fault

Internal Fault

Fall 1 2

∆ϕ min = 74°74°

180°

0°

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Typical REB500 Feature:q decentralised protection system, location might be in a a centralised panel or distributed (e.g. in the feeder protection panels)q continuous selfsupervision which supervises around 90 – 95 % of all HW components and SW tasks in the protection system and will block the system automatically in case of a HW / SW faultq very easy to find faulty components since the fault indication of the continuous selfsupervision is very detailed and a very small number of modules / electronic cards are availableq restrained differential current measurement (INX-5) and phase comparison (phase angle) (INX-2) algorithm which evaluates reconstructed fundamental current values (Fourier filtered values). The system will approximate the saturated current values to it’s origin with a from ABB patented (so called “maximum prolongation”) algorithm: UNBLOCKING METHOD (the system is never blocked due to CT saturation). No problem in case of evolving faults (fault evolves from external to internal)


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Typical REB500 Feature:q the restrained differential current measurement; phase comparison (phase angle) measurement and the maximum prolongation algorithm could be activated individually for special applicationq typical tripping time around 25msq integration of CB failure and End fault Protection as well as Line & Transformer Protection Functions is possible. Additional measurement functions as event- & disturbance recorder as well as additional release functions like I> or U< are availableq low CT requirements: 2 ms of current signal must be available. This represents 5 times saturation on symmetrical fault currentsq state of the art: installation from year 1994 – futureq over 1500 systems are in service (so far)


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Å Ikmin < | ∑ I |differential current measurement with RMS current values

Çsset < |∑ I | / ∑ | Iin |stabilising / restraining measurement with quantity Ires = ∑ | Iin |

with RMS current values & TRIP CBs

É external fault detection (decision 1.2 ms after zero crossing)

detection internal / external fault with instantaneous / sampledcurrent values

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Low Impedance Measurement Principle - BBP Type REB670– numerical relay generationRepresentation of the protection zone:

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Low Impedance Measurement Principle - BBP Type REB670– numerical relay generationCalculation of the instantaneous value of the differential current:

Calculation of the instantaneous sum of positive currents:

Calculation of the instantaneous sum of negative currents:

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Low Impedance Measurement Principle - BBP Type REB670– numerical relay generationCalculation of the incoming and outgoing currents:

Calculation of the RMS value of e.g. Iin (same for Iout and Idiff)

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Low Impedance Measurement Principle - BBP Type REB670– numerical relay generationCondition at Internal Fault:

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Low Impedance Measurement Principle - BBP Type REB670– numerical relay generationCondition at Internal Fault:

sudden split between of RMS Iin and RMS Ioutwill indicate an internal fault

if Å & Ç (Ikmin & s) is fulfilled the protection will trip since É will not see an external fault

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Low Impedance Measurement Principle - BBP Type REB670– numerical relay generationCondition at External Fault with CT Saturation:

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Low Impedance Measurement Principle - BBP Type REB670– numerical relay generationCondition at External Fault with CT Saturation:

É will detect an external fault within 1.2ms after the Iin zero crossing (before the CT gets into saturation) and will block till the next zero crossing is reached

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Test assembly:

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Test values & result:The CT TX war pre- magnetised with a DC current in order to get maximum remanence. Therefore the CT saturates within 1.2 ms!

The primary test current level was 26kA RMS with the full DC offset

The BBP system REB670 remains fully stable !!!

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Low Impedance Measurement Principle - BBP Type REB670– numerical relay generationStabilised / Restraint Characteristic

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Low Impedance Measurement Principle - BBP Type REB670– numerical relay generationStabilised / Restraint Characteristic

Setting:- Maximum load < Ikmin (Diff Oper Level) < minimum short circuit currentto prevent false operation in case of shorted CT and to detect lowest possible fault current

The sensitive (non restraint) operational level is designed to be able to detect internal busbar faults in low impedance earthed power systems: Limited earth fault current to certain level (300 –2000A)

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Typical REB670 Feature:q centralised protection system, location in a centralised panelq continuous selfsupervision which supervises the most of the HW components and SW tasks in the protection system and will block the system automatically in case of a HW / SW faultq very easy to find faulty components since a very small number of modules / electronic cards are availableq restrained differential current measurement algorithm which evaluates RMS current values. The system can decides within 1.2ms after the zero crossing of the current if the fault is external or internal. In case of external fault the measurement will be blocked till the next zero crossing: BLOCKING METHOD. A blocking time which is too long delays the tripping command in case of evolving faults (fault evolves from external to internal)


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Typical REB670 Feature:q very low (“almost no”) CT requirements: the system was successfully tested with just 1.2 ms of current signal. This represents >> 5 times saturation on symmetrical fault currentsq tripping time around one halfcycleq integration of CB Failure, OC protection as well as event- & disturbance recorder, monitoring function is possibleq state of the art: installation from year 2005 – futureq the system is a consequently further development / improvement of the well proven BBP systems RADSS, REB103, RED521


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Busbar fault condition

I1 =1000A

single injection Calculation examples Internal fault condition

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Calculation examples

∆ U = ∆ Isec * RR

= 0.5A * 2000Ω= 1 kV (spike)à TRIP

Σ Iin = + + I1

= + 1 kA= 1 kA

Σ I = + + I1

= + 1 kA= 1 kA

∆ Isec = I1/N= 1 kA / 2000 = 0.5 A

∆ I = + I1= + 1 kA= 1 kA

∆ I = + I1= + 1 kA= 1 kA

High Impedance System

(with CT ratio: N = 2000A / 1A;Impedance: RR = 2000 Ω;Knee Point V: UK = 400V)

Low Impedance Measurement System

REB670


REB500

Internal fault condition

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Diff

eren

tial c

urre

nt I d

iff=

| ΣI |

trip measurement system !!!⇒ ( if I∆ > Ikmin)



Restraint current IRest = Σ | Iin |

no faultIkmin

kREB500= 0,85

k= 1

0

Internal fa

ult REB500

Internal fault R

EB670

kREB670= 0,53


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Busbar fault condition

I1 = I2 = I3 = I4 =1000A 2500A 1500A 2000A

multiple injection Calculation examples Internal fault condition

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= 3.5A * 2000Ω= 7 kV (spike)à TRIP

Σ Iin = ++ I1++ I2+ + I3++ I4

= + 1 kA + 2.5 kA + 1.5 kA + 2 kA= 7 kA

Σ I = ++ I1++ I2+ + I3+ + I4

= + 1 kA + 2.5 kA + 1.5 kA + 2 kA= 7 kA

∆ Isec = I1/N= 7 kA / 2000 = 3.5 A

∆ I = + I1 + I2 + I3 + I4 = + 1 kA + 2.5 kA + 1.5 kA + 2 kA= 7 kA





REB670


REB500

Calculation examples Internal fault condition

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Diff

eren

tial c

urre

nt I d

iff=

| ΣI |

trip measurement system !!!⇒ ( if I∆ > Ikmin)




no faultIkmin

kREB500= 0,85

k= 1

0

Internal fa

ult REB500

Internal fault R

EB670

kREB670= 0,53

load depending tripping value!!!


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e.g. line fault

External fault condition

I2 = I3 = I4 =2500A 1500A 2000A

I1 =6000A


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= 0A * 2000Ω= 0 kVà NO TRIP

Σ Iin = + I2+ +I3++ I4

= 2.5 kA + 1.5 kA + 2 kA= 6 kA

Σ I = ++ I1++ I2+ +I3++ I4

= + 6 kA + 2.5 kA + 1.5 kA + 2 kA= 12 kA

∆ Isec = I1/N= 0 kA / 2000 = 0 A

∆ I = + I1 + I2 + I3 + I4 = - 6 kA + 2.5 kA + 1.5 kA + 2 kA= 0 kA





REB670


REB500

Calculation examples External fault condition

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Diff

eren

tial c

urre

nt I d

iff=

| ΣI |

no trip stable !!!




no faultIkmin

kREB500= 0,85

k= 1

0

Internal fa

ult REB500

Internal fault R

EB670

kREB670= 0,53

External fault condition

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during fault condition (Ι)

Current transformer failure (Ι)

I2 = I3 = I4 =2500A 1500A 2000A

I1 =6000A

CT shorted !!!


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= 1A * 2000Ω= 2 kV (spike)à TRIP !!!

Σ Iin = + + I1

= + 6 kA = 6 kA

Σ I = + + I1+ + I2 + + I3 + + I4

= + 6 kA + 2.5 kA + 1.5 kA + 0 kA= 10 kA

∆ Isec= I1/N= 2 kA / 2000 = 1 A






REB670


REB500

Calculation examples Current transformer failure (Ι)

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Diff

eren

tial c

urre

nt I d

iff=

| ΣI |




no faultIkmin

kREB500= 0,85

k= 1

0

Internal fa

ult REB500

Internal fault R

EB670

kREB670= 0,53

Current transformer failure (Ι)

REB500: no trip stableREB670: no trip stable

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during fault condition (ΙΙ)

I2 = I3 = I4 =2500A 1500A 2000A

I1 =6000A

CT shorted !!!

Calculation examples Current transformer failure (ΙΙ)

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= 3A * 2000Ω= 6 kV (spike)à TRIP !!!

Σ Iin = + + I2 + + I3+ + I4

= + 2.5 kA + 1.5 kA + 2 kA= 6 kA

Σ I = + + I1+ + I2 + + I3 + + I4

= + 0 kA + 2.5 kA + 1.5 kA + 2 kA= 6 kA

∆ Isec= I1/N= 6 kA / 2000 = 3 A






REB670


REB500

Calculation examples Current transformer failure (ΙΙ)

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Diff

eren

tial c

urre

nt I d

iff=

| ΣI |




no faultIkmin

kREB500= 0,85

k= 1

0

Internal fa

ult REB500

Internal fault R

EB670

kREB670= 0,53

Current transformer failure (ΙΙ)

⇒ trip measurement system !!!(worst case condition)

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during load condition

I2 = I3 = I4 =250A 150A 200A

I1 =600A

CT shorted !!!

Calculation examples Current transformer failure (ΙΙΙ)

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= 1.2A * 2000Ω= 2.4kV (spike)à possible TRIP !!!

Σ Iin = + + I1+ + I2 + + I3 + + I4

= + 250 A + 150 A + 200 A= 600 A

Σ l = + + I1+ + I2 + + I3 + + I4

= + 0 kA + 250 A + 150 A + 200 A= 600 A

∆ Isec = I1/N= 0.6 kA / 2000 = 1.2 A

∆ I = + I1 + I2 + I3 + I4 = + 0 kA + 250 A + 150 A + 200 A= 600 A

∆ I = + I1 + I2 + I3 + I4 = + 0 kA + 250 A + 150 A + 200 A= 600 A




REB670


REB500

Calculation examples Current transformer failure (ΙΙΙ)

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Diff

eren

tial c

urre

nt I d

iff=

| ΣI |




no faultIkmin

kREB500= 0,85

k= 1

0

Internal fa

ult REB500

Internal fault R

EB670

kREB670= 0,53

Current transformer failure (ΙΙΙ)

⇒ measurement system stable !!!⇒ differential current alarm !!!

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WOpen CT / Differential Current AlarmWith a Differential Current Supervision it is possible to detect open / missing CTs during load condition

The Differential Current Supervision sends a TIME DELAYED ALARM and there is a setting option to BLOCKthe Protection system zone selectively (REB670: also Phase selectively)

The Supervision is able to detect q a missing CT input (e.g. CT circuit not connected to the system)q a wrong CT ratioq a wrong current direction

Therefore the PICK UP VALUE of the Differential Current Supervision should be set lower than the lowest possible load current. The time delay 2–5 seconds)

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⇒ the “differential current / Open CT alarm” is able to detect a missing / wrong CT input

⇒ therefore the “differential current alarm” is very important and must not be ignored by the operating personal

If not, there is a risk of maloperation !!!

Open CT / Differential Current Alarm

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WAdditional Tripping / Release Criterias

Additional Tripping / Release Criterias are used to get

q Additional SECURITY

or

q Additional FAULT LOCATION

The usage is depending on the

CUSTOMERS PHILISOPIE

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Release forSECURITY

&TRIP CBs

Tripping forFAULT LOCATION

Measurement System

≥1

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Release forSECURITY

&TRIP CBs

Neutral Differential Current Measurement

Measurement System

≥1

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WAdditional Tripping / Release CriteriasNeutral Differential Current Measurementis designed to be able to detect internal busbar faults in low impedance earthed power systems: Limited earth fault current to certain level (300 –2000A)

No Trip for Phase Differential Measurement !!!

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WAdditional Tripping / Release CriteriasNeutral Differential Current Measurement

Δ I = ∑IN

IRest = ∑IN

(IN = Neutral Current)

and therefore:

K = ∑IN / ∑IN = IK / IK = 1

TRIP

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Check

Zone

&TRIP CBs


Measurement System

≥1

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WAdditional Tripping / Release CriteriasCheck Zone

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W

Diff

eren

tial c

urre

nt I d

iff=

| ΣI |


no faultIkmin

k= 1

0

Internal fa

ult REB500

kfault

Additional Tripping / Release CriteriasCheck Zone

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WAdditional Tripping / Release CriteriasCheck Zone

q The stability factor k must be calculated very carefully !

q The Phase Comparison Algorithm is not used in the REB500 system

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Over Current

&TRIP CBs


Measurement System

≥1

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WAdditional Tripping / Release CriteriasOver Current ReleaseOnly that feeders on which a settable over current value is reached will be tripped in case of a trip of the busbar protection

I1 = I2 = I3 = I4 =300A 250A 50A 100A

I> I> I> I>

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WAdditional Tripping / Release CriteriasOver Current ReleaseOnly that feeders on which a settable over current value is reached will be tripped in case of a trip of the busbar protection

I1 = I2 = I3 = I4 =1000A 2500A 1500A 2000A

I> I> I> I>

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U<Under Voltage

&TRIP CBs


Measurement System

≥1

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WAdditional Tripping / Release CriteriasUnder Voltage ReleaseThe busbar zone which should be tripped must fulfil a settable under voltage value

U

U U

U

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WAdditional Tripping / Release CriteriasUnder Voltage ReleaseThe busbar zone which should be tripped must fulfil a settable under voltage value

U

U <U

U

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WIntertripping

Tripping flow chart

trip all CBs connected to zone x

TRIP BBP

zone x

TRIP CB

TRIP CB

TRIP CB

Measurement

system

Intertripping

system

just the Intertripping system can send a tripping signal to the CB because it “knows” which CB to trip (the measurement systems are only

responsible for measuring !)

Detailed information in a separate presentation !

chp133 bbp ms

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