Chp133 Bbp Ms

ABB

Technology and Solutions

Protection and Substation Automation

© A B B S w it z e rl a n d L td . -1 C H P 1 3 3 _ B B P _ M S / 2 0 0 7 0 9 / R W

Topic:

Busbar

Protection

Measurement

System

ABB

Busbar Protection – Measurement System

r Introduction

r BBP Requirement

r BBP Basics

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

r The “problem” on CT Saturation

r High Impedance Measurement Principle

r Low Impedance Measurement Principle

q Example and Features of different Methods / Algorithms

q INX-2

q INX-5

q REB500

q REB670

r Calculation examples: Differential & Restraining Current / Differential Voltage

r Open CT / Differential current Supervision

r Additional Release / Tripping Criterias

r Intertripping

ABB

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

ABB

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

ABB

BBP Requirements

Number the requirements depending on the importance

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

___ RELIABILITY (extensive self- supervision)

___ 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)

ABB

Who knows

Mr. Kirchhoff ?

BBP Basics

ABB

Kirchhoff’s 1st Law: Node Rule

I1 + I2 + I3 =

Σ

I =

0

The sum of all

currents must be zero

ABB

Kirchhoff’s 1st Law: Node Rule

I1 + I2 + I3 =

Σ

I

≠

0

⇒ Fault on the busbar

⇒ Trip circuit breaker

If

ABB

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 segregated 3 (4) measurement systems: R; S; T (& special: N)

ABB

External Fault

BBP Basics

ABB

Internal Fault

BBP Basics

⇒ High Differential Current

⇒ Trip

I₁ I₂

ABB

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

ABB

Internal Fault – with DC component

BBP Basics

⇒ High Differential Current

⇒ Trip

I₁ I₂

ABB

Protection Zones

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

B u s b a r Busbar L in e T ra n s fo rm e r G e n e ra to r -T ra n s fo rm e r BB G

ABB

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

< I

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

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

ABB

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

> I

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

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

ABB

External Fault

CT Saturation

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

ABB

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

ABB

High Impedance Measurement Principle

q The only BBP system which can handle CT

saturation without any other quantity than I

(

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.

ABB

High Impedance Measurement Principle

CT2 feeder 1 feeder 2 RR BB 1 CT1 _U1 UR RL1 RL2 UR > 0 U2 Im Im

Principle / Components

Line resistance from CT to relay

High impedance (input)

I2

I1

ABB

High Impedance Measurement Principle

CT refresher course:

Excitation or magnetizing current

ABB

High Impedance Measurement Principle

CT refresher course:

Excitation or magnetizing current

Magnetizing Curve

Knee point voltage

(when saturation starts)

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

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

ABB

High Impedance Measurement Principle

CT2 feeder 1 feeder 2 RR BB 1 CT1 _U1 UR RL1 RL2 UR > 0 U2 Im Im

Internal Fault

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.

I2

I1

ABB

High Impedance Measurement Principle

CT2 feeder 1 feeder 2 RR BB 1 CT1 _U1 UR RL1 RL2 UR > 0 U2 Im Im

Internal Fault

General setting rule: (since U_{R max} = U_k)

R_R = High Impedance (e.g. 2000Ω) U_R = Voltage at the high impedance U_k = CT knee point voltage (e.g. 400V) N = CT ratio (e.g. 4000A/1A)

U_set = overvoltage pick up setting

I2

I1

I_diff = Σ I

• U_set≤ 400V

ABB

High Impedance Measurement Principle

feeder 1 feeder 2 RR BB 1 CT1 _U1 UR RL1 RL2 UR > 0 U2 Im Im

External Fault

I2

I1

I_diff = 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.

ABB

High Impedance Measurement Principle

feeder 1 feeder 2 RR BB 1 CT1 _U1 UR RL1 RL2 UR > 0 U2 Im Im

External Fault

I2

I1

I_diff = 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 R_CT (winding resistant) will result (du/di = r <<<<<<).

The High impedance will be bypassed by the relatively small sum of R_W + 2R_L2. Therefore the voltage U_R will not reach the pick up level.

ABB

Setting rules for stability: UR = Voltage at the high impedance

I_kmax = maximum possible ext. fault current (e.g. 45kA) N = CT ratio (e.g. 4000A/1A)

U_set = overvoltage pick up setting R_CT = CT winding resistant (e.g. 6Ω) R_L2 = lead resistant (e.g. 2Ω)

2.5 = safety margin I2 I1 I_diff = Σ I ‚ U_set≥ 2.5 / 4000 * 45kA * (6Ω + 2 * 2Ω) ≥ 281V

External Fault

U_set ≥ 2.5 / N * I_kmax * (R_CT + 2 * R_L2)

R_CT

ABB

R_R= High Impedance (e.g. 2000Ω)

I_kmin = minimum possible fault current (e.g. 1kA) N = CT ratio (e.g. 4000A/1A)

U_set= overvoltage pick up setting

I_M = magnetising current at UK/2 (e.g. 0.3mA) x = number of CTs (e.g. 2)

Actual value of primary pick-up current

High Impedance Measurement Principle

Requirements: • U_set ≤ 400V ‚ U_set ≥ 281V

Minimum pick up value for the detection of the minimum primary fault current

U_set ≤ (I_kmin / N – x * I_M) * R_R

U_set ≤ (1000A / 4000 – 2 * 3mA) * 2KΩ U_set ≤ 488 V

Minimum primary fault current detection with actual setting of U_set = 300 V: I_kmin = N * (U_set / R_R + x * I_M)

I_kmin = 2000 * (300V / 2000Ω + 2 * 3mA) I_kmin = 624 A

ABB

High Impedance Measurement Principle

If necessary,

q an additional parallel resistor R_P can be connected to change / adapt

the sensitivity

q 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)

ABB

High Impedance Measurement Principle

There is also the possibility to insert a current instead of voltage measurement.

Advantage: the I_kmin can be set directly in a current value: I_kmin = I_set * N

Alternatives (2)

ABB

High Impedance Measurement Principle

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

ABB

High Impedance Measurement Principle

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

ABB

High Impedance Measurement Principle

Multiple Busbar with CT Switching and Check Zone

I X X X II + I _II Checkzone Discriminating Zone

ABB

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

ABB

Low Impedance Measurement Principle – BBP Type

INX-2

– electronic relay generation

I

< |

∑ I |

differential current measurement with instantaneous values

Phase Comparison

phase angle supervision = current direction supervision with

instantaneous values

&

- Maximum load < I_kmin < minimum short circuit current

to prevent false operation in case of shorted CT and to detect lowest possible fault current

ABB

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 fault

q 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 available

q differential current and phase comparison (phase angle) measurement system

which evaluates instantaneous current values. The system includes no special CT saturation detection facility

q 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 12ms

q integration of CB failure and End fault Protection is possible q installation from around year 1968 – 1985

q 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

ABB

Low Impedance Measurement Principle

CT refresher course:

The areas

are equal

t

A1

=

A 2

=

A 3

=

∫

i(t) dt

•

10ms

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

I_al = 1: current on

which the CT starts to saturates

5 – times saturation means

ABB

I

< |

∑ I |

differential current measurement with instantaneous values

k

< |∑ I | / ∑ | I |

stabilising / restraining measure-ment with quantity I_res= ∑ | 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

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

D

if

fe

re

n

ti

a

l

c

u

rr

e

n

t

I

=

|

Σ

I

|

Restraint current I

=

Σ

| I |

inte rnal faul t no fault

I

k= 0,8

k= 1

0

Stabilised / Restraint Characteristic

Setting:

- Maximum load < I_kmin < minimum short circuit current

to prevent false operation in case of shorted CT and to detect lowest

possible fault current - K typically to 0.8

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

Internal Fault

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

External Fault – without CT saturation

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

External Fault – with CT saturation

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

External Fault – with CT saturation

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

External Fault – with CT saturation

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

External Fault – with CT saturation

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

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

External Fault – with CT saturation

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

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

External Fault – with CT saturation

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

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

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

External Fault – with CT saturation

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+)

– static relay generation

Neg BLOCKING

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

External Fault – with CT saturation

(B+)

neg I diff

– static relay generation

neg I diff pos I diff pos I diff (B+) (B-) (B-)

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

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

– static relay generation

&

B-Idiff pos

&

B+

Idiff neg

≥1

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

External Fault – with CT saturation

The Stability is maintained

– static relay generation

(B+) neg I diff neg I diff pos I diff pos I diff (B+) (B-) (B-)

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

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

ABB

Low Impedance Measurement Principle – BBP Type

INX-5

Internal Fault – with CT saturation & full DC offset

TRIP (no blocking)

(Idiff +)

(B+) (B+)

(B+)

(Idiff +) (Idiff +)

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

ABB

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 fault

q 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 available

q 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)

Low Impedance Measurement Principle – BBP Type

INX-5

ABB

Typical INX-5 Feature:

q low CT requirements: 2 ms of current signal must be available.

This represents 5 times saturation on symmetrical fault currents

q tripping time around 12ms

q integration of CB failure and End fault Protection is possible q installation from around year 1980 – 2003

q at present, the systems are still being extended frequently q around 800 systems are / were installed

Low Impedance Measurement Principle – BBP Type

INX-5

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

I

< |

∑ I |

differential current measurement with fundamental current values

k

< |∑ I | / ∑ | I |

stabilising / restraining measure-ment with quantity I_res = ∑ | I | with

fundamental current values

&

TRIP CBs

Phase Comparison

phase angle supervision = current direction supervision with fundamental current values

F ir s t h a rm o n ic ( fu n d a m e n ta l) fi lt e ri n g b y F o u ri e r fi lt e r

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

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

I₁ I₁ I₁ I₁ I₂ I₂ I_{2 I} 2 0 _t 0 I₂ t

Primary current

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

ABB

Secondary

current

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

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

ABB

Fundamental

frequency

component

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

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

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

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

Fundamental

frequency

component

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

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

Result with extreme CT saturation

t ms 50 I_N I / In Ires / In

Restrained differential current algorithm Restrained differential current and phase comparison algorithms which

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

Result with extreme CT saturation

t ms 50 I_N I / In t

Restrained differential current algorithm

k

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

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

Result with extreme CT saturation

t ms 50 I_N I / In t

Phase comparison algorithm

k P h a s e s h if t Δ α

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

ABB

Restrained differential current and phase comparison

algorithms which evaluate the fundamental wave of the

reconstructed current signal:

q The REB500 system will evaluate reconstructed

fundamental 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

Low Impedance Measurement Principle - BBP Type

REB500

ABB

Maximum Prolongation Algorithm

Low Impedance Measurement Principle - BBP Type

REB500

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

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

I₁ I1 I1 I₁ I₂ I₂ I_{2 I} 2 0 _t 0 I₁ I₂ t

Reconstructed

current signal

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

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

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

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

Result using the “Maximum Prolongation Algorithm”

with extreme CT saturation

t ms 50 I_N I / In Ires / In

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

t ms 50 I_N I / In t

Restrained differential current algorithm

k

Result using the “Maximum Prolongation Algorithm”

with extreme CT saturation

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

t ms 50 I_N I / In t

Phase comparison algorithm

k P h a s e s h if t Δ α

Result using the “Maximum Prolongation Algorithm”

with extreme CT saturation

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

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

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

I

< |

∑ I |

differential current measurement with reconstructed fundamental

current values

k

< |∑ I | / ∑ | I |

stabilising / restraining measure-ment with quantity I_res = ∑ | I | with reconstructed fundamental current

values

&

TRIP CBs

Phase Comparison

phase angle supervision = current direction supervision with reconstructed fundamental current

values F ir s t h a rm o n ic ( fu n d a m e n ta l) fi lt e ri n g b y F o u ri e r fi lt e r m a x im u m p ro lo n g a ti o n o n a ll C T C u rr e n t s ig n a l

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

Measurement Algorithm: Stabilized differential current

Restraint Current I

Differential current

I

I

k= 0,85

k= 1

0

ABB

Low Impedance Measurement Principle - BBP Type

REB500

– numerical relay generation

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 I₂ I₁ Tripping area P h a s e d if fe re n c e ∆ϕ No Fault Internal Fault Fall 1 2 ∆ϕ _min = 74° 74° 180° 0°

ABB

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 self- supervision 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 fault

q very easy to find faulty components since the fault indication of

the continuous self- supervision is very detailed and a very small number of modules / electronic cards are available

q 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)

Low Impedance Measurement Principle - BBP Type

REB500

ABB

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 application

q typical tripping time around 25ms

q 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 available

q low CT requirements: 2 ms of current signal must be available.

This represents 5 times saturation on symmetrical fault currents

q state of the art: installation from year 1994 – future q over 1500 systems are in service (so far)

Low Impedance Measurement Principle - BBP Type

REB500

ABB

Low Impedance Measurement Principle - BBP Type

REB670

– numerical relay generation

• I

< |

∑ I |

differential current measurement with RMS current values

‚s

< |∑ I | / ∑ | I

|

stabilising / restraining measurement with quantity I_res= ∑ | I_in |

with RMS current values

&

TRIP CBs

ƒ external fault detection

(decision 1.2 ms after zero crossing)

detection internal / external fault with instantaneous / sampled current values

ABB

Low Impedance Measurement Principle - BBP Type

REB670

– numerical relay generation

ABB

Low Impedance Measurement Principle - BBP Type

REB670

– numerical relay generation

Calculation of the instantaneous value of the differential current:

Calculation of the instantaneous sum of positive currents:

ABB

Low Impedance Measurement Principle - BBP Type

REB670

– numerical relay generation

Calculation of the incoming and outgoing currents:

ABB

Low Impedance Measurement Principle - BBP Type

REB670

– numerical relay generation

ABB

Low Impedance Measurement Principle - BBP Type

REB670

– numerical relay generation

Condition at Internal Fault:

sudden split between of RMS I_in and RMS I_out will indicate an internal fault

if • & ‚ (I_kmin & s) is fulfilled the protection will trip since ƒ will not see an external fault

ABB

Low Impedance Measurement Principle - BBP Type

REB670

– numerical relay generation

ABB

Low Impedance Measurement Principle - BBP Type

REB670

– numerical relay generation

Condition at External Fault with CT Saturation:

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

ABB

Low Impedance Measurement Principle - BBP Type

REB670

– numerical relay generation

Test assembly:

ABB

Low Impedance Measurement Principle - BBP Type

REB670

– numerical relay generation

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

ABB

Low Impedance Measurement Principle - BBP Type

REB670

– numerical relay generation

ABB

Low Impedance Measurement Principle - BBP Type

REB670

– numerical relay generation

Stabilised / Restraint Characteristic Setting:

- Maximum load < I_kmin (Diff Oper Level) < minimum short circuit current to 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)

ABB

Typical REB670 Feature:

q centralised protection system, location in a centralised panel

q continuous self- supervision 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 fault

q very easy to find faulty components since a very small number of

modules / electronic cards are available

q 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)

Low Impedance Measurement Principle - BBP Type

REB670

ABB

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 currents

q tripping time around one halfcycle

q integration of CB Failure, OC protection as well as event- &

disturbance recorder, monitoring function is possible

q state of the art: installation from year 2005 – future

q the system is a consequently further development / improvement

of the well proven BBP systems RADSS, REB103, RED521

Low Impedance Measurement Principle - BBP Type

REB670

ABB

Busbar fault condition

I1 = 1000A

single injection

ABB

Calculation examples

(with CT ratio: N = 2000A / 1A; Impedance: R_R= 2000 Ω; Knee Point V: UK = 400V) Low Impedance Measurement System REB670 Low Impedance Measurement System REB500

ABB

D

if

fe

re

n

ti

a

l

c

u

rr

e

n

t

I

=

|

Σ

I

|

►trip measurement system !!!

⇒ ( if I∆ > I_kmin)

Calculation examples

Restraint current I_Rest = Σ | I |

Restraint current I_Rest = Σ | I_in |

no fault

I

k

= 0,85

k= 1

0

k

= 0,53

ABB

Busbar fault condition

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

multiple injection

ABB

(with CT ratio: N = 2000A / 1A; Impedance: R_R= 2000 Ω; Knee Point V: UK = 400V) Low Impedance Measurement System REB670 Low Impedance Measurement System REB500

ABB

D

if

fe

re

n

ti

a

l

c

u

rr

e

n

t

I

=

|

Σ

I

|

►trip measurement system !!!

⇒ ( if I∆ > I_kmin)

Calculation examples

Restraint current I_Rest = Σ | I |

Restraint current I_Rest = Σ | I_in |

no fault

I

k

= 0,85

k= 1

0

k

= 0,53

load depending tripping value!!!

Internal fault condition

ABB

e.g. line fault

External fault condition

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

6000A

ABB

(with CT ratio: N = 2000A / 1A; Impedance: R_R= 2000 Ω; Knee Point V: UK = 400V) Low Impedance Measurement System REB670 Low Impedance Measurement System REB500

ABB

D

if

fe

re

n

ti

a

l

c

u

rr

e

n

t

I

=

|

Σ

I

|

►no trip

►stable !!!

Calculation examples

Restraint current I_Rest = Σ | I |

Restraint current I_Rest = Σ | I_in |

no fault

I

k

= 0,85

k= 1

0

k

= 0,53

ABB

during fault condition (

Ι)

Current transformer failure (

Ι

)

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

6000A

CT shorted !!!

ABB

(with CT ratio: N = 2000A / 1A; Impedance: R_R= 2000 Ω; Knee Point V: UK = 400V) Low Impedance Measurement System REB670 Low Impedance Measurement System REB500

ABB

D

if

fe

re

n

ti

a

l

c

u

rr

e

n

t

I

=

|

Σ

I

|

Calculation examples

Restraint current I_Rest = Σ | I |

Restraint current I_Rest = Σ | I_in |

no fault

I

k

= 0,85

k= 1

0

k

= 0,53

Current transformer failure (

Ι

)

REB500: no trip ►stable