Is Limiter Overview Presentation

7/22/2019 Is Limiter Overview Presentation

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Is Limiters Introduction to Is Limiters STEP Fault Limiting Scheme Tripping Criteria Blocking Logic Inter-tripping to Bus Section

Breakers Interlocking Control Supply Is Limiter LV Compartment Alarm

and Status Signals Testing Is Limiter Control Panel Is Limiter Simulation

Is Limiter Overview


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Is Limiter Overview

INTRODUCTION to Is LIMITERS

Is Limiters interrupts instantaneous fault currentsame as fuse but the tripping is initiated by an

external circuit.

The tripping of Is Limiters limits the prospectivefault current by dividing the fault contributing

sources.

It does not clear the fault. The fault is cleared bythe protection device closest to the fault.


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Is Limiter Overview

INTRODUCTION (Cont.)

Operation of Is Limiter


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Fault Current IEC DefinitionsINTRODUCTION (Cont.)

Is Limiter Overview


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Interrupting Devices

Circuitbreakers

Fuses

Is Limiters

There are two differences between circuitbreakers and fuses- One is that circuit breaker interrupts currentat current zero while fuse interrupts theinstantaneous current.

- The second difference is that for operation ofthe circuit breaker it receives a command froman external control circuit.The Is limiter sits in between the two. Is limiterinterrupts instantaneous fault same as fuse butneeds an external circuit to initiate operationsame as circuit breaker.


Is Limiter Overview


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Interrupting Device Ratings

Circuit Breaker Ratings: Breaking :

Symmetrical Asymmetrical Zero crossing is required to interrupt

current

Making Short time rating

Fuse Ratings: Cut off current Let through energyIs Limiter Ratings: Max short circuit current (initial

symmetrical)

Max rate of rise. For ACG limiters it is44.429 kA/ms

All devices have continuous

current and voltage rating


Is Limiter Overview


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.For higher rated currents

IS-limiters can be

connected in parallel.

Technical data

Rated

Voltage

Rated

Current

Switching

Capability0,75 kV

12,00 kV

17,50 kV

24,00 kV

36,00 kV40,50 kV

1250 A - 5000 A

1250 A - 4000 A

1250 A - 4000 A

1250 A - 3000 A

1250 A - 2500 A1250 A - 2500 A

140 kA RMS210 kA RMS210 kA RMS140 kA RMS140 kA RMS140 kA RMS


Is Limiter Overview


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T2

T0

T1

T3

Total operating time of the circuit breaker:

T1: Operating time of the protection relay: 30 - 40 ms

T2: Operating time of the circuit breaker: 40 - 80 ms

T3: Arc duration: 10 - 20 ms

T0: Response time of the protection relay: 30 - 40 ms

T

Total operating time of the IS-

limiter:

T : 5 - 10 ms

IS-limiter - Circuit Breaker

t

i


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i = i1+ i2without IS-limiter

i1

Current curve at the short-circuit location

Breaking of a short-circuit

current with IS-limiter

i2

u

t

i

126 kA

63 kA

Ikperm.= 25 kA=

IK= 25 kA=

T1 IK= 25 kA=

T2

i1

Single line diagram ofa busbar systemwith IS-limiter

i = i1+ i2with IS-limiter

i2

i = i1 + i2

i1 i2

i = i1 + i2

i1


Is Limiter Overview


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di

dt( )33di

dt( )2

i

t

iLimit

Detection of the Short-circuit current

2

4

1

1 Short-circuit currentwithout IS-limiter

2 Short-circuit currentIS-limiter tripped

3 Over current

IS-limiter not

tripped

4 Peak value of

service current

ilimit^(di/dt)


Is Limiter Overview


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Schedule for tripping of the Is-limiter

T1T2

T0: Reaching time for tripping criteria

(instantaneous value anddi/dt).

T4T0t

i

T3

.

T1: Response time of the electronic approx. 15 s

T2: Time for opening the bursting bridgeand for commutating the

current to the fuse element approx. 85 s

T3: Melting time of the fuse element approx. 500 s

T4: Arc duration

iA: Tripping criteria are reached

(instantaneous value and di/dt).iB: Current at beginning of fuse element's melting

iC: Let-through current

iC

iB

iA


Is Limiter Overview


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Is Limiter Overview

STEP FAULT LIMITING SCHEME

An integrated scheme consisting of three Is limiters,

summation CTs, and a logic control panel is provided to

achieve a reliable operation of Is limiters when requiredand to block its operation to prevent unnecessary and

spurious tripping.

Summation CTs are installed in each of the generator

incomers, the grid incomers and bus sections to monitor

the actual fault currents.

Current Limiting Reactor is provided at phase1 & phase2

Intertie to reduce the fault levels to within the Is Limiters

and Shah Deniz 11kV fuses breaking capacity.


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Is Limiter Overview

TRIPPING CRITERIA

Is Limiter must prevent short circuit currents exceeding

the permissible values as below:

- Breaking current of 50kA- Peak Short circuit Current of 158kA

- Initial Symmetrical Short circuit current of 58kA.

The tripping criteria is based on total summation fault

current and the current through the Is limiter. If both these

values exceed the preset value the Is limiter will trip. Tripping

of the Is Limiter is also dependent on the direction of current.

The tripping values for the summation current and the

current through the Is limiter are 7kA and 42kA respectively.

These values are factory set and cannot be changed by the

operator on site.


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Is Limiter Overview

BLOCKING LOGIC

The operation of the Is limiters is not activated for the

following:

-To prevent unnecessary operation of more than one Is

limiter for the same fault.

-To prevent operation of Is limiters for external gridfault.

- To prevent operation if the summation current does

not exceed the tripping value.


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Is Limiter Overview

INTER-TRIPPING TO BUS SECTION BREAKERS

The Is Limiter operates independently for each

phase. If the tripping values for one phase are

exceeded the Is Limiter for that phase only will trip.

If the tripping values for two phases are exceeded

the Is Limiters for those phases will trip.

For three phase isolation intertripping is providedsuch that tripping of the Is Limiter will trip the

associated bus section breaker.

The tripping values of the Is Limiters are set such

the circuit breaker interrupting capacity is not

exceeded.


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Is Limiter Overview

INTERLOCKING

A solenoid operated Interlocking is provided

such that the Is Limiter truck cannot be insertedor withdrawn unless both sides of the Is limiter

are de-energised.

In addition interlocking is provided such thatthe associated bus section breaker cannot be

closed unless the Is Limiter is ready for

operation.


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Is Limiter Overview

CONTROL SUPPLY

For high reliability two 110V AC supplies:

- The main power supply via voltage transformer (VT)- The Secondary power supply from UPS

These two power supplies are provided with an auto

changeover scheme. Normal operation will be with the

power supply from the voltage transformer. Upon loss

of mains power the auxiliary supply will be switched to

UPS. Similarly upon restoration of main power the

auxiliary supply will be switched back the voltage

transformer.


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Is Limiter Overview

IS LIMITER LV COMPARTMENT ALARM AND STATUSSIGNALS

Alarm and status signals are sent to PMS, logic control

panel and to the associated bus section breaker.

The followings are the interface between LV

Compartment and Logic Control Panel:

- Is Limiter Blocking

- Is Limiter Deactivation of Tripping Criteria

- Tripping Criteria Status

- Is Limiter Blocked

- Is Limiter Tripped- Is Limiter Ready


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Is Limiter Overview

TESTING

The testing of the trip values will normally becarried out by specialist engineer using vendor

supplied test inserts and testing equipment. Refer

to acceptance test procedure, vendor document

reference PTCS01A-H0191.


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Is Limiter Overview

IS LIMITER CONTROL PANEL

A logic control panel is provided to implement thematrix logic. In order to achieve high reliability the

matrix logic is implemented both by using hard wired

control relay and a PLC. If there is any discrepancy

between the hard wired logic and the PLC logic an alarmis raised.

The control panel consists of hard wired logic and the

supervisory PLC. The PLC has dual redundant processors

running in synchronism with bumpless transfer from the

primary processor to the secondary processor.


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Is Limiter Overview

In-Service/Overide Selection:

- For a fault on each Is limiter an alarm is received from

the Is Limiter cubicle to the control panel. The operator

can take the faulty Is Limiter out of service without

affecting the operation of other Is Limiters. A key

operated in-service/over-ride switch is provided for this

for each Is Limiter.

Alarms:

- PLC Watchdog Fault

- Incorrect activation/blocking criteria outputs from

hardwired control section

IS LIMITER CONTROL PANEL (Cont)


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Is Limiter Overview

- Discrepancy check of main generator/grid circuit breaker

status signals- Discrepancy between verified IS Limiter

activation/blocking status and outputs from the hardwired

relay logic

- Common fault including control supply fault of Is Limiterfault to PMS

- Is Limiter Control Panel fault to PMS

-Common alarm to the ICSS for any alarm present in the

logic control panel including the Is Limiter fault alarms.

Control Supply

- Dual UPS supplies with auto changeover.

IS LIMITER CONTROL PANEL (Cont)


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Is Limiter Overview

IS LIMITER SIMULATION

The IS limiters is simulated in a spreadsheet for a 3-

phase fault at any 11kV busbar, with the system in any

operating configuration. This will also check the Is limiter

blocking or activation of selectivity criteria, dependent on

the number of main generators/grids supplies connected

to the 11kV system. The fault currents are calculated withIS limiter operation and also ignoring Is limiter operation

in accordance with BS-EN 60909-0:2001.

Documents

Is Limiter Overview Presentation