Protection Systems

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REQUIREMENT OF PROTECTION SYSTEMS ENGINEERING
Knowledge Management System
ELECTRICAL

Key Words : Safety Regulations, Insurance Requirement, Dependability, Security, Reliability, Sensitivity.

Submitted by : Pramod Kumar,AGM(PE-Elect), CC, EOC, 9868390543, [email protected]

17/12/2007

PROTECTION SYSTEMS

AN OVERVIEW

Pramod Kumar DGM (PE ELEC.)

TYPICAL PLANT SLD

Requirements of PROTECTION SYSTEMS
§

External Requirements
Ø Ø Ø Ø Ø Ø Ø

Safety regulations Equipment Warranties Insurance Requirements Industry standards Prudent utility Practice Safety grounding Power quality

Requirements of PROTECTION SYSTEMS
§ Power System Requirements Ø Planning and Operating Criteria requirementUse of appropriate duplicate protection and backup protection. Ø Specific requirements of the power system element being protected Ø Prevent damage to healthy equipment that conducts fault current during a fault

Protection Criteria
ØCriteria specific to the equipment within the protective zone must be met.These are construction specific requirements. ØCriteria specific to other equipments supplying fault current to the faulted element.These are fault current withstand requirements such as through fault capability of power transformer. ØCriteria specific to the stability of the network.These are topology specific time limits associated with voltage and transient stability.

PROTECTION SYSTEMS PERFORMANCE

ØDependability ØSecurity ØReliability ØSpeed of Operation ØSelectivity ØSensitivity

PROTECTION SYSTEMS PERFORMANCE
§

Dependability
The probability of not having a failure to operate under given conditions for a given time interval

§

Security/Stability
The probability of not having an unwanted operation (for no fault/ out of zone fault) under given conditions for a given time interval.

§

Reliability
The probability that a protection can perform a required function under given conditions for a given time interval

PROTECTION SYSTEMS PERFORMANCE Selectivity
The ability to detect a fault within a specified zone of a network and to trip the appropriate circuit breaker(s) to clear this fault with a minimum disturbance to the rest of that network




Sensitivity
Ability of the system to detect the threshold value of an abnormal condition to initiate protective action.

Example: Performance of Transformer and Reactor protections during a given time interval
Type of Operation Correct operation (Nc) Incorrect operation (Nuu) Failure to operate (Nf) Operation causing non-power system fault tripping (Nus) Number of operation 130 3 0 17

Dependability, D = Nc/(Nc + Nf) = 130/(130+0) = 1.0 Security, S = Nc/(Nc+Nus+Nuu) = 130/(130+17+3) R = Nc/(Nc+ Nf+Nus+Nuu) = 130/(130+0+17+3)

= 0.867

Reliability,

= 0.867

Protection System Design Key aspects of protection system design:
n n n n

Zone overlapping Co-ordination Primary, Supplementary & Back up Relays Single failure criterion

Protection System Design
n

Zone Overlapping
Ø

Ø Ø

Protection zones are the regions of primary sensitivity Zones are decided by the CT locations Proper overlapping of zones for the primary protections to avoid blind zones. Determination of graded settings to achieve selectivity

n

Coordination
Ø

Protection System Design
§ Primary Relays Ø Relays with in a particular zone that should operate for prescribed abnormalities with in that zone § Back up Relays Ø Relays outside a given primary protection zone, independently of the primary Relays.

Protection Scheme Design
§ Single failure criterion A design criterion whereby a system must not fail to operate even if one component fails to operate.
Ø

Ø

Ø

With respect to the primary protection relay interpretation of the single failure criterion caters primarily for a failed or defective relay, and not a failure to operate as a result of a performance deficiency inherent within the design of the relay. Main protection functions used to protect EHV equipment are duplicated. Redundancy introduced into all possible components that make up the system from the CT and VT inputs and DC supplies to the circuit-breaker trip coils.

AC/DC SEGREGATION

Developments In RELAYING TECHNOLOGY
n

n

ELECTROMECHANICAL n Mechanical force causing operation of a relay n Mech force is generated through the electrical actuating quantity.( Eg: current in a winding or two) n Use magnets/coils/induction disc etc to realise relay characteristics STATIC RELAYS (From early 1960s) n No moving parts to create the relay characteristics. n Use analogue electronic devices to create relay chars. characteristics n Earlier versions use transistors and diodes n Later ones use integrated circuits

Developments In RELAYING TECHNOLOGY
n

n

DIGITAL RELAYS (Early 1980s) n A/D conversion for input analogue quantities n Microprocessors and micro controllers replaced analogue circuits to develop relay logics n Communication facility to a remote computer NUMERICAL RELAYS n Natural replacement of digital relays n Specialised digital signal processors n Powerful micro processors n Single hardware item provides a range of functions.(One box solution) n Recording /logging/measurements features added.

CHRONOLOGY OF DEVELOPMENT
TECHNOLOGY ELECTRO MECHANICAL
Ø

FEATURES Galvanic isolation in simple cheap and reliable method Ø Resistant to mechanical shocks. Ø High burden on CTs Ø Operating characteristics at times affected by aging of elements. Ø Space requirement is substantial. Ø Technology is now obsolete. Availability of spares is an issue. User programming to the extend of adjusting relay characteristics. Ø Device became compact. Ø Wear and tear was avoided due to absence of moving parts. Ø Burden on CT/VT reduced to a certain extend. Ø Very susceptible to electrical interferences, requiring effective shielding.
Ø

STATIC

CHRONOLOGY OF DEVELOPMENT
TECHNOLOGY DIGITAL FEATURES More accurate relay characteristics. Wider range of settings. Communication is possible. Time of operation is increased if the sampling frequency is inadequate. Functions limited to only protection functions / only one in a hardware system.

Latest in the family : NUMERICAL RELAYS

WHAT IS A NUMERICAL RELAY?
NUMERICAL RELAY Analogue Signals
DIGITAL SIGNAL PROCESSOR

PROCESSOR
DATA PROCESSING ALGORITHM DECESION MAKING PRGRAMABLE LOGICS CONDITION MONITORING EVENT LOGGING DISTURBANCE RECORDING MEASUREMENTS

PRIMARY EQUIPMENT CT/PT

EXTERNAL BINARY INPUTS

DIGITAL I/P TRIP COMMAND KEY PAD

BREAKER

O/P RELAYS

DISPLAY

Communication port OWS/SCADA/ DCS

OPERATOR INTERFACE

REMOTE STATION

NUMERICAL RELAYS: FEATURES Processor based protective system Converts the analogue input quantities to digital quantities Protective algorithms realised in the processor Trip output to breaker issued through o/p relays Communicates to SCADA through communication ports

n n

n n

n

Numerical Relays : Advantages
Ø

Ø Ø

Ø Ø Ø Ø Ø

Powerful processors used for realising the algorithms, result in high accuracy No mechanical moving parts: free from aging problems Integration of many protections in one hardware unit : space saving Flexibility in operating characteristics Integration with computerised control system Self diagnosis Easy for upgradation, keypad for user interface Many setting groups with manual/automatic change over facility.

NUMERICAL RELAYS: EXTRA FEATURES

Ø
Ø Ø Ø Ø Ø

CT/VT supervision Disturbance Recording Event logging Measuring. User defined/ programmable Logics. CB monitoring.

Present Status of adoption of Numerical Relays for SWYD/Gen Prot. in NTPC Projects
n

EARLIER PROJECTS : Combination of electro mechanical/static TALCHER ST-II / SIMHADRI /Faridabad : Combination of electromechanical /static/numerical relays UNCHAHAR –III / VINDHYACHAL-III/KAHALGAON II:/SIPATI/II/BARH/ALL FUTURE PROJECTS ALL NUMERICAL RELAYS

n

n

Present status of adoption of Numerical Relays for Switchgear
§

Existing practice
Combination of Electromechanical /static relays

§

Korba-III onwards
ALL NUMERICAL RELAYS

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