In the name ofThe most beneficent & The most

merciful

RADIO AND TV ANTENNA

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RACHNA UNIVERSITY OF ENGINEERING & TECHNOLOGY GUJRANWALA

DEPARTMENT OF ELECTRICAL ENGINEERING

RADIO AND TV ANTENNA

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RADIO AND TV ANTENNA 3

OVER-CURRENT PROTECTION

PRESENTED BY:SARA MUQEET 06-RCET-EE-12FATIMA TASEER 06-RCET-EE-21ASAD NAEEM 06-RCET-EE-22HAMID GULZAR 06-RCET-EE-32

RADIO AND TV ANTENNA 4

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Simple Power SystemEvery power system has three major components

1) Generation: source of power, ideally with a specified voltage and frequency

2) Transmission system: transmits power; ideally as a perfect conductor

3) Load: consumes power; ideally with a constant resistive value

LoadT.L

Transmission Line

Generator

Distribution

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PROTECTION SYSTEM

The protection system is designed and managed to deliver the energy to the utilization points with:

Reliability Economy Expensive equipment safety like:

Generator Transformer Transmission lines Bus bars

FAULT IN POWER SYSTEM

Fault is defined as any abnormal condition that

effects the basic requirements of normal power

system.

When any fault occurs in any power system, then:– Current increases– Voltage decreases– Frequency varies– Phase difference created

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IMPORTANT CONSIDERATIONS WHEN DESIGN PROTECTION SYSTEM

Types of fault and abnormal Conditions to be protected against

Quantities available for measurement Types of protection available Speed Fault position discrimination Dependability / reliability Security / stability

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Basic Components of Power System Protection

Voltage transformers and current transformers. To monitor and give accurate feedback about healthiness of a system.

Relays to accurately sense all types of faults and issue trip commands to circuit breaker to disconnect the faulty system.

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Type of protection

Over current. Directional over current. Distance. Over voltage. Differential. Reverse power. Other.

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PROTECTION RELAY

Relay is a device which detects the defective lines or

apparatus in a power system and initiates an appropriate

control action.

OR

An electrical relay is defined as a device which operates

when the prescribed quantity is out of limits

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FUNCTION OF RELAY:

-to detect the presence of fault-identify the faulted components-initiate appropriate circuit breaker-remove the effective component from circuit

PURPOSE:-control-protection-regulation

Fault Clearing Time It is the time between the instant of fault and

instant of final are interruption.

It is the sum of relay-time and circuit breaker-time.

Fault clearing time = Relay time + breaker time

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Relay time:

The relay time is the time between the instant of occurrence of fault and the instant of closure of relay contacts.

Circuit breaker time: The breaker time is the total of time taken by operating

mechanism to open to circuit breaker contacts and the arching time. It is also called total break time.

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TYPES OF RELAYS

There are five basic types of relays. MAGNITUDE RELAYS: Its operation based on the magnitude of

input quantities. Over current relay is an example of this type of relay.

DIRECTIONAL RELAYS: It responds to the phase angle difference between two AC quantities, for example, phase angle of a sinusoidal current with respect to sinusoidal voltage.

RATIO RELAY: It responds to the ratio of two AC quantities. The most common ratio relay is impedances relay.

DIFFERENTIAL RELAY: It responds to the algebraic sum of two or more inputs.

PILOT RELAYS: These relays use communicated

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OVER-CURRENT PROTECTION

-The protection in which the relay picks up when the magnitude of current exceeds the pickup level.

-over current includes short-circuit protection.

-Short circuits can be

-Phase faults

-Earth faults

-Winding faults

Short-circuit currents are generally several

times (5 to 20) full load current. Hence fast

fault clearance is always desirable on short

-circuits.

PRIMARY REQUIREMENT OF OVERCURRENT PROTECTION

Primary requirements of over-current protection are:-The protection should not operate for starting

currents, permissible over current, current surges. To achieve this, the time delay is provided (in case of inverse relays).

-The protection should be co-ordinated with neighboring over current protection.

-over current relay is a basic element of over current protection.

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Setting Rules Pickup Setting

a. It should be above normal currents & below minimum fault

currents.

b. If possible, it may provide a backup-role.

c. The setting is calculated using max load current and

minimum fault current. Time-Delay Setting

a. A time dial provides relative positions between the moving

and fixed contacts.

b. Dial setting from ½ (fastest) to 10 (slowest)

APPLICATIONS OF OVERCURRENT RELAYS

MOTOR PROTECTION:-used against overloads and short-circuits in stator windings of motor. -Inverse time and instantaneous over current phase and ground over current relays used for motors above 1000kW.TRANSFORMER PROTECTION:

-used only when the cost of over current relays are not justified -extensively also at power-transformer locations for external-fault back-

up protection.LINE PROTECTION:-on some sub transmission lines where the cost of distance relaying

cannot be justified.-primary ground-fault protection on most transmission lines where

distance relays are used for phase faults-for ground back-up protection on most lines having pilot relaying for

primary protection.

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OVERCURRENT RELAY RATINGS

In order for an over current protective device to operate properly, over current protective device ratings must be properly selected.These ratings include voltage, ampere and interrupting rating. Of the three of the ratings, perhaps the most important and most often

overlookedis the interrupting rating. If the interrupting rating is not properly.selected, a serious hazard for equipment and personnel will exist.Current limiting can be considered as another over current protectivedevice rating, although not all over current protective devices are

required to have this characteristic.

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VOLTAGE RATING

The voltage rating of the over current protective device must be atleast equal to or greater than the circuit voltage. The over currentprotective device rating can be higher than the system voltage butnever lower.The voltage ratingdetermines the ability of the over current protective device to suppressand extinguish the internal arcing that occurs during the openingof an over current condition. If an over current protective device isused with a voltage rating lower than the circuit voltage, arc suppressionand the ability to extinguish the arc will be impaired and, undersome over current conditions, the over current protective device maynot clear the over current safely

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AMPERE RATING

Every over current protective device has a specific ampere rating. In selecting the ampere rating of the over current protective device, consideration must be given to the type of load and code requirements.

The ampere rating of a over current protecting device normally should not

exceed the current carrying capacity of the conductorsAs a general rule, the ampere rating of a over current

protecting device is selected at 125% of the continuous load current

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INTERRUPTING CURRENT RATING

Interrupting rating is defined asthe highest current at rated voltage that a device is intended to

interruptunder standard test conditions.An over current protective device must be able to withstand

the destructive energy of short-circuit currents. If a fault current exceeds the interrupting rating of the over

current protective device, the device may actually rupture, causing additional damage.

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SETTINGS IN OVER CURRENT RELAY

There are two types of settings

1) Current Setting 2) Time Setting

CURRENT SETTING:

The over current relay is set at 50% to 200% of the rated current. The actual r.m.s current flowing in the relay is expressed as a multiple of the setting current (pick-up current) is known as the plug setting multiplier (PSM).PSM = Secondary current Relay current setting

Time Setting:

The operating time of the relay can be set at a desired value. In induction disc type relay, the angular distance by which the moving part of the relay travels for closing the contacts can be adjusted to get different operating time. There are 10 steps in which time can be set. The term time multiplier setting (TMS) is used for these steps of time settings.

SARA MUQEET KHAN2006-RCET-EE-12

TYPES OF OVERCURRENT RELAYS

OVERCURRENT RELAY

INSTANTANEOUS TIMEOVERCURRENT RELAY

TIME OVERCURRENT RELAY

DEFINITE TIME

INVERSE TIME

MODERETLY INVERSE

VERY INVERSE

EXTREMELYINVERSE

INSTANTANEOUS TIME OVERCURRENT RELAY

-operates in a definite time when current exceeds its pick-up value.

-operating time is constant.

-there is no intentional time delay.

-it operates in 0.1s or less

TIME OVERCURRENT RELAY

DEFINITE TIME OVERCURRENT RELAY

-operates after a predetermined time, as current exceeds its pick-up value.

-operating time is constant-its operation is independent of the

magnitude of current above the pick-up value.

-it has pick-up and time dial settings,desired time delay can be set with the help of an intentional time delay mechanism.

INVERSE TIME OVERCURRENT RELAY

-operates when current exceeds its pick-up value

-operating time depends on the magnitude of current

-there is inverse relation between current and operating time

-based on the inverseness it has three different types

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INVERSE DEFINITE MINIMUM TIME OVERCURRENT(IDMT)

RELAY

-gives inverse time current characteristics at lower values of fault current and definite time characteristics at higher values

-an inverse characteristic is obtained if the value of plug setting multiplier is below 10, for values between 10 and 20, characteristics tend towards definite time characteristics.

-widely used for the protection of distribution lines

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VERY INVERSE TIME OVERCURRENT RELAY

-gives more inverse characteristics than that of IDMT.

-used where there is a reduction in fault current, as the distance from source increases.

-particularly effective with ground faults because of their steep characteristics.

EXTREMELY INVERSEOVERCURRENT RELAY

-it has more inverse characteristics than that of IDMT and very inverse overcurrent relay.

-suitable for the protection of machines against overheating

-for the protection of alternators, transformers.expensive cables,etc.

TIME- CURRENT CHARACTERISTIC CURVES FOR DIFFERENT TYPES OF

TIME OVERCURRENT RELAYS

ReferencesProtective Relay Application Guide

The Art and Science of Protecticve RelaysByC. Russel Masin

Power System ProtectionByPadthankay

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Thank you !

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