Instrument Transformer, CT, PT, Differential Relay.

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2. Protective Relaying
(Presentation)
Presented to:
Prof. Brig. Almas Anjum
Presented By:
Mian Farhan Ullah

3. Introduction, Types and Application of
• Instrument Transformer
• Current Transformer
• Potential Transformer
• Differential Relay
Presentation Contents
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4. Transformers is a device;
• Transfers electric power from one circuit to another.
• It does so without change of frequency.
• It accomplishes this by electromagnetic induction.
• It is divided into core & shell types of transformers.
• For measurement purpose we uses
INSTRUMENT TRANSFORMRS.
Instrument Transformers
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5. • These are special types of transformers used for the
measurement of voltage , current ,power & energy. As the
name suggests , these transformers are used in conjunction with
the relevant instruments such a ammeters , voltmeters
, wattmeter's & energy meters.
Instrument Transformers
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6. Instrument Transformers
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7. • For the purpose of measurement of large currents and high
voltage in transformer we uses instrument transformer.
• It also make it possible to measure it with low range voltmeters
and low range ammeters.
• For these purpose, specially constructed accurate ratio
instrument transformers are employed in conjunction with many
measuring instruments.
• They are basically of two types –
1. Current Transformers
2. Potential Transformers
Need of Instrument Transformers
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8. • It would not be economical to have a ammeter to measure
600amps in a conductor directly , but we can have an ammeter
range 0-5amps which corresponds to 0-600amps.
• Similarly , for measuring voltage of 132,000 volts directly it would
not be economical , so we place 0-220 volts will be corresponds
to 0- 132,000 volts & economical.
• The degree to which an instrument transformer produces a
current or voltage i. e. proportionate to the one to be monitored
is to it’s accuracy.
Application of Instrument
Transformers
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9. Current Transformer
• Current transformers can perform circuit control, measure current for
power measurement and perform roles for safety protection and
current limiting.
• They can also cause circuit events to occur when the monitored
current reaches a specified level.
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CT at Grid Station

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CT Connection
with Electrical
Line in Grid
Station

12. • Current transformers are used extensively for measuring current and
monitoring the operation of the power grid.
• Current transformers can be mounted on the low voltage or high
voltage leads of a power transformer; sometimes a section of a bus-
bar can be removed to replace a current transformer.
• Often, multiple CTs are installed as a "load" for various uses. For
example, protection devices and revenue metering may use separate
CTs to provide isolation between metering and protection circuits.
Application of CT
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13. A PT or sometimes called VT is a step-down transformer having many
primary turns but few secondary turns.
• In a step-down transformer the voltage decreases and the current
increases, thus voltage can be easily measured by using a low-range
voltmeter instrument.
• The voltage is stepped-down in a known ratio called the voltage ratio.
Potential Transformers
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14. Construction and working of P.T.:
Construction
• A potential transformer has many primary winding turns but few number
of secondary winding turns that makes it a step-down transformer.
• A Voltmeter is connected to the secondary winding is usually a voltmeter.
Working (Measurement):
• Primary terminals are connected in parallel across the line to which the
voltage is to be measured.
• The voltmeter reading gives the transformed value of the voltage across
the secondary terminals.
Potential Transformers
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15. VP
Vs
Voltmeter & Relay
Potential Transformer
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16. 1. For Metering Purpose.
2. Required for Synchronization of Feeders / Generator with Grid.
3. For Feed back of AVR.
4. Distance Protection of feeders.
5. Impedance protection of Generators eg. Back up Imp. , Field Failure ,
Pole slip etc.
6. Any protection which require voltage signal eg. Freq. , over flux , over
/under voltage etc.
Application of Potential Transformers
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17. Differential Protection Relay
The relay whose operation depends on the phase difference of
two or more electrical quantities is known as the differential
protection relay.
It works on the principle of
comparison between the
phase angle and the
magnitude of the same
electrical quantities.
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18. Types of Differential Relay
Current Differential Relay
A relay which senses and operates the phase difference between the
current entering into the electrical system and the current leaving
the electrical system is called a current differential relay.
For External Faults
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19. Types of Differential Relay
Voltage Differential Relay
The current differential relay is not suitable for the protection of the
feeders. For the protection of the feeders, the voltage balance
differential relays are used. The voltage differential relay uses two
similar current transformer places across the protective zone with the
help of pilot wire.
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20. Applications of Differential Relay
Bus Bar Zone of Protections
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