This presentation discusses various differential protection schemes including circulating current, balanced voltage, percentage differential, transmission line, and carrier aided protection schemes. The circulating current scheme is suitable for pilot wire resistances up to 1000 ohms and capacitances up to 2.5 microfarads. The percentage differential protection relay is used for protection of generators and transformers, providing about 85% earth fault protection for generator windings. Carrier aided protection is most widely used for ultra-high and extra-high voltage power line protection utilizing carrier signals of 500-700 kHz.

1. Sharad Institute of Technology College of
Engineering, Yadrav (Ichalkarnji)
A
Presentation On
differential protection
Presented By,
Mr. Chetan Patil.
Assistant Professor
Department of Electrical Engineering

2. 
 Circulating Current Scheme.
 Balanced Voltage Scheme.
 Percentage Differential Relay.
 Transmission Line Protection.
 Carrier Aided Protection Scheme.
Content

3. Circulating Current Scheme
 This scheme is suitable for pilot
wire resistance up to 1000 Ω and
capacitance between pilot wire is
up to 2.5µF.
 Under normal operating condition
the polarity of C.T secondary is as
shown in figure.
 Under this condition current does
not flow through the operating
coil. In case of fault the polarity of
C.T is reversed and current flow
through the operating coil. And
hence relay will be operate.

4. Balanced Voltage Scheme
 The operating coil of relay
is placed in series with pilot
wires and hence current
does not flow through the
pilot wires under normal
condition.
 In case of fault the polarity
of reverse end C.T is
reversed. Hence the current
flows through the pilot
wires and the operating coil
of relay and hence relay
will be operate.

5. Percentage Differential Relay
 The percentage differential
protection relay is used for
protection of generator and
transformer.
 There are main two types of
coils are used,
 R.C=Restraining Coil.
 O.C=Operating Coil.
 Such type of system
provides about 85% of earth
fault protection to the
generator winding.

6. Transmission Line Protection
 The differential protection used
for the protection of
transmission line with the help
of induction disc type relay
such system is called as
Transley System.
 This system works on principle
of Balanced Voltage Scheme.
 This system can be used for
long pilots having a loop
resistance up to 1000Ω.

7. Carrier Aided Protection Scheme
 This is most widely used for the
protection of UHV and EHV
power lines.
 The frequency of carrier signal
is about 500KHz to 700KHz.
 This system is cheaper and more
reliable.

8. 
The differential protection used for the protection of transmission line, the
percentage differential protection relay is used for protection of generator
and transformer where as carrier aided protection relay is most widely
used for the protection of UHV and EHV power lines.
Conclusion

9. 
Thank You

10. 
 Power system protection & Switchgear: B.Ram &
B.N. Vishwakarma.
 Switchgear & Protection: Sunil S.Rao, Khanna
Publications.
References