Power system Protection

Pratap Mysore

HDR Engineering Inc.

February 9, 2013

Faculty/Industry Workshop

NAPA, CA

Power System One Line

GSU – Generator Step up Transformer

G

Generator

GSU

transformer

Shunt

Reactor

Transmission line

Shunt

Capacitor

Distribution

Transformer

Normal Operating Conditions

• Voltages are within the specified values.

• Current flowing in circuits are not above the rated values

• Frequency is within the specified range

Abnormal /Fault conditions

• Insulation failures due to lightning or switching transients or sustained overvoltages.

• Short circuits resulting in excessive fault currents.

Protective Relay

• detects short circuits and/or abnormal

operating conditions that may affect the

equipment/ the system.

• Isolates only the faulty equipment.

Protective Relay Requirement

Isolate faulty equipment as soon as possible

G

Generator

Transformer –GSU

Redundancy/ Backup Protection

• What happens if the relay doesn’t operate?

Add a second set of relaying

Make sure that some other relay clears the

fault such as a relay looking into the

generator from the system.

• What happens if the breaker fails to

operate?

Backup Protection

Provide a relay to detect this condition

and trip adjacent sources for the fault.

This could be at the same location or at a

remote location.

Generator Protection –Redundancy

With Back up Isolate faulty equipment as soon as possible

Another relay looking from

the transformer into the

generator or the relay

protecting the bus can also

provide the backup function.

G

Generator

Transformer –GSU

Primary protection

Secondary protection

Breaker failure Relay

Trip Trip

Initiate

Breaker

Failure

Zones of Protection

G

Generator Transformer –

GSU

Shunt

Reactor

Transmission line

Shunt

Capacitor

Zones of Protection

1- Generator 2- Transformer

3-Unit protection 4-Bus protection

5- Line protection 6- Shunt Capacitor

7- Shunt Reactor

1

2 3

4

5

6

7

Instrument Transformers

• Current Transformer

– Selection for Metering and Protection applications

– Effect DC offset, Remanence.

• Potential Transformer –Wound VT, Coupling Capacitor Voltage Transformer

Mathematical Tools

• Network reduction techniques

• Symmetrical components

• Sequence Network development

• Sequence Impedance of power system components

• How to get sequence impedance values from test reports/measure if they are not available.

• Modeling of equipment in Fault programs

Power System Equipment

Rotating Equipment

• Substation Equipment – Bus

– Transformer

– Breaker

– Shunt Capacitor

– Shunt Reactor

• Transmission line

Static Equipment

• Generators

• Motors

Protection of Power System Equipment

Static Equipment (Those without moving parts)

• Bus Protection - Types, Challenges due to high short circuit currents. Relay setting examples

• Transformer Protection – Methods to detect energization current versus fault currents- Available techniques. V/Hz protection. Relay setting Examples

• Transmission Line – Types, Effect of Mutual impedance, in-feed, Setting Examples.

– Transmission line Relay - Communication assisted schemes

• Breaker Failure Detection schemes

Shunt Capacitor & Reactor

• Shunt Capacitor bank- Types, Failure modes,

protection methods available, Relay setting

examples of two common types of capacitor

• Shunt Reactor –Types Air core (Dry) or oil

filled .

– Additional Overvoltage protection for oil filled

Reactors

Relays for System Restoration

• Auto reclosing

• Auto sectionalizing

• Synchro-check

Distribution Protection

• Distribution feeder configurations

• Protection Methods

• This also covers Distribution Transformer/ bus

protection

Rotating Equipment

• Generator -Additional protection schemes such as loss of excitation, Reverse Power to prevent motoring, unbalance (negative Sequence) protection

• Motor Protection- Thermal overload, unbalance protection schemes

Questions?