PROTECTION

• To remove a fault before it takes down the entire system
• It is able to detect the fault and clear it through fault clearing devices (CBs)

• Protection System is each individual protective arrangement
• Protection Scheme is the whole co-ordinated combination of each individual protection arrangement

Only a minimum portion of the power system should be disconnected to isolate a fault

Schemes must be able to discrimminate between signals which require action, and those that do not

Ability to operate without failure whenever a fault or abnormal condition exists

Schemes must relate to each other so they operate in the right order

• Primary Protection and Standby Protection(backup)
• -increased dependability
• -one protection may be removed for maintenance and the equipment reamain protected

• Current will rise
• Voltage will fall

• Provides useable quantities of voltage and current for:
• metering and control
• protective relays

The amount of load connected to the secondary of the CT (ohmic value)

Could saturate the CT, no longer accurately reflect system current

• The section of power system that a particular protection covers
• defined by the system they protect
• boundaries determined by the location of CTs

• The section of power system that is tripped by protection
• boundaries determined by the CB locations

Protection zones are typically 'overlapped' to prevent the possibility of unprotected areas

• A generator zone protection senses a generator fault and initiates protection operation. If the CB fails to open, 'Breaker Fail' protection operates to trip the adjacent zone
• Breaker fail monitors for fault current flow through the CB that failed to open

Used for analysis of 3 phase electrical power systems using vectors for the three phase quantities

• Generators produce positive sequence voltage and current
• Currents and voltages have a positive phase rotation
• Each phase is equal in magnitude
• Under balanced conditions only positive sequence exists

• May exist in addition to positive sequence if conditions become unbalanced due to unbalanced loads or a fault
• Unbalanced currents and voltages between phases result in Negative Sequence (negative phase rotation)

• When conditions are unbalanced and there is a path to ground, positive, negative, and Zero Sequence quantities will exist
• For zero sequence, phase quantities are equal in magnitude and in phase

• Remedial Action Scheme
• Automatic protection system designed to detect abnormal or predetermined system conditions, and take actions to maintain reliability

• Maintain angular stability
• Control frequency
• Prevent thermal overload
• Voltage control

• Generation Shedding(GenShed)
• Immediately disconnects generator to reduce amount of power being transmitted on to the system following a transmission contingency
• Maintains angular stability

• Telemetry: communication of data
• Status Reporting: reports change of status of a device
• Alarm Reporting: reports corresponding alarm points to control centre
• Supervisory Control: allows remote operation of devices

• Master Station: the control centre (FVO & SIO)
• Remote Terminal Units(RTUs): the send/receive point at the station or equipment
• Communication Facility: Microwave signals/towers, power line carriers, etc