Transcript PRESENTATION ON SUBSTATION DESIGN AND CONSTRUCTION

PRESENTATION ON
SUBSTATION DESIGN
FRANCIS ARTHUR
Substation
There are four major types of electric substations:
Switchyard at a generating station:
These facilities connect the generators to the utility grid and also
provide off-site power to the plant.
Customer Substation:
Functions as the main source of electric power supply for one (or
more) business customers. The technical requirements and the
business case for this type of facility depend highly on the
customer’s requirements.
Substation
Switching Substation:
Facilitate the transfer of bulk power across the network. Their feeders
typically originate from generating switchyards. They enable the
transmission of large blocks of energy from the generators to the load
centers.
Distribution Substation:
Provide the distribution circuits that directly supply most electric
customers.
Substation Project Triggers
 Load Growth
 System Stability
 System Reliability
 System Capacity
Substation Design
Challenge
Optimal technical performance at least cost.
Design Considerations
Low life cycle cost
Safety
Standardization (Equipment and Station Configurations)
Substation Configurations
Single Bus
All elements (transformers and transmission lines) are directly connected to one bus
Advantages
Cost of construction is relatively low
Disadvantages
Reliability is low
Low Operational Flexibility (E.g Outage required on associated element for
maintenance of switchgear)
Suitable Where:
Load & Availability requirements are low
Substation Configurations
Typical Single Line Diagram
Typical Layout
Substation Configurations
Main and Transfer Bus
All elements (transformers and transmission lines) are directly connected to Main bus
Advantages
Cost of construction is relatively low
Operational Flexibility Higher than single bus scheme due to Transfer Bus and Tie
Breaker (Outage is not required on associated element for maintenance of switchgear)
Disadvantages
Reliability is low
Suitable Where:
Load & Availability requirements are low
Substation Configurations
Typical Single Line Diagram
Typical Layout
Substation Configurations
Double Bus Single Breaker
Connects each circuit to two buses, and there is a tie breaker between the buses.
Advantages
Cost of construction is relatively low
Reliability Higher than Main & Transfer bus scheme (Bus fault limited to affected bus
due to availability of tie breaker)
Disadvantages
Low Operational Flexibility (E.g Outage required on associated element for maintenance
of switchgear)
Suitable Where: Load Transfer & Improved Operating Reliability are Important
Substation Configurations
Typical Layout
Typical Layout
Substation Configurations
Double Bus Double Breaker Scheme
Involves two breakers and two buses for each element
Advantages
Increased reliability (Bus fault does not affect any element)
Increased Operational Flexibility (E.g No outage required for maintenance of circuit
breakers)
Disadvantages
Cost of construction is relatively high
Suitable Where: reliability and availability of the circuit is a high priority.
Substation Configurations
Typical Single Line Diagram
Substation Configurations
Ring Bus
All breakers are arranged in a ring with elements connected between two breakers.
Advantages
Increased reliability (Bus fault limited to affected section & faults to individual elements
do not affect others)
Increased Operational Flexibility (E.g No outage required on associated element for
maintenance of switchgear)
Disadvantages
Cost of construction is relatively high
Suitable Where: reliability and availability of the circuit is a high priority.
Substation Configurations
Typical Single Line Diagram
Typical Layout
Substation Configurations
Breaker and a Half Bus Scheme
Configured with a circuit between two breakers in a three-breaker line-up with two buses
Advantages
Increased reliability (Bus fault does not affect any element)
Increased Operational Flexibility (E.g No outage required for maintenance of circuit
breakers)
Disadvantages
Cost of construction is relatively high but justifiable due to above advantages
Suitable Where: reliability and availability of the circuit is a high priority.
Substation Configurations
Typical Single Line Diagram
Typical Layout
Substation Equipment
Categories of Equipment:
 Switchgear
 Power Transformers
 Capacitor Banks & SVC
 Instrument Transformers
 Protection and Control Equipment
 Auxiliaries
 SCADA and Communication
Switchgear
Disconnector Switch with Earthing Blade
Disconnector Switch Without Earthing Blade
Disconnect Switch
 Mechanical device that conducts electrical current and provides an open point in a
circuit for isolation.
 Disconnect switches are also installed to by pass breakers or other equipment for
maintenance.
 They are designed for no-load switching.
Key Requirements
 Open and Close reliably whenever necessary
 Carry current continuously without overheating
 To remain in the closed position under fault current conditions
Circuit Breakers
Live Tank
Dead Tank
Circuit Breaker
A mechanical switching device capable of making , carrying ,
and breaking currents under normal circuit conditions and
also breaking currents under specified abnormal conditions
such as a short circuit.
Surge Arresters
Devices deployed to protect
power system equipment from
being subjected to lightning or
switching surges.
Power Transformer
A transformer is an electrical
device for
converting ac
power at a certain voltage
level into ac power at a
different voltage, but at the
same frequency.
Inductively couples load to
the power system at different
voltages.
Capacitor Banks
Deployed for local reactive
power compensation at the
load.
Required for voltage support
and reduction of transmission
losses.
Static Var Compensators (SVC)
Deployed for dynamic local
reactive power compensation at the
load.
Required for voltage support and
reduction of transmission losses.
 Relies on power electronic and
other static controllers to enhance
control and increase power transfer
capability.
Instrument Transformers
Current Transformer
Voltage Transformer
Instrument Transformers
A high precision transformer designed to:
 Provide input into measurement and/or control equipment.
Examples: Voltmeters Ammeters Watthour Meters, Relays.
Transform currents or voltages from a usually high value to a value
easy to handle by protective relays and instruments.
Protection & Control Equipment
Protection & Control Equipment
Dedicated Protection panels for
transmission
lines,
power
transformers or capacitor banks.
Protection
Equipment
ensure
speedy isolation of equipment in the
event of fault by initiating commands
to circuit breakers based on set
current or voltage limits.
Control Equipment facilitate the
control of switchgear either from the
control room or at the switchyard.
Substation Auxiliaries
Substation auxiliaries encompass all systems that make the operating voltages of
415Vac, 125Vdc and 48Vdc available at the substation. It includes the following:
 Auxiliary Transformers (usually 34.5/0.415kV, 100 (or 250kVA)
 Diesel generator sets
 Solar Power Systems
125Vdc Rectifiers & 125Vdc Battery Banks
 48Vdc Rectifiers & 48Vdc Battery Banks
 Automatic Change over switches
 AC & DC Distribution Boards
Substation Auxiliaries
Auxiliary Transformer
Generator
Substation Auxiliaries
125Vdc Rectifier
Battery Banks
Substation Auxiliaries
48Vdc Rectifier
Change Over Panel
Rectifier
A rectifier is an electrical device that converts
alternating current (AC), which periodically reverses
direction, to direct current (DC), which flows in only one
direction. The process is known as rectification.
(Source: Wikipedia)
Substation Auxiliaries
AC Distribution Panel
DC Distribution Panel
SCADA & Communication
Power Line Carrier (PLC)
SCADA & Communication
PLC is the superimposition of various signals (ie. data, voice, Fax etc.) on the power line
at different frequencies thus relying on the power line as the carrier of the signals.
Functions:
 Provides means of high speed fault clearing through use of communication schemes to
confirm faulted line section.
 Aids in implementation of breaker failure schemes
 Aids in remote control requirements
Goal:
 To transmit a signal of high quality to the receiving end such that the receiver can
interpret the signal.
SCADA & Communication
Transmitters & Receivers
The carrier transmitters and
receivers are usually mounted in a
rack
or
cabinet
in
the
communication room. (Egs. ETL &
FOX panels).
SCADA & Communication
Line Tuners
Works in conjunction with the
coupling capacitor to provide a
low impedance path for the
carrier
energy
to
the
transmission line and a high
impedance path to the power
frequency energy.
SCADA & Communication
Line Traps
Directs the carrier signal off the
substation bus towards the remote
line terminal.
 Presents a high impedance path
for the carrier energy towards the
bus thus directing onto the remote
line terminal.
 The coil of the line trap presents a
low impedance path to the power
frequency.
SCADA & Communication
RTU
A remote terminal unit (RTU) is
a microprocessor-controlled electronic
device that interfaces objects in the
physical world to a distributed control
system or SCADA (supervisory control and
data acquisition) system by transmitting
telemetry data to a master system, and by
using messages from the master
supervisory system to control connected
objects. (Source: Wikipedia)
SCADA & Communication
Substation Grounding
Substation grounding is a means of channeling excessive fault currents
to ground with the view to preventing damage to equipment and
protecting personnel from being subjected to unsafe potentials.
It is achieved with a mat made up of horizontal interconnected bare
conductors and ground rods to which all equipment structures are
bonded.
 The grounding system includes all of the interconnected grounding
facilities in the substation area, including the ground grid, overhead
ground wires, neutral conductors, underground cables, iron rods in
foundations etc.
Substation Grounding
Reasons for Grounding
It provides a means of dissipating electric current into the earth without
exceeding the operating limits of the equipment.
It provides a safe environment to protect personnel in the vicinity of
grounded facilities from the dangers of electric shock under fault
conditions.
Substation Grounding
Circumstances for Human Electric Shock
Relatively high fault current to ground in relation to the area of the grounding system
and its resistance to remote earth.
Soil resistivity and distribution of ground currents such that high potential gradients may
occur at points at the earth surface.
Presence of a person at such a point, time, and position that the body is bridging two
points of high potential difference.
Absence of sufficient contact resistance or other series resistance to limit current
through the body to a safe value under the above circumstances.
Duration of the fault and body contact and, hence, of the flow of current through a
human body for a sufficient time to cause harm at the given current intensity.
Substation Grounding
The Design Problem?
To provide a safe condition for personnel within and around
the substation area by limiting voltages to safe values.
To provide an adequate earthing system at minimum cost.
Substation Grounding Design
Substation Grounding
Earth Grid
Operating Platform
Insulation Coordination
 Over voltages introduce stress to the power system insulation.
 Insulation coordination is a combination of measures to prevent the breakdown of
insulation.
 It is a means of achieving technically acceptable level of insulation that is matched to
the level of surge protection.
It comprises the following systems:
 Electrical Clearances
 Insulation Levels
Insulation Coordination
Insulation Coordination
Insulation Coordination
Insulation Coordination
Advantages
 Reliable operation of high voltage systems
Minimized equipment damage
 Reduced outages
 Reduced Operational Losses
Lightning Protection
Effects of Lightning in Electrical Installations
 Introduces over voltages and damage to non-restoring (solid) insulation
 Extreme local heating (vaporization of material, explosion)
 Direct strikes generate fields and large mechanical forces
 Generates electromagnetic (EMI) and radio frequency interference
(RFI) which disturb telecommunication equipment and low voltage digital
(and analogue) signal equipment.
Lightning Protection – Shield wires
Lightning Protection – Spikes