Chapter 1

INTRODUCTION

Interconnected Power System

Basic Of Electrical Power System

What is the Electrical Energy?

Need Of Electrical Energy?

How it is generated?

Where it is generated?

Siting of generating Station.

Generation

Fuel energy is converted into heat energy.

It converts into mechanical energy.

Mechanical energy is converted to electrical energy.

Transmission System

It connect the generation and distribution system.

It consists of extra high voltage (200 kV to 400 kV) line interconnecting large generator at major load centre.

These lines transmitting large amount of power over a long distance(1000 km usually).

Subtransmission line consist of 66kV to 132kV.

Distribution system.

It connects all the loads in a particular area to the transmission system.

Power Grid For the economical and technological reason individual power systems are

organized in the form of connected areas or which is called regional grid.

Regional grid operates technically and economically independently and interconnected to form a national grid.

May be form into international grid.

Indian power grid consist of

-- Northern Region(NR),

-- Eastern Region(ER),

-- Western Region(WR),

-- Southern Region(SR) and

-- North-East Region(NER).

It means all the regional grid are connected to AC transmission path in which all the generator must be operated at the same frequency or they are in synchronism.

What is meant by synchronism?

Load can be connected in shunt to the line.

Two generators are connected to the transmission line. If the magnitude is same but

the frequency is different, what will be the power and is it tolerable?

Power System Interconnection

Reliability --Under condition of sudden increase in load or loss of generation, it is immediately possible to

borrow power from adjoining interconnected area.

Economic -- to reduce the reserve generation capacity.

Advantage It provides capacity savings by seasonal exchange of power between areas having

opposing winter and summer requirement.

It facilitates transmission of peak power.

It also gives the flexibility to meet unexpected emergency load.

Interconnected systems help maintain frequency, avoid voltage collapse, and reduce the chance of undesirable load-shed situations.

Interconnections between systems that use different technologies and/or fuels to generate electricity provide greater security in the event that one kind of generation becomes limited.

Interconnections permit planned outages of generating and transmission facilities for maintenance to be coordinated so that overall cost and reliability for the interconnected network is optimized

Disadvantage

Interconnection causes larger current to flow on transmission line

under faulty condition.

All the synchronous machine of all interconnected power system

must be operated stably and in synchronize manner.

Disturbance caused by short circuit area must be rapidly

disconnected before it can seriously affect adjoining areas.

Load Dispatch Centre

The function of load dispatch control center includes optimum

scheduling, dispatch of power across various regions and

coordination the event of power exchange between different

regions in real time.

LDC is an important link between generation and transmission.

Coordinates the power requirement of the consumer.

To achieve the twin objectives of economy and reliability, we have

to adopt appropriate technology, tools & management systems in

the day-to-day operation, control, & maintenance of power system.

Objectives of Load Dispatch Centre:

To ensure the reliable uninterrupted supply to the consumers at

all the points of the network considering System Security and

Integrity.

To look after to limit the duration and the extent of

repercussions due to occurrence of faults in the System.

To monitor that fault is removed, supply is made available and the

system normally is restored within shortest possible time.

To give special attention so that essential services like Railways,

Hospitals, Water Works and Ordnance Factories etc., get the

uninterrupted supply on priority basis.

To ensure maximum utilization of available generation and

transmission networks to meet the present demand, with a view

to minimize the operating cost of the system.

To regulate the loading of the transmission lines and the

equipment, Bus Voltages at Sub-stations & the standard

frequency upto the optimum system operation limits.

Now that the grid in India has interstate connections, L.D.

has to monitor and control the power exchanges between

other Utilities (intrastate and interstate) by strictly adhering

to Availability Based Tariff.

Requisites of a LDC

Reliable and far reaching communication network.

Accurate SCADA system.

Fast data processor and data formatting system.

Visual display systems for data streaming in and out.

Functions of LDC

Load balance and quality of supply.

Maintenance scheduling of generating units and transmission lines.

Economic load dispatch.

Grid discipline.

Load forecasting or demand estimations.

System security and islanding facility.

Energy distribution and load study pattern.

Event analysis and preventive measures.

Coordination with neighbor grids.

Public relations and consumer interaction.

Cascade Tripping/ Blackout

The phenomenon of tripping of generators in series is called cascade tripping.

A cascade is a dynamic phenomenon that cannot be stopped by human intervention once started.

The blackouts start with short circuits (faults) on several transmission lines in short succession -sometimes resulting from natural causes such as lightning or wind etc.

A fault causes a high current and low voltage on the line containing the fault.

A protective relay for that line detects the high current and low voltage and quickly trips the circuit breakers to isolate that line (generator) from the rest of the power system.

When this generator trips -the frequency will drop and the load will be divided amongst the generators those are working.

Overload causes the remaining machines to trip resulting in total supply failure in the grid.

It occurs when there is a sequential tripping of numerous transmission lines and generators in a widening geographic area.

Power swings and voltage fluctuations caused by these initial events (discussed above) can cause other lines to detect high currents and low voltages that appear to be faults, even if faults do not actually exist on those other lines.

Generators are tripped off during a cascade to protect them from severe power and voltage swings.

Protective relay systems work well to protect lines and generators from damage and to isolate them from the system under normal and abnormal system conditions.

This leads to more and more lines and generators being tripped, widening the blackout area.

Connectivity to other state grids gets lost in this process, which may even lead to entire connected grid blacking out with major tie-line trips or huge generational losses in the grid.

Special protection schemes are thus required to safeguard the system as its very hard to restore supply after cascade tripping.

Islanding Cascading failures and blackouts are the most significant threats for

power system security.

If the process of cascading failure proceeds due to further line tripping then the system will face uncontrolled islanding situation.

Creating of uncontrolled islands with deficiency in MW or MVAr power balance, are the main reason for system blackout.

In order to prevent system blackout due to uncontrolled islanding, intentional islanding has been considered as a preventive strategy against system blackout.

Islanding refers to a condition where a facility runs on its own alternative power source when energy is not coming from a common grid.

Such a power source can also feed energy back into the grid.

Islanding can either happen as the result of a power black-out or be set up intentionally.

The process of islanding is implemented by a distributed generator.

This is the alternate power source that enables the facility to function independently.

Possible sources of energy include solar power, wind, coal, and nuclear energy.

Some generators can be run by fossil fuels, though these are extremely expensive for larger facilities.

Clean and environmentally safe solar power is generally a favored form of alternative power, though it may not be as efficient as fossil fuels.

Some facilities will use more than one form of alternative energy when islanding.

One common configuration is a building that uses both solar panels and wind power generated from turbines.

A system like this can be more effective because the two power sources are often complementary, with one compensating for the weaknesses of the other.

Some distributed generators may also be used along with the power from an electrical utility.

Intentional islanding can be a practical solution for facilities located far from standard electrical utilities.