Detecting Power Grid Synchronization Failure on

Sensing Frequency or Voltage Beyond Acceptable

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Detecting Power Grid Synchronization Failure

Synchronization means the minimization of difference in voltage, frequency and phase angle between the corresponding phases of the generator output and grid supply. An alternating current generator must be synchronized with the grid prior to connection. It can’t deliver the power unless it is running at same frequency as the network.

Synchronization must occur before connecting the generator to a grid. Synchronization can be achieved manually or automatically. The purpose of synchronization is to monitor, access, enable, and automatically take the control action to prevent the abnormalities of voltage and frequency.

Introduction

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Rules Must Be Followed for Power Grid Synchronization

Voltage Fluctuation:

When a generator is synchronized with a power grid.

There is a voltage fluctuation on the distribution line.

During synchronization the voltage fluctuation should not exceed 3% at

the at the point of common coupling.

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Synchronization Limits:

The limits allowing for synchronization are.

Phase angle- +/-20 degrees

Maximum voltage difference – 7%

Maximum slip frequency – 0.44%

Rules Must Be Followed for Power Grid Synchronization

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Relays:

For checking the synchronization “synch check relay” must be used.

The usage of relays can’t apply for induction generators.

The use of synch check relay is to accept as a backup during synchronization.

It ensures a generator will not connect to a dead distribution line.

Rules Must Be Followed for Power Grid Synchronization

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Synchronization of Induction Generators

Standard motor controllers will be used to synchronization of induction

generators.

Turbine shaft power will be used to mechanically drive the generators up to

synchronization speed.

The speed of the motors depends on supplied frequency and number of

poles on the generators.

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Synchronization of Synchronous Machines

For synchronous generators output waveform should be in phase with

the grid voltage waveform.

The rate of change of phase angle between the grid and the machine

(generator) must be within the specified limits.

Some other rules are variable speed drive arrangement to maintain a

constant output frequency.

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Failure of Synchronization

There are various reasons for failure of power grid synchronization.

Synchronization circuit may fail for responding to a received input pulse.

It happens when the received input pulse is shorted than the sampling period of the synchronizer.

Then no synchronized representation will take place.

Synchronization circuit may fail, when the pulse rate of the input signal is higher than the synchronization rate of the synchronizer.

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Synchronization Failures and their Detections

Generators and some local loads have become disconnected from main

distribution lines due to some issues.

Due to this there is a reduction in quality of supply.

It may prevent automatic reconnection of devices. This is called as islanding.

Islanding must be detected and producing power must be stopped immediately.

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Following Hazards May Take Place Due to Islanding

Line voltages may excessive; when distributing lines and generators are disconnected the line is not earthed.

Due to Islanding synchronization can’t be maintained.

The fault level contribution from the grid to sub-station may be lost.

Due to this sufficient current may not be generated.

The voltage levels may go outside of normal operating limits, and the quality of supply may be reduced.

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Detection Methods of Islanding

Detection of islanding can be done through active and passive methods.

Passive methods look for transient events on the grid.

Active methods will probe the grid by sending signals from the distribution point of grid.

Loss of Mains Protection (LoM) will be designed to sense the disconnection of

generators.

The blind area is called Non Detection Zone (NDZ).

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Which Microcontrollers Are Used in This Project?

40 pin 8051 Microcontrollers are used in this project.

The Microcontroller monitors the under/over voltage being derived from a set of comparators.

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Applications of Power Grid Failure Detection

Lighting is one of the main causes for power system faults.

The major advantage is detecting the synchronization failure between generators and power grid.

When there is an Under/over voltage or under/over frequency.

The comparator will detect the difference the actual power and reactive.

If there is no failure of power grid synchronization then the detectors will give the zero values.

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Block Diagram

• 8051 series Microcontroller• LCD• Op-Amps• 555 timer• Crystal• Resistors• Capacitors

• Diodes• Transformer• Voltage Regulator• Relay• Transistors• Slide Switch• Lamp

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Hardware Requirements

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