Power Generation Clyde

8/2/2019 Power Generation Clyde

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Power Generation


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Faradays Law

An electrical current flowing in a conductor will induce

a magnetic field around the conductor Right hand rule

Changing the magnetic flux around a conductor willgenerate an electrical current


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Electromagnet

Remember the days from elementary school where

you took wire and wrapped it around a nail, hooked itto a 6 volt lantern battery to produce a simpleelectromagnet

Think about how a magnetic pickup for speedmeasurement works. It is a simple permanent magnetwith a coil of wire wrapped around it.

The gear teeth change the magnetic flux whichresults in voltage being generated in the coil ofwires


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How Does a Generator Work

A simple AC generator consists of two parts:

Rotor

- Turned by the driver and consists of a coil of wireswound around a magnetic material to produce arotating magnetic field

Stator or Armature

- Rotating magnetic field induces a voltage in this coil ofwires


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Multiple Pole Generator

Adding additional magnets or poles will change the

frequency for a given speed

RPM = FrequencyPairs of Poles

60 *


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Generator Field

The generator field provides the power for the rotating

electromagnet The voltage regulator adjusts the DC voltage that is

used for the field

If the unit is not synchronized with another generator,

increasing the field voltage increases the outputvoltage of the generator

If the unit is synchronized with another generator,increasing the field voltage lowers the power factor ofthe generator

The field must operate within set limits to assure thatthere is sufficient magnetic field to produce the voltage


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3 Generators

3 generators have 3 windings in the stator that arespaced 120 apart to produce 3 independent outputs

Time

VoltagePhase

A

Phase

B

Phase

C


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Frequency or Isochronous Control

The output frequency is controlled by changing the

speed of the generator As the load changes, the turbine controller will

change the energy input to hold the speed constant

A simple PID controller could be used for this purpose

PIDSpeed Setpoint

Speed

Control Outputto Valve


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Load or Droop Control

In some of the older control systems, droop control

was the standard mode of control Droop control is Proportional control only

The speed/load curve for a droop controller looks likethe following:

Speed

Load

Setpoint=3600 rpm

25% 100%75%50%

3420 rpm

Frequency

60 Hz

57 Hz

Droop settingof 5%


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Droop Control

Generator control system has been refined to allow

other control variables to be used for the loadreference

Allows linear control through out the operatingrange

PIDSpeed

Speed Setpoint

Control Outputto Valve

+-

Sync Speed * Droop *% Output Selector PCD

Power


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Droop Control Curve

Increasing the setpoint will increase the load with the

modified control configuration

Speed

Load

Setpoint=3600 rpm

25% 100%75%50%

Frequency

60 Hz

57 Hz

Droop settingof 5%

Setpoint=3780 rpm


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Droop / Isochronous Control

The control system monitors the status of the breakers

in the system to determine whether operation shouldbe as an isochronous unit or as a droop control unit

Also monitors breakers to determine is load rejectionshave occurred so that a feed-forward response can beinitiated to prevent undesirable actions such as a trip


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Load Sharing

With multiple generators connected to the grid, it may

be desirable to have the generators sharing the loadproportional to their size

accomplished by monitoring the load of allmachines and taking the average

- this average becomes the setpoint for eachgenerator


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Parallel Isochronous Control

In some systems, it may be desirable for all of the

generators to operate collectively to control thefrequency of the system. This is called ParallelIsochronous control


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Infinite Buss Theory

The Infinite Buss theory was used to simplify the

control of generators. It stated that the power grid wasso large and inflexible that no single generator couldaffect the frequency of the system

good in theory, but not in reality


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Power Factor

Power factor is the phase relationship between the voltageand current

Voltage leading current is a lagging power factor

Voltage lagging current is a leading power factor

Power factor is the cosine of the angle between the voltageand current

Time

Voltage

Current

60PF = cosine (60)PF = .5


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Power Factor Control

Power factor of the installed electrical system isdetermined by the installed equipment

induction motors lagging power factor

capacitors leading power factor

Generator can be used to supply vars (imaginary powerthat is used to generate the magnetic field in motors,etc.)

Power factor is adjusted by changing the fieldexcitation

Generator has a defined operating area that must be

adhered to Control system can be used to protection the

generator from over/under excitation


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Generator Capacity Curve

Defines the operating area of

the generator Stability limit

Stator heating limit

MW limit

Rotor heating

Max excitation current

Rated MVA

Operating point

Power Factor

+MVAR

-MVAR

MW

Rotor Field Heating Limit

Maximum Excitation Limit

MW Limit

Rated MVA

Stator Heating Limit

Stability Limit

PF = Cos

Generator OperatingPoint


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Synchronization

Synchronization allows multiple generators to be

placed on line If the generators are not synchronized correctly, severe

damage can result to the generators

Synchronization is nothing more than the alignment of

the rotating magnetic fields in the generators Three conditions must be met for the synchronization

to be successful

Frequencies must be matched

Voltages must be matched Phase angles must be matched


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Synchronization Frequency

The units must be operating at the same relativefrequency for synchronization to be successful

Low generator frequency

- generator speeds up instantly on breaker closure

High generator frequency

- generator slows down instantly on breaker closure Units are not designed for the sudden speed changes if

not synchronized correctly

During synchronization, the speed of the generator isslightly higher than the buss frequency to allow currentto flow from the generator when the breaker closes


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Synchronization Voltage

Voltages must be matched prior to synchronization

Low generator voltage will result in an in-rush ofcurrent into the generator

- rotor heating

- may trip protection relays

Generator voltage slightly higher than bussrecommended to allow current flow into grid

On breaker closure, field controls Power Factor insteadof voltage


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Synchronization Phase

Synchroscope measures the voltage difference

between the buss and generator to determine thephase angle

Breaker should be closed when there is no phasedifference between the two signals


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Synchronization Phase Example

Time

Voltage Buss Gen

Time

Voltage

Buss

Gen

Generator out of phase

Generator in phase


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Automatic Synchronizers

Automatic synchronizers are often used to perform the

synchronization task Match the frequency, voltage, and phase but also have

some intelligence

generator frequency is slightly than buss and that

the phase angle is changing to assure that theunits are operating correctly

anticipate the closing speed of the breaker toassure that the breaker closes at 0 phasedifference

detect and close on dead busses

Require the use of a synch check relay


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Generator Metering and Synchronization


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Generator Relaying

Relaying is used to protect the generator from abnormal

conditions like over-current, voltage unbalance, currentdifferential, power, etc.

This can be a number of individual protective devicesor a single relay that is designed to incorporate all ofthe functions


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IEEE Numbering System

IEEE C37.2 defines device numbers

25 Sync Check Relay25A Automatic Synchronizing Relay

27 Undervoltage Relay

32 Power Relay

37 Undercurrent Relay

40 Loss of Field Relay

41 Field Relay

43 Manual Selector Switch49 Temperature Relay

50 Instantaneous Overcurrent Relay

51 Time Overcurrent Relay

52 AC Circuit Breaker

55 Power Factor Relay

59 Overvoltage Relay

65 Governor74 Alarm Relay

81 Frequency Relay

86 Lockout Relay

90 Voltage Regulator


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Typical One Line Diagram


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Generator and Voltage Regulator


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Relaying and Metering


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Synchronization

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